Arsenic Adsorption on Modified Clay Minerals in Contaminated Soil and Water: Impact of pH and Competitive Anions. Issue 4 (9th February 2021) - Mukhopadhyay, Raj
Abstract: This study evaluates the arsenic adsorption behavior of Fe‐exchanged smectite and phosphate‐bound kaolinite, in soil, tap water and double distilled water in the presence of competing anions such as silicate, phosphate, and sulfate, and at variable pH values. The maximum amounts of As adsorbed in soil are 620.6 and 607.6 µg g –1 at pH 5 by Fe‐exchanged smectite and phosphate‐bound kaolinite, respectively. The pH‐modified Freundlich equation fits well ( R 2 > 0.96) to the adsorption data, distinguishing the effect of pH on adsorption. The coefficients of pH‐value are 0.04 and 0.05 for phosphate‐bound kaolinite and Fe‐exchanged smectite, suggesting that low pH is suitable for the adsorption. The As adsorption is decreased in tap water at low pH compared to the soil due to the presence of iron (Fe 2+/3+ ), sulfate, and bicarbonate in tap water. Among the competing anions in distilled water, phosphate is the most interfering anion for As adsorption. The competition coefficients of As‐phosphate binary adsorption derived from the Sheindorf equation are 3.93 and 0.56 for Fe‐exchanged smectite and phosphate‐bound kaolinite at pH 5. The Fe‐exchanged smectite can be used more effectively than phosphate‐bound kaolinite for As remediation in systems having low pH (pH ≈5) and high phosphate concentration. Abstract : Arsenic is one of the major contaminants in soil and water impacting millions of people worldwide. Iron‐exchanged smectite and phosphate‐bound kaolinite are evaluated for remediation of arsenic‐contaminated soil and water under different pH conditions and in the presence of competitive anions. It is found that the iron‐exchanged smectite performs remarkably well at low pH and high phosphate concentration.