The acid dissolution characteristics of arsenic fixed by iron-silicon material
JU Lin1, GUO Xiang1, YAO Ai-jun1, QIU Rong-liang2,3,4, TANG Ye-tao2,3
1. School of Geography and Planning, Sun Yat-sen University, Guangzhou 510275, China; 2. School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China; 3. Guangdong Provincial Key Lab of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, China; 4. Guangdong Laboratory for Lingnan Modern Agriculture, South China Agriculture University, Guangzhou 510642, China
Abstract：In order to assess the environmental stability of As immobilized by IS (IS-As) under acidification conditions, the acid dissolution characteristics of IS-As were investigated by using acidimetric titration method and X-ray powder diffraction (XRD) analyses. The results showed that IS was strongly resilient to the acid dissolution. The As fixed by IS was the most sensitive to acid dissolution in the pH range of 7.68~11.48, in this range the acid dissolution rate of AsO43- was fast, this non acid-stable As accounted for 37.5% of total dissolved As. The As dissolution rate was relatively low in the pH range of 7.68~4.10. In this range, the proportion of weak acid-stable As accounted for 7% of total As and of acid-stable As was 55.5% of total As. XRD results showed that the dissolution order of major As containing minerals in IS under acidic conditions (ranked from high pH values to low pH values) was:Ca3(AsO4)2 > AlAsO4 > As2O3 > Ca4SiAs4 > FeAs3O9·4H2O > Mn2As2O7/SiAs2. The acid dissolution rate of elements from IS-As was in the order:S(94.8%)>Na(93.0%)>Ca(78.8%)>As(44.5%)>Mg(41.7%)>Al(37.6%)>Mn(37.5%)>Fe(5.5%). Results demonstrated that the non acid-stable As in IS was mainly Ca bound As, the weak acid-stable As was primarily and weakly binding with Mg-, Mn-,Fe bearing minerals, and the acid-stable As was dominantly and strongly binding with Fe-Mn-Si containing minerals. The results provided some basis for the safety risk evaluation of applying IS on soils for the remediation of As contamination. It also provided a new reference for the selection of remediation materials for As contaminated soils as well as studies of soil As speciation.
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