KH₂PO₄-aided soil washing for removing arsenic from water-stable soil aggregates collected in southern China

Abstract

Removal of arsenic (As) from soil aggregates with particle sizes of > 2.0, 2.0–0.25, 0.25–0.053, < 0.053 mm by soil washing of KH2PO4 and the kinetics of As releasing from soil aggregates were investigated. Effects of KH2PO4 concentration, ratio of liquid/soil and washing duration on the removal were fully explored. The results showed that the high As removal was obtained in > 2 mm aggregates (48.56%) and < 0.053 mm aggregates (42.88%) under the optimum condition (KH2PO4 concentration of 0.1 mol/L, and liquid/soil ratio (10 mL/g) for 360 min). 62.82% of As was extracted from aggregates with size less than 0.25 mm. Only 11.88% was contributed by the large aggregates (> 2.0mm). Using KH2PO4 washing, it was also found that extracted As is mainly in form of either specifically sorbed As or As associated with oxides of Fe and Al. Elovich model can describe the removal process of As more precisely than Two-constant kinetic models. The optimum washing conditions and removal process is also applied to bulk soil. This technique in this study is reliable, cost-effective and offers a great potential for practical application in soil remediation. Keywords: Arsenic (As), Potassium dihydrogen phosphate (KH2PO4), Soil aggregates, Soil washing