Effect of Stabilizer Addition on Soil Arsenic Speciation and Investigation of Its Mechanism

Abstract

Arsenic toxicity, mobility and bioaccessibility are influenced by its different speciation in soil, which exerts different impacts on the environment. In this study, coal fly ash, dried sludge, ferrous sulfate and broken peanut shell were used as stabilizers to investigate their stabilizing effects on As in soil as well as relationships between pH, soil organic matter content, cation exchange capacity and speciation of soil As. The results showed rise in soil pH, soil organic matter content and residual arsenic content after the addition of stabilizers. Addition of 10% coal fly ash and 10% dried sludge led to the decrease in the content of exchangeable As, carbonate bound As, Fe-Mn oxide bound As, organic bound As by 34.2%, 17.5%, 19.9%, 53.7%, respectively. Addition of ferrous sulfate could preferably stabilize As in soil. When 10% coal fly ash, 10% dried sludge and 1% ferrous sulfate were added concurrently, the decrease in the content of exchangeable As, carbonate bound As, Fe-Mn oxide bound As, organic bound As was 62.3%, 55.2%, 29.6%, 58.2%, respectively, with an increase in residual arsenic content by 8.1%. After the addition of 10% coal fly ash, 10% dried sludge, 1% ferrous sulfate and 1% broken peanut shell, a most conspicuous decrease in the content of exchangeable As by 73.3% was observed. Appropriate application of coal fly ash, dry sludge and ferrous sulfate converted a proportion of exchangeable, carbonate bounded, Fe-Mn bounded, organic bounded As into residual As, which reduced As's toxicity. The rise in pH led to increasing residual As content and decreasing exchangeable As, carbonate bounded As, Fe-Mn bounded As and organic bounded As content, and As was most stable at the approach of neutral condition. The rise in organic matter content led to increasing carbonate bounded As and residual As content and decreasing exchangeable As, Fe-Mn bounded As, organic bounded As content. The rise in cation exchange capacity led to increasing residual As content and decreasing exchangeable As, carbonate bounded As, Fe-Mn bounded As and organic bounded As content.