Arsenic removal from aqueous solutions by adsorption on laterite soil

Abstract

Laterite soil was used as an adsorbent for arsenic removal from contaminated groundwater. Effects of pH, adsorbent dose, adsorbent size, contact time, initial arsenic concentration and presence of interfering species on arsenic removal were found out. Laterite soil was found to be very effective for arsenic adsorption. It was found that 4 h contact time was sufficient for ∼ 98% and ∼95% removal from the contaminated water samples at an adsorbent dose of 10 g/L and 20 g/L for As(III) and As(V) respectively at an initial concentration level of 0.5 mg/L at a pH of 5.7 ± 0.2. Although there was no significant interference from Cl−, NO3 −, SO4 − 2, Ca2 +and Fe2 +/3 + on arsenite removal but its removal was little affected due to the presence of HPO4 − 2 and SiO3 − 2. Arsenate removal efficiency, however, was decreased to a large extent in presence of HPO4 − 2 and SiO3 − 2. The other ions Cl−, NO3 −, SO4 − 2, Ca2 + and Fe2 +/3 + had no significant interference on arsenate removal. The common organic contaminants such as 2,4-dichlorophenoxyacetic acid (2,4- D), atrazine, endosulfan and humic acid had no effect on As(III) removal, but they (excepting 2,4-D) cause decrease in the removal efficiency for As(V). Both Langmuir and Freundlich adsorption isotherm models fitted well and the maximum adsorption capacity was estimated to be 1.384 mg/g and 0.04 mg/g for arsenite and arsenate respectively. The real arsenic contaminated groundwater was also tested and it was found that laterite soil is very effective for arsenic removal from real groundwater sample, and up to ∼ 99% removal could be achieved under normal condition. The advantage of the material is that the pH of the raw water did not change after arsenic removal, and iron was not leached.