Applied Clay Science 146 (2017) 343–349
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Research paper
Drinking water treatment sludge as an efficient adsorbent for heavy metals removal
MARK
S.A. Abo-El-Eneina, Ahmed Shebla,⁎, S.A. Abo El-Dahabb a b
Chemistry Department, Faculty of Science, Ain Shams University, Abbassia 11566, Cairo, Egypt Holding Company for Water and Wastewater, Egypt
A R T I C L E I N F O
A B S T R A C T
Keywords: Drinking water treatment sludge Lead cadmium nickel removals Adsorption Quartz Illite Albite
Green chemists paid much more attention towards the alternative ways to reutilize waste materials instead of its disposal in a non-ecofriendly manner. In this study, drinking-water treatment sludge (DWTS), which is a byproduct resulted from drinking water treatment plants, was successfully applied as an adsorbent for Pb(II), Cd(II) and Ni(II) removal from wastewater. The physicochemical characteristics of DWTS were investigated using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and N2 adsorption-desorption isotherms. The XRD analysis revealed that the DWTS under study consists of quartz and illite phases which had been reported for their adsorption efficiency. Firing of DWTS at 500 °C causes the appearance of albite phase in addition to previous ones which enhances the adsorption capacity of these materials. The influence of different parameters such as firing temperature of DWTS, contact time, pH, DWTS dose and initial metal ions concentration on the adsorption of heavy metal ions and, consequently, on their removal were investigated. DWTS exhibit an adsorption efficiency towards Pb(II) > Cd(II) > Ni(II). The extremely high efficiency of DWTS towards Pb(II) adsorption can nominate it as a specific low-cost adsorbent for Pb ions.
1. Introduction Drinking-water treatment sludge (DWTS) is a by-product from the coagulation-flocculation process using aluminum or iron based salts to precipitate clay, colloidal particles, algae and humic substances from water resources. Due to its high production rate and its environmentally unfavored disposal to landfill, several researchers paid a considerable attention for using this waste material in different applications especially those of low cost. The chemical composition of DWTS varies depending on the source of water under treatment as well as the type of coagulant used. These applications include utilization of DWTS for ceramic products (Zamora et al., 2008; Kizinievic et al., 2013; Mymrin et al., 2017), cement and concrete production (Rodríguez et al., 2010; Sales et al., 2011; Hwang et al., 2017) as well as wastewater treatment as an adsorbent for the removal of phenolic compounds (Fragoso and Duarte, 2012), phosphates (Razali et al., 2007; Piaskowski, 2013), dyes from textile industry discharge (Chu, 1999) and heavy metals (Ippolito et al., 2011; Siswoyo et al., 2014). Pollution of water resources by heavy metals such as lead, cadmium and nickel which are continuously discharged in huge amounts from different growing industrial activities has been recognized (Ribeiro
⁎
Corresponding author. E-mail address:
[email protected] (A. Shebl).
http://dx.doi.org/10.1016/j.clay.2017.06.027 Received 1 May 2017; Received in revised form 13 June 2017; Accepted 23 June 2017 0169-1317/ © 2017 Elsevier B.V. All rights reserved.
et al., 2012; Yang and Cui, 2013; Keränen et al., 2015). These heavy metals are considered as hazardous materials where their toxicity to living organisms comes from their tendency to accumulate in living tissues since they are not biodegradable causing several health hazards like kidney problems, anemia, lung cancer and dyspnoea (Ahmaruzzaman, 2011; Visa et al., 2012). Therefore, a tremendous number of researches deals with the removal of such heavy metals especially via adsorption process (Bailey et al., 1999; Babel and Kurniawan, 2003; Ngah and Hanafiah, 2008; Tofighy and Mohammadi, 2015; Castaldi et al., 2015; Isaac et al., 2015; Dobrowolski et al., 2017; Azimi et al., 2017). The aim of this study is to get a beneficial use of DWTS as a low cost adsorbent for the removal of lead, cadmium and nickel metal ions from wastewater. 2. Experimental 2.1. Starting materials The material used in this investigation is DWTS waste produced during 4 months from El-Fustat drinking water treatment plant (Egypt).
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(XRD) analysis using a stabilized X-ray generator fitted with a copper target X-ray tube, (Geiger Muller tube). The settings used were tube run at 30 kV, 15 mA divergence, receiving and scatter solids, 1, 1, cm and 1 respectively and chart speed 100 C.P.S. Adsorption–desorption isotherm of purified N2 at 77K was carried out using Nova 2000, Quanta Chrome (commercial BET unit). The external morphology of DWTS was observed using scanning electron microscope (SEM) FEI Quanta 250 FEG. The heavy metals analysis was examined using Inductive Coupled Plasma (ICP) instrument Perkin Elmer Model: ICP – OES Optima 7300 DV; in which an ICP source consists of a flowing stream of argon gas ionized by an applied radio frequency field typically oscillating at 40 MHz; this generates about 6000 to 8000 K which called plasma. The high temperature of the plasma excites atomic emission efficiently. Ionization of a high percentage of atoms produces ionic emission spectra.
Table 1 Chemical oxide composition of DWTS. Oxide
Weight, %
SiO2 Al2O3 Fe2O3 CaO Na2O MgO K2O Sulphate as SO3 Loss on ignition (L.O.I)
36.51 22.21 5.65 2.66 1.35 1.34 0.49 0.08 28.1
Its chemical composition is given in Table 1. 2.2. Preparation and firing of DWTS
3. Results and discussion
DWTS was dried at 110 °C for 48 h, and then crushed. The crushed DWTS was fired at different temperatures of 100, 400, 500, 600 and 700 °C for a period of 2 h and then quenched in air.
3.1. Physicochemical characteristics of DWTS 3.1.1. Chemical composition The results of chemical analysis of DWTS are given in Table 1 in terms of oxide composition. It is obvious that DWTS composed mainly of silica and alumina as a result of precipitated clay as well as coagulant used in the treatment.
2.3. Chemicals The synthetic solutions used in this study were prepared from Pb (NO3)2 99% produced by LOBA Chemie, Cd(NO3)2·4H2O 99% produced by LOBA Chemie and Ni(NO3)2·6H2O 98% produced by Oxford laboratory reagent. Solutions of 0.1 M nitric acid and ammonium hydroxide were used to adjust pH.
3.1.2. X-ray diffraction analysis The mineral composition of DWTS, fired at different temperatures, was identified by means of XRD analysis as shown in Fig. 1. The results indicate the presence of quartz and illite phases in all samples while albite phase appears additionally at 500 °C. It had been recorded in previous researches the potential application of quartz- silicon oxide(Tikhomolova et al., 2001; Reich et al., 2010; Al-Anber, 2010; Bellucci et al., 2015) and illite (Ozdes et al., 2011; Benedicto et al., 2014a, 2014b; Cui et al., 2015) in heavy metal removal as adsorbents. Illite is a clay mineral of the layer type 2:1. It has the general formula of KyAl4(Si8−y, Aly)O20(OH)4, usually with 1 < y < 1.5, and composed of two silica tetrahedral sheets that sandwich an alumina octahedral sheet (Alvarez-Puebla et al., 2005; Hongxia et al., 2016). The efficiency of illite as an adsorbent for heavy metal ions is ascribed to ion exchange reaction with its potassium ions that are trapped in its interlayer spaces; as well as inner-sphere complexes formation through ^SieO− and ^AleO− groups are located at the edges (McBride, 1994; Sheng et al., 1999; Celis et al., 2000; Gu and Evans, 2007).
2.4. Batch adsorption experiments Batch adsorption experiments including the effects of firing temperature, contact time, adsorbent dosage, initial metals concentration and initial solution pH were studied. Batch experiments were carried out at room temperature by addition of known weight of burnt DWTS into a number of 100 mL glass stoppered conical flasks on a rotary shaker at 200 rpm containing individual 50 mL of nitrate solutions of Pb(II), Cd(II) or Ni(II) (100 mg/L) in distilled water. The effect of firing temperature was conducted to DWTS by shaking 0.5 g of DWTS, after burning at different temperatures (100, 400, 500, 600 and 700 °C), with 50 mL of the individual nitrate solutions of Pb (II), Cd(II) or Ni(II) (100 mg/L) in distilled water for 24 h. The effect of contact time was conducted by shaking 0.5 g of burnt DWTS at optimum firing temperature and individual nitrate solutions of Pb, Cd or Ni (100 mg/L) in distilled water for different time intervals of 2, 4, 6, 8, 12 and 24 h. The effect of initial pH was performed by shaking 0.5 g of burnt DWTS at optimum conditions of firing temperature and contact time and individual nitrate solutions of Pb, Cd or Ni (100 mg/L) at different initial pH values of 3, 4, 5, 6, 6.5, 7, 7.5, 8 in addition to original pH value of metal nitrate solution. The effect of adsorbent dosage was conducted by adding desired amounts of burnt DWTS (0.5, 1, 1.5 and 2 g) at the optimum conditions with 50 mL of the individual nitrate solutions of Pb(II), Cd(II) or Ni(II) (100 mg/L) in distilled water. The effect of initial metals concentration was conducted by adding 2 g of burnt DWTS to 50 mL of the individual nitrate solutions of Pb(II), Cd(II) or Ni(II) having different concentrations of 100, 200, 300, 450 and 650 mg/L in distilled water. Effect of competitive adsorption at the optimum conditions was also carried out by mixing groups of Pb(II)-Cd(II), Pb(II)-Ni(II) and Pb(II)-Cd(II)-Ni(II) at different initial concentrations of 200 and 450 ppm.
Q+I Q I
I
I
o
I
700 C
o
Intensity
600 C A
Q+A
o
500 C o
400 C
o
100 C 10
2.5. Methods for physicochemical characterization
20
30
40
50
60
2 θ (deg.)
DWTS was characterized by X-ray fluorescence (XRF) technique using Pnanalytical Axios advanced XRF; as well as X-ray diffraction
Fig. 1. XRD analysis of the DWTS fired at different temperatures. (Q = quartz, I = illite and A = albite).
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Table 2 Surface area and pore structure characteristics of DWTS after thermal treatment at 100, 500 and 700 °C. Temperature (°C)
SBET
C constant
Vp (mL/g)
Mean pore radius (Å)
St (m2/g)
Most probable radius (Å)
100 500 700
22.61 61.92 50.27
30.66 58.2 65.32
0.0655 0.1550 0.1738
57.95 50.01 69.15
22.00 83.10 68.27
18.90 18.66 18.91
The presence of albite mineral, which is an alumino silicate of the formula NaAlSi3O8 (sodium feldspar), in addition to quartz and illite in DWTS fired at 500 °C can enhance the adsorption capacity as it will be clearly evidenced later in this study that albite is already examined for its efficiency as an adsorbent for both organic and inorganic materials (Chernyshova et al., 2001; Vidyadhar et al., 2002; Feng et al., 2013; Liu et al., 2015).
50
(a)
Volume adsorbed (cc/g)
40
3.1.3. Surface area and pore structure characteristics The main surface and pore structure characteristics of the DWTS, after thermal treatment at 100, 500 and 700 °C, were studied using nitrogen gas adsorption at liquid nitrogen temperature (77.2 K) and the results are summarized in Table 2. The adsorption-desorption isotherms are shown in Fig. 2a–c for the DWTS samples after heat treatment at 100, 500 and 700 °C, respectively. Evidently, the adsorption-desorption isotherm obtained for the DWTS heated at 100 °C shows that the adsorption process is irreversible indicated the presence of the type of constricted “ink bottle” pores. The ink bottle type of pores is hinted by Kraemer (1931), developed by McBain (1935) and others (Rao, 1941; Katz, 1949). It consists of a wider body with a narrow entrance as shown from the hysteresis loop which is closed at a relative pressure (p/po) of 0.45 from which the radius of narrow pores can be calculated (Fig. 2a); meanwhile, the radius of wider pores can be calculated from the relative vapor pressure of 0.70 where capillary condensation takes place where the radii of narrow entrance and wider body could be calculated by using Kelvin equation (Abo-El-Enein et al., 1974). However, thermal treatment of the DWTS at 500 °C resulted in a sort of pore opening as indicated by the wider hysteresis loop which is closed at a relative vapor pressure of 0.35 just after the formation of the first adsorbed layer (monolayer capacity), (Fig. 2b), with a consequent increase in the specific surface area of the DWTS heated at 500 °C, (Table 2).Therefore, a large number of pores become accessible for the removal of a larger fraction of pollutants as reported later in this study (Fig. 4). Moreover, thermal treatment of the DWTS at 700 °C resulted in a sort of sintering with a consequent decrease in the specific surface area where mesopores become more dominant; mesopores possess lower surface areas and larger pore volumes as compared with micropores (Fig. 2c). This could be clearly distinguished from the results of Table 2. Therefore, the percentage removal of pollutants by the DWTS after thermal treatment at 700 °C decreases as reported later in this study (Fig. 4).
30
20
10
0 0.0
0.2
0.4
0.6
P/P
0.8
1.0
o
120
(b)
Volume adsorbed (cc/g)
100
80
60
40
20
0 0.0
0.2
0.4
0.6
0.8
1.0
P/Po 140
(c)
Volume adsorbed (cc/g)
120
3.1.4. Scanning electron microscopy analysis Fig. 3a–c represents the SEM micrographs of DWTS heated at 100 °C, 500 °C and 700 °C, respectively. The microstructure of DWTS heated at 100 °C displayed a more porous structure with the appearance of large and rod-like particles as representing a more open structure consisting mainly of mesoporous (Fig. 3a); the results of XRD analysis indicated that as well the presence of the only phases indentified are quarts and illite as well as the presence of algae and diatoms are coated by amorphous layers of hydration products. The SEM micrograph of DWTS fired at 500 °C shown in Fig. 3b displayed the formation of albite particles which appeared as small fibers and wrinkled foils together with nearly amorphous and microcrystalline particles; which appeared as coatings around the grains;
100 80 60 40 20 0 0.0
0.2
0.4
0.6
P/P
0.8
1.0
o
Fig. 2. N2 adsorption-desorption isotherms of DWTS after thermal treatment at (a) 100 °C, (b) 500 °C and (c) 700 °C.
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100 90
Removal (%)
80 70 60 50 40 30
Pb Cd Ni
20 10 0 100
200
300
400
500
600
700
800
Firing Temperature (oC) Fig. 4. Effect of firing temperature of DWTS on the removal percent of metal ions (metal ion conc. = 100 ppm; adsorbent dose = 0.5 g; solution volume = 50 ml; contact time = 24 h; temperature = 25 ± 2 °C; agitation speed = 200 rpm; pH = 5.5).
3.2. Factors affecting the efficiency of metal ions removal 3.2.1. Effect of firing temperature Fig. 4 shows the effect of firing temperature of DWTS on the removal percent of Pb(II), Cd(II) and Ni(II) from their aqueous solutions of original pH value = 5.5 (DWTS dose = 0.5 g and contact time = 24 h). Evidently, firing of DWTS has no considerable effect on its adsorptive capacity towards Pb(II) where its removal percent is nearly 100% at all firing temperatures; whereas for Cd(II) its removal percent increases with the increasing of firing temperature up to 500 °C then decreases. The removal percentage of Ni(II) increases up to 600 °C, then decreases. From the aforementioned observations, for economic consideration 500 °C was chosen as an optimum firing temperature of DWTS for the removal of metal ions under investigation since the removal percent of Ni(II) does not change appreciably from 500 to 600 °C.
3.2.2. Effect of contact time Fig. 5 shows the effect of contact time on the removal percent of Pb (II), Cd(II) and Ni(II) from their aqueous solutions of original pH value = 5.5 using 0.5 g of DWTS fired at the optimum firing temperature of 500 °C. It was observed that the removal percent increases with increasing contact time, and then gradually reaches to an almost 100 Fig. 3. SEM images of DWTS heated at a) 100 °C, b) 500 °C and c) 700 °C.
80
Removal (%)
such a structure leads to an increase in the surface area available for adsorption of larger amounts of metal ions from their aqueous solution. These SEM micrographs are also confirmed by the increase in surface area available for the removal of metal ions; the contents of pore size distribution proved that the pore system is composed mainly of mesopores which are accessible for adsorption of larger amounts of metal ions. Thermal treatment of DWTS at 700 °C, however, the results of SEM micrograph displayed the presence of quartz and illite phases in addition to algae and diatoms with the disappearance of albite phases within a noticeable decrease in surface area available to the removal of small fraction of metal ions as confirmed by the results of pore structure which indicated assort of pore narrowing with consequent decrease in the fraction of mesopores which are accessible to the removal of metal ions, Fig. 3c.
60
40
Pb Cd Ni
20
0 0
5
10
15
20
25
Time (Hours) Fig. 5. Effect of contact time on the removal percent of metal ions (metal ion conc. = 100 ppm; adsorbent dose = 0.5 g; adsorbent firing temperature = 500 °C; solution volume = 50 ml; temperature = 25 ± 2 °C; agitation speed = 200 rpm; pH = 5.5).
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100
100 90
80
70 60
Removal (%)
Removal (%)
80
50 40 30
Pb Cd Ni
20 10
60
40
Pb Cd Ni
20
0 3
4
5
6
7
8
9
0
pH
0.5
1.0
1.5
2.0
Dose (g)
Fig. 6. Effect of initial solution pH on the removal percent of metal ions (metal ion conc. = 100 ppm; adsorbent dose = 0.5 g; adsorbent firing temperature = 500 °C; solution volume = 50 ml; contact time = 4 h; temperature = 25 ± 2 °C; agitation speed = 200 rpm).
Fig. 7. Effect of burnt DWTS dose on the removal percent of metal ions (metal ion conc. = 100 ppm; adsorbent firing temperature = 500 °C; solution volume = 50 ml; contact time = 4 h; temperature = 25 ± 2 °C; agitation speed = 200 rpm; pH = 5.5).
equilibrium value in 4 h. The fast metals removal in the initial stages of contact time is attributed to the large amount of available active sites especially for Pb(II) adsorption which shows removal percent closing to 100% even before 4 h. Evidently, the progressive removal of Cd(II) and Ni(II) ions takes place in a slower rate. According to these results, the optimum contact time was fixed at 4 h for Cd(II) and Ni(II) where the removal percents are 91 and 78%, respectively.
100 90 80
Removal (%)
70
3.2.3. Effect of pH Fig. 6 shows the effect of solution pH on the removal percent of metal ions using 0.5 g of DWTS fired at the optimum firing temperature of 500 °C and contact time of 4 h. The metal ions removal percent increases by increasing the pH value of the solution. This could be explained as follows: at lower pH the protonation takes place on the DWTS surface blocking the active sites available for positive metals ions adsorption while as pH value increases the protonation will be decreased and the negative charges on DWTS surface will be more exposed resulting in electrostic attraction towards positive metal ions in solution.
60 50 40 30
Pb Cd Ni
20 10 0 100
200
300
400
500
600
700
Concentration (ppm) Fig. 8. Effect of initial metal ions concentration on the removal percent of metal ions (adsorbent dose = 2 g; adsorbent firing temperature = 500 °C; solution volume = 50 ml; contact time = 4 h; temperature = 25 ± 2 °C; agitation speed = 200 rpm; pH = 5.5).
3.2.4. Effect of burnt DWTS dose The effect of burnt DWTS dosage on heavy metal removal, at the optimum firing temperature (500 °C) of DWTS optimum contact time (4 h) and optimum initial pH (5.5), was studied by varying the dosage of burnt DWTS and the results are shown in Fig. 7. Evidently, an almost complete removal of Pb(II) as obtained by using the different dosages of burnt DWTS where the removal efficiency reached 99% with varying the dose from 0.5 up to 2 g. For Cd(II) and Ni(II) the removal percents increase with increasing burnt DWTS dose till 2 g, where the removal efficiency reached almost 99%. This is mainly due to the increase of the adsorbent sites by increasing dosage level up to 2 g. Thus, it can be concluded that the optimum dose for heavy metals removal is 2 g with the removal efficiency of 99%.
one. 3.2.6. Competitive metal ions adsorption The competitive adsorption of metals under study was investigated by applying two binary mixtures of Cd(II) and Ni(II) individually with Pb(II) in addition to a tertiary mixture of all of them together. The experiment was carried out using DWTS fired at optimum temperature of 500 °C, optimum contact time (4 h), optimum initial pH (5.5) and optimum fired DWTS dose (2 g). Two initial concentrations of metal ions of 200 ppm and 450 ppm were utilized. The results of the removal percent of each metal ion are shown in Table 3. The high affinity of DWTS towards Pb(II) adsorption almost does not change whatever the metal ion present in the mixture as well as the initial concentration applied. For Cd(II) and Ni(II) in the binary and tertiary mixtures with Pb(II), increasing the initial concentration causes a decrease in their removal percents but the decrease in that of Ni(II) is twice that of Cd(II)in the binary mixtures and is five times that of Cd(II) in the tertiary mixture. Generally, the removal percent of metals is found to be in the order Pb(II) > Cd(II) > Ni(II) in the tertiary mixtures. This trend matches with the order of ionic radius of metals and hydration energy but doesn't match with other characteristics listed in Table 4.
3.2.5. Effect of initial metal ions concentration Fig. 8 shows that the effect of initial metal ions concentration on efficiency of their removal, at optimum firing temperature of DWTS (500 °C), optimum contact time (4 h), optimum initial pH (5.5) and optimum fired DWTS dose (2 g). The Pb(II) removal does not affected by the increase of the initial metal ion concentration where an almost complete removal is obtained at all initial concentrations. For Cd(II) and Ni(II) the removal percent is almost 100% at initial concentration of 100 ppm. Afterwards the removal percent decreases considerably. Therefore initial concentration of 100 ppm was chosen as the optimum 347
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Table 3 Removal percent of Pb(II), Cd(II) and Ni(II) in binary and tertiary mixtures. Pb-Cd mixture
Pb(II) removal % Cd(II) removal % Ni(II) removal %
Pb-Ni mixture
Pb-Cd-Ni mixture
At 200 ppm
At 450 ppm
At 200 ppm
At 450 ppm
At 200 ppm
At 450 ppm
99.9% 85% –
97.6% 72% –
99.2% – 80%
97.8 – 54%
99.3% 74% 66%
98.5% 70.2% 45%
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Table 4 Some chemical characteristics of the metal ions under study. Metal
Ionic radius (Å)
Hydrated radius (Å)
Hydration energy (kJ mol− 1)
Hydrolysis constant (pKh)
Electronegativity
Pb(II) Cd(II) Ni(II)
1.19 0.97 0.72
4.01 4.26 4.04
−1481 −1807 −2106
7.8 11.7 9.4
2.33 1.69 1.91
The ionic radius decreases in the order Pb2+ (1.119 Å) > Cd2+ (0.97 Å) > Ni2+ (0.72 Å). The larger the ionic radius, the more dispersed is the charge and the less strongly held is the hydration water. Consequently, the hydration capacity of the ion becomes smaller and the binding of the ion and water phase becomes weaker; leading to strong adsorption of the ion on the adsorbent surface (Bohli et al., 2013). 4. Conclusions DWTS was successfully evaluated as an efficient adsorbent for the heavy metals under study, in the order: Pb(II) > Cd(II) > Ni(II). Studying the influence of various parameters such as firing temperature of DWTS, contact time, pH, DWTS dose and initial metal ions concentration on the adsorption of these heavy metals, as well as competitive adsorption experiments, revealed the extremely high adsorption efficiency of DWTS towards Pb(II). Accordingly, DWTS is recommended to be used as a specific adsorbent for Pb ions. Acknowledgements This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. References Abo-El-Enein, S.A., Daimon, M., Ohsawa, S., Kondo, R., 1974. Hydration of low porosity slag-lime pastes. Cem. Concr. Res. 4, 299–312. Ahmaruzzaman, M., 2011. Industrial wastes as low-cost potential adsorbents for the treatment of wastewater laden with heavy metals. Adv. Colloid Interfac. 166, 36–59. Alvarez-Puebla, R.A., dos Santos Jr., D.S., Blanco, C., Echeverria, J.C., Garrido, J.J., 2005. Particle and surface characterization of a natural illite and study of its copper retention. J. Colloid Interface Sci. 285, 41–49. Al-Anber, M.A., 2010. Removal of high-level Fe3 + from aqueous solution using natural inorganic materials: bentonite (NB) and quartz (NQ). Desalination 250, 885–891. Azimi, A., Azari, A., Rezakazemi, M., Ansarpour, M., 2017. Removal of heavy metals from industrial wastewaters: a review. ChemBioEng Rev. 4, 37–59. Babel, S., Kurniawan, T.A., 2003. Low-cost adsorbents for heavy metals uptake from contaminated water: a review. J. Hazard. Mater. B 97, 219–243. Bailey, S.E., Olin, T.J., Bricka, R.M., Adrian, D.D., 1999. A review of potentially low-cost sorbents for heavy metals. Water Res. 33 (11), 2469–2479. Bellucci, F., Lee, S.S., Kubicki, J.D., Bandura, A.V., Zhang, Z., Wesolowski, D.J., Fenter, P., 2015. Rb adsorption at the quartz (101)-aqueous Interface: comparison of resonant anomalous X-ray reflectivity with ab-initio calculations. J. Phys. Chem. C 119 (9), 4778–4788. Benedicto, A., Missana, T., Fernandez, A.M., 2014a. Interlayer collapse affects on cesium adsorption onto illite. Environ. Sci. Technol. 48, 4909–4915. Benedicto, A., Degueldre, C., Missana, T., 2014b. Gallium sorption on montmorillonite and illite colloids: experimental study and modelling by ionic exchange and surface complexation. Appl. Geochem. 40, 43–50. Bohli, T., Villaescusa, I., Ouederni, A., 2013. Comparative study of bivalent cationic metals adsorption Pb(II), Cd(II), Ni(II) and Cu(II) on olive stones chemically activated
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