Abstract-In this study, natural common clays were used as raw materials to be modified with ferric and ferrous solutions to develop improved efficient and low cost adsorbents. The adsorbents (Raw Clay, Clay/FeSO 4 , and Clay/FeCl 3 ) were investigated for arsenate removal from synthetic aqueous solution in batch studies with respect to contact time, solution pH, initial As(V) concentration, and temperature. The results showed that As(V) uptake was pH dependent and the high efficiency occurred in the acidic condition. The adsorption kinetic data were fitted well with the pseudo second order adsorption model. The estimated maximum adsorption capacity from Langmuir model was 0.44, 1.50, and 0.86 mg/g for Raw Clay, Clay/FeSO 4 , and Clay/FeCl 3 , respectively. The values of a dimensionless constant separation factor (R L ) and the magnitude of the adsorption intensity (1/n) showed that As(V) was adsorbed favorably on all adsorbents. The thermodynamic parameters indicated that the adsorption is spontaneous and endothermic and an irregular increase of the randomness at the adsorbent-adsorbate interface during the adsorption.

In this study, natural clay, iron oxide, and iron powder were combined to develop low-cost iron mixed porous pellet adsorbent for arsenate and arsenite removal from aqueous solution in batch experiments. The augmented simplex centroid mixture design was applied to obtain the optimum proportion of each constituent. Higher correlation coefficient of the models (R 2 > 0.95), good distribution of residuals, and lower values of p value (<0.05) indicated that the method is suitable for determining the optimum mixture proportion. Extensive decrease of both arsenate and arsenite adsorption occurred in the alkaline condition (pH > 9). Kinetic and isotherm experimental data of both arsenate and arsenite were well described by the pseudo-second order and Sips models, respectively. The maximum adsorption capacity of arsenate and arsenite derived from Sips model were 13.33 and 19.06 mg/g, respectively. The separation and heterogeneity factors showed that both arsenate and arsenite were favorably adsorbed. Among coexisting anions, phosphate significantly showed negative effect on the adsorption of either arsenate or arsenite. The adsorbent could be effectively reused for several times after its regeneration and was considered as non-hazardous material after adsorption.

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Arsenic-polluted water is a global concern and puts millions of people at risk of developing cancer. The improvement of aqueous solution coexisting with arsenite and arsenate using iron mixed porous clay pellets was investigated in batch and fixed-bed column systems. Batch studies showed that the removal rate occurred in two main phases with an equilibrium time of 52 h. The pseudo-second-order model well described the experimental data. Isotherm data were well fitted by the Langmuir–Freundlich model. The removal efficiency was significantly reduced in alkaline solution and the presence of phosphate ions. The column study revealed that the breakthrough time and saturation time increased with lower feeding flow rate, higher bed height, and lower initial adsorbate concentration. The Thomas model provided good performance for predicting the column experimental data.

Many people in Cambodia consume groundwater with arsenic concentrations above the WHO guideline. In this study, an iron-mixed porous pellet adsorbent was put into a lightweight bio-sand filter to treat arsenic. The filter was intermittently charged daily with 30 L influent water until the effluent arsenic concentration exceeded 10 μg/L. The results indicated that the Morrill Dispersion Index was less than 2.0, implying that the filter had preferential plug flow. Head loss accumulation led to flow rate reduction over a period of 30 days. Arsenic removal efficiency was between 97 and 99% for the influent concentration, being in the range 355 to 587 μg/L. No significant leaching of iron or organic carbon was observed. The high dissolved oxygen concentration is likely to have contributed to the aerobic conditions in the filter bed. The filter removed arsenic more efficiently than was achieved in some previous studies and might be suitable to provide household-scale, arsenic-safe drinking water.