Initial Arsenate Research Articles

The removal of sulphate from mine water by precipitation as ettringite and the utilisation of the precipitate as a sorbent for arsenate removal

The aim of this research was to investigate sulphate removal from mine water by precipitation as ettringite (Ca6Al2(SO4)3(OH)12·26H2O) and the utilisation of the precipitate as a sorbent for arsenate removal. The mine water sulphate concentration was reduced by 85–90% from the initial 1400 mg/L during ettringite precipitation depending on the treatment method. The precipitation conditions were also simulated with MINEQL + software, and the computational results were compared with the experimental results. The precipitated solids were characterised with X-ray diffraction and a scanning electron microscope. The precipitated solids were tested as sorbents for arsenate removal from the model solution. The arsenic(V) model solution concentration reduced 86–96% from the initial 1.5 mg/L with a 1 g/L sorbent dosage. The effect of initial arsenate concentration on the sorption of arsenate on the precipitate was studied and Langmuir, Freundlich, and Langmuir-Freundlich sorption isotherm models were fitted to the experimental data. The maximum arsenate sorption capacity (qm = 11.2 ± 4.7 mg/g) of the precipitate was obtained from the Langmuir-Freundlich isotherm. The results indicate that the precipitate produced during sulphate removal from mine water by precipitation as ettringite could be further used as a sorbent for arsenate removal.

Removal mechanism of arsenate by bimetallic and trimetallic hydrocalumites depending on arsenate concentration

We investigated the influence of initial arsenate concentration (C0) in the 5th order of magnitude on removal of arsenate by hydrocalumite (bimetallic layered double hydroxide, LDH) and Mg-doped hydrocalumite (trimetallic LDH) from aqueous solution. These hydrocalumites were prepared by the microwave-assisted hydrothermal treatment. There is a trend that the larger adsorption density of arsenate (Qe) values is observed with bimetallic LDH under low C0 values and with trimetallic LDH under high C0 values. The transitional C0 values ranged at 2.10–2.96mM. Comprehensively understanding characterization results for the solid residues after adsorption of arsenate by X-ray diffraction, 27Al-nuclear magnetic resonance, and scanning electron microscopy–energy dispersive X-ray, the mechanism to remove arsenate was dependent on arsenate concentrations. At low arsenate concentration, partial intercalation and dissolution–reprecipitation (DR) happened together. With increasing C0, full intercalation and DR happened to bring out one phase of arsenate-bearing hydrocalumite. Under the very high C0, DR mechanism happened at the edge sites of LDH sheets, leading that the newly formed massive precipitates block the further intercalation with nitrate. As a result, two phases of LDH were observed. The greater Qe with bimetallic LDH in low concentration comes from high crystallinity to enhance partial ion-exchange, and greater Qe with trimetallic LDH in high concentration is derived from more fragile properties to enhance DR mechanism.

Exploring Arsenic Adsorption at low Concentration onto Modified Leonardite

The removal of As(V) from aqueous solutions by leonardite loaded with ferric ions (Fe-leonardite) has been investigated. The influence of pH, contact time, and arsenate concentration on the adsorption process were evaluated. Batch kinetic studies showed that equilibrium time was reached at 24 h of contact time. Equilibrium data obtained with low initial arsenate concentrations (10–400 ppb) were fitted to both Langmuir and Freundlich models, and the maximum adsorption capacity was estimated to be 322 μg g−1. Arsenic sorption was evaluated in continuous mode to reproduce industrial applications and to determine the conditions where the process was controlled by either mass transfer or reaction rate. A maximum sorption capacity of 905 μg g−1 was obtained in continuous experiments. These results indicate that Fe-leonardite is a great potential material for removing arsenate at low initial concentrations from contaminated water.

Arsenate removal by layered double hydroxides embedded into spherical polymer beads: Batch and column studies

ABSTRACTIn this study, the performance of poly(layered double hydroxides) [poly(LDHs)] beads as an adsorbent for arsenate removal from aqueous solution was investigated. The poly(LDHs) beads were prepared by immobilizing LDHs into spherical alginate/polyvinyl alcohol (PVA)-glutaraldehyde beads (spherical polymer beads). Batch adsorption studies were conducted to assess the effect of contact time, solution pH, initial arsenate concentrations and co-existing anions on arsenate removal performance. The potential reuse of these poly(LDHs) beads was also investigated. Approximately 79.1 to 91.2% of arsenic was removed from an arsenate solution (50 mg As L−1) by poly(LDHs). The adsorption data were well described by the pseudo–second-order kinetics model and the Langmuir isotherm model, and the adsorption capacities of these poly(LDHs) beads at pH 8 were from 1.64 to 1.73 mg As g−1, as calculated from the Langmuir adsorption isotherm. The adsorption ability of the poly(LDHs) beads decreased by approximately 5–6% after 5 adsorption-desorption cycles. Phosphates markedly decreased arsenate removal. The effect of co-existing anions on the adsorption capacity declined in the following order: HPO42− >> HCO3− > SO42− > Cl−. A fixed-bed column study was conducted with real-life arsenic-containing water. The breakthrough time was found to be from 7 to 10 h. Under optimized conditions, the poly(LDHs) removed more than 82% of total arsenic. The results obtained in this study will be useful for further extending the adsorbents to the field scale or for designing pilot plants in future studies. From the viewpoint of environmental friendliness, the poly(LDHs) beads are a potential cost-effective adsorbent for arsenate removal in water treatment.

Use of drinking water treatment solids for arsenate removal from desalination concentrate

Desalination of impaired water can be hindered by the limited options for concentrate disposal. Selective removal of specific contaminants using inexpensive adsorbents is an attractive option to address the challenges of concentrate management. In this study, two types of ferric-based drinking water treatment solids (DWTS) were examined for arsenate removal from reverse osmosis concentrate during continuous-flow once-through column experiments. Arsenate sorption was investigated under different operating conditions including pH, arsenate concentration, hydraulic retention time, loading rate, temperature, and moisture content of the DWTS. Arsenate removal by the DWTS was affected primarily by surface complexation, electrostatic interactions, and arsenate speciation. Results indicated that arsenate sorption was highly dependent on initial pH and initial arsenate concentration. Acidic conditions enhanced arsenate sorption as a result of weaker electrostatic repulsion between predominantly monovalent H2AsO4− and negatively charged particles in the DWTS. High initial arsenate concentration increased the driving force for arsenate sorption to the DWTS surface. Tests revealed that the potential risks associated with the use of DWTS include the leaching of organic contaminants and ammonia, which can be alleviated by using wet DWTS or discarding the initially treated effluent that contains high organic concentration.

Kinetic and thermodynamic analysis of adsorption of arsenic (III) with waste crab shells

Research Article| May 13 2014 Kinetic and thermodynamic analysis of adsorption of arsenic (III) with waste crab shells Zhibin Zhang; Zhibin Zhang 1School of Municipal and Environmental Engineering, Shandong Jianzhu University, Jinan 250101, China2Center for Sustainable Development & Global Competitiveness, Stanford University, Stanford, CA 94305, USA Search for other works by this author on: This Site PubMed Google Scholar Xiaorui Zhang; Xiaorui Zhang 1School of Municipal and Environmental Engineering, Shandong Jianzhu University, Jinan 250101, China Search for other works by this author on: This Site PubMed Google Scholar Shimiao Yu; Shimiao Yu 3Shandong Provincial Urban Construction Design Institute, Jinan 250001, China Search for other works by this author on: This Site PubMed Google Scholar Yanhao Zhang; Yanhao Zhang 1School of Municipal and Environmental Engineering, Shandong Jianzhu University, Jinan 250101, China E-mail: sdzyh66@126.com Search for other works by this author on: This Site PubMed Google Scholar Ning Wang; Ning Wang 1School of Municipal and Environmental Engineering, Shandong Jianzhu University, Jinan 250101, China Search for other works by this author on: This Site PubMed Google Scholar Cuizhen Sun; Cuizhen Sun 1School of Municipal and Environmental Engineering, Shandong Jianzhu University, Jinan 250101, China Search for other works by this author on: This Site PubMed Google Scholar Zheng Ma Zheng Ma 1School of Municipal and Environmental Engineering, Shandong Jianzhu University, Jinan 250101, China Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2014) 63 (8): 642–649. https://doi.org/10.2166/aqua.2014.196 Article history Received: December 11 2013 Accepted: April 14 2014 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation Zhibin Zhang, Xiaorui Zhang, Shimiao Yu, Yanhao Zhang, Ning Wang, Cuizhen Sun, Zheng Ma; Kinetic and thermodynamic analysis of adsorption of arsenic (III) with waste crab shells. Journal of Water Supply: Research and Technology-Aqua 1 December 2014; 63 (8): 642–649. doi: https://doi.org/10.2166/aqua.2014.196 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Recently, pollution incidents in surface water occurred frequently all over the world, which normally caused the surface water to have lower concentrations of heavy metals. A low cost waste crab shell (WCS) has been studied for the removal of arsenic from the contaminated surface water. The adsorption kinetics of WCS for low concentration (<1 mg/L) of arsenic (III) in a controlled batch system was studied. The effects of initial arsenic (III) concentrations, temperature, pH, and WCS biomass dose on the adsorption were investigated. Under the conditions set in this research, the maximum adsorption capacity for arsenic (III) was 165.78 mg/kg at 0.928 mg/L of initial arsenic (III) concentrations, pH 7.0, 40 °C, and 2.0 g/L of WCS biomass. The kinetics fitted the pseudo-second-order model better than models, such as pseudo-first-order model, Elovich kinetic model, and intra-particle diffusion model, etc. An examination of thermodynamic parameters showed that the adsorption of arsenic (III) with WCS was non-spontaneous and endothermic, as well as a physical process. The results suggested that WCS adsorption may be a useful option for arsenic removal from slightly arsenic-contaminated surface water. adsorption, arsenic, kinetics, thermodynamic, waste crab shells This content is only available as a PDF. © IWA Publishing 2014 You do not currently have access to this content.

Effect of metal composition in lanthanum-doped ferric-based layered double hydroxides and their calcined products on adsorption of arsenate

A series of lanthanum-doped ferric-based layered double hydroxides with the carbonate intercalation (Mg–Fe–La–LDHs) of different M2+/M3+ molar ratio and their corresponding calcined products were successfully synthesized and characterized. In order to understand the effect of metal compositions in these materials on their adsorption performances for arsenate, various factors such as solution pH, contact time and initial arsenate concentrations were investigated. The results showed that the maximum adsorption capacity for Mg–Fe–La–LDHs decreased with the increment of the M2+/M3+ molar ratio, but the reversed trend occurred for the calcined products of Mg–Fe–La–CLDHs. This difference is closely related to the different adsorption mechanisms for layered double hydroxides (LDHs) and calcined layered double hydroxide (CLDHs). It was found that the adsorption isotherms can be well described by the Langmuir equation, and the adsorption kinetics followed the pseudo-second-order kinetic model. The results suggested that the obtained Mg–Fe–La–LDHs with lower molar ratio of M2+/M3+ in the materials were more suitable for removal of arsenate, while their calcined products Mg–Fe–La–CLDHs with higher molar ratio of M2+/M3+ were efficient adsorbents for arsenate. When the M2+/M3+ molar ratio in the material was 4.38, the maximum adsorption capacity of CLDH-3 was as high as 47.4 mg g−1.

Batch and Fixed-Bed Column Studies of Arsenic Adsorption on the Natural and Modified Clinoptilolite

The samples of natural and iron-modified clinoptilolite (GC, Na-GC, Fe1-GC, and Fe2-GC) were assessed as adsorbent for arsenate removal by batch and column studies. The influences of retention time, pH, adsorbent dosage, and initial arsenate concentration on the arsenate adsorption efficiency were investigated. The experiments demonstrated that Fe1-GC has the highest arsenate removal efficiency with the adsorption capacity of 8.4 μg g−1 at equilibrium time of 60 min. Both the Fe1-GC and Fe2-GC removed arsenate effectively over the initial pH range 4–10. Adsorption capacity of Fe1-GC was adequately described by Freundlich isotherm. According to the results of the desorption performance experiments, the Fe1-GC was used six times until arsenic removal efficiency was reduced to 19 %. The adsorption percentage of arsenic increased with the diminish of initial concentration of arsenic and increase of adsorbent dose for all types of clinoptilolite. The column study demonstrated that Fe1-GC was achieved to reduce final arsenate of about 10 μg L−1 or below for up to 300 bed volumes in a continuous flow mode. The results of this study show that Fe1-GC can be used as an alternative adsorbent for arsenate removal.

Arsenate adsorption on waste eggshell modified by goethite, α-MnO2 and goethite/α-MnO2

An efficient adsorbents for arsenate removal was developed by modification of calcined eggshell with goethite (calcined eggshell/goethite; sorbent 1), α-MnO2 (calcined eggshell/α-MnO2; sorbent 2) and hybride system goethite/α-MnO2 (calcined eggshell/goethite/α-MnO2; sorbent 3). Methods and processes for preparation of novel adsorbents were defined and obtained materials were characterized by BET, XRD, SEM and FTIR analysis. The influence of functionalization methods, solution pH, contact time, temperature, interfering ions and initial arsenate concentration on efficiencies of arsenate adsorption were studied in a batch system. Based on the orthogonal distance regression (ODR) fitting, using R2, MARE and RMSRE statistical criteria, Langmuir and Sips equations were chosen for description of adsorption equilibriums on sorbents 1 and 3, respectively. The maximum adsorption capacities of 33.38mgg−1, 13.54mgg−1 and 47.04mgg−1 for sorbents 1–3, respectively, were obtained. Time-dependent study revealed that pseudo-second-order equation fitted well the kinetic data, while the Weber Morison model predicted intra-particle diffusion as main adsorption rate controlling step. Thermodynamic parameters indicated exothermic, feasible and spontaneous nature of adsorption process on sorbents 1 and 3. Results of Visual MINTEQ equilibrium speciation modeling program was used for studying pH, ionic strength and interfering ions influences on arsenate adsorption.

Factorial design analysis of As(V) adsorption onto iron-aluminum binary oxide-doped clinoptilolite

Arsenic adsorption onto an iron-aluminum binary oxide-doped clinoptilolite was studied by using response surface methodology. The Box–Behnken experimental design was used to estimate the effects of major process parameters, namely pH (3–7), temperature (25–65°C), and initial arsenate (As(V)) concentration (0.5–9.5 mg L−1). The experimental data fitted to the empirical second-order model was found to be significant, as was evident from the model F-value of 341.23. The coefficient of determination value of second-order regression model was found to be 0.9977 (Radj = 0.9948), indicating the accuracy and general availability of the model. The initial arsenic concentration of 9.4 mg L−1, pH of 6.0, and temperature f 62.4°C were found to be optimum for maximum As(V) uptake. The results showed that adsorption capacity increased with increasing temperature, indicating the endothermic nature of the adsorption process.

Microwave assisted synthesis of polycinnamamide Mg/Al mixed oxide nanocomposite and its application towards the removal of arsenate from aqueous medium

Microwave assisted synthesis of polycinnamamide Mg/Al mixed oxide nanocomposite was carried out and its ability for the removal of arsenate from water through adsorption has been investigated in the present study. Characterization of the nanocomposite was made by FE-SEM, EDX, TGA/DSC, FTIR, XRD and elemental analysis (CHNS) techniques. The effect of various parameters viz. contact time, pH (6–12), initial arsenate concentration (1–50mg/l), interfering anions, etc. has been investigated to determine the adsorption capacity of PCMA. Adsorption kinetic study showed that the adsorption process followed the first order kinetics and the data revealed that the uptake rate of arsenate was rapid at the beginning and equilibrium was established after 60min. The Lagergren rate constants and intraparticle diffusion rate constant (at 25°C) were found to be 0.069 and 0.41 respectively. The maximum adsorption capacity calculated from Langmuir isotherm model was found to be 11.54mg/g at 25°C. The mean free energies calculated from D.R. adsorption isotherm were found to be 15.2, 15.5 and 15.8kJmol−1 at 25, 35 and 45°C respectively. Thermodynamic study indicated an endothermic nature of the adsorption and a spontaneous and favorable process. The interfering anions reduced the arsenate adsorption in the order of, carbonate>bicarbonate>phosphate>chloride>sulfate>nitrate.

Process Optimization for Arsenic Adsorption onto Natural Zeolite Incorporating Metal Oxides by Response Surface Methodology

Arsenic (As) adsorption onto metal oxide-precipitated clinoptilolite was investigated by using response surface methodology (RSM). Box–Behnken experimental design combined with RSM was used to examine and to optimize major process parameters. The quadratic statistical model was defined by three independent variables namely, pH (3–7), temperature (25–65 °C), and initial arsenate (As(V)) concentration (0.5–9.5 mg L−1) while adsorption capacities of modified zeolites were designated as dependent variables. The iron oxide-precipitated zeolite (ZNa–Fe) was found to be more effective adsorbent when compared with aluminum oxide-modified one (ZNa–Al). The maximum As(V) adsorption capacities for ZNa–Fe and ZNa–Al were observed at pH 3.0 and pH 4.96, respectively. In the chosen range, higher adsorption capacities were achieved with increasing temperature, indicating the endothermic behavior of process for both samples. Initial As(V) concentration had a marked favorable effect on the amount of As(V) adsorbed onto adsorbents in the selected field. The constructed polynomial model was found significant, as was evident from the model F values (FZNa–Fe = 414.95 and F ZNa–Al = 167.17). The coefficients of determination values of second-order polynomial regression models were found as 0.9981 and 0.9953 for ZNa–Fe and ZNa–Al, respectively, indicating the accuracy and general availability of the model.

Synthesis of mesoporous Cu/Mg/Fe layered double hydroxide and its adsorption performance for arsenate in aqueous solutions

The mesoporous Cu/Mg/Fe layered double hydroxide (Cu/Mg/Fe-LDH) with carbonate intercalation was synthesized and used for the removal of arsenate from aqueous solutions. The Cu/Mg/Fe-LDH was characterized by Fourier transform infrared spectrometry, X-ray diffraction crystallography, scanning electron microscopy, X-ray photoelectron spectroscopy and Brunauer-Emmett-Teller. Effects of various physico-chemical parameters such as pH, adsorbent dosage, contact time and initial arsenate concentration on the adsorption of arsenate onto Cu/Mg/Fe-LDH were investigated. Results showed that it was efficient for the removal of arsenate, and the removal efficiency of arsenate increased with the increment of the adsorbent dosage, while the arsenate adsorption capacity decreased with increase of initial pH from 3 to 11. The adsorption isotherms can be well described by the Langmuir model with R2 > 0.99. Its adsorption kinetics followed the pseudo second-order kinetic model. Coexisting ions such as HPO42−, CO32−, SO42− and NO3− could compete with arsenate for adsorption sites on the Cu/Mg/Fe-LDH. The adsorption of arsenate on the adsorbent can be mainly attributed to the ion exchange process. It was found that the synthesized Cu/Mg/Fe-LDH can reduce the arsenate concentration down to a final level of < 10 μg/L under the experimental conditions, and makes it a potential material for the decontamination of arsenate polluted water.

Thermodynamic and kinetic studies of As(V) removal from water by zirconium oxide-coated marine sand

Arsenic contamination of groundwater is a major threat to human beings globally. Among various methods available for arsenic removal, adsorption is fast, inexpensive, selective, accurate, reproducible and eco-friendly in nature. The present paper describes removal of arsenate from water on zirconium oxide-coated sand (novel adsorbent). In the present work, zirconium oxide-coated sand was prepared and characterised by infrared and X-ray diffraction techniques. Batch experiments were performed to optimise different adsorption parameters such as initial arsenate concentration (100-1,000 μg/L), dose (1-8 g/L), pH of the solution (2-14), contact time (15-150 min.), and temperature (20, 30, 35 and 40 °C). The experimental data were analysed by Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models. Furthermore, thermodynamic and kinetic parameters were evaluated to know the mode of adsorption between ZrOCMS and As(V). The maximum removal of arsenic, 97 %, was achieved at initial arsenic concentration of 200 μg/L, after 75 min at dosage of 5.0 g/L, pH 7.0 and 27 ± 2 °C. For 600 μg/L concentration, the maximum Langmuir monolayer adsorption capacity was found to be 270 μg/g at 35 °C. Kinetic modelling data indicated that adsorption process followed pseudo-second-order kinetics. The mechanism is controlled by liquid film diffusion model. Thermodynamic parameter, ΔH°, was -57.782, while the values of ΔG° were -9.460, -12.183, -13.343 and -13.905 kJ/mol at 20, 30, 35 and 40 °C, respectively, suggesting exothermic and spontaneous nature of the process. The change in entropy, ΔS°= -0.23 kJ/mol indicated that the entropy decreased due to adsorption of arsenate ion onto the solid adsorbent. The results indicated that the reported zirconium oxide-coated marine sand (ZrOCMS) was good adsorbent with 97 % removal capacity at 200 μg/L concentration. It is interesting to note that the permissible limit of arsenic as per World Health Organization is 10 μg/L, and in real situation, this low concentration can be achieved through this adsorbent. Besides, the adsorption capacity showed that this adsorbent may be used for the removal of arsenic from any natural water resource.

Gender and segmental study of arsenate uptake by the everted gut sacs of mice

Background: Humans are exposed to both inorganic and organic arsenic through environmental, medicinal and occupational situations. The main source of arsenic exposure is drinking water with high levels of arsenic. Aim: This study was undertaken to investigate the gender and segmental difference in arsenate (As V) uptake by everted gut sacs of mice. Materials & methods: By using the everted gut sac technique, the serosal and mucosal uptake of Arsenate (2 mM) in both sexes of mice was studied in the intestinal segments. The Arsenate in the samples of fluid present in serosal and mucosal compartments of everted gut sacs was estimated by Hydride-Generation Atomic Absorption Spectrophotometer. Results: There was a steady increase in both serosal and mucosal uptake of Arsenate in both duodenum and ileum with a rise in the initial Arsenate concentration of the incubation medium. The mucosal uptake of Arsenate was significantly higher in duodenum than ileum (P<0.001). Both serosal and mucosal uptakes were elevated in the duodenal segment of male mice when compared to female mice except mucosal uptake in ileum. Conclusion: These results indicate that there is a gender and segmental difference in the up take of AS (V), which can be explored pharmaceutically to reduce the arsenic toxicity in pop ulation at risk.

Biosorption of arsenic (III) from aqueous solution by living cells of Bacillus cereus

In this work, removal of arsenic (III) from aqueous solution by living cells (Bacillus cereus), biosorption mechanism, and characterization studies have been reported. B. cereus cell surface was characterized using SEM-EDX and FTIR. Dependence of biosorption on pH of the solution, biosorbent dose, initial arsenic (III) concentration, contact time, and temperature had been studied to achieve optimum condition. The maximum biosorption capacity of living cells of B. cereus for arsenic (III) was found to be 32.42 mg/g at pH 7.5, at optimum conditions of contact time of 30 min, biomass dosage of 6 g/L, and temperature of 30 ± 2 °C. Biosorption data of arsenic (III) are fitted to linearly transformed Langmuir isotherm with R (2) (correlation coefficient) >0.99. The pseudo-second-order model description of the kinetics of arsenic (III) is successfully applied to predict the rate constant of biosorption. Thermodynamic parameters reveal the endothermic, spontaneous, and feasible nature of sorption process of arsenic (III) onto B. cereus biomass. The arsenic (III) ions are desorbed from B. cereus using both 1 M HCl and 1 M HNO(3).

Adsorption of arsenate on Cu/Mg/Fe/La layered double hydroxide from aqueous solutions

A novel layered double hydroxide containing lanthanum (Cu/Mg/Fe/La-LDH) has been synthesized and used for the removal of arsenate from aqueous solutions. The purpose of incorporation of La3+ into LDHs was tried to enhance the uptake efficiency of arsenate and broaden the application field of LDHs functional materials. Effects of various physico-chemical factors such as solution pH, adsorbent dosage, contact time and initial arsenate concentrations on the adsorption of arsenate onto Cu/Mg/Fe/La-LDH were investigated. Results showed that the removal efficiency of arsenate increased with the increment of the lanthanum content in Cu/Mg/Fe/La-LDH adsorbents, and the optimized lanthanum content was 20% of the total trivalent metals composition (Fe3+ and La3+). The adsorption isotherms can be well described by Langmuir equation, and the adsorption kinetics of arsenate followed the pseudo-second-order kinetic model. Coexistent ions such as HPO42−, CO32−, SO42−, Cl− and NO3− exhibited obvious competition with arsenate for the adsorption on Cu/Mg/Fe/La-LDH. The solution pH significantly affected the removal efficiency, which was closely related to the change of arsenate species distribution under different pH conditions. The predominant adsorption mechanism can be mainly attributed to the processes including ion exchange and layer ligand exchange.

Predicting Arsenate Adsorption on Iron-Coated Sand Based on a Surface Complexation Model

Equations were developed to predict arsenate sorption on iron oxide coated sand, on the basis of the constant capacitance surface complexation model, assuming formation of bidentate surface complexes between arsenate and iron oxyhydroxide surface sites. The developed equations can predict arsenate adsorption when initial arsenate concentration, adsorbent concentration, and solution pH are known. The average discrepancy between experimental data and modeling results was less than 5%. The maximum arsenate sorption capacity is the only parameter required that needs to be estimated from experimental data. The developed equations were validated by modeling arsenate adsorption on iron oxide sand over the pH range 5–8, under various initial arsenate concentrations and iron oxide coated sand solid concentrations. The developed predictive equation can also be used for calculating arsenate adsorption performance on iron impregnated activated carbon. Finally, the developed equation can be used to calculate sorption media dose requirements by specifying initial arsenate concentration, arsenate removal goal, and solution pH.

The removal of arsenic from water with natural and modified clinoptilolite

The presence of increased arsenic concentrations in Eastern Croatia is a consequence of the geological composition of the soil. Because of its known harmful effects, arsenic removal is of high importance and adsorption represents an attractive and economically efficient approach to arsenic removal. The use of zeolites obtained from the Donje Jesenje deposit, Croatia (CZ) and the Zlatokop deposit in Vranjska Banja, Serbia (SZ) in Na- and Fe–Na-modified forms was investigated in order to effectively remove arsenate and arsenite from aqueous solutions. The adsorption kinetics of arsenic was studied as a function of the initial arsenate and arsenite concentrations (30–300 μg · L−1), equilibration time (3–48 h), pH (5–10) and in the presence of sulfate and phosphate at initial concentrations of 0.2–0.5 mg · L−1. In order to estimate sorption constants designating the sorption capacity and affinity of the zeolites samples, the experimental results were fitted to the Langmuir and Freundlich sorption isotherms. Desorption tests conducted with 1–3 mol · L−1 HCl indicated that arsenate sorption was irreversible. The results obtained indicated that use of the Serbian zeolite in the Fe–Na-modified form (Fe–Na-SZ) was favourable for arsenate removal from water containing up to 30 μg As · L−1.

Removal of arsenate from groundwater by electrocoagulation method

Arsenic, a toxic metalloid in drinking water, has become a major threat for human beings and other organisms. In the present work, attempts have been made to remove arsenate from the synthetic as well as natural water of Ballia district, India by electrocoagulation method. Efforts have also been made to optimize the various parameters such as initial arsenate concentration, pH, applied voltage, processing time, and working temperature. Electrocoagulation is a fast, inexpensive, selective, accurate, reproducible, and eco-friendly method for arsenate removal from groundwater. The present paper describes an electrocoagulation method for arsenate removal from groundwater using iron and zinc as anode and cathode, respectively. The maximum removal of arsenate was 98.8% at 2.0 mg L(-1), 7.0, 3.0 V, 10.0 min, and 30°C as arsenate concentration, pH, applied voltage, processing time, and working temperature, respectively. Relative standard deviation, coefficient of determination (r (2)), and confidence limits were varied from 1.50% to 1.59%, 0.9996% to 0.9998%, and 96.0% to 99.0%, respectively. The treated water was clear, colorless, and odorless without any secondary contamination. The developed and validated method was applied for arsenate removal of two samples of groundwater of Ballia district, U.P., India, having 0.563 to 0.805 mg L(-1), arsenate concentrations. The reported method is capable for the removal of arsenate completely (100% removal) from groundwater of Ballia district. There was no change in the groundwater quality after the removal of arsenate. The treated water was safe for drinking, bathing, and recreation purposes. Therefore, this method may be the choice of arsenate removal from natural groundwater.