Dissolution behavior of As and Cd in submerged paddy soil after treatment with stabilizing agents

Abstract

Steelmaking slag (SS) is an industrial byproduct generated through metal refining processes. It has been applied as an agent to stabilize farmland soils containinated both by arsenic and heavy metals in the Republic of Korea. However, the efficacy of this technique has not been established yet under anoxic conditions such as in the case of submerged rice paddy fields. Under anoxic conditions, As might be dissociated easily from solid surfaces where it is adsorbed reversibly. In this study, laboratory-scale column tests were conducted to artificially manipulate anoxic conditions in submerged paddy fields and we observed the release behavior of As and heavy metals, mainly cadmium (Cd). Limestone (LS) was also applied in the test for the purpose of comparison because it is usually applied as a common additive. The leachate samples were collected and chemical changes were monitored during the test period. Results suggest that anoxic conditions were developed during submersion, and that As or heavy metal fractions bound to ferrous (Fe)/manganese (Mn) oxides were easily dissociated. However, it was also shown that SS and LS significantly decreased the dissolution of Cd and As in the pore water; their removal rates in the SS-treated soil were 87% and 32%, respectively, of those in the control soil. On the other hand it appeared that SS was more effective than LS to stabilize Cd as well as As under submerged conditions. Therefore, SS might be an optimal stabilizing agent for dealing with As and other heavy metal contaminants in rice paddy soils that are periodically exposed to reducing environments. (C) 2015 Elsevier B.V. All rights reserved.