Kinetics Of Arsenic Sorption Research Articles

Raw and modified Pakistani Kaolin as an efficient adsorbent for the removal of arsenic from groundwater

Raw and modified Nagarparkar Pakistani Kaolin (RNK) were used to remove arsenic from groundwater by adsorption technique. Both the RNK samples were analyzed by XRD and SEM to examine their crystallinity and morphology. Iron-modified kaolin showed increased Si/Al ratio of 23% compared to 14% obtained with NaCl-modified kaolin indicating the influence of iron on kaolin properties in terms of its structural de-complexation reflected by higher groundwater arsenic removal. Only 1.50 gg-1 (15%) arsenic removal efficiency was observed using raw RNK at equilibrium time; however, after treatment with NaCl (0.10 M) and FeCl3 (0.1 and 0.01M) the treated solutions exhibited arsenic removal efficiency in the range of 9.2 gg-1 (92%) and 8.6 gg-1 (86%) using iron-modified MNK-1 and MNK-2, respectively. RNK and MNK equilibrium for arsenic sorption was reached in 60 min. The process kinetics transpired that Pseudo-second-order rate equation provided better kinetics of arsenic sorption with Iron-modified MNK-1 treatment protocol depicting about 1% of an average error for the amount of arsenic adsorbed on the adsorbent compared to 89% observed with pseudo-first-order model,. The experimental results indicated that arsenic adsorption was more rapid and efficient at lower initial concentration of the modifying agent. This study demonstrated that the initial arsenate concentrations as well as the iron content in the MNK affect the quantity of arsenic adsorbed on the adsorbents.

Modelling heavy metals contamination in groundwater of Southern Punjab, Pakistan

The present study aimed to develop a numerical simulation to predict the chemistry change of groundwater heavy metals pollution (mainly arsenic pollution) in the Southern region of the Punjab Province of Pakistan. This work is the first attempt in modelling the transport of groundwater heavy metals pollution in the area using a 1D reactive transport model. PHREEQC was employed to perform the numerical simulation. The conceptual model represented the 1D numerical transport model with the homogenous mineral composition having uniform transport of the municipal wastewater. A 100 m column—20 cell transport model was used with a time step of 5000 years, making a simulated timescale of 100,000 years. The simulation was carried out using quartz, illite, and calcite kinetics. Arsenic sorption kinetics were also incorporated in the simulation. The results revealed that the concentrations of four out of ten heavy metals and three out of eight inorganic ions were above the drinking water quality standards at the end of the simulation making the groundwater unsafe for drinking purposes. The arsenic concentration was found out to be 3.79 mg/l against 100,000 year which is 379 times the international drinking water standard and about 76 times the national drinking water standard for arsenic. It is concluded that the groundwater, regardless of the natural soil treatment, will be highly contaminated after 100,000 years, particularly with heavy metals including arsenic, cadmium, iron, lead, and nickel. The groundwater quality can be enhanced by appreciating the preventive measures recommended in this study.

Arsenic(V) sorption kinetics in long-term arsenic pesticide contaminated soils

Historic As contamination of soils occurs throughout the world from mining, industrial and agricultural activities. Sorption processes and rate may strongly influence soil As mobility, which further influences As bioavailability and toxicity. We investigated the kinetics of As(V) sorption by adding the arsenic onto both pristine (non-contaminated) and historically contaminated soils from arsenicals in two contrasting soil types (ferralitic and sandy). Results suggest both pseudo-second order (PSO) and Elovich kinetic models produce robust correlations with good data fits to linearized plots (R2 ≈ 0.900–0.999) that describe the arsenic sorption kinetics for both contaminated and pristine soils. The arsenic sorption data are generally best described by the Elovich model with smaller normalized standard deviations (Δq <5%) than PSO model. In addition, the surface binding to exchangeable and specific sorption of fresh arsenic (63–96%) sites has an impact on the overall low rate of As(V) sorption in the aged contaminated soils. Pristine soils “particularly ferralitic soils” show intra-particle diffusion and/or surface precipitation, which can contribute to a greater irreversibility of As(V) binding in soil. In contrast, the As(V) sorption occurred in the pristine sandy soil in a similar fashion to that of the aged contaminated soil, most likely due to both soil groups having limited strong binding sites. The detailed knowledge from this study provides new insights into the reclamation and management of As contaminated sites.

Sorption of Arsenic from Desalination Concentrate onto Drinking Water Treatment Solids: Operating Conditions and Kinetics

Selective removal of arsenic from aqueous solutions with high salinity is required for safe disposal of the concentrate and protection of the environment. The use of drinking water treatment solids (DWTS) to remove arsenic from reverse osmosis (RO) concentrate was studied by batch sorption experiments. The impacts of solution chemistry, contact time, sorbent dosage, and arsenic concentration on sorption were investigated, and arsenic sorption kinetics and isotherms were modeled. The results indicated that DWTS were effective in removing arsenic from RO concentrate. The arsenic sorption process followed a pseudo-second-order kinetic model. Multilayer adsorption was simulated by Freundlich equation. The maximum sorption capacities were calculated to be 170 mg arsenic per gram of DWTS. Arsenic sorption was enhanced by surface precipitation onto the DWTS due to the high amount of calcium in the RO concentrate and the formation of ternary complexes between arsenic and natural organic matter (NOM) bound by the polyvalent cations in DWTS. The interactions between arsenic and NOM in the solid phase and aqueous phase exhibited two-sided effects on arsenic sorption onto DWTS. NOM in aqueous solution hindered the arsenic sorption onto DWTS, while the high organic matter content in solid DWTS phase enhanced arsenic sorption.

Arsenic removal from groundwater by Anjili tree sawdust impregnated with ferric hydroxide and activated alumina

Arsenic is a toxic element found naturally in groundwater. Due to its carcinogenicity, risk for heart diseases and diabetes, arsenic needs to be removed from groundwater for potable application. ‘Anjili’ tree sawdust was chemically modified with ferric hydroxide and activated alumina (SFAA) and used as an adsorbent for the removal of arsenic from groundwater. The adsorbent was characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) to study the pore structure and surface functional groups. Effect of contact time, initial concentration, pH, particle size and temperature was studied. Arsenic adsorbed by SFAA followed Freundlich adsorption isotherm. Maximum sorption of arsenic by SFAA adsorbent occurred at pH 6.5. Arsenic sorption kinetics followed a pseudo-second-order model. The maximum sorption capacity at 303 K was found to be 54.32 mg/g for As(III) and 77.60 mg/g for As(V). Interference of other ions on the adsorption was in the order of PO43− &amp;gt; SO42− &amp;gt; HCO3− &amp;gt; NO3−.

Distribution of iron in activated carbon composites: assessment of arsenic removal behavior

The main objectives of this study were to evaluate the effectiveness of using iron impregnated granular activated carbon (AC) to remove arsenic from water and to assess the partitioning behavior of arsenic under a variety of conditions. Iron impregnated granular activated carbon (AC-Fe) composites were prepared with different ferric (Fe+3) concentrations, ranging from 0.09 to 3.0 M. These AC-Fe composites were able to remove 92–98% of the arsenate [As(V)] and 42–65% of the arsenite [As(III)]. The composite containing the lowest iron concentration (1.54%) was the most effective at arsenic sorption. Langmuir model fit indicated that the maximum 125 mg As(V)/gFe and 98.4 mg As(III)/gFe can be sorbed by the composite. The kinetics of arsenic sorption is well explained by pseudo first-order kinetics. The arsenate removal efficiency was found to decrease with increasing solution pH, while the As(III) removal efficiency was found to increase. The background ionic strength (IS) had no significant effect of on As(V) removal, but As(III) removal increased when the IS was greater than 50 mM NaCl. Our results indicate that a small amount of iron embedded efficiently in AC may have considerable potential in removing arsenic from water.

Nano-structured iron(III)–cerium(IV) mixed oxide: Synthesis, characterization and arsenic sorption kinetics in the presence of co-existing ions aiming to apply for high arsenic groundwater treatment

Here, we aim to develop an efficient material by eco-friendly green synthetic route that was characterized to be nano-structured. The thermal stability of the sample was well established from the consistent particle size at different temperature and also, from differential thermal analysis. The bimetal mixed oxide contained agglomerated crystalline nano-particles of dimension 10-20nm, and its empirical composition as FeCe1.1O7.6. The surface area (m2g-1), pore volume (cm3 g-1) and maximum pore width (nm) obtained from BET analysis were found to be 104, 0.1316 and 5.68 respectively. Use of this material for estimating arsenic sorption kinetics in presence of some groundwater occurring ions revealed that the pseudo-second order kinetic model is unambiguously the best fit option to describe the nature of the reactions. Groundwater occurring ions exhibit a notable decrease of As(V)-sorption capacity (no other ion>chloride∼silicate>sulfate>bicarbonate>phosphate). However, As(III)-sorption capacity of the bimetal mixed oxide was nominally influenced by the presence of the above ions in the reaction system. Rate determining step of arsenic sorption reactions was confirmed to be a multistage process in the presence of the above ions at pH∼7.0 and 30°C.

Removal of Arsenic from Aqueous Solutions by Sorption onto Sewage Sludge-Based Sorbent

This study aimed at evaluating and comparing the removal of arsenic from solutions by a low-cost waste-based sorbent, produced by pyrolysing sewage sludge under appropriate conditions, and by a commercially activated carbon. Batch sorption experiments were performed under isothermal conditions (20°C), in order to evaluate the effect of pH on the arsenic sorption kinetics and on the equilibrium sorption capacity of the materials under study. Kinetic data revealed that the arsenic sorption was faster onto the activated carbon than onto the pyrolysed sludge. The sorption process was well described by both the pseudo-first and pseudo-second-order kinetics equations for both materials. Changes in the initial solution pH have distinct effects on the removal of arsenic onto pyrolysed sludge and activated carbon. While for pyrolysed sludge, pH affects essentially the equilibrium time, for activated carbon it affects the sorption capacity. Equilibrium results were well described by both Freundlich and Langmuir isotherm models, although fittings corresponding to the Langmuir isotherm were slightly better. The Langmuir maximum sorption capacity determined for the pyrolysed sludge was 71 μg g−1, while for activated carbon was 229 μg g−1. Despite the relative lower capacity of the pyrolysed sludge, the considerable lower cost and the valorisation of the sludge may justify further research on its use for water decontamination.

Removal of arsenic from drinking water using modified natural zeolite

Arsenic removal from drinking water by adsorption on natural and iron modified clinoptilolite was investigated. The structure of modified and unmodified clinoptilolite samples from the Gördes–Manisa deposit was studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The elemental composition and specific surface areas of zeolitic samples were also determined. The pretreatment of clinoptilolite using NaCl and FeCl3 solutions (0.1 and 0.01M) resulted in 9.2 (92%) and 8.4 (84%) μgg−1 of arsenic uptake, whereas only 1.5μgg−1 of arsenic uptake could be detected in the untreated zeolite at equilibrium time. The time required to attain equilibrium for arsenic sorption on all types of clinoptilolite was 60min. The saturation time was independent of concentration of the initial arsenic solution. The pseudo-second-order rate equation described better the kinetics of arsenic sorption with good correlation coefficients than pseudo-first-order equation. At lower initial arsenate concentration, arsenate exhibited greater removal rates and best removed when the clinoptilolite modified by 0.1M FeCl3 was used for adsorbent. This study showed that the amount of arsenic adsorbed on the adsorbents not only depends on the iron concentration in the clinoptilolite, but also depends on the initial arsenate concentrations.

Biosorption of arsenic from aqueous solution using agricultural residue ‘rice polish’

‘Rice polish’ (an agricultural residue) was utilized successfully for the removal of arsenic from aqueous solution. Various parameters viz. pH, biosorbent dosage, initial metal ion concentration and temperature were studied. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models were used and the system followed all three isotherms, showing sorption to be monolayer on the heterogeneous surface of the biosorbent. The maximum sorption capacity calculated using Langmuir model was 138.88 μg/g for As(III) at 20 °C and pH 7.0 and 147.05 μg/g at 20 °C and pH 4.0 for As(V). The mean sorption energy ( E) calculated from D–R model indicated chemisorption nature of sorption. Study of thermodynamic parameters revealed the exothermic, spontaneous and feasible nature of sorption process in case of both As(III) and As(V). The pseudo-second-order rate equation described better the kinetics of arsenic sorption with good correlation coefficients than pseudo-first-order equation. Mass transfer, intraparticle diffusion, richenberg and elovich models were applied to the data and it was found that initially the sorption of arsenic was governed by film diffusion followed by intraparticle diffusion. Rice polish was found to be efficient in removing arsenic from aqueous solution as compared to other biosorbents already used for the removal of arsenic.

Evaluating a drinking-water waste by-product as a novel sorbent for arsenic

Arsenic (As) carcinogenicity to humans and other living organisms has promulgated extensive research on As treatment technologies with varying levels of success; generally, the most efficient methods come with a significantly higher cost burden and they usually perform better in removing As(V) than As(III) from solution. In the reported study, a novel sorbent, a waste by-product of the drinking-water treatment process, namely, drinking-water treatment residuals (WTRs) were evaluated for their ability to adsorb both As(V) and As(III). Drinking-WTRs can be obtained free-of-charge from drinking-water treatment plants, and they have been successfully used to reduce soluble phosphorus (P) concentrations in poorly P-sorbing soils. Phosphate and arsenate molecules have the same tetrahedral geometry, and they chemically behave in a similar manner. We hypothesized that the WTRs would be effective sorbents for both As(V) and As(III) species. Two WTRs (one Fe- and one Al-based) were used in batch experiments to optimize the maximum As(V) and As(III) sorption capacities, utilizing the effects of solid:solution ratios and reaction kinetics. Results showed that both WTRs exhibited high affinities for soluble As(V) and As(III), exhibiting Freundlich type adsorption with no obvious plateau after 2-d of reaction (15 000 mg kg −1). The Al-WTR was highly effective in removing both As(V) and As(III), although As(III) removal was much slower. The Fe-WTR showed greater affinity for As(III) than for As(V) and reached As(III) sorption capacity levels similar to those obtained with the Al-WTR-As(V) system (15 000 mg kg −1). Arsenic sorption kinetics were biphasic, similar to what has been observed with P sorption by the WTRs. Minimal (<3%) desorption of sorbed As(III) and As(V) was observed, using phosphate as the desorbing ligand. Dissolved Fe 2+ concentrations measured during As(III) sorption were significantly correlated ( r 2 = 0.74, p < 0.005) with the amount of As(III) sorbed by the Fe-WTR. Lack of correlation between Fe 2+ in solution and sorbed As(V) ( r 2 = 0.2) suggests reductive dissolution of the Fe-WTR mediating As(III) sorption. Results show promising potential for the WTRs in irreversibly retaining As(V) and As(III) that should be further tested in field settings.

Removal of As(V) species from extremely contaminated mining water

The effective removal of arsenic compounds from strongly contaminated mining water with a high content of As (about 50 mg/l) and other metals, especially iron (about 5000 mg/l) has been studied. The process ran in two steps. At first, the raw acid mining water containing predominantly Fe 2+ ions was partially precipitated with a small amount of an alkaline agent. On a small portion of the precipitated iron (about 30–40%), more then 90% of the arsenic was adsorbed forming a toxic precipitate, which was then stirred under an inert agent (Ar) and further in air for 1 h. Secondly, the precipitation of the first step liquid residue (using the same or a different alkaline agent) enabled the final treatment of the mining water at pH ∼8.5. While arsenic was substantially removed by the first precipitation, the other components including residual iron, manganese, zinc and sulfates were precipitated quantitatively during the second step. The mass of the second precipitate depended strongly on the alkaline agent used in the second step. The mechanism and kinetics of arsenic sorption onto iron species, and phase changes of the sorbent during the sorption process were investigated. The composition of the precipitates was verified by XRD and XRF analyses, as well as by infrared and Raman spectroscopy. The precipitation of a raw mining water resulted in formation of a complex inorganic system where amorphous phases dominated. Various crystalline phases, predominantly concerning Fe(II)–Fe(III), As, Zn and sulfates also appeared, depending on the actual oxidizing state of the whole system and on redistribution of its components. The two-step precipitation of arsenic contaminated mining water results in a significant ecological and economical improvement due to the decrease in the amount of waste toxic mass.