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Migration experiment and numerical simulation of modified nanoscale zero-valent iron (nZVI) in porous media
Journal of Hydrology 579 (2019) 124193
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Research papers
Migration experiment and numerical simulation of modified nanoscale zerovalent iron (nZVI) in porous media
T
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Yu Liua,b, Yongxiang Zhanga,b, , Shuangshuang Lana,b, Shukai Houa,b a b
College of Architectural Engineering, Beijing University of Technology, Beijing 100124, China Key Laboratory of Beijing for Water Quality Science and Water Environment Recovery Engineering, Beijing 100124, China
A R T I C LE I N FO
A B S T R A C T
This manuscript was handled by Huaming Guo, Editor-in-Chief
A packed column experiment was carried out to study the migration process of modified nano-zero-valent iron (nZVI) in porous media and the change process of hydraulic characteristics of porous media. In view of the complexity of the migration mechanism of modified nZVI in porous media, an unsteady variable parameter mathematical model considering the effects of interception, Brownian diffusion, gravity settling and the change of porous media properties was established. By fitting the model with the experimental data, the changes of various mechanisms in the experimental process were studied. The results show that the higher the injection flow rate, the higher the concentration at the outlet, and the lower the injection concentration, the higher the throughput. The distribution of iron particles in porous media is not uniform, the maximum at the entrance and the lowest at the exit. The model fits the test results well under various test conditions. The model analysis shows that in the process of particle injection, the particle size is small at the beginning, and the particles are mainly attached to the surface of the medium due to Brownian motion. As the experiment proceeds, the particle size increases, the Brownian motion effect decreases, but the interception and gravity settlement effect strengthens. In addition, during the whole process, the porosity of the medium decreases gradually, and the probability of collision between particles and porous media increases, which leads to the increase of the deposition rate coefficient.
Keywords: Modified nanoscale zero valent iron Migration Distribution Laboratory test Mathematical model
1. Introduction Nano-scale zero-valent (nZVI) has strong reducibility, large specific surface area and high reactivity (Choe et al., 2001; Liu et al., 2010). It has good removal effect for nitrobenzene, chlorohydrocarbons and other organic matters, and has become one of the more promising and effective remediation materials in the field of underground environmental remediation (Efecan et al., 2009; Li et al., 2019; Ponder et al., 2000; Qu et al., 2019; Scott et al., 2011; Xu et al., 2014; Zhang et al., 2009). Injecting nZVI suspension into underground can effectively degrade most chlorinated organic pollutants, inorganic anions and toxic heavy metals dissolved in solution (Elliott and Zhang, 2003; O’Carroll et al., 2013; Quinn et al., 2005; Tosco et al., 2014; Wei et al., 2010). Nevertheless, there are some major problems that prevent the effective application of nZVI in groundwater remediation. An important obstacle to the wide application of nZVI is the tendency of rapid aggregation and settling of nZVI particles in aqueous suspension (Kocur et al., 2014). Because of the strong magnetic force and van der Waals force between particles, nZVI particles are easy to
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agglomerate when suspended in water, forming a dendritic or reticular structure, which may be much larger than the micron scale. This results in the aggregation and adhesion of nZVI particles on the surface of environmental particles during injection, which limits the mobility of nZVI. In addition, the reaction rate with pollutants is also reduced due to the reduction of specific surface area. (Li et al., 2006; Phenrat et al., 2007; Schrick et al., 2004; Shen et al., 2011). In recent years, the research on modification technology of nZVI has been emerging, which greatly improves the migration of nZVI. By adding organic dispersants such as poly acrylic acid (PAA) and carboxymethyl starch cellulose (CMC) into nZVI suspension, the van der Waals force between particles is reduced, the steric hindrance is increased, and the polymerization probability is reduced (Comba and Sethi, 2009; Fatisson et al., 2010; he et al., 2010; He and Zhao, 2005; Jiemvarangkul et al., 2011; Kim et al., 2009). The migration distance of organic dispersants stabilized nZVI in porous media has been greatly increased relative to that of bare nZVI. However, compared with stable solutions, the stability of modified nZVI is still limited, and its migration characteristics in porous media still remains to be explored.
Corresponding author at: College of Architectural Engineering, Beijing University of Technology, Beijing 100124, China. E-mail address: [email protected] (Y. Zhang).
https://doi.org/10.1016/j.jhydrol.2019.124193 Received 30 May 2019; Received in revised form 23 September 2019; Accepted 27 September 2019 Available online 28 September 2019 0022-1694/ © 2019 Elsevier B.V. All rights reserved.
Journal of Hydrology 579 (2019) 124193
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Piezometer
Sample Peristaltic pump 30cm Quartz sand column
N2
Piezometer Modified nZVI suspension Fig. 1. Experimentation device schematic. Table 1 Summary of dimensionless parameters governing particle filtration. Parameter
Calculation formula
Physical explanation
NR
dp dc
The ratio of particle size to porous medium size
NPe
Udc D∞ A kT A
Proportion of convective and diffusive transport represented by Peclet number
NvdW
NA NG
Van der Waals Number Characterization of the Ratio of Van der Waals Interaction to Particle Heat Energy Attraction number: represents the combined effect of van der Waals gravity and fluid velocity on the deposition rate of intercepted particles。
12πμap2 U
Gravity Number: ratio of Settlement Velocity of Stokes Particles to Fluid Velocity
2 2 ap (ρp − ρf ) g 9 μU
where dp is the particle diameter, dc is the particle diameter of porous media, U is the fluid approach velocity, D∞ is the bulk diffusion coefficient (described by StokesEinstein equation), A is the Hamaker constant (4 × 10−20J ), k is the Boltzmann constant (1.38 × 10−16gcm2s −2K−1), T is fluid absolute temperature, ap is particle radius, ρp is the particle density, ρf is the fluid density, μ is the absolute fluid viscosity, and g is the gravitational acceleration (981 × cms −2 ). Table 2 Collision frequency functions for the coalesced fractal sphere (CFS) model. Parameter
Calculation formula
βBR (vi, vj )
2kT 3μ
βSH (vi, vj )
G 1 − 3/ DF 1/ DF DF 3 v (vi + v1/ ) j π 0 1 g π − 3 (ρ0 − ρw ) 1/3 ⎛ ⎞ v0 − 1/ DF 12μ 6 ⎝ ρw ⎠ 1 g π − 3 (ρ0 − ρw ) ⎛ ⎞ v04/3 − 3/ DF 12μ 6 ⎝ ρw ⎠
βDS (vi, vj ) βDS (vi, vj )
DF 1/ DF (vi1/ DF + v1/ )(vi−1/ DF + v− ) j j
()
DF 2 (vi1/ DF + v1/ ) × |vi(DF − 1)/ DF − v j(DF − 1)/ DF |(2 ≤DF ≤3) j
()
DF 2 DF (vi1/ DF + v1/ ) × |vi1/ DF − v1/ |(DF ≤2) j j
where v0 is volume of a monomer, vi and vj is solid volume of i and j-mer aggregate respectively, ρ0 is density of monomers, and ρw is density of water.
The fluidity of nZVI particles is too large to uniformly distribute in polluted groundwater, which may also cause secondary pollution to the environment (Krol et al., 2013; Li et al., 2018; Ren et al., 2017). Because of the active nature of nZVI, iron ions and iron oxides are easily released into the environment, which will have unpredictable and serious toxic effects on organisms and even ecosystems. At present,
most studies focus on the toxicity of nZVI to microorganisms (Chaithawiwat et al., 2016; Li et al., 2010). However, some scholars have found that nZVI can also affect barley (El-Temsah and Joner, 2012b), earthworms (El-Temsah and Joner, 2012a) and fish (Chen et al., 2011), and further observations have found that nZVI can even change the physical and chemical properties of the environment (Cullen
2
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nZVI in site scale test. Transport and deposition of particle suspensions in porous media and the effects on porous media have been discussed in previous studies. These studies suggested that the deposition of suspended particles through porous media mainly includes three functions: interception, sedimentation and Brownian diffusion (Bai and Tien, 2000; Herzig et al., 1970; Rajagopalan and Tien, 1976; Tufenkji and Elimelech, 2004; Yao et al., 1971). Bai and Tien (Bai and Tien, 2000) suggested that when particle suspension passes through porous media, the structure and surface conditions of the medium undergo continuous changes (the parameters of the medium change), which in turn affect the filtration or deposition rate. Therefore, particle suspension through porous media is essentially an unsteady process, and the hydraulic parameters and effluent concentration of porous media usually change with time. Yao et al. (1971) proposed a conceptual model of water and wastewater filtration process by means of micro-analysis method, and compared it with laboratory test results. It is proposed that smaller particles are intercepted by diffusion while larger particles are intercepted by interception and settlement. Tufenkji and Elimelech (Tufenkji and Elimelech, 2004) proposed an equation for predicting the single-collector contact efficiency (η0 ) in physicochemical particle filtration in saturated porous media. The correlation equation is developed assuming that the overall single-collector efficiency can be calculated as the sum of the contributions of the individual transport mechanisms Brownian diffusion, interception, and gravitational sedimentation. The migration and distribution characteristics of modified nZVI in porous media have been discussed in previous studies. These studies suggested that nZVI is different from other particles, it is unstable in water and easy to agglomerate into large particles. Jiemvarangkul et al. (2011) modified nano-zero-valent iron by three kinds of polyelectrolytes (PV3A, PAA and soybean protein). The migration of nano-zerovalent iron before and after modification was compared by column and batch experiments. It was proposed that modified nano-zero-valent iron with adjustable travel distance could be prepared to form iron reaction zone in designated target area and achieve the purpose of in-situ pollution control. The aggregation of nZVI particles will affect their deposition in porous media, and the particle size determines the contact efficiency of a single collector (η0 ). Raychoudhury et al. (2012) investigated the transport and deposition of carboxymethyl cellulose (CMC) modified zero-valent iron (nZVI) nanoparticles in laboratoryscale sand-filled columns, a modified colloid transport model which couples the governing transport equation to the aggregation kinetics equation was developed, however, the effect of the variation of porous media parameters on migration process is not considered. The migration of nZVI will affect the hydraulic characteristics of porous media, which conversely affects the nZVI migration. The parameters are time
Fig. 2. Calculation process of the model.
et al., 2011; Tilston et al., 2013). Understanding the migration of nZVI in porous media is essential to evaluate the potential of nZVI to travel from injection points to untargeted environmental compartments, and to assess the microbial community exposure to nZVI (Lefevre et al., 2016). The study of the migration and distribution of modified nZVI in porous media can provide theoretical basis for the occurrence and development of plugging in the process of injecting nZVI suspension into porous media. The numerical model can simulate and reproduce the migration process of nZVI in porous media, and quantitatively predict the distribution of nZVI in porous media in different periods. It is of great significance for the development of nZVI with adjustable migration distance and the prediction of the underground injection process of
Fig. 3. Breakthrough curve of nZVI. 3
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Fig. 4. Change process of permeability coefficient of packed column.
continuously injected for 10 min to ensure deoxidation, while continuously stirring to ensure the uniformity of the dispersant. Then the sodium borohydride solution with 150 ml concentration was dripped at the speed of 10 ml/min. The theoretical concentration of iron in the suspension prepared by this method is 1 g/L. Modified nano-zero-valent iron suspension with different concentration can be prepared by changing the amount of reagent.
Table 3 Summary of dimensionless parameters governing particle filtration. Flow ml/ min
Concentration g/L
Collision efficiency between particles and media αpc
Collision efficiency between particles αpp
12 12 12 8 8 8 4 4 4
3 1 0.3 3 1 0.3 3 1 0.3
0.61 0.60 0.57 0.67 0.65 0.63 0.72 0.70 0.69
1.23 1.1 0.82 1.22 1.11 0.80 1.18 1.09 0.79
2.1.2. Packed column experiments The experimental device is shown in Fig. 1. In order to ensure the uniformity of water distribution, glass beads with a diameter of 0.3 cm were filled in the inlet and outlet of the column with a size of 2 cm. The rest is filled with quartz sand with particle size of 0.5–0.7 mm. Pressure gauges are set at the inlet and outlet to monitor the inlet and outlet pressure. After filling, deoxidized water is pumped into the column by a peristaltic pump to get rid of the gas in the column and obtain a stable flow pattern. Nine groups of penetration experiments were carried out with 12 ml/min, 8 ml/min and 4 ml/min as injection flow rates, and the concentration of injected suspension was 3 g/l, 1 g/l and 0.3 g/l. The pH value of the suspension is 7.4 ± 0.4 and the temperature is 278 K. The concentration of iron in the effluent was measured, as well as the change of inlet and outlet pressure during the whole process was monitored. The total iron concentrations were measured by atomic absorption (AA) method (Jiemvarangkul et al., 2011). In order to quantitatively analyze the occurrence of plugging in porous media during the injection process, and explain the migration characteristics of nZVI particles in the medium in detail, the distribution of residual iron particles in the medium during the injection of modified nano-zero-valent iron was measured by parallel experiments. Among the six groups of packed columns with the same parameters, 1 g/l and 8 ml/min were injected into the suspension, and the experiments were stopped at the injection volumes of 2, 4, 6, 8, 10 and 12 pore volumes (PVs), respectively. The quartz sand in the column was taken out and divided into 10 parts every 3 cm. The concentration of iron in the solution was measured after soaking with dilute hydrochloric acid in a certain volume, and the solid phase concentration in the medium at that time was calculated.
varied, therefore a non-stationary variable parameter model is required. The objectives of this study were to assess the kinetics of PAA-nZVI particles polymerization and the changes of the hydraulic parameters caused by the deposition of PAA-nZVI, as well as the effects of these two actions on the migration of PAA-nZVI in porous media. In this study, PAA-nZVI suspension was prepared by chemical reduction method. Column transport experiments for different nanoparticle concentrations and different injection flow rates were performed to study the migration characteristics of PAA-nZVI in porous media and its influence on the hydraulic characteristics of porous media. A non-stationary variable parameter mathematical model was established, which coupled with the kinetics of PAA-nZVI particles polymerization and the change of porous media properties, and the effluent nZVI concentrations over time were fitted to the modified particulate transport model to assess whether the model could account for the observed shape of the experimental breakthrough curves. The parameter change process of Brownian motion, interception and settlement caused by the change of particle size and hydraulic characteristics of porous media during PAAnZVI migration were analyzed based on this model.
2. Materials and methods 2.1. Migration experiment scheme 2.1.1. Synthesis of PAA-nZVI In this study, nZVI was prepared by chemical reduction and poly acrylic acid (PAA) was used as dispersant (Sun et al., 2007). The specific operation is as follows: take ferrous sulfate g-heptahydrate in three flasks, add 350 ml of anaerobic water to dissolve it, and add 1 ml of PAA (optimal dosage) (Jiemvarangkul et al., 2011), during which nitrogen is
2.2. Numerical simulation method The migration of modified nano-zero-valent iron in porous media is a complex process. With the deposition in porous media, the structure and surface conditions of the medium undergo continuous changes (the parameters of the medium change), which in turn affect the filtration or 4
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Fig. 5. Experimental breakthrough curves with model fit.
single-collector contact efficiency controlled by diffusion, interception and settling mechanisms (Tufenkji and Elimelech, 2004).
deposition rate. Therefore, the migration of PAA-nZVI in porous media is essentially an unsteady process. Hydraulic parameters of porous media and effluent concentration (or filtrate mass) usually change with time. In this paper, the following methods are used to establish the mathematical model.
2.2.2. Computation of single-collector contact efficiency η0 is calculated according to the following Equation:
η0 = ηD + ηI + ηG
where ηD is the collision efficiency of the 3 between nZVI particles and collector, ηI is the interception mechanism and ηG is the settlement mechanism. η0 can be calculated using the methods proposed by Tufenkji and Elimelech (2004) Particle size, porous medium size, porosity and Darcy velocity are the main factors affecting the calculation. The specific calculation method is as follows:
2.2.1. Basic equation of solute transport in porous media In porous media, traditional migration is usually described in Eq. (1).
∂C ∂ 2C ∂C =D 2 −v − kdep C ∂t ∂x ∂x
ρ
∂Cs = kdep C ∂t
(1)
(2)
where C is the mass concentration of suspended particles, Cs is the concentration of particles deposited on the solid phase, D is the dispersion coefficient of hydrodynamics, v is the pore velocity, and kdep is the deposition rate coefficient of particles. kdep is calculated according to the following Equation (Rajagopalan and Tien, 1976):
3(1 − ε ) v kdep = ⎡ αpc ⎤ η0 ⎢ ⎥ ⎣ 2dc ε ⎦
(4)
−0.715 0.052 ηD = 2.4AS1/3 NR−0.081 NPe NvdW
(5)
ηI = 0.55AS NR1.675 N A0.125
(6)
0.053 ηG = 0.22NR−0.24 NG1.11 NvdW
(7)
The physical explanations and calculation formulas of the dimensionless parameters are listed in Table 1. 2.2.3. Effect on porous media Residual nano-zero-valent iron in porous media will lead to changes in hydraulic characteristics of the media, thus affecting the concentration of effluent. There is a certain relationship among solid concentration, porosity and permeability. Suspended particles deposit in the pore
(3)
where αpc is the collision efficiency between particles and collectors, ε is the porosity, dc is the particle diameter of porous media, and η0 is the 5
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Fig. 6. Experimental permeability coefficient of packed column with model fit.
particles, and the second term indicates that the k -mer particle number concentrations is decreased as a result of collisions that lead to further aggregation. Aggregation kinetics is controlled by the particle–particle attachment efficiency, αpp , which is the fraction of particle–particle collisions resulting in attachment and is dependent on solution chemistry. β (i, j ) represents the reaction constants between order i and j under Brownian motion (βBR ), fluid shear (βSH ) and differential settlement (βDS ), which are derived from the calculation method in Table 2. β (i, j ) is computed using the Coalesced Fractal Sphere model (Lee et al., 2000) as Eq. (11).
of aquifer medium and occupy part of the pore space, resulting in the decrease of porosity of medium, which can be described as: (8)
ε = ε0 − σCs
where ε is the porosity at a certain time after injection, ε0 is the initial porosity, and σ is the volume of pore blocked by suspended particles per unit mass. The relationship between permeability and porosity is expressed by Kozeny-Carmen equation (Nooruddin and Hossain, 2011).
Kt = K 0 ∙
ε3 (1 − ε0 )2 ∙ (1 − ε )2 ε03
β = βBR + βSH + βDS
(9)
(11)
where Kt is the permeability coefficient at t moment after injection, K 0 is the initial permeability coefficient.
The particle size of aggregates is measured by the following equation (Gierczycki and Al-Rashed, 2008; Maximova and Dahl, 2006):
2.2.4. Polymerization of particles The migration of nano-zero-valent iron in porous media is accompanied by the process of particle aggregation (Raychoudhury et al., 2012). Because of particle aggregation, the particle size increases, which has a great influence on the deposition rate coefficient of particles (kdep ). The agglomeration kinetics of nZVI particles can be described by the Eq. (10) (Lee et al., 2000).
dp (i) = (Ni
1/ Df
(12)
where Ni is the number of particles forming aggregates, Df is the fractal dimension of the formed aggregates, which is adopted 2 (Raychoudhury et al., 2012), dp (i) is the diameter of the polymer formed by Ni particles and dp (i = 1) represents the diameter of a single particle. 2.2.5. Implementation of model algorithms The finite difference method is used to solve the Eqs. (1), (2) and (10). The sand column is discretized into 30 grids with a length of 1 cm and time step is 20 s. For each time step, Eqs. (10)–(12) is first solved to obtain the particle size distribution at that time. Based on this particle size, the deposition coefficient (kdep ) is calculated by Eqs. (3)–(9). Finally, kdep is introduced into Eqs. (1) and (2) to calculate the concentration at that time step. The calculation process is shown in the
Z
⎛ dnk ⎞ = 1 αpp ∑ β (i, j ) ni nj − αpp nk ∑ β (i, k ) ni 2 ⎝ dt ⎠ i+j=k i=1
) × dp (i = 1)
(10)
whereni , nj and nk is the i , j and k -mer particle number concentrations, Z is the maximum number of size categories. The first term on the right side of the equation indicates that the k -mer particle number concentrations is increased by the aggregation of i-mer particles and j-mer 6
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Fig. 7. Experimental and simulated results of the distribution of iron in the medium.
at the outlet of the packed column is shown in Fig. 3, and the permeability coefficient of the test column is shown in Fig. 4. It can be seen that under various conditions, the penetration curves show similar trends. With the experiment proceeding, the injection volume increases, the nZVI suspension penetrates the packed column gradually, the outlet concentration gradually increases to the maximum, and then the outlet concentration gradually decreases. This is because with the injection of nano-zero-valent iron, the residual particles in porous media gradually increase and occupy the pore volume. The deposition efficiency of nano-zero-valent iron in porous media increases, so the concentration at the outlet decreases gradually. The injection rate and concentration have different effects on the penetration curve. The larger the injection flow rate and the higher the concentration at the outlet, the smaller the residual amount of nanozero-valent iron particles in the sand column. When the injection flow rate is 12 ml/min, the maximum relative concentration at the exit reaches 0.70, 0.62 and 0.59, respectively, while at the injection flow rate of 4 ml/s, it is only 0.28, 0.27 and 0.19, with the injection concentration of 3 g/L, 1 g/L and 0.3 g/L. The injection rate and concentration also have some influence on the change of permeability coefficient. Generally speaking, when the flow rate is low and the concentration is high, the particles intercept quickly in porous media, and the permeability coefficient decreases rapidly, and vice versa. When the injection flow rate is 4 ml/min and 12 ml/min, the permeability coefficient of the packed column reaches 0.6 of the initial permeability coefficient when the injection volume is 1 PV, 4 PV, 8 PV and 3.5 PV, 7 PV and 10 PV, respectively, with the injection concentration of 3 g/L, 1 g/L and 0.3 g/L. When the injection concentration is 0.3 g/l and 3 g/l, the permeability coefficient of the packed column reaches 0.6 at 8PV, 9PV, 13PV and 0.6PV, 1.7PV and 3.5PV, respectively, with the injection flow of 4 ml/min, 8 ml/min and 12 ml/min. This is because when the injection flow rate is large, the shear effect of water flow on suspension particles is larger, fewer iron particles are
Fig. 8. Change of the deposition rate coefficient with the particle size and porosity.
Fig. 2. 3. Results and discussion 3.1. Experimental results Under various conditions, the iron concentration penetration curve 7
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Fig. 9. Transfer of modified nanoscale zero valent iron in porous media.
the concentration at the exit of the whole process does not change much, and the larger the flow rate, the higher the stable concentration; when the injection concentration is 1 g/L, the penetration curve has a gradual downward trend and the concentration of effluent decreases gradually; when the injection concentration is 3 g/L, the concentration of effluent decreases rapidly. This is because the higher the concentration, the more collisions between nZVI particles and porous media particles, the faster the particles occupy the pore volume, resulting in the rapid growth of kdep . In addition, the higher the particle concentration, the more collisions between nZVI particles, and the faster the particles aggregate into large-scale aggregates, resulting in further increase of kdep . The simulated permeability is close to 0 at a small PV (especially in the condition of 4 ml/min and 3 g/l), while it still remains 0.1–0.2 when PV is large for the experimental results. This is due to the serious blockage of the test column at high injection concentration. Under the action of water flow scouring, the nZVI particles attached to the porous media surface flow out again with the water. The process is complex and random, involving many mechanisms such as shear, torque, desorption and so on. The injection volume and concentration will be controlled in field application to avoid such a situation. So it is not considered in this article.
intercepted and adhered to the surface of porous media, and the permeability coefficient decreases slowly. When the injection concentration is high, there are more suspended particles in the water flow. Because of the higher basic concentration, the amount of iron remaining in porous media increases rapidly and permeability coefficient decreases faster.
3.2. Model fitting results The numerical model is established by using the method described in Section 2.2. The model parameters are shown in Table 3. Among them, parameters αpc and αpp were obtained by fitting and adjusting parameters, and particle size was obtained by TEM electron microscopy. The other parameters are all worthwhile according to the actual measurement. The fitting results show that the collision efficiency between particles and media (αpc ) is higher when the concentration is high, as well as between particles and particles (αpp ). Injection flow has little effect on αpp , but has a greater impact on αpc . The larger the injection flow, the lower the αpc . The fitting of the measured and simulated data of the change of outlet concentration and permeability coefficient under different experimental conditions is shown in Figs. 5 and 6, respectively. It can be seen from the graph that when the injection concentration is 0.3 g/L, 8
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Fig. 10. Changes of deposition rate coefficient and each mechanism.
more pore volume, and the deposition rate coefficient (kdep ) increases. The change of kdep in the process of change is shown in Fig. 10(a), and the change of each mechanism is shown in Fig. 10(b)–(d), respectively. It can be seen from the graph that with the injection of nZVI, the particles gradually occupy the pore space of porous media, making the pore volume gradually reduce. At the beginning of the experiment, the particle size of nZVI particles is smaller and the Brownian motion is stronger, which makes the kdep higher. The nZVI particles are easy to adsorb on the surface of porous media. With the experiment proceeding, the reaction coefficient has a rapid decline process, which is due to the aggregation of nZVI, which makes the average particle size increase and the diffusion effect decrease. At this stage, the diffusion effect of nZVI gradually weakens, and the pore space of porous media is not occupied too much. nZVI particles are most likely to migrate with water flow. As the experiment continues, the particle size continues to increase, the interception and sedimentation effects increase, and the impact efficiency increases with the decrease of porosity. Therefore, the reaction coefficient increases and the nZVI is difficult to pass through.
3.3. Spatial distribution of nZVI in medium In order to quantitatively analyze the whole process, the following conditions are selected to further analyze the whole process: injection concentration of 1 g/L with flow rate of 8 ml/min. The experimental and simulated results of the distribution of iron in the medium is shown in Fig. 7 at different times. From the graph, the simulation results of the model fit the test results well, the amount of iron retained in the medium increases gradually with the experiment. The distribution of iron is not uniform. It is the largest at the entrance and the lowest at the exit. With the increase of injection volume, most of the iron is intercepted at the entrance. This is because the interception begins at the entrance, and with the increase of interception, the interception rate increases, leading to a further increase in the gap. 3.4. Process mechanism According to the model of this method, the reaction coefficient is mainly affected by porosity and particle size. The deposition rate coefficients of different particle sizes and porosity are calculated according to Eqs. (3)–(7), as shown in Fig. 8. The deposition rate coefficient decreases first and then increases with the increase of particle size, and increases with the decrease of porosity, forming a surface as shown in the figure. The model established in this study describes the deposition and transport process of the nZVI particles in porous media as shown in Fig. 9. When nZVI particles pass through the packed column, some particles flow out with water, some are intercepted by porous media, and the interception rate is controlled by the parameter kdep . Because of the limited dispersion stability of particles, particles will gather together to form polymer, which makes the particle size increase. Particle polymerization process is described by polymerization kinetics and controlled by parameter αpp . With the injection of nZVI particle suspension, the intercepted nZVI particles gradually increase, occupying
4. Conclusions The migration of modified nZVI in porous media was studied by packed column experiments. An unsteady coupled model considering the polymerization between nZVI particles and the influence of nZVI attachment on the hydraulic properties of porous media was established. The migration process of modified nZVI in porous media was analyzed by combining experiment with model. The main conclusions are as follows: (1) The flow rate and the concentration of iron have great influence on the migration of modified nZVI in porous media. Under the experimental conditions of this study, when the flow rate is high, the residual amount of nZVI in porous media is less, the hydraulic characteristics of porous media change slowly, and the rate of iron passage is higher. When the concentration is high, the residual 9
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amount of nZVI in porous media is large, the hydraulic characteristics of the packed column change rapidly, the passing rate of iron is low. (2) The distribution of nZVI in porous media is not uniform, there are more nZVI at the entrance, and it decreases with the increase of distance. The main reason for this phenomenon is that interception begins at the entrance, and with the increase of interception, the interception rate increases, leading to a further increase in the gap. (3) In the initial stage of migration, the particle size is small, and the particles are easy to diffuse and adsorb to the surface of the medium, as well as the aggregation between particles is strong. With the progress of the experiment, the particle size increases and the Brownian motion decreases, mainly gravity sedimentation and interception.
Jiemvarangkul, P., Zhang, W.X., Lien, H.L., 2011. Enhanced transport of polyelectrolyte stabilized nanoscale zero-valent iron (nZVI) in porous media. Chem. Eng. J. 170 (2–3), 482–491. https://doi.org/10.1016/j.cej.2011.02.065. Kim, H.J., Phenrat, T., Tilton, R.D., Lowry, G.V., 2009. Fe-0 nanoparticles remain mobile in porous media after aging due to slow desorption of polymeric surface modifiers. Environ. Sci. Technol. 43 (10), 3824–3830. https://doi.org/10.1021/es802978s. Kocur, C.M., et al., 2014. Characterization of nZVI mobility in a field scale test. Environ. Sci. Technol. 48 (5), 2862–2869. https://doi.org/10.1021/es4044209. Krol, M.M., et al., 2013. A field-validated model for in situ transport of polymer-stabilized nZVI and implications for subsurface injection. Environ. Sci. Technol. 47 (13), 7332–7340. https://doi.org/10.1021/es3041412. Lee, D.G., Bonner, J.S., Garton, L.S., Ernest, A.N.S., Autenrieth, R.L., 2000. Modeling coagulation kinetics incorporating fractal theories: a fractal rectilinear approach. Water Res. 34 (7), 1987–2000. https://doi.org/10.1016/s0043-1354(99)00354-1. Lefevre, E., Bossa, N., Wiesner, M.R., Gunsch, C.K., 2016. A review of the environmental implications of in situ remediation by nanoscale zero valent iron (nZVI): behavior, transport and impacts on microbial communities. Sci. Total Environ. 565, 889–901. https://doi.org/10.1016/j.scitotenv.2016.02.003. Li, P., Lin, K., Fang, Z., Zhang, W., 2018. Degradation of nitrate and secondary pollution in drinking water by S-NZVI prepared from steel pickling waste liquor. J. HydroEnviron. Res. https://doi.org/10.1016/j.jher.2018.01.005. Li, X., et al., 2019. Immobilization of phosphorus in sediments by nano zero-valent iron (nZVI) from the view of mineral composition. Sci. Total Environ. 694, 133695. https://doi.org/10.1016/j.scitotenv.2019.133695. Li, X.Q., Elliott, D.W., Zhang, W.X., 2006. Zero-valent iron nanoparticles for abatement of environmental pollutants: materials and engineering aspects. Crit. Rev. Solid State Mat. Sci. 31 (4), 111–122. https://doi.org/10.1080/10408430601057611. Li, Z., Greden, K., Alvarez, P.J.J., Gregory, K.B., Lowry, G.V., 2010. Adsorbed polymer and NOM limits adhesion and toxicity of nano scale zerovalent iron to E. coli. Environ. Sci. Technol. 44 (9), 3462–3467. https://doi.org/10.1021/es9031198. Liu, T.Y., et al., 2010. Effects of physicochemical factors on Cr(VI) removal from leachate by zero-valent iron and alpha-Fe2O3 nanoparticles. Water Sci. Technol. 61 (11), 2759–2767. https://doi.org/10.2166/wst.2010.167. Maximova, N., Dahl, O., 2006. Environmental implications of aggregation phenomena: current understanding. Curr. Opin. Colloid Interface Sci. 11 (4), 246–266. https:// doi.org/10.1016/j.cocis.2006.06.001. Nooruddin, H.A., Hossain, M.E., 2011. Modified Kozeny-Carmen correlation for enhanced hydraulic flow unit characterization. J. Pet. Sci. Eng. 80 (1), 107–115. https://doi. org/10.1016/j.petrol.2011.11.003. O’Carroll, D., Sleep, B., Krol, M., Boparai, H., Kocur, C., 2013. Nanoscale zero valent iron and bimetallic particles for contaminated site remediation. Adv. Water Resour. 51, 104–122. https://doi.org/10.1016/j.advwatres.2012.02.005. Phenrat, T., Saleh, N., Sirk, K., Tilton, R.D., Lowry, G.V., 2007. Aggregation and sedimentation of aqueous nanoscale zerovalent iron dispersions. Environ. Sci. Technol. 41 (1), 284–290. https://doi.org/10.1021/es061349a. Ponder, S.M., Darab, J.G., Mallouk, T.E., 2000. Remediation of Cr(VI) and Pb(II) aqueous solutions using supported, nanoscale zero-valent iron. Environ. Sci. Technol. 34 (12), 2564–2569. https://doi.org/10.1021/es9911420. Qu, G., et al., 2019. Magnetic Fe3O4 assembled on nZVI supported on activated carbon fiber for Cr(VI) and Cu(II) removal from aqueous solution through a permeable reactive column. Environ. Sci. Pollut. Res. 26 (5), 5176–5188. https://doi.org/10. 1007/s11356-018-3985-8. Quinn, J., et al., 2005. Field demonstration of DNAPL dehalogenation using emulsified zero-valent iron. Environ. Sci. Technol. 39 (5), 1309–1318. https://doi.org/10.1021/ es0490018. Rajagopalan, R., Tien, C., 1976. Trajectory analysis of deep-bed filtration with the spherein-cell porous media model. AIChE J. 22 (3), 523–533. https://doi.org/10.1002/aic. 690220316. Raychoudhury, T., Tufenkji, N., Ghoshal, S., 2012. Aggregation and deposition kinetics of carboxymethyl cellulose-modified zero-valent iron nanoparticles in porous media. Water Res. 46 (6), 1735–1744. https://doi.org/10.1016/j.watres.2011.12.045. Ren, J., Woo, Y.C., Yao, M., Tijing, L.D., Shon, H.K., 2017. Enhancement of nanoscale zero-valent iron immobilization onto electrospun polymeric nanofiber mats for groundwater remediation. Process Saf. Environ. Protect. 112, 200–208. https://doi. org/10.1016/j.psep.2017.04.027. Schrick, B., Hydutsky, B.W., Blough, J.L., Mallouk, T.E., 2004. Delivery vehicles for zerovalent metal nanoparticles in soil and groundwater. Chem. Mat. 16 (11), 2187–2193. https://doi.org/10.1021/cm0218108. Scott, T.B., Popescu, I.C., Crane, R.A., Noubactep, C., 2011. Nano-scale metallic iron for the treatment of solutions containing multiple inorganic contaminants. J. Hazard. Mater. 186 (1), 280–287. https://doi.org/10.1016/j.jhazmat.2010.10.113. Shen, X., et al., 2011. Foam, a promising vehicle to deliver nanoparticles for vadose zone remediation. J. Hazard. Mater. 186 (2–3), 1773–1780. https://doi.org/10.1016/j. jhazmat.2010.12.071. Sun, Y.P., Li, X.Q., Zhang, W.X., Wang, H.P., 2007. A method for the preparation of stable dispersion of zero-valent iron nanoparticles. Colloid Surf. A-Physicochem. Eng. Asp. 308 (1–3), 60–66. https://doi.org/10.1016/j.colsurfa.2007.05.029. Tilston, E.L., Collins, C.D., Mitchell, G.R., Princivalle, J., Shaw, L.J., 2013. Nanoscale zerovalent iron alters soil bacterial community structure and inhibits chloroaromatic biodegradation potential in Aroclor 1242-contaminated soil. Environ. Pollut. 173, 38–46. https://doi.org/10.1016/j.envpol.2012.09.018. Tosco, T., Petrangeli Papini, M., Cruz Viggi, C., Sethi, R., 2014. Nanoscale zerovalent iron particles for groundwater remediation: a review. J. Clean. Product. 77, 10–21. https://doi.org/10.1016/j.jclepro.2013.12.026. Tufenkji, N., Elimelech, M., 2004. Correlation equation for predicting single-collector efficiency in physicochemical filtration in saturated porous media. Environ. Sci.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The work was supported by the Beijing Municipal Science and Technology Commission (Z161100004516015) and National Key Research and Development Project of China (2016YFC0401404). References Bai, R.B., Tien, C., 2000. Effect of deposition in deep-bed filtration: determination and search of rate parameters. J. Colloid Interface Sci. 231 (2), 299–311. https://doi.org/ 10.1006/jcis.2000.7130. Chaithawiwat, K., et al., 2016. Impact of nanoscale zero valent iron on bacteria is growth phase dependent. Chemosphere 144, 352–359. https://doi.org/10.1016/j. chemosphere.2015.09.025. Chen, P.-J., Su, C.-H., Tseng, C.-Y., Tan, S.-W., Cheng, C.-H., 2011. Toxicity assessments of nanoscale zerovalent iron and its oxidation products in medaka (Oryzias latipes) fish. Mar. Pollut. Bull. 63 (5–12), 339–346. https://doi.org/10.1016/j.marpolbul.2011. 02.045. Choe, S., Lee, S.H., Chang, Y.Y., Hwang, K.Y., Khim, J., 2001. Rapid reductive destruction of hazardous organic compounds by nanoscale Fe-0. Chemosphere 42 (4), 367–372. https://doi.org/10.1016/s0045-6535(00)00147-8. Comba, S., Sethi, R., 2009. Stabilization of highly concentrated suspensions of iron nanoparticles using shear-thinning gels of xanthan gum. Water Res. 43 (15), 3717–3726. https://doi.org/10.1016/j.watres.2009.05.046. Cullen, L.G., Tilston, E.L., Mitchell, G.R., Collins, C.D., Shaw, L.J., 2011. Assessing the impact of nano- and micro-scale zerovalent iron particles on soil microbial activities: particle reactivity interferes with assay conditions and interpretation of genuine microbial effects. Chemosphere 82 (11), 1675–1682. https://doi.org/10.1016/j. chemosphere.2010.11.009. Efecan, N., Shahwan, T., Eroglu, A.E., Lieberwirth, I., 2009. Characterization of the uptake of aqueous Ni2+ ions on nanoparticles of zero-valent iron (nZVI). Desalination 249 (3), 1048–1054. https://doi.org/10.1016/j.desal.2009.06.054. El-Temsah, Y.S., Joner, E.J., 2012a. Ecotoxicological effects on earthworms of fresh and aged nano-sized zero-valent iron (nZVI) in soil. Chemosphere 89 (1), 76–82. https:// doi.org/10.1016/j.chemosphere.2012.04.020. El-Temsah, Y.S., Joner, E.J., 2012b. Impact of Fe and Ag nanoparticles on seed germination and differences in bioavailability during exposure in aqueous suspension and soil. Environ. Toxicol. 27 (1), 42–49. https://doi.org/10.1002/tox.20610. Elliott, D.W., Zhang, W.X., 2003. Field assessment of nanoscale bimetallic particles for groundwater treatment. Abstr. Pap. Am. Chem. Soc. 225 U971. Fatisson, J., Ghoshal, S., Tufenkji, N., 2010. Deposition of carboxymethylcellulose-coated zero-valent iron nanoparticles onto silica: roles of solution chemistry and organic molecules. Langmuir 26 (15), 12832–12840. https://doi.org/10.1021/la1006633. Gierczycki, A.T., Al-Rashed, M.H., 2008. Aggregation and breakage of solid particles in suspensions agitated in a vibrating mixer: a fractal approach. Chem. Eng. Commun. 195 (4), 427–434. https://doi.org/10.1080/00986440701707537. He, F., Zhao, D., Paul, C., 2010. Field assessment of carboxymethyl cellulose stabilized iron nanoparticles for in situ destruction of chlorinated solvents in source zones. Water Res. 44, 2360–2370. https://doi.org/10.1016/j.watres.2009.12.041. He, F., Zhao, D.Y., 2005. Preparation and characterization of a new class of starch-stabilized bimetallic nanoparticles for degradation of chlorinated hydrocarbons in water. Environ. Sci. Technol. 39 (9), 3314–3320. https://doi.org/10.1021/ es048743y. Herzig, J.P., Leclerc, D.M., Goff, P.L., 1970. Flow of suspensions through porous Media—Application to deep filtration. Ind. Eng. Chem. 62 (5), 8–35. https://doi.org/ 10.1021/ie50725a003.
10
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Y. Liu, et al.
1007/s11270-013-1845-1. Yao, K.M., Habibian, M.T., O'Melia, C.R., 1971. Water and waste water filtration: concepts and applications. Environ. Sci. Technol. 5 (11), 1105–1112. https://doi.org/10. 1021/es60058a005. Zhang, X., Lin, Y.M., Chen, Z.L., 2009. 2,4,6-Trinitrotoluene reduction kinetics in aqueous solution using nanoscale zero-valent iron. J. Hazard. Mater. 165 (1–3), 923–927. https://doi.org/10.1016/j.jhazmat.2008.10.075.
Technol. 38 (2), 529–536. https://doi.org/10.1021/es034049r. Wei, Y.T., et al., 2010. Influence of nanoscale zero-valent iron on geochemical properties of groundwater and vinyl chloride degradation: a field case study. Water Res. 44 (1), 131–140. https://doi.org/10.1016/j.watres.2009.09.012. Xu, C.-H., Zhu, L.-J., Wang, X.-H., Lin, S., Chen, Y.-M., 2014. Fast and highly efficient removal of chromate from aqueous solution using nanoscale zero-valent iron/activated carbon (NZVI/AC). Water Air & Soil Pollut. 225 (2), 1845. https://doi.org/10.
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Research papers
Migration experiment and numerical simulation of modified nanoscale zerovalent iron (nZVI) in porous media
T
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Yu Liua,b, Yongxiang Zhanga,b, , Shuangshuang Lana,b, Shukai Houa,b a b
College of Architectural Engineering, Beijing University of Technology, Beijing 100124, China Key Laboratory of Beijing for Water Quality Science and Water Environment Recovery Engineering, Beijing 100124, China
A R T I C LE I N FO
A B S T R A C T
This manuscript was handled by Huaming Guo, Editor-in-Chief
A packed column experiment was carried out to study the migration process of modified nano-zero-valent iron (nZVI) in porous media and the change process of hydraulic characteristics of porous media. In view of the complexity of the migration mechanism of modified nZVI in porous media, an unsteady variable parameter mathematical model considering the effects of interception, Brownian diffusion, gravity settling and the change of porous media properties was established. By fitting the model with the experimental data, the changes of various mechanisms in the experimental process were studied. The results show that the higher the injection flow rate, the higher the concentration at the outlet, and the lower the injection concentration, the higher the throughput. The distribution of iron particles in porous media is not uniform, the maximum at the entrance and the lowest at the exit. The model fits the test results well under various test conditions. The model analysis shows that in the process of particle injection, the particle size is small at the beginning, and the particles are mainly attached to the surface of the medium due to Brownian motion. As the experiment proceeds, the particle size increases, the Brownian motion effect decreases, but the interception and gravity settlement effect strengthens. In addition, during the whole process, the porosity of the medium decreases gradually, and the probability of collision between particles and porous media increases, which leads to the increase of the deposition rate coefficient.
Keywords: Modified nanoscale zero valent iron Migration Distribution Laboratory test Mathematical model
1. Introduction Nano-scale zero-valent (nZVI) has strong reducibility, large specific surface area and high reactivity (Choe et al., 2001; Liu et al., 2010). It has good removal effect for nitrobenzene, chlorohydrocarbons and other organic matters, and has become one of the more promising and effective remediation materials in the field of underground environmental remediation (Efecan et al., 2009; Li et al., 2019; Ponder et al., 2000; Qu et al., 2019; Scott et al., 2011; Xu et al., 2014; Zhang et al., 2009). Injecting nZVI suspension into underground can effectively degrade most chlorinated organic pollutants, inorganic anions and toxic heavy metals dissolved in solution (Elliott and Zhang, 2003; O’Carroll et al., 2013; Quinn et al., 2005; Tosco et al., 2014; Wei et al., 2010). Nevertheless, there are some major problems that prevent the effective application of nZVI in groundwater remediation. An important obstacle to the wide application of nZVI is the tendency of rapid aggregation and settling of nZVI particles in aqueous suspension (Kocur et al., 2014). Because of the strong magnetic force and van der Waals force between particles, nZVI particles are easy to
⁎
agglomerate when suspended in water, forming a dendritic or reticular structure, which may be much larger than the micron scale. This results in the aggregation and adhesion of nZVI particles on the surface of environmental particles during injection, which limits the mobility of nZVI. In addition, the reaction rate with pollutants is also reduced due to the reduction of specific surface area. (Li et al., 2006; Phenrat et al., 2007; Schrick et al., 2004; Shen et al., 2011). In recent years, the research on modification technology of nZVI has been emerging, which greatly improves the migration of nZVI. By adding organic dispersants such as poly acrylic acid (PAA) and carboxymethyl starch cellulose (CMC) into nZVI suspension, the van der Waals force between particles is reduced, the steric hindrance is increased, and the polymerization probability is reduced (Comba and Sethi, 2009; Fatisson et al., 2010; he et al., 2010; He and Zhao, 2005; Jiemvarangkul et al., 2011; Kim et al., 2009). The migration distance of organic dispersants stabilized nZVI in porous media has been greatly increased relative to that of bare nZVI. However, compared with stable solutions, the stability of modified nZVI is still limited, and its migration characteristics in porous media still remains to be explored.
Corresponding author at: College of Architectural Engineering, Beijing University of Technology, Beijing 100124, China. E-mail address: [email protected] (Y. Zhang).
https://doi.org/10.1016/j.jhydrol.2019.124193 Received 30 May 2019; Received in revised form 23 September 2019; Accepted 27 September 2019 Available online 28 September 2019 0022-1694/ © 2019 Elsevier B.V. All rights reserved.
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Piezometer
Sample Peristaltic pump 30cm Quartz sand column
N2
Piezometer Modified nZVI suspension Fig. 1. Experimentation device schematic. Table 1 Summary of dimensionless parameters governing particle filtration. Parameter
Calculation formula
Physical explanation
NR
dp dc
The ratio of particle size to porous medium size
NPe
Udc D∞ A kT A
Proportion of convective and diffusive transport represented by Peclet number
NvdW
NA NG
Van der Waals Number Characterization of the Ratio of Van der Waals Interaction to Particle Heat Energy Attraction number: represents the combined effect of van der Waals gravity and fluid velocity on the deposition rate of intercepted particles。
12πμap2 U
Gravity Number: ratio of Settlement Velocity of Stokes Particles to Fluid Velocity
2 2 ap (ρp − ρf ) g 9 μU
where dp is the particle diameter, dc is the particle diameter of porous media, U is the fluid approach velocity, D∞ is the bulk diffusion coefficient (described by StokesEinstein equation), A is the Hamaker constant (4 × 10−20J ), k is the Boltzmann constant (1.38 × 10−16gcm2s −2K−1), T is fluid absolute temperature, ap is particle radius, ρp is the particle density, ρf is the fluid density, μ is the absolute fluid viscosity, and g is the gravitational acceleration (981 × cms −2 ). Table 2 Collision frequency functions for the coalesced fractal sphere (CFS) model. Parameter
Calculation formula
βBR (vi, vj )
2kT 3μ
βSH (vi, vj )
G 1 − 3/ DF 1/ DF DF 3 v (vi + v1/ ) j π 0 1 g π − 3 (ρ0 − ρw ) 1/3 ⎛ ⎞ v0 − 1/ DF 12μ 6 ⎝ ρw ⎠ 1 g π − 3 (ρ0 − ρw ) ⎛ ⎞ v04/3 − 3/ DF 12μ 6 ⎝ ρw ⎠
βDS (vi, vj ) βDS (vi, vj )
DF 1/ DF (vi1/ DF + v1/ )(vi−1/ DF + v− ) j j
()
DF 2 (vi1/ DF + v1/ ) × |vi(DF − 1)/ DF − v j(DF − 1)/ DF |(2 ≤DF ≤3) j
()
DF 2 DF (vi1/ DF + v1/ ) × |vi1/ DF − v1/ |(DF ≤2) j j
where v0 is volume of a monomer, vi and vj is solid volume of i and j-mer aggregate respectively, ρ0 is density of monomers, and ρw is density of water.
The fluidity of nZVI particles is too large to uniformly distribute in polluted groundwater, which may also cause secondary pollution to the environment (Krol et al., 2013; Li et al., 2018; Ren et al., 2017). Because of the active nature of nZVI, iron ions and iron oxides are easily released into the environment, which will have unpredictable and serious toxic effects on organisms and even ecosystems. At present,
most studies focus on the toxicity of nZVI to microorganisms (Chaithawiwat et al., 2016; Li et al., 2010). However, some scholars have found that nZVI can also affect barley (El-Temsah and Joner, 2012b), earthworms (El-Temsah and Joner, 2012a) and fish (Chen et al., 2011), and further observations have found that nZVI can even change the physical and chemical properties of the environment (Cullen
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nZVI in site scale test. Transport and deposition of particle suspensions in porous media and the effects on porous media have been discussed in previous studies. These studies suggested that the deposition of suspended particles through porous media mainly includes three functions: interception, sedimentation and Brownian diffusion (Bai and Tien, 2000; Herzig et al., 1970; Rajagopalan and Tien, 1976; Tufenkji and Elimelech, 2004; Yao et al., 1971). Bai and Tien (Bai and Tien, 2000) suggested that when particle suspension passes through porous media, the structure and surface conditions of the medium undergo continuous changes (the parameters of the medium change), which in turn affect the filtration or deposition rate. Therefore, particle suspension through porous media is essentially an unsteady process, and the hydraulic parameters and effluent concentration of porous media usually change with time. Yao et al. (1971) proposed a conceptual model of water and wastewater filtration process by means of micro-analysis method, and compared it with laboratory test results. It is proposed that smaller particles are intercepted by diffusion while larger particles are intercepted by interception and settlement. Tufenkji and Elimelech (Tufenkji and Elimelech, 2004) proposed an equation for predicting the single-collector contact efficiency (η0 ) in physicochemical particle filtration in saturated porous media. The correlation equation is developed assuming that the overall single-collector efficiency can be calculated as the sum of the contributions of the individual transport mechanisms Brownian diffusion, interception, and gravitational sedimentation. The migration and distribution characteristics of modified nZVI in porous media have been discussed in previous studies. These studies suggested that nZVI is different from other particles, it is unstable in water and easy to agglomerate into large particles. Jiemvarangkul et al. (2011) modified nano-zero-valent iron by three kinds of polyelectrolytes (PV3A, PAA and soybean protein). The migration of nano-zerovalent iron before and after modification was compared by column and batch experiments. It was proposed that modified nano-zero-valent iron with adjustable travel distance could be prepared to form iron reaction zone in designated target area and achieve the purpose of in-situ pollution control. The aggregation of nZVI particles will affect their deposition in porous media, and the particle size determines the contact efficiency of a single collector (η0 ). Raychoudhury et al. (2012) investigated the transport and deposition of carboxymethyl cellulose (CMC) modified zero-valent iron (nZVI) nanoparticles in laboratoryscale sand-filled columns, a modified colloid transport model which couples the governing transport equation to the aggregation kinetics equation was developed, however, the effect of the variation of porous media parameters on migration process is not considered. The migration of nZVI will affect the hydraulic characteristics of porous media, which conversely affects the nZVI migration. The parameters are time
Fig. 2. Calculation process of the model.
et al., 2011; Tilston et al., 2013). Understanding the migration of nZVI in porous media is essential to evaluate the potential of nZVI to travel from injection points to untargeted environmental compartments, and to assess the microbial community exposure to nZVI (Lefevre et al., 2016). The study of the migration and distribution of modified nZVI in porous media can provide theoretical basis for the occurrence and development of plugging in the process of injecting nZVI suspension into porous media. The numerical model can simulate and reproduce the migration process of nZVI in porous media, and quantitatively predict the distribution of nZVI in porous media in different periods. It is of great significance for the development of nZVI with adjustable migration distance and the prediction of the underground injection process of
Fig. 3. Breakthrough curve of nZVI. 3
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Fig. 4. Change process of permeability coefficient of packed column.
continuously injected for 10 min to ensure deoxidation, while continuously stirring to ensure the uniformity of the dispersant. Then the sodium borohydride solution with 150 ml concentration was dripped at the speed of 10 ml/min. The theoretical concentration of iron in the suspension prepared by this method is 1 g/L. Modified nano-zero-valent iron suspension with different concentration can be prepared by changing the amount of reagent.
Table 3 Summary of dimensionless parameters governing particle filtration. Flow ml/ min
Concentration g/L
Collision efficiency between particles and media αpc
Collision efficiency between particles αpp
12 12 12 8 8 8 4 4 4
3 1 0.3 3 1 0.3 3 1 0.3
0.61 0.60 0.57 0.67 0.65 0.63 0.72 0.70 0.69
1.23 1.1 0.82 1.22 1.11 0.80 1.18 1.09 0.79
2.1.2. Packed column experiments The experimental device is shown in Fig. 1. In order to ensure the uniformity of water distribution, glass beads with a diameter of 0.3 cm were filled in the inlet and outlet of the column with a size of 2 cm. The rest is filled with quartz sand with particle size of 0.5–0.7 mm. Pressure gauges are set at the inlet and outlet to monitor the inlet and outlet pressure. After filling, deoxidized water is pumped into the column by a peristaltic pump to get rid of the gas in the column and obtain a stable flow pattern. Nine groups of penetration experiments were carried out with 12 ml/min, 8 ml/min and 4 ml/min as injection flow rates, and the concentration of injected suspension was 3 g/l, 1 g/l and 0.3 g/l. The pH value of the suspension is 7.4 ± 0.4 and the temperature is 278 K. The concentration of iron in the effluent was measured, as well as the change of inlet and outlet pressure during the whole process was monitored. The total iron concentrations were measured by atomic absorption (AA) method (Jiemvarangkul et al., 2011). In order to quantitatively analyze the occurrence of plugging in porous media during the injection process, and explain the migration characteristics of nZVI particles in the medium in detail, the distribution of residual iron particles in the medium during the injection of modified nano-zero-valent iron was measured by parallel experiments. Among the six groups of packed columns with the same parameters, 1 g/l and 8 ml/min were injected into the suspension, and the experiments were stopped at the injection volumes of 2, 4, 6, 8, 10 and 12 pore volumes (PVs), respectively. The quartz sand in the column was taken out and divided into 10 parts every 3 cm. The concentration of iron in the solution was measured after soaking with dilute hydrochloric acid in a certain volume, and the solid phase concentration in the medium at that time was calculated.
varied, therefore a non-stationary variable parameter model is required. The objectives of this study were to assess the kinetics of PAA-nZVI particles polymerization and the changes of the hydraulic parameters caused by the deposition of PAA-nZVI, as well as the effects of these two actions on the migration of PAA-nZVI in porous media. In this study, PAA-nZVI suspension was prepared by chemical reduction method. Column transport experiments for different nanoparticle concentrations and different injection flow rates were performed to study the migration characteristics of PAA-nZVI in porous media and its influence on the hydraulic characteristics of porous media. A non-stationary variable parameter mathematical model was established, which coupled with the kinetics of PAA-nZVI particles polymerization and the change of porous media properties, and the effluent nZVI concentrations over time were fitted to the modified particulate transport model to assess whether the model could account for the observed shape of the experimental breakthrough curves. The parameter change process of Brownian motion, interception and settlement caused by the change of particle size and hydraulic characteristics of porous media during PAAnZVI migration were analyzed based on this model.
2. Materials and methods 2.1. Migration experiment scheme 2.1.1. Synthesis of PAA-nZVI In this study, nZVI was prepared by chemical reduction and poly acrylic acid (PAA) was used as dispersant (Sun et al., 2007). The specific operation is as follows: take ferrous sulfate g-heptahydrate in three flasks, add 350 ml of anaerobic water to dissolve it, and add 1 ml of PAA (optimal dosage) (Jiemvarangkul et al., 2011), during which nitrogen is
2.2. Numerical simulation method The migration of modified nano-zero-valent iron in porous media is a complex process. With the deposition in porous media, the structure and surface conditions of the medium undergo continuous changes (the parameters of the medium change), which in turn affect the filtration or 4
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Fig. 5. Experimental breakthrough curves with model fit.
single-collector contact efficiency controlled by diffusion, interception and settling mechanisms (Tufenkji and Elimelech, 2004).
deposition rate. Therefore, the migration of PAA-nZVI in porous media is essentially an unsteady process. Hydraulic parameters of porous media and effluent concentration (or filtrate mass) usually change with time. In this paper, the following methods are used to establish the mathematical model.
2.2.2. Computation of single-collector contact efficiency η0 is calculated according to the following Equation:
η0 = ηD + ηI + ηG
where ηD is the collision efficiency of the 3 between nZVI particles and collector, ηI is the interception mechanism and ηG is the settlement mechanism. η0 can be calculated using the methods proposed by Tufenkji and Elimelech (2004) Particle size, porous medium size, porosity and Darcy velocity are the main factors affecting the calculation. The specific calculation method is as follows:
2.2.1. Basic equation of solute transport in porous media In porous media, traditional migration is usually described in Eq. (1).
∂C ∂ 2C ∂C =D 2 −v − kdep C ∂t ∂x ∂x
ρ
∂Cs = kdep C ∂t
(1)
(2)
where C is the mass concentration of suspended particles, Cs is the concentration of particles deposited on the solid phase, D is the dispersion coefficient of hydrodynamics, v is the pore velocity, and kdep is the deposition rate coefficient of particles. kdep is calculated according to the following Equation (Rajagopalan and Tien, 1976):
3(1 − ε ) v kdep = ⎡ αpc ⎤ η0 ⎢ ⎥ ⎣ 2dc ε ⎦
(4)
−0.715 0.052 ηD = 2.4AS1/3 NR−0.081 NPe NvdW
(5)
ηI = 0.55AS NR1.675 N A0.125
(6)
0.053 ηG = 0.22NR−0.24 NG1.11 NvdW
(7)
The physical explanations and calculation formulas of the dimensionless parameters are listed in Table 1. 2.2.3. Effect on porous media Residual nano-zero-valent iron in porous media will lead to changes in hydraulic characteristics of the media, thus affecting the concentration of effluent. There is a certain relationship among solid concentration, porosity and permeability. Suspended particles deposit in the pore
(3)
where αpc is the collision efficiency between particles and collectors, ε is the porosity, dc is the particle diameter of porous media, and η0 is the 5
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Fig. 6. Experimental permeability coefficient of packed column with model fit.
particles, and the second term indicates that the k -mer particle number concentrations is decreased as a result of collisions that lead to further aggregation. Aggregation kinetics is controlled by the particle–particle attachment efficiency, αpp , which is the fraction of particle–particle collisions resulting in attachment and is dependent on solution chemistry. β (i, j ) represents the reaction constants between order i and j under Brownian motion (βBR ), fluid shear (βSH ) and differential settlement (βDS ), which are derived from the calculation method in Table 2. β (i, j ) is computed using the Coalesced Fractal Sphere model (Lee et al., 2000) as Eq. (11).
of aquifer medium and occupy part of the pore space, resulting in the decrease of porosity of medium, which can be described as: (8)
ε = ε0 − σCs
where ε is the porosity at a certain time after injection, ε0 is the initial porosity, and σ is the volume of pore blocked by suspended particles per unit mass. The relationship between permeability and porosity is expressed by Kozeny-Carmen equation (Nooruddin and Hossain, 2011).
Kt = K 0 ∙
ε3 (1 − ε0 )2 ∙ (1 − ε )2 ε03
β = βBR + βSH + βDS
(9)
(11)
where Kt is the permeability coefficient at t moment after injection, K 0 is the initial permeability coefficient.
The particle size of aggregates is measured by the following equation (Gierczycki and Al-Rashed, 2008; Maximova and Dahl, 2006):
2.2.4. Polymerization of particles The migration of nano-zero-valent iron in porous media is accompanied by the process of particle aggregation (Raychoudhury et al., 2012). Because of particle aggregation, the particle size increases, which has a great influence on the deposition rate coefficient of particles (kdep ). The agglomeration kinetics of nZVI particles can be described by the Eq. (10) (Lee et al., 2000).
dp (i) = (Ni
1/ Df
(12)
where Ni is the number of particles forming aggregates, Df is the fractal dimension of the formed aggregates, which is adopted 2 (Raychoudhury et al., 2012), dp (i) is the diameter of the polymer formed by Ni particles and dp (i = 1) represents the diameter of a single particle. 2.2.5. Implementation of model algorithms The finite difference method is used to solve the Eqs. (1), (2) and (10). The sand column is discretized into 30 grids with a length of 1 cm and time step is 20 s. For each time step, Eqs. (10)–(12) is first solved to obtain the particle size distribution at that time. Based on this particle size, the deposition coefficient (kdep ) is calculated by Eqs. (3)–(9). Finally, kdep is introduced into Eqs. (1) and (2) to calculate the concentration at that time step. The calculation process is shown in the
Z
⎛ dnk ⎞ = 1 αpp ∑ β (i, j ) ni nj − αpp nk ∑ β (i, k ) ni 2 ⎝ dt ⎠ i+j=k i=1
) × dp (i = 1)
(10)
whereni , nj and nk is the i , j and k -mer particle number concentrations, Z is the maximum number of size categories. The first term on the right side of the equation indicates that the k -mer particle number concentrations is increased by the aggregation of i-mer particles and j-mer 6
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Fig. 7. Experimental and simulated results of the distribution of iron in the medium.
at the outlet of the packed column is shown in Fig. 3, and the permeability coefficient of the test column is shown in Fig. 4. It can be seen that under various conditions, the penetration curves show similar trends. With the experiment proceeding, the injection volume increases, the nZVI suspension penetrates the packed column gradually, the outlet concentration gradually increases to the maximum, and then the outlet concentration gradually decreases. This is because with the injection of nano-zero-valent iron, the residual particles in porous media gradually increase and occupy the pore volume. The deposition efficiency of nano-zero-valent iron in porous media increases, so the concentration at the outlet decreases gradually. The injection rate and concentration have different effects on the penetration curve. The larger the injection flow rate and the higher the concentration at the outlet, the smaller the residual amount of nanozero-valent iron particles in the sand column. When the injection flow rate is 12 ml/min, the maximum relative concentration at the exit reaches 0.70, 0.62 and 0.59, respectively, while at the injection flow rate of 4 ml/s, it is only 0.28, 0.27 and 0.19, with the injection concentration of 3 g/L, 1 g/L and 0.3 g/L. The injection rate and concentration also have some influence on the change of permeability coefficient. Generally speaking, when the flow rate is low and the concentration is high, the particles intercept quickly in porous media, and the permeability coefficient decreases rapidly, and vice versa. When the injection flow rate is 4 ml/min and 12 ml/min, the permeability coefficient of the packed column reaches 0.6 of the initial permeability coefficient when the injection volume is 1 PV, 4 PV, 8 PV and 3.5 PV, 7 PV and 10 PV, respectively, with the injection concentration of 3 g/L, 1 g/L and 0.3 g/L. When the injection concentration is 0.3 g/l and 3 g/l, the permeability coefficient of the packed column reaches 0.6 at 8PV, 9PV, 13PV and 0.6PV, 1.7PV and 3.5PV, respectively, with the injection flow of 4 ml/min, 8 ml/min and 12 ml/min. This is because when the injection flow rate is large, the shear effect of water flow on suspension particles is larger, fewer iron particles are
Fig. 8. Change of the deposition rate coefficient with the particle size and porosity.
Fig. 2. 3. Results and discussion 3.1. Experimental results Under various conditions, the iron concentration penetration curve 7
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Fig. 9. Transfer of modified nanoscale zero valent iron in porous media.
the concentration at the exit of the whole process does not change much, and the larger the flow rate, the higher the stable concentration; when the injection concentration is 1 g/L, the penetration curve has a gradual downward trend and the concentration of effluent decreases gradually; when the injection concentration is 3 g/L, the concentration of effluent decreases rapidly. This is because the higher the concentration, the more collisions between nZVI particles and porous media particles, the faster the particles occupy the pore volume, resulting in the rapid growth of kdep . In addition, the higher the particle concentration, the more collisions between nZVI particles, and the faster the particles aggregate into large-scale aggregates, resulting in further increase of kdep . The simulated permeability is close to 0 at a small PV (especially in the condition of 4 ml/min and 3 g/l), while it still remains 0.1–0.2 when PV is large for the experimental results. This is due to the serious blockage of the test column at high injection concentration. Under the action of water flow scouring, the nZVI particles attached to the porous media surface flow out again with the water. The process is complex and random, involving many mechanisms such as shear, torque, desorption and so on. The injection volume and concentration will be controlled in field application to avoid such a situation. So it is not considered in this article.
intercepted and adhered to the surface of porous media, and the permeability coefficient decreases slowly. When the injection concentration is high, there are more suspended particles in the water flow. Because of the higher basic concentration, the amount of iron remaining in porous media increases rapidly and permeability coefficient decreases faster.
3.2. Model fitting results The numerical model is established by using the method described in Section 2.2. The model parameters are shown in Table 3. Among them, parameters αpc and αpp were obtained by fitting and adjusting parameters, and particle size was obtained by TEM electron microscopy. The other parameters are all worthwhile according to the actual measurement. The fitting results show that the collision efficiency between particles and media (αpc ) is higher when the concentration is high, as well as between particles and particles (αpp ). Injection flow has little effect on αpp , but has a greater impact on αpc . The larger the injection flow, the lower the αpc . The fitting of the measured and simulated data of the change of outlet concentration and permeability coefficient under different experimental conditions is shown in Figs. 5 and 6, respectively. It can be seen from the graph that when the injection concentration is 0.3 g/L, 8
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Fig. 10. Changes of deposition rate coefficient and each mechanism.
more pore volume, and the deposition rate coefficient (kdep ) increases. The change of kdep in the process of change is shown in Fig. 10(a), and the change of each mechanism is shown in Fig. 10(b)–(d), respectively. It can be seen from the graph that with the injection of nZVI, the particles gradually occupy the pore space of porous media, making the pore volume gradually reduce. At the beginning of the experiment, the particle size of nZVI particles is smaller and the Brownian motion is stronger, which makes the kdep higher. The nZVI particles are easy to adsorb on the surface of porous media. With the experiment proceeding, the reaction coefficient has a rapid decline process, which is due to the aggregation of nZVI, which makes the average particle size increase and the diffusion effect decrease. At this stage, the diffusion effect of nZVI gradually weakens, and the pore space of porous media is not occupied too much. nZVI particles are most likely to migrate with water flow. As the experiment continues, the particle size continues to increase, the interception and sedimentation effects increase, and the impact efficiency increases with the decrease of porosity. Therefore, the reaction coefficient increases and the nZVI is difficult to pass through.
3.3. Spatial distribution of nZVI in medium In order to quantitatively analyze the whole process, the following conditions are selected to further analyze the whole process: injection concentration of 1 g/L with flow rate of 8 ml/min. The experimental and simulated results of the distribution of iron in the medium is shown in Fig. 7 at different times. From the graph, the simulation results of the model fit the test results well, the amount of iron retained in the medium increases gradually with the experiment. The distribution of iron is not uniform. It is the largest at the entrance and the lowest at the exit. With the increase of injection volume, most of the iron is intercepted at the entrance. This is because the interception begins at the entrance, and with the increase of interception, the interception rate increases, leading to a further increase in the gap. 3.4. Process mechanism According to the model of this method, the reaction coefficient is mainly affected by porosity and particle size. The deposition rate coefficients of different particle sizes and porosity are calculated according to Eqs. (3)–(7), as shown in Fig. 8. The deposition rate coefficient decreases first and then increases with the increase of particle size, and increases with the decrease of porosity, forming a surface as shown in the figure. The model established in this study describes the deposition and transport process of the nZVI particles in porous media as shown in Fig. 9. When nZVI particles pass through the packed column, some particles flow out with water, some are intercepted by porous media, and the interception rate is controlled by the parameter kdep . Because of the limited dispersion stability of particles, particles will gather together to form polymer, which makes the particle size increase. Particle polymerization process is described by polymerization kinetics and controlled by parameter αpp . With the injection of nZVI particle suspension, the intercepted nZVI particles gradually increase, occupying
4. Conclusions The migration of modified nZVI in porous media was studied by packed column experiments. An unsteady coupled model considering the polymerization between nZVI particles and the influence of nZVI attachment on the hydraulic properties of porous media was established. The migration process of modified nZVI in porous media was analyzed by combining experiment with model. The main conclusions are as follows: (1) The flow rate and the concentration of iron have great influence on the migration of modified nZVI in porous media. Under the experimental conditions of this study, when the flow rate is high, the residual amount of nZVI in porous media is less, the hydraulic characteristics of porous media change slowly, and the rate of iron passage is higher. When the concentration is high, the residual 9
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amount of nZVI in porous media is large, the hydraulic characteristics of the packed column change rapidly, the passing rate of iron is low. (2) The distribution of nZVI in porous media is not uniform, there are more nZVI at the entrance, and it decreases with the increase of distance. The main reason for this phenomenon is that interception begins at the entrance, and with the increase of interception, the interception rate increases, leading to a further increase in the gap. (3) In the initial stage of migration, the particle size is small, and the particles are easy to diffuse and adsorb to the surface of the medium, as well as the aggregation between particles is strong. With the progress of the experiment, the particle size increases and the Brownian motion decreases, mainly gravity sedimentation and interception.
Jiemvarangkul, P., Zhang, W.X., Lien, H.L., 2011. Enhanced transport of polyelectrolyte stabilized nanoscale zero-valent iron (nZVI) in porous media. Chem. Eng. J. 170 (2–3), 482–491. https://doi.org/10.1016/j.cej.2011.02.065. Kim, H.J., Phenrat, T., Tilton, R.D., Lowry, G.V., 2009. Fe-0 nanoparticles remain mobile in porous media after aging due to slow desorption of polymeric surface modifiers. Environ. Sci. Technol. 43 (10), 3824–3830. https://doi.org/10.1021/es802978s. Kocur, C.M., et al., 2014. Characterization of nZVI mobility in a field scale test. Environ. Sci. Technol. 48 (5), 2862–2869. https://doi.org/10.1021/es4044209. Krol, M.M., et al., 2013. A field-validated model for in situ transport of polymer-stabilized nZVI and implications for subsurface injection. Environ. Sci. Technol. 47 (13), 7332–7340. https://doi.org/10.1021/es3041412. Lee, D.G., Bonner, J.S., Garton, L.S., Ernest, A.N.S., Autenrieth, R.L., 2000. Modeling coagulation kinetics incorporating fractal theories: a fractal rectilinear approach. Water Res. 34 (7), 1987–2000. https://doi.org/10.1016/s0043-1354(99)00354-1. Lefevre, E., Bossa, N., Wiesner, M.R., Gunsch, C.K., 2016. A review of the environmental implications of in situ remediation by nanoscale zero valent iron (nZVI): behavior, transport and impacts on microbial communities. Sci. Total Environ. 565, 889–901. https://doi.org/10.1016/j.scitotenv.2016.02.003. Li, P., Lin, K., Fang, Z., Zhang, W., 2018. Degradation of nitrate and secondary pollution in drinking water by S-NZVI prepared from steel pickling waste liquor. J. HydroEnviron. Res. https://doi.org/10.1016/j.jher.2018.01.005. Li, X., et al., 2019. Immobilization of phosphorus in sediments by nano zero-valent iron (nZVI) from the view of mineral composition. Sci. Total Environ. 694, 133695. https://doi.org/10.1016/j.scitotenv.2019.133695. Li, X.Q., Elliott, D.W., Zhang, W.X., 2006. Zero-valent iron nanoparticles for abatement of environmental pollutants: materials and engineering aspects. Crit. Rev. Solid State Mat. Sci. 31 (4), 111–122. https://doi.org/10.1080/10408430601057611. Li, Z., Greden, K., Alvarez, P.J.J., Gregory, K.B., Lowry, G.V., 2010. Adsorbed polymer and NOM limits adhesion and toxicity of nano scale zerovalent iron to E. coli. Environ. Sci. Technol. 44 (9), 3462–3467. https://doi.org/10.1021/es9031198. Liu, T.Y., et al., 2010. Effects of physicochemical factors on Cr(VI) removal from leachate by zero-valent iron and alpha-Fe2O3 nanoparticles. Water Sci. Technol. 61 (11), 2759–2767. https://doi.org/10.2166/wst.2010.167. Maximova, N., Dahl, O., 2006. Environmental implications of aggregation phenomena: current understanding. Curr. Opin. Colloid Interface Sci. 11 (4), 246–266. https:// doi.org/10.1016/j.cocis.2006.06.001. Nooruddin, H.A., Hossain, M.E., 2011. Modified Kozeny-Carmen correlation for enhanced hydraulic flow unit characterization. J. Pet. Sci. Eng. 80 (1), 107–115. https://doi. org/10.1016/j.petrol.2011.11.003. O’Carroll, D., Sleep, B., Krol, M., Boparai, H., Kocur, C., 2013. Nanoscale zero valent iron and bimetallic particles for contaminated site remediation. Adv. Water Resour. 51, 104–122. https://doi.org/10.1016/j.advwatres.2012.02.005. Phenrat, T., Saleh, N., Sirk, K., Tilton, R.D., Lowry, G.V., 2007. Aggregation and sedimentation of aqueous nanoscale zerovalent iron dispersions. Environ. Sci. Technol. 41 (1), 284–290. https://doi.org/10.1021/es061349a. Ponder, S.M., Darab, J.G., Mallouk, T.E., 2000. Remediation of Cr(VI) and Pb(II) aqueous solutions using supported, nanoscale zero-valent iron. Environ. Sci. Technol. 34 (12), 2564–2569. https://doi.org/10.1021/es9911420. Qu, G., et al., 2019. Magnetic Fe3O4 assembled on nZVI supported on activated carbon fiber for Cr(VI) and Cu(II) removal from aqueous solution through a permeable reactive column. Environ. Sci. Pollut. Res. 26 (5), 5176–5188. https://doi.org/10. 1007/s11356-018-3985-8. Quinn, J., et al., 2005. Field demonstration of DNAPL dehalogenation using emulsified zero-valent iron. Environ. Sci. Technol. 39 (5), 1309–1318. https://doi.org/10.1021/ es0490018. Rajagopalan, R., Tien, C., 1976. Trajectory analysis of deep-bed filtration with the spherein-cell porous media model. AIChE J. 22 (3), 523–533. https://doi.org/10.1002/aic. 690220316. Raychoudhury, T., Tufenkji, N., Ghoshal, S., 2012. Aggregation and deposition kinetics of carboxymethyl cellulose-modified zero-valent iron nanoparticles in porous media. Water Res. 46 (6), 1735–1744. https://doi.org/10.1016/j.watres.2011.12.045. Ren, J., Woo, Y.C., Yao, M., Tijing, L.D., Shon, H.K., 2017. Enhancement of nanoscale zero-valent iron immobilization onto electrospun polymeric nanofiber mats for groundwater remediation. Process Saf. Environ. Protect. 112, 200–208. https://doi. org/10.1016/j.psep.2017.04.027. Schrick, B., Hydutsky, B.W., Blough, J.L., Mallouk, T.E., 2004. Delivery vehicles for zerovalent metal nanoparticles in soil and groundwater. Chem. Mat. 16 (11), 2187–2193. https://doi.org/10.1021/cm0218108. Scott, T.B., Popescu, I.C., Crane, R.A., Noubactep, C., 2011. Nano-scale metallic iron for the treatment of solutions containing multiple inorganic contaminants. J. Hazard. Mater. 186 (1), 280–287. https://doi.org/10.1016/j.jhazmat.2010.10.113. Shen, X., et al., 2011. Foam, a promising vehicle to deliver nanoparticles for vadose zone remediation. J. Hazard. Mater. 186 (2–3), 1773–1780. https://doi.org/10.1016/j. jhazmat.2010.12.071. Sun, Y.P., Li, X.Q., Zhang, W.X., Wang, H.P., 2007. A method for the preparation of stable dispersion of zero-valent iron nanoparticles. Colloid Surf. A-Physicochem. Eng. Asp. 308 (1–3), 60–66. https://doi.org/10.1016/j.colsurfa.2007.05.029. Tilston, E.L., Collins, C.D., Mitchell, G.R., Princivalle, J., Shaw, L.J., 2013. Nanoscale zerovalent iron alters soil bacterial community structure and inhibits chloroaromatic biodegradation potential in Aroclor 1242-contaminated soil. Environ. Pollut. 173, 38–46. https://doi.org/10.1016/j.envpol.2012.09.018. Tosco, T., Petrangeli Papini, M., Cruz Viggi, C., Sethi, R., 2014. Nanoscale zerovalent iron particles for groundwater remediation: a review. J. Clean. Product. 77, 10–21. https://doi.org/10.1016/j.jclepro.2013.12.026. Tufenkji, N., Elimelech, M., 2004. Correlation equation for predicting single-collector efficiency in physicochemical filtration in saturated porous media. Environ. Sci.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The work was supported by the Beijing Municipal Science and Technology Commission (Z161100004516015) and National Key Research and Development Project of China (2016YFC0401404). References Bai, R.B., Tien, C., 2000. Effect of deposition in deep-bed filtration: determination and search of rate parameters. J. Colloid Interface Sci. 231 (2), 299–311. https://doi.org/ 10.1006/jcis.2000.7130. Chaithawiwat, K., et al., 2016. Impact of nanoscale zero valent iron on bacteria is growth phase dependent. Chemosphere 144, 352–359. https://doi.org/10.1016/j. chemosphere.2015.09.025. Chen, P.-J., Su, C.-H., Tseng, C.-Y., Tan, S.-W., Cheng, C.-H., 2011. Toxicity assessments of nanoscale zerovalent iron and its oxidation products in medaka (Oryzias latipes) fish. Mar. Pollut. Bull. 63 (5–12), 339–346. https://doi.org/10.1016/j.marpolbul.2011. 02.045. Choe, S., Lee, S.H., Chang, Y.Y., Hwang, K.Y., Khim, J., 2001. Rapid reductive destruction of hazardous organic compounds by nanoscale Fe-0. Chemosphere 42 (4), 367–372. https://doi.org/10.1016/s0045-6535(00)00147-8. Comba, S., Sethi, R., 2009. Stabilization of highly concentrated suspensions of iron nanoparticles using shear-thinning gels of xanthan gum. Water Res. 43 (15), 3717–3726. https://doi.org/10.1016/j.watres.2009.05.046. Cullen, L.G., Tilston, E.L., Mitchell, G.R., Collins, C.D., Shaw, L.J., 2011. Assessing the impact of nano- and micro-scale zerovalent iron particles on soil microbial activities: particle reactivity interferes with assay conditions and interpretation of genuine microbial effects. Chemosphere 82 (11), 1675–1682. https://doi.org/10.1016/j. chemosphere.2010.11.009. Efecan, N., Shahwan, T., Eroglu, A.E., Lieberwirth, I., 2009. Characterization of the uptake of aqueous Ni2+ ions on nanoparticles of zero-valent iron (nZVI). Desalination 249 (3), 1048–1054. https://doi.org/10.1016/j.desal.2009.06.054. El-Temsah, Y.S., Joner, E.J., 2012a. Ecotoxicological effects on earthworms of fresh and aged nano-sized zero-valent iron (nZVI) in soil. Chemosphere 89 (1), 76–82. https:// doi.org/10.1016/j.chemosphere.2012.04.020. El-Temsah, Y.S., Joner, E.J., 2012b. Impact of Fe and Ag nanoparticles on seed germination and differences in bioavailability during exposure in aqueous suspension and soil. Environ. Toxicol. 27 (1), 42–49. https://doi.org/10.1002/tox.20610. Elliott, D.W., Zhang, W.X., 2003. Field assessment of nanoscale bimetallic particles for groundwater treatment. Abstr. Pap. Am. Chem. Soc. 225 U971. Fatisson, J., Ghoshal, S., Tufenkji, N., 2010. Deposition of carboxymethylcellulose-coated zero-valent iron nanoparticles onto silica: roles of solution chemistry and organic molecules. Langmuir 26 (15), 12832–12840. https://doi.org/10.1021/la1006633. Gierczycki, A.T., Al-Rashed, M.H., 2008. Aggregation and breakage of solid particles in suspensions agitated in a vibrating mixer: a fractal approach. Chem. Eng. Commun. 195 (4), 427–434. https://doi.org/10.1080/00986440701707537. He, F., Zhao, D., Paul, C., 2010. Field assessment of carboxymethyl cellulose stabilized iron nanoparticles for in situ destruction of chlorinated solvents in source zones. Water Res. 44, 2360–2370. https://doi.org/10.1016/j.watres.2009.12.041. He, F., Zhao, D.Y., 2005. Preparation and characterization of a new class of starch-stabilized bimetallic nanoparticles for degradation of chlorinated hydrocarbons in water. Environ. Sci. Technol. 39 (9), 3314–3320. https://doi.org/10.1021/ es048743y. Herzig, J.P., Leclerc, D.M., Goff, P.L., 1970. Flow of suspensions through porous Media—Application to deep filtration. Ind. Eng. Chem. 62 (5), 8–35. https://doi.org/ 10.1021/ie50725a003.
10
Journal of Hydrology 579 (2019) 124193
Y. Liu, et al.
1007/s11270-013-1845-1. Yao, K.M., Habibian, M.T., O'Melia, C.R., 1971. Water and waste water filtration: concepts and applications. Environ. Sci. Technol. 5 (11), 1105–1112. https://doi.org/10. 1021/es60058a005. Zhang, X., Lin, Y.M., Chen, Z.L., 2009. 2,4,6-Trinitrotoluene reduction kinetics in aqueous solution using nanoscale zero-valent iron. J. Hazard. Mater. 165 (1–3), 923–927. https://doi.org/10.1016/j.jhazmat.2008.10.075.
Technol. 38 (2), 529–536. https://doi.org/10.1021/es034049r. Wei, Y.T., et al., 2010. Influence of nanoscale zero-valent iron on geochemical properties of groundwater and vinyl chloride degradation: a field case study. Water Res. 44 (1), 131–140. https://doi.org/10.1016/j.watres.2009.09.012. Xu, C.-H., Zhu, L.-J., Wang, X.-H., Lin, S., Chen, Y.-M., 2014. Fast and highly efficient removal of chromate from aqueous solution using nanoscale zero-valent iron/activated carbon (NZVI/AC). Water Air & Soil Pollut. 225 (2), 1845. https://doi.org/10.
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