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Removal of Cr(VI) oxoanion from contaminated water using granular jujube stems as a porous adsorbent
Author’s Accepted Manuscript Removal of Cr(VI) oxoanion from contaminated water using granular Jujube stems as a porous adsorbent Mohammad Hossein Salmani, Fateme Sahlabadi, Hadi Eslami, Mohammad Taghi Ghaneian, Iraj Rezapour Balaneji, Tahereh Jasemi Zad www.elsevier.com/locate/gsd
PII: DOI: Reference:
S2352-801X(18)30124-3 https://doi.org/10.1016/j.gsd.2018.12.001 GSD180
To appear in: Groundwater for Sustainable Development Received date: 13 June 2018 Revised date: 15 November 2018 Accepted date: 3 December 2018 Cite this article as: Mohammad Hossein Salmani, Fateme Sahlabadi, Hadi Eslami, Mohammad Taghi Ghaneian, Iraj Rezapour Balaneji and Tahereh Jasemi Zad, Removal of Cr(VI) oxoanion from contaminated water using granular Jujube stems as a porous adsorbent, Groundwater for Sustainable Development, https://doi.org/10.1016/j.gsd.2018.12.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Removal of Cr(VI) oxoanion from contaminated water using granular Jujube stems as a porous adsorbent Mohammad Hossein Salmani1, Fateme Sahlabadi2, Hadi Eslami3, Mohammad Taghi Ghaneian1, Iraj Rezapour Balaneji4, Tahereh Jasemi Zad1* 1
Environmental Science and Technology Research Center, Department of Environmental Health Engineering,
School of Public Health, Shahid Sadoughi University of Medical Sciences, Yazd, I. R. Iran 2
Department of Environmental Health Engineering, Social determinants of health research center University of
Medical Sciences, Birjand, I. R. Iran 3
Department of Environmental Health Engineering, School of Health, Rafsanjan University of Medical
Sceiences, Rafsanjan, I. R. Iran. 4
Department of Food Hygiene and Safety, School of Public Health, Shahid Sadoughi University of Medical
Science, Yazd, I. R. Iran
*
Corresponding author: Alem square, Gomnam Shohada Blvd, Department of Environmental Health
Engineering, Shahid Sadoughi University of Medical Sciences, Yazd, I. R. Iran. Tel: +9834192234, [email protected]
Abstract The efficiency of granular Jujube stems (GJS) was investigated in removal of hazardous Cr(VI) oxoanion from contaminated solutions. The GJS was prepared under standard conditions and sized in 40-60 mesh using ASTM standard sieves. The effects of pH (3, 5, 7), adsorbent dose (4, 6 and 10 g/L), initial Cr(VI) concentration (0.5, 2 and 10 mg/L) and contact time (15, 30, 60, 120, 180, 240 min and 24 h) were investigated on the removal of Cr(VI) by batch experiments at laboratory scale. Scanning Electron Microscope (SEM)Energy dispersive X-ray analysis (EDX) analysis showed that the GJS has a porous structure
1
and rough surface. Also, the pores of GJS after Cr(VI) adsorption were completely covered by Cr(VI) oxoanions. The obtained results indicated that the Cr(VI) removal efficiency increased by increasing of adsorbent dose and contact time and it decreased by increasing of pH solution and initial Cr(VI) concentration. Optimal conditions for Cr(VI) adsorption were the adsorbent dose of 6 g/L, 60 min contact time, and pH=3. The maximum removal efficiency and adsorption capacity were obtained 99.8% and 4.76 mg/g at optimum conditions. The experimental data were well fitted with the Freundlich isotherm and pseudofirst-order kinetics model. According to the results, GJS is able to adsorb the Cr(VI) oxoanion from aqueous solutions and can be used as an effective and appropriate adsorbent to remove Cr(VI) from wastewater. Graphical Abstract:
Keywords: Adsorption; Chromium (VI); Jujube stems; Isotherm; Kinetics
2
1. Introduction The toxicity of some heavy metals on environmental and human health is one of the most important problems for the chemistry and environmental health researchers (Eslami et al., 2018; Miri et al., 2017). Heavy metals are extremely toxic that accumulate well into the food chain and animal tissues (Li et al., 2014). Water pollution is a major worldwide concern due to the discharge of heavy metals from industrial, municipal and agricultural effluents to the environment (Khosravi et al., 2017; Salam et al., 2011). Heavy metals (such as Cr, Ni, Pb, Cd,…) are not biodegradable, and their presence in aquatic environment has led to bioaccumulation in living organisms that cause health problems in animals, plants and humans (Dubey and Gopal, 2007; Eslami et al., 2017; Wongsasuluk et al., 2014). Chromium is the earth’s 21st most abundant element and exists in the trivalent form Cr(III) (H3CrO3), and the hexavalent form Cr(VI) (H2Cr2O7), in the aquatic environment (Rafati et al., 2010). The Cr(VI) oxoanion is more toxic than Cr(III) due to high water solubility and mobility (Tahar et al., 2018).
Cr(VI) species are very toxic and have a serious adverse effect such as
carcinogenic and mutagenic (Cronje et al., 2011; Dubey and Gopal, 2007). Chromium compounds are widely used for the chrome plating, stainless steel welding, dyeing, etc (Demirbas et al., 2004). In the recent years, the level of Cr(VI) in surface waters is rising due to discharge of industrial wastewater to the environment (Dubey and Gopal, 2007). Several treatment technologies such as chemical precipitation (Mohan and Pittman Jr, 2006), ion
exchange
(Dabrowski
et
al.,
2004),
membrane
separation,
ultrafiltration,
electrocoagulation (Akbal and Camcı, 2011), reverse osmosis (Dubey and Gopal, 2007), dialysis/ electrodialysis (Mohammadi et al., 2005), and adsorption by nanomaterials (Fu et al., 2017; Rafati et al., 2016) have been developed for the removal of Cr(VI) from the contaminated water and wastewater. The process efficiency, capital and operational costs are the main limitations for application of these methods especially in real scales (Ebrahimi et al., 3
2018; Mohan et al., 2014). Adsorption process is a simple, low-cost and high-efficiency method especially for the removal of heavy metals from the aqueous environments (Inyang et al., 2016; Rafati et al., 2018). In this technique, the material are accumulated in the interface between the liquid and solid phases (Gupta, 2009). Recently, low-cost and effective adsorbent such as sawdust, rice polish, waste tea, clays, and fly ash have been modified by researchers for removal of heavy metals from the aqueous environments (Gupta et al., 2015; Kamranifar et al., 2018). The present study, granular jujube stems (GJS) as a natural and low-cost adsorbent was used for the removal efficiency of Cr(VI) oxoanion from the pollutant solution. The effect of various parameters such as adsorbent dose, initial Cr(VI) concentration, contact time, and the pH of solutions was investigated on the removal efficiency of adsorption process by GJS. Also, the adsorption kinetics and isotherm was studied at the optimum conditions. 2. Materials and methods 2.1. Chemicals and instruments All chemicals in this study were pure analytical (> 99%) from Merck Co. A stock solution of 1000 mg/L Cr(VI) was prepared by dissolving of K2Cr2O7 salt in double distilled water. The pH of solutions were adjusted using NaOH 0.1 N or H2SO4 1 N solution by the pH meter HACH, model HQ40d, USA after calibrated with standard buffer solutions. The Cr(VI) concentration in unknown samples were measured by UV/Vis spectrophotometer (SP-3000 Plus, OPTIMA Co, Japan) followed by the calibration (concentration vs. absorbance) at wavelength 540 nm in the presence of 1,5-diphenylcarbazide reagent. SEM (Scanning Electron Microscope) and EDX (Energy dispersive X-ray analysis) (Phenom ProX, Nederland) were used for determination of the adsorbent characteristic before and after the adsorption process. 4
2.2. Preparation of granular Jujube stems adsorbent Jujube stems were collected from Birjand city, in the east of Iran. Jujube stems were washed with the distilled water three times and were then dried in oven (105 ºC) for 12 h. For preparation of granular adsorbent, jujube stems crushed by an electrical mill and then sieved through standard sieves of 40-60 mesh. 2.3. Adsorption experiment The adsorption experiments were done by adding the appropriate amount of adsorbent to a series of 100 ml various initial Cr(VI) concentration into the Erlenmeyer. The Erlenmeyers were sealed and then placed into the orbital shaker (GFL 3005, Germany) at 120 RPM. The effects of main parameters such as pH (3, 5, 7), adsorbent dose (4, 6 and 10 g/L), initial Cr(VI) concentration (0.5, 2, 10 mg/L), and contact time (15, 30, 60, 120, 180, 240 min and 24 h) were studied in the batch adsorption process. At the end of each experiment, the adsorbent particles were separated from the suspension by filtration through Whatman No. 47 filter paper and the residual Cr(VI) concentration was measured in the filtrated solutions. The percentage of Cr removal (R) and the amount of Cr(VI) adsorbed per unit of GJS mass at equilibrium, qe (mg/g), were calculated using the Eq. 1 and 2 (Dehghani et al., 2016): ( )
(
(1)
)
(2)
Where C0, Ce and C are the initial, equilibrium and final concentrations of Cr(VI) (mg/L), respectively, V is the volume of solution (L), and m is the mass of adsorbent (g). 3. Results and discussion 3.1. Characteristic of GJS adsorbent 5
SEM images of GJS adsorbent before and after adsorption of Cr(VI) are shown in Fig. 1a and b, respectively. As it can be seen, the GJS before Cr(VI) adsorption has a porous structure and rough surface. The pores and surfaces of GJS were completely covered after Cr(VI) adsorption and filled by Cr(VI) oxoanions. Also, EDX analysis of GJS befor and after Cr(VI) adsorption (Fig. 1c, d) confirm that the Cr(VI) element was adsorbed on the surface of GJS.
3.2. Effect of solution pH The solution pH is an important parameter that controlled the adsorption process (Cho et al., 2005). Solution pH has a significant impact on the uptake of the metal ions due to the effect on the surface charge and the degree of the adsorbent ionization (Vaghetti et al., 2008). The effect of solution pH on the Cr(VI) removal by the GJS is presented in the Fig. 2. As can be seen, the Cr(VI) removal decreased remarkably with increasing of pH so that with increasing of pH from 3 to 7, removal efficiency decreased from 99.8% to 88.5%. In our study, the most Cr(VI) removal efficiency by GJS occurred at acidic condition (pH=3) that was agreement with the study of Hamadi et al., 2001 entitled the adsorption kinetics for the removal of Cr(VI) from aqueous solution by adsorbents derived from tyres and sawdust (Hamadi et al., 2001). 3.3. Effect of adsorbent dose The adsorbent dose is another important parameters that must be optimized in adsorption process. Fig. 3 represents the effect of adsorbent dose on the Cr(VI) removal efficiency. By increasing of adsorbent dose, the removal efficiency increased, so that by increasing of adsorbent dose from 4 to 10 g/L, Cr(VI) removal efficiency increased from 90.8% to 99.8% at 2 mg/L Cr(VI) concentration and 180 min contact time. It is due to this fact that the availability of adsorbent sites is limited to the ions in the batch adsorption (Chen et al., 2015). 6
As a result, The optimal adsorbent dose for Cr(VI) removal was 6 g/L. Dubey and Gopal studied on the Cr(VI) removal by two low cost adsorbents which were prepared using agricultural wastes. They investigated the Cr(VI) removal by different amounts of adsorbents in range of 0.625 to 7.5 g/L. They observed that removal efficiency of the adsorbents generally increased with increasing of the amount of adsorbents. Both of the used adsorbents showed no further increase in adsorption capacity after a certain amount of adsorbent that was added from 0.625 to 5 g/L (Dubey and Gopal, 2007). Dakiky et al., examined the selective adsorption of Cr(VI) from industrial wastewater by low-cost adsorbents such as wool, pine needles, olive cake, almond shells, sawdust, cactus leaves and coal. The adsorbent doses were used from 2 to 24 g/L and their results showed that increasing the adsorbent dose increased the Cr(VI) removal percentage (Dakiky et al., 2002). 3.4. Effects of initial Cr(VI) concentration and contact time The results of initial Cr(VI) concentration on the removal efficiency at pH=3 and 6 g/L adsorbent dose are shown in Fig. 4. According to the results, the removal efficiency decreased by increasing the initial Cr(VI) concentration,. The Cr(VI) removal efficiency at contact time of 180 min for initial Cr(VI) concentration of 0.5 and 2 mg/L were higher than 99% while it was 92.1% for 10 mg/L that indicates the removal efficiency decreased with increasing the initial Cr(VI) concentration. The contact time is one of the parameters that affects the design and operation of the adsorption process. As is shown in Fig. 3, the removal efficiency increased by increasing of contact time. So, by increasing the contact time from 15 to 240 min, at initial Cr(VI) concentration of 2 mg/L, the Cr(VI) removal efficiency increased from 71.7% to 99.8%. The effect of contact time on the adsorption process showed that the Cr(VI) adsorption at 180 min
7
reached to equilibrium and then with increasing the contact time, the adsorption removal efficiency had no significant change. According to Fig. 4, by increasing initial Cr(VI) concentration and the contact time, the Cr(VI) removal efficiency decreased. In fact, adsorbent has the definite active sites which saturated by pollutant in high concentration of pollutant so the removal efficiency of pollutant decreased in the high amount of adsorbents (Shao-feng et al., 2005). By increasing the contact time, the contact between pollutant and adsorbent surface increased and so the removal efficiency increased (Argun and Dursun, 2008). Also, the initial adsorption rate increased rapidly and the equilibrium was attained at 60 min with Cr(VI) removal efficiency of 82.3%. Vaghetti et al., (2008) applied the Brazilian-pine fruit coat as a biosorbent to remove Cr(VI) from aqueous solution and investigated the Cr adsorption was depended on pH and contact time. They found that the optimum pH was 2 for maximum Cr removal and contact time for achieving equilibrium was 10 h (Vaghetti et al., 2008). In the present study, contact time for achieving equilibrium was 180 min and optimum contact time was 60 min. In order to investigate the adsorption capacity of Cr(VI) by the GJS, the qe values were calculated for different conditions. According to data obtained in this stage, the amount of qe for GJS were 0.83, 3.30 and 15.36 mg/g for initial Cr(VI) concentrations of 0.5, 2 and 10 mg/L, respectively. So by increasing of initial Cr(VI) concentration, adsorption capacity increased. 3.5. Adsorption kinetics The pseudo-first and second order equations present the simple kinetics analysis of an adsorption process and its linear equations are given as the Eq. 3 and 4, respectively (Dehghani et al., 2016): (
)
(3) 8
(4)
Where, the k1 and k2 are the pseudo-first-order and the pseudo-second-order adsorption rate constant, respectively. Also, the qe and qt are the amount of Cr(VI) adsorbed (mg/g) at equilibrium and at time t, respectively (Kaušpėdienė et al., 2010). Fig. 5 shows the pseudo-first and second order kinetics models for the adsorption of Cr(VI) by GJS. Based on determination coefficient (R2) for kinetics models, Cr(VI) adsorption data were well fitted by pseudo-first-order kinetics (R2= 0.991). The qe and k1 in the pseudo-first order kinetics model were 0.83 mg/g and 0.0024 min-1, respectively. Dakiky et al., have studied the selective adsorption of Cr(VI) from industrial wastewater using low-cost abundantly available adsorbents and their results showed that adsorption process followed by pseudo-first-order kinetics (Dakiky et al., 2002). Levankumar et al. investigated batch adsorptin of Cr(VI) from aqueous solutions by Ocimum americanum L. seed pods and their results showed that the adsorption kinetics was followed to first order kinetics model (Levankumar et al., 2009). 3.6. Adsorption Isotherms In the present study, Langmuir, Freundlich and Temkin adsorption isotherm models were used to analysis the Cr(VI) adsorption data by GJS based on experimental data at optimal condition. The linear form of Langmuir equation is given as Eq. 5:
(5)
Where, qe is the equilibrium adsorbate concentration in solid phase (mg/g), qmax is the maximum adsorption capacity (mg/g), Ce the adsorbate concentration at equilibrium (mg/L) and KL is the Langmuir constant (L/mg). 9
The linear Freundlich equation is given in the Eq. 6: (6)
The qe and Ce are as explained above, KF is the Freundlich constant (mg/g), and 1/n indicates the intensity of adsorption. The linear form of Temkin isotherm model is as Eq. 7 (Momčilović et al., 2013): (7) Where, BT and KT are Temkin constants related to heat and potential of sorbtion, respectively. Determination coefficient (R2) of the fitted experimental data with Langmuir, Freundlich and Temkin linear adsorption isotherm models were 0.6460, 0.9343 and 0.6954, respectively. Therefore, the adsorption process of Cr(VI) by GJS were well fitted to the Freundlich isotherm model (Fig. 6). KF and n in Freundlich model for the adsorption of Cr(VI) by GJS were 4.76 mg/g and 0.65, respectively that indicate the adsorption of Cr(VI) was favorable at optimum condition. 4. Conclusion The main purpose of this study was the application of granular jujube stems (GJS) as a natural and porous adsorbent for improving the removal efficiency of Cr(VI) oxoanion from the aqueous solution. SEM images before and after Cr(VI) adsorption showed that the GJS had a porous structure and rough surface, Also, the pores and surfaces of GJS were completely covered and became smooth by Cr(VI) oxoanions after adsorption process. The results of the present study showed that the Cr(VI) removal efficiency decreased by increasing of pH so that the maximum removal efficiency was obtained at pH=3. Also by increasing of adsorbent the removal efficiency was increased and by increasing of initial 10
Cr(VI) concentration, the removal efficiency decreased. Also, by increasing the contact time from 15 to 180 min, removal efficiency increased and the adsorption process reached to equilibrium at 180 min. According to the results, granular jujube stems is favorable to adsorption of Cr(VI) from the aqueous solutions. Acknowledgment The research funded by Environmental Science and Technology Research Center of Shahid Sadoughi University of Medical Sciences and Health Services, Yazd, Iran. References Akbal, F., Camcı, S., 2011. Copper, chromium and nickel removal from metal plating wastewater by electrocoagulation. Desalination 269, 214-222. Argun, M.E., Dursun, S., 2008. A new approach to modification of natural adsorbent for heavy metal adsorption. Bioresour. Technol. 99, 2516-2527. Chen, T., Zhou, Z., Han, R., Meng, R., Wang, H., Lu, W., 2015. Adsorption of cadmium by biochar derived from municipal sewage sludge: impact factors and adsorption mechanism. Chemosphere 134, 286-293. Cho, H., Oh, D., Kim, K., 2005. A study on removal characteristics of heavy metals from aqueous solution by fly ash. J. Hazard. Mater. 127, 187-195. Cronje, K., Chetty, K., Carsky, M., Sahu, J., Meikap, B., 2011. Optimization of chromium (VI) sorption potential using developed activated carbon from sugarcane bagasse with chemical activation by zinc chloride. Desalination 275, 276-284. abrowski, A., ubicki, ., odko cieln , ., obens, ., 200 . Selective removal of the heav metal ions from waters and industrial wastewaters by ion-exchange method. Chemosphere 56, 91106. Dakiky, M., Khamis, M., Manassra, A., Mer'Eb, M., 2002. Selective adsorption of chromium (VI) in industrial wastewater using low-cost abundantly available adsorbents. Adv. Environ. Res. 6, 533-540. Dehghani, M.H., Sanaei, D., Ali, I., Bhatnagar, A., 2016. Removal of chromium (VI) from aqueous solution using treated waste newspaper as a low-cost adsorbent: Kinetic modeling and isotherm studies. J. Mol. Liq. 215, 671-679. Demirbas, E., Kobya, M., Senturk, E., Ozkan, T., 2004. Adsorption kinetics for the removal of chromium (VI) from aqueous solutions on the activated carbons prepared from agricultural wastes. Water Sa 30, 533-539.
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Dubey, S.P., Gopal, K., 2007. Adsorption of chromium (VI) on low cost adsorbents derived from agricultural waste material: a comparative study. J. Hazard. Mater. 145, 465-470. Ebrahimi, A., Hashemi, H., Eslami, H., Fallahzadeh, R.A., Khosravi, R., Askari, R., Ghahramani, E., 2018. Kinetics of biogas production and chemical oxygen demand removal from compost leachate in an anaerobic migrating blanket reactor. J. Environ. Manage. 206, 707-714. Eslami, H., Ehrampoush, M.H., Esmaeili, A., Ebrahimi, A.A., Salmani, M.H., Ghaneian, M.T., Falahzadeh, H., 2018. Efficient photocatalytic oxidation of arsenite from contaminated water by Fe2O3-Mn2O3 nanocomposite under UVA radiation and process optimization with experimental design. Chemosphere 207, 303-312. Eslami, H., Ehrampoush, M.H., Ghaneian, M.T., Mokhtari, M., Ebrahimi, A., 2017. Effect of Organic Loading Rates on biodegradation of linear alkyl benzene sulfonate, oil and grease in greywater by Integrated Fixed-film Activated Sludge (IFAS). J. Environ. Manage. 193, 312317. Fu, R., Zhang, X., Xu, Z., Guo, X., Bi, D., Zhang, W., 2017. Fast and highly efficient removal of chromium (VI) using humus-supported nanoscale zero-valent iron: Influencing factors, kinetics and mechanism. Sep. Purif. Technol. 174, 362-371. Gupta, V., 2009. Application of low-cost adsorbents for dye removal–A review. J. Environ. Manage. 90, 2313-2342. Gupta, V.K., Nayak, A., Agarwal, S., 2015. Bioadsorbents for remediation of heavy metals: current status and their future prospects. Environ. Eng. Res. 20, 1-18. Hamadi, N.K., Chen, X.D., Farid, M.M., Lu, M.G., 2001. Adsorption kinetics for the removal of chromium (VI) from aqueous solution by adsorbents derived from used tyres and sawdust. Chem. Eng. J. 84, 95-105. Inyang, M.I., Gao, B., Yao, Y., Xue, Y., Zimmerman, A., Mosa, A., Pullammanappallil, P., Ok, Y.S., Cao, X., 2016. A review of biochar as a low-cost adsorbent for aqueous heavy metal removal. Crit. Rev. Environ. Sci. Technol. 46, 406-433. Kamranifar, M., Khodadadi, M., Samiei, V., Dehdashti, B., Sepehr, M.N., Rafati, L., Nasseh, N., 2018. Comparison the removal of reactive red 195 dye using powder and ash of barberry stem as a low cost adsorbent from aqueous solutions: Isotherm and kinetic study. J. Mol. Liq. 255, 572-577. Kaušpėdienė, ., Kazlauskienė, ., Gefenienė, A., Binkienė, ., 2010. Comparison of the efficienc of activated carbon and neutral polymeric adsorbent in removal of chromium complex dye from aqueous solutions. J. Hazard. Mater. 179, 933-939. Khosravi, R., Eslami, H., Almodaresi, S.A., Heidari, M., Fallahzadeh, R.A., Taghavi, M., Khodadadi, M., Peirovi, R., 2017. Use of geographic information system and water quality index to assess groundwater quality for drinking purpose in Birjand City, Iran. Desalin. Water. Treat. 67, 7483. Levankumar, L., Muthukumaran, V., Gobinath, M., 2009. Batch adsorption and kinetics of chromium (VI) removal from aqueous solutions by Ocimum americanum L. seed pods. J. Hazard. Mater. 161, 709-713. Li, Z., Ma, Z., van der Kuijp, T.J., Yuan, Z., Huang, L., 2014. A review of soil heavy metal pollution from mines in China: pollution and health risk assessment. Sci Total Environ. 468, 843-853. 12
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Fig. 1. SEM images and EDX analysis of GJS before (a and c) and after (b and d) adsorption of Cr(VI)
14
Cr (VI) removal %
110 100 90 80 70 60 50 40 30 20 10 0
pH=7 pH=5 pH=3
0
30
60
90
120
150
180
210
Time (min) Fig. 2. Effect of pH on the Cr(VI) removal (C0 = 2 mg/L, adsorbent dose=6 g/L)
15
110
Cr (VI) removal %
100 90 80 70 60 50 40 30
4 g/L
20
6 g/L
10
10 g/L
0 0
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Time (min) Fig. 3. Effect of adsorbent dose on the Cr(VI) removal (C 0= 2 mg/L and pH=3)
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270
Cr (VI) removal %
110 100 90 80 70 60 50 40 30 20 10 0
0.5 mg/L 2 mg/L 10 mg/L 0
30
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Time (min) Fig. 4. Effect of initial Cr(VI) concentration on the removal efficiency (adsorbent dose=6 g/L, pH=3)
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2.8 2.75 2.7
y = 0.0024x + 2.3014 R² = 0.991
2.65
ln(q-qt)
2.6 2.55 2.5 2.45 2.4 2.35 2.3 2.25
0
30
60
90
120
150
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210
150
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210
Time(min) 14
b
12 10
y = 0.0623x + 1.0551 R² = 0.9848
t/qt
8 6 4 2 0 0
30
60
90 120 time(min)
Fig. 5. The pseudo-first (a) and second (b) order kinetic plot for the adsorption of Cr(VI) by GJS
18
3
y = 1.5391x + 1.5606 R² = 0.9343
Ln qe
2.5 2 1.5 1 0.5 0 -1.5
-1
-0.5
-0.5
0
0.5
Ln Ce Fig. 6. The Freundlich isotherm for the adsorption of Cr(VI) by GJS
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1
Highlight
A new porous adsorbent was investigated to efficient removal of Cr (VI) The maximum removal efficiency (99.8%) was at pH=3, adsorbent dose of 6 g/L and 60 min contact time. The experimental data well fitted with the Freundlich isotherm and pseudo-first-order kinetic model.
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PII: DOI: Reference:
S2352-801X(18)30124-3 https://doi.org/10.1016/j.gsd.2018.12.001 GSD180
To appear in: Groundwater for Sustainable Development Received date: 13 June 2018 Revised date: 15 November 2018 Accepted date: 3 December 2018 Cite this article as: Mohammad Hossein Salmani, Fateme Sahlabadi, Hadi Eslami, Mohammad Taghi Ghaneian, Iraj Rezapour Balaneji and Tahereh Jasemi Zad, Removal of Cr(VI) oxoanion from contaminated water using granular Jujube stems as a porous adsorbent, Groundwater for Sustainable Development, https://doi.org/10.1016/j.gsd.2018.12.001 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Removal of Cr(VI) oxoanion from contaminated water using granular Jujube stems as a porous adsorbent Mohammad Hossein Salmani1, Fateme Sahlabadi2, Hadi Eslami3, Mohammad Taghi Ghaneian1, Iraj Rezapour Balaneji4, Tahereh Jasemi Zad1* 1
Environmental Science and Technology Research Center, Department of Environmental Health Engineering,
School of Public Health, Shahid Sadoughi University of Medical Sciences, Yazd, I. R. Iran 2
Department of Environmental Health Engineering, Social determinants of health research center University of
Medical Sciences, Birjand, I. R. Iran 3
Department of Environmental Health Engineering, School of Health, Rafsanjan University of Medical
Sceiences, Rafsanjan, I. R. Iran. 4
Department of Food Hygiene and Safety, School of Public Health, Shahid Sadoughi University of Medical
Science, Yazd, I. R. Iran
*
Corresponding author: Alem square, Gomnam Shohada Blvd, Department of Environmental Health
Engineering, Shahid Sadoughi University of Medical Sciences, Yazd, I. R. Iran. Tel: +9834192234, [email protected]
Abstract The efficiency of granular Jujube stems (GJS) was investigated in removal of hazardous Cr(VI) oxoanion from contaminated solutions. The GJS was prepared under standard conditions and sized in 40-60 mesh using ASTM standard sieves. The effects of pH (3, 5, 7), adsorbent dose (4, 6 and 10 g/L), initial Cr(VI) concentration (0.5, 2 and 10 mg/L) and contact time (15, 30, 60, 120, 180, 240 min and 24 h) were investigated on the removal of Cr(VI) by batch experiments at laboratory scale. Scanning Electron Microscope (SEM)Energy dispersive X-ray analysis (EDX) analysis showed that the GJS has a porous structure
1
and rough surface. Also, the pores of GJS after Cr(VI) adsorption were completely covered by Cr(VI) oxoanions. The obtained results indicated that the Cr(VI) removal efficiency increased by increasing of adsorbent dose and contact time and it decreased by increasing of pH solution and initial Cr(VI) concentration. Optimal conditions for Cr(VI) adsorption were the adsorbent dose of 6 g/L, 60 min contact time, and pH=3. The maximum removal efficiency and adsorption capacity were obtained 99.8% and 4.76 mg/g at optimum conditions. The experimental data were well fitted with the Freundlich isotherm and pseudofirst-order kinetics model. According to the results, GJS is able to adsorb the Cr(VI) oxoanion from aqueous solutions and can be used as an effective and appropriate adsorbent to remove Cr(VI) from wastewater. Graphical Abstract:
Keywords: Adsorption; Chromium (VI); Jujube stems; Isotherm; Kinetics
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1. Introduction The toxicity of some heavy metals on environmental and human health is one of the most important problems for the chemistry and environmental health researchers (Eslami et al., 2018; Miri et al., 2017). Heavy metals are extremely toxic that accumulate well into the food chain and animal tissues (Li et al., 2014). Water pollution is a major worldwide concern due to the discharge of heavy metals from industrial, municipal and agricultural effluents to the environment (Khosravi et al., 2017; Salam et al., 2011). Heavy metals (such as Cr, Ni, Pb, Cd,…) are not biodegradable, and their presence in aquatic environment has led to bioaccumulation in living organisms that cause health problems in animals, plants and humans (Dubey and Gopal, 2007; Eslami et al., 2017; Wongsasuluk et al., 2014). Chromium is the earth’s 21st most abundant element and exists in the trivalent form Cr(III) (H3CrO3), and the hexavalent form Cr(VI) (H2Cr2O7), in the aquatic environment (Rafati et al., 2010). The Cr(VI) oxoanion is more toxic than Cr(III) due to high water solubility and mobility (Tahar et al., 2018).
Cr(VI) species are very toxic and have a serious adverse effect such as
carcinogenic and mutagenic (Cronje et al., 2011; Dubey and Gopal, 2007). Chromium compounds are widely used for the chrome plating, stainless steel welding, dyeing, etc (Demirbas et al., 2004). In the recent years, the level of Cr(VI) in surface waters is rising due to discharge of industrial wastewater to the environment (Dubey and Gopal, 2007). Several treatment technologies such as chemical precipitation (Mohan and Pittman Jr, 2006), ion
exchange
(Dabrowski
et
al.,
2004),
membrane
separation,
ultrafiltration,
electrocoagulation (Akbal and Camcı, 2011), reverse osmosis (Dubey and Gopal, 2007), dialysis/ electrodialysis (Mohammadi et al., 2005), and adsorption by nanomaterials (Fu et al., 2017; Rafati et al., 2016) have been developed for the removal of Cr(VI) from the contaminated water and wastewater. The process efficiency, capital and operational costs are the main limitations for application of these methods especially in real scales (Ebrahimi et al., 3
2018; Mohan et al., 2014). Adsorption process is a simple, low-cost and high-efficiency method especially for the removal of heavy metals from the aqueous environments (Inyang et al., 2016; Rafati et al., 2018). In this technique, the material are accumulated in the interface between the liquid and solid phases (Gupta, 2009). Recently, low-cost and effective adsorbent such as sawdust, rice polish, waste tea, clays, and fly ash have been modified by researchers for removal of heavy metals from the aqueous environments (Gupta et al., 2015; Kamranifar et al., 2018). The present study, granular jujube stems (GJS) as a natural and low-cost adsorbent was used for the removal efficiency of Cr(VI) oxoanion from the pollutant solution. The effect of various parameters such as adsorbent dose, initial Cr(VI) concentration, contact time, and the pH of solutions was investigated on the removal efficiency of adsorption process by GJS. Also, the adsorption kinetics and isotherm was studied at the optimum conditions. 2. Materials and methods 2.1. Chemicals and instruments All chemicals in this study were pure analytical (> 99%) from Merck Co. A stock solution of 1000 mg/L Cr(VI) was prepared by dissolving of K2Cr2O7 salt in double distilled water. The pH of solutions were adjusted using NaOH 0.1 N or H2SO4 1 N solution by the pH meter HACH, model HQ40d, USA after calibrated with standard buffer solutions. The Cr(VI) concentration in unknown samples were measured by UV/Vis spectrophotometer (SP-3000 Plus, OPTIMA Co, Japan) followed by the calibration (concentration vs. absorbance) at wavelength 540 nm in the presence of 1,5-diphenylcarbazide reagent. SEM (Scanning Electron Microscope) and EDX (Energy dispersive X-ray analysis) (Phenom ProX, Nederland) were used for determination of the adsorbent characteristic before and after the adsorption process. 4
2.2. Preparation of granular Jujube stems adsorbent Jujube stems were collected from Birjand city, in the east of Iran. Jujube stems were washed with the distilled water three times and were then dried in oven (105 ºC) for 12 h. For preparation of granular adsorbent, jujube stems crushed by an electrical mill and then sieved through standard sieves of 40-60 mesh. 2.3. Adsorption experiment The adsorption experiments were done by adding the appropriate amount of adsorbent to a series of 100 ml various initial Cr(VI) concentration into the Erlenmeyer. The Erlenmeyers were sealed and then placed into the orbital shaker (GFL 3005, Germany) at 120 RPM. The effects of main parameters such as pH (3, 5, 7), adsorbent dose (4, 6 and 10 g/L), initial Cr(VI) concentration (0.5, 2, 10 mg/L), and contact time (15, 30, 60, 120, 180, 240 min and 24 h) were studied in the batch adsorption process. At the end of each experiment, the adsorbent particles were separated from the suspension by filtration through Whatman No. 47 filter paper and the residual Cr(VI) concentration was measured in the filtrated solutions. The percentage of Cr removal (R) and the amount of Cr(VI) adsorbed per unit of GJS mass at equilibrium, qe (mg/g), were calculated using the Eq. 1 and 2 (Dehghani et al., 2016): ( )
(
(1)
)
(2)
Where C0, Ce and C are the initial, equilibrium and final concentrations of Cr(VI) (mg/L), respectively, V is the volume of solution (L), and m is the mass of adsorbent (g). 3. Results and discussion 3.1. Characteristic of GJS adsorbent 5
SEM images of GJS adsorbent before and after adsorption of Cr(VI) are shown in Fig. 1a and b, respectively. As it can be seen, the GJS before Cr(VI) adsorption has a porous structure and rough surface. The pores and surfaces of GJS were completely covered after Cr(VI) adsorption and filled by Cr(VI) oxoanions. Also, EDX analysis of GJS befor and after Cr(VI) adsorption (Fig. 1c, d) confirm that the Cr(VI) element was adsorbed on the surface of GJS.
3.2. Effect of solution pH The solution pH is an important parameter that controlled the adsorption process (Cho et al., 2005). Solution pH has a significant impact on the uptake of the metal ions due to the effect on the surface charge and the degree of the adsorbent ionization (Vaghetti et al., 2008). The effect of solution pH on the Cr(VI) removal by the GJS is presented in the Fig. 2. As can be seen, the Cr(VI) removal decreased remarkably with increasing of pH so that with increasing of pH from 3 to 7, removal efficiency decreased from 99.8% to 88.5%. In our study, the most Cr(VI) removal efficiency by GJS occurred at acidic condition (pH=3) that was agreement with the study of Hamadi et al., 2001 entitled the adsorption kinetics for the removal of Cr(VI) from aqueous solution by adsorbents derived from tyres and sawdust (Hamadi et al., 2001). 3.3. Effect of adsorbent dose The adsorbent dose is another important parameters that must be optimized in adsorption process. Fig. 3 represents the effect of adsorbent dose on the Cr(VI) removal efficiency. By increasing of adsorbent dose, the removal efficiency increased, so that by increasing of adsorbent dose from 4 to 10 g/L, Cr(VI) removal efficiency increased from 90.8% to 99.8% at 2 mg/L Cr(VI) concentration and 180 min contact time. It is due to this fact that the availability of adsorbent sites is limited to the ions in the batch adsorption (Chen et al., 2015). 6
As a result, The optimal adsorbent dose for Cr(VI) removal was 6 g/L. Dubey and Gopal studied on the Cr(VI) removal by two low cost adsorbents which were prepared using agricultural wastes. They investigated the Cr(VI) removal by different amounts of adsorbents in range of 0.625 to 7.5 g/L. They observed that removal efficiency of the adsorbents generally increased with increasing of the amount of adsorbents. Both of the used adsorbents showed no further increase in adsorption capacity after a certain amount of adsorbent that was added from 0.625 to 5 g/L (Dubey and Gopal, 2007). Dakiky et al., examined the selective adsorption of Cr(VI) from industrial wastewater by low-cost adsorbents such as wool, pine needles, olive cake, almond shells, sawdust, cactus leaves and coal. The adsorbent doses were used from 2 to 24 g/L and their results showed that increasing the adsorbent dose increased the Cr(VI) removal percentage (Dakiky et al., 2002). 3.4. Effects of initial Cr(VI) concentration and contact time The results of initial Cr(VI) concentration on the removal efficiency at pH=3 and 6 g/L adsorbent dose are shown in Fig. 4. According to the results, the removal efficiency decreased by increasing the initial Cr(VI) concentration,. The Cr(VI) removal efficiency at contact time of 180 min for initial Cr(VI) concentration of 0.5 and 2 mg/L were higher than 99% while it was 92.1% for 10 mg/L that indicates the removal efficiency decreased with increasing the initial Cr(VI) concentration. The contact time is one of the parameters that affects the design and operation of the adsorption process. As is shown in Fig. 3, the removal efficiency increased by increasing of contact time. So, by increasing the contact time from 15 to 240 min, at initial Cr(VI) concentration of 2 mg/L, the Cr(VI) removal efficiency increased from 71.7% to 99.8%. The effect of contact time on the adsorption process showed that the Cr(VI) adsorption at 180 min
7
reached to equilibrium and then with increasing the contact time, the adsorption removal efficiency had no significant change. According to Fig. 4, by increasing initial Cr(VI) concentration and the contact time, the Cr(VI) removal efficiency decreased. In fact, adsorbent has the definite active sites which saturated by pollutant in high concentration of pollutant so the removal efficiency of pollutant decreased in the high amount of adsorbents (Shao-feng et al., 2005). By increasing the contact time, the contact between pollutant and adsorbent surface increased and so the removal efficiency increased (Argun and Dursun, 2008). Also, the initial adsorption rate increased rapidly and the equilibrium was attained at 60 min with Cr(VI) removal efficiency of 82.3%. Vaghetti et al., (2008) applied the Brazilian-pine fruit coat as a biosorbent to remove Cr(VI) from aqueous solution and investigated the Cr adsorption was depended on pH and contact time. They found that the optimum pH was 2 for maximum Cr removal and contact time for achieving equilibrium was 10 h (Vaghetti et al., 2008). In the present study, contact time for achieving equilibrium was 180 min and optimum contact time was 60 min. In order to investigate the adsorption capacity of Cr(VI) by the GJS, the qe values were calculated for different conditions. According to data obtained in this stage, the amount of qe for GJS were 0.83, 3.30 and 15.36 mg/g for initial Cr(VI) concentrations of 0.5, 2 and 10 mg/L, respectively. So by increasing of initial Cr(VI) concentration, adsorption capacity increased. 3.5. Adsorption kinetics The pseudo-first and second order equations present the simple kinetics analysis of an adsorption process and its linear equations are given as the Eq. 3 and 4, respectively (Dehghani et al., 2016): (
)
(3) 8
(4)
Where, the k1 and k2 are the pseudo-first-order and the pseudo-second-order adsorption rate constant, respectively. Also, the qe and qt are the amount of Cr(VI) adsorbed (mg/g) at equilibrium and at time t, respectively (Kaušpėdienė et al., 2010). Fig. 5 shows the pseudo-first and second order kinetics models for the adsorption of Cr(VI) by GJS. Based on determination coefficient (R2) for kinetics models, Cr(VI) adsorption data were well fitted by pseudo-first-order kinetics (R2= 0.991). The qe and k1 in the pseudo-first order kinetics model were 0.83 mg/g and 0.0024 min-1, respectively. Dakiky et al., have studied the selective adsorption of Cr(VI) from industrial wastewater using low-cost abundantly available adsorbents and their results showed that adsorption process followed by pseudo-first-order kinetics (Dakiky et al., 2002). Levankumar et al. investigated batch adsorptin of Cr(VI) from aqueous solutions by Ocimum americanum L. seed pods and their results showed that the adsorption kinetics was followed to first order kinetics model (Levankumar et al., 2009). 3.6. Adsorption Isotherms In the present study, Langmuir, Freundlich and Temkin adsorption isotherm models were used to analysis the Cr(VI) adsorption data by GJS based on experimental data at optimal condition. The linear form of Langmuir equation is given as Eq. 5:
(5)
Where, qe is the equilibrium adsorbate concentration in solid phase (mg/g), qmax is the maximum adsorption capacity (mg/g), Ce the adsorbate concentration at equilibrium (mg/L) and KL is the Langmuir constant (L/mg). 9
The linear Freundlich equation is given in the Eq. 6: (6)
The qe and Ce are as explained above, KF is the Freundlich constant (mg/g), and 1/n indicates the intensity of adsorption. The linear form of Temkin isotherm model is as Eq. 7 (Momčilović et al., 2013): (7) Where, BT and KT are Temkin constants related to heat and potential of sorbtion, respectively. Determination coefficient (R2) of the fitted experimental data with Langmuir, Freundlich and Temkin linear adsorption isotherm models were 0.6460, 0.9343 and 0.6954, respectively. Therefore, the adsorption process of Cr(VI) by GJS were well fitted to the Freundlich isotherm model (Fig. 6). KF and n in Freundlich model for the adsorption of Cr(VI) by GJS were 4.76 mg/g and 0.65, respectively that indicate the adsorption of Cr(VI) was favorable at optimum condition. 4. Conclusion The main purpose of this study was the application of granular jujube stems (GJS) as a natural and porous adsorbent for improving the removal efficiency of Cr(VI) oxoanion from the aqueous solution. SEM images before and after Cr(VI) adsorption showed that the GJS had a porous structure and rough surface, Also, the pores and surfaces of GJS were completely covered and became smooth by Cr(VI) oxoanions after adsorption process. The results of the present study showed that the Cr(VI) removal efficiency decreased by increasing of pH so that the maximum removal efficiency was obtained at pH=3. Also by increasing of adsorbent the removal efficiency was increased and by increasing of initial 10
Cr(VI) concentration, the removal efficiency decreased. Also, by increasing the contact time from 15 to 180 min, removal efficiency increased and the adsorption process reached to equilibrium at 180 min. According to the results, granular jujube stems is favorable to adsorption of Cr(VI) from the aqueous solutions. Acknowledgment The research funded by Environmental Science and Technology Research Center of Shahid Sadoughi University of Medical Sciences and Health Services, Yazd, Iran. References Akbal, F., Camcı, S., 2011. Copper, chromium and nickel removal from metal plating wastewater by electrocoagulation. Desalination 269, 214-222. Argun, M.E., Dursun, S., 2008. A new approach to modification of natural adsorbent for heavy metal adsorption. Bioresour. Technol. 99, 2516-2527. Chen, T., Zhou, Z., Han, R., Meng, R., Wang, H., Lu, W., 2015. Adsorption of cadmium by biochar derived from municipal sewage sludge: impact factors and adsorption mechanism. Chemosphere 134, 286-293. Cho, H., Oh, D., Kim, K., 2005. A study on removal characteristics of heavy metals from aqueous solution by fly ash. J. Hazard. Mater. 127, 187-195. Cronje, K., Chetty, K., Carsky, M., Sahu, J., Meikap, B., 2011. Optimization of chromium (VI) sorption potential using developed activated carbon from sugarcane bagasse with chemical activation by zinc chloride. Desalination 275, 276-284. abrowski, A., ubicki, ., odko cieln , ., obens, ., 200 . Selective removal of the heav metal ions from waters and industrial wastewaters by ion-exchange method. Chemosphere 56, 91106. Dakiky, M., Khamis, M., Manassra, A., Mer'Eb, M., 2002. Selective adsorption of chromium (VI) in industrial wastewater using low-cost abundantly available adsorbents. Adv. Environ. Res. 6, 533-540. Dehghani, M.H., Sanaei, D., Ali, I., Bhatnagar, A., 2016. Removal of chromium (VI) from aqueous solution using treated waste newspaper as a low-cost adsorbent: Kinetic modeling and isotherm studies. J. Mol. Liq. 215, 671-679. Demirbas, E., Kobya, M., Senturk, E., Ozkan, T., 2004. Adsorption kinetics for the removal of chromium (VI) from aqueous solutions on the activated carbons prepared from agricultural wastes. Water Sa 30, 533-539.
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Dubey, S.P., Gopal, K., 2007. Adsorption of chromium (VI) on low cost adsorbents derived from agricultural waste material: a comparative study. J. Hazard. Mater. 145, 465-470. Ebrahimi, A., Hashemi, H., Eslami, H., Fallahzadeh, R.A., Khosravi, R., Askari, R., Ghahramani, E., 2018. Kinetics of biogas production and chemical oxygen demand removal from compost leachate in an anaerobic migrating blanket reactor. J. Environ. Manage. 206, 707-714. Eslami, H., Ehrampoush, M.H., Esmaeili, A., Ebrahimi, A.A., Salmani, M.H., Ghaneian, M.T., Falahzadeh, H., 2018. Efficient photocatalytic oxidation of arsenite from contaminated water by Fe2O3-Mn2O3 nanocomposite under UVA radiation and process optimization with experimental design. Chemosphere 207, 303-312. Eslami, H., Ehrampoush, M.H., Ghaneian, M.T., Mokhtari, M., Ebrahimi, A., 2017. Effect of Organic Loading Rates on biodegradation of linear alkyl benzene sulfonate, oil and grease in greywater by Integrated Fixed-film Activated Sludge (IFAS). J. Environ. Manage. 193, 312317. Fu, R., Zhang, X., Xu, Z., Guo, X., Bi, D., Zhang, W., 2017. Fast and highly efficient removal of chromium (VI) using humus-supported nanoscale zero-valent iron: Influencing factors, kinetics and mechanism. Sep. Purif. Technol. 174, 362-371. Gupta, V., 2009. Application of low-cost adsorbents for dye removal–A review. J. Environ. Manage. 90, 2313-2342. Gupta, V.K., Nayak, A., Agarwal, S., 2015. Bioadsorbents for remediation of heavy metals: current status and their future prospects. Environ. Eng. Res. 20, 1-18. Hamadi, N.K., Chen, X.D., Farid, M.M., Lu, M.G., 2001. Adsorption kinetics for the removal of chromium (VI) from aqueous solution by adsorbents derived from used tyres and sawdust. Chem. Eng. J. 84, 95-105. Inyang, M.I., Gao, B., Yao, Y., Xue, Y., Zimmerman, A., Mosa, A., Pullammanappallil, P., Ok, Y.S., Cao, X., 2016. A review of biochar as a low-cost adsorbent for aqueous heavy metal removal. Crit. Rev. Environ. Sci. Technol. 46, 406-433. Kamranifar, M., Khodadadi, M., Samiei, V., Dehdashti, B., Sepehr, M.N., Rafati, L., Nasseh, N., 2018. Comparison the removal of reactive red 195 dye using powder and ash of barberry stem as a low cost adsorbent from aqueous solutions: Isotherm and kinetic study. J. Mol. Liq. 255, 572-577. Kaušpėdienė, ., Kazlauskienė, ., Gefenienė, A., Binkienė, ., 2010. Comparison of the efficienc of activated carbon and neutral polymeric adsorbent in removal of chromium complex dye from aqueous solutions. J. Hazard. Mater. 179, 933-939. Khosravi, R., Eslami, H., Almodaresi, S.A., Heidari, M., Fallahzadeh, R.A., Taghavi, M., Khodadadi, M., Peirovi, R., 2017. Use of geographic information system and water quality index to assess groundwater quality for drinking purpose in Birjand City, Iran. Desalin. Water. Treat. 67, 7483. Levankumar, L., Muthukumaran, V., Gobinath, M., 2009. Batch adsorption and kinetics of chromium (VI) removal from aqueous solutions by Ocimum americanum L. seed pods. J. Hazard. Mater. 161, 709-713. Li, Z., Ma, Z., van der Kuijp, T.J., Yuan, Z., Huang, L., 2014. A review of soil heavy metal pollution from mines in China: pollution and health risk assessment. Sci Total Environ. 468, 843-853. 12
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Fig. 1. SEM images and EDX analysis of GJS before (a and c) and after (b and d) adsorption of Cr(VI)
14
Cr (VI) removal %
110 100 90 80 70 60 50 40 30 20 10 0
pH=7 pH=5 pH=3
0
30
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Time (min) Fig. 2. Effect of pH on the Cr(VI) removal (C0 = 2 mg/L, adsorbent dose=6 g/L)
15
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Cr (VI) removal %
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20
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0 0
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Time (min) Fig. 3. Effect of adsorbent dose on the Cr(VI) removal (C 0= 2 mg/L and pH=3)
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Cr (VI) removal %
110 100 90 80 70 60 50 40 30 20 10 0
0.5 mg/L 2 mg/L 10 mg/L 0
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Time (min) Fig. 4. Effect of initial Cr(VI) concentration on the removal efficiency (adsorbent dose=6 g/L, pH=3)
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2.8 2.75 2.7
y = 0.0024x + 2.3014 R² = 0.991
2.65
ln(q-qt)
2.6 2.55 2.5 2.45 2.4 2.35 2.3 2.25
0
30
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Time(min) 14
b
12 10
y = 0.0623x + 1.0551 R² = 0.9848
t/qt
8 6 4 2 0 0
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Fig. 5. The pseudo-first (a) and second (b) order kinetic plot for the adsorption of Cr(VI) by GJS
18
3
y = 1.5391x + 1.5606 R² = 0.9343
Ln qe
2.5 2 1.5 1 0.5 0 -1.5
-1
-0.5
-0.5
0
0.5
Ln Ce Fig. 6. The Freundlich isotherm for the adsorption of Cr(VI) by GJS
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1
Highlight
A new porous adsorbent was investigated to efficient removal of Cr (VI) The maximum removal efficiency (99.8%) was at pH=3, adsorbent dose of 6 g/L and 60 min contact time. The experimental data well fitted with the Freundlich isotherm and pseudo-first-order kinetic model.
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