A comparison study on heavy metal/metalloid stabilization in Maozhou River sediment by five types of amendments

Abstract

River sediment pollution by heavy metals/metalloids has attracted widespread attention due to a serious threat to the ecosystem and human health. As an effective and economical alternative, the stabilization method was considered by previous studies for the remediation of sediments polluted by metals/metalloids. However, a comprehensive study is required for an extensive comparison on the effects of metal/metalloid immobilization based on the application of different materials as sediment amendments. In this study, the Maozhou River was selected as the study area, and the stabilization method was applied for the remediation of the river sediment polluted by metals and metalloids. Five materials (CaCO3, Ca(OH)2, zeolite, kaolin, FeCl2) were selected as amendments for the metal/metalloid stabilization in the collected sediment. A modified BCR procedure was employed for the speciation analysis of heavy metals and metalloid in the sediment before and after remediation. A TCLP (toxicity characteristic leaching procedure) investigation was performed to further evaluate the immobilization of heavy metals in acidic environment. The sediment of the Maozhou River was heavily polluted by heavy metals and metalloid. The speciation of As, Pb, Cr, and Mn mainly exists as residual fraction (F4), while that of Ni, Cu, and Zn was identified as exchangeable metal and carbonate-associated fraction (F1) and fraction associated with Fe-Mn oxides (F2). Moreover, the F2 fraction of Co was observed as the major speciation. Through the application of five materials (CaCO3, Ca(OH)2, zeolite, kaolin, FeCl2) as sediment amendments, the metal/metalloid speciation was transferred into F4. When five amendments were compared, the stabilization effect can be ordered as CaCO3 > zeolite > FeCl2 > kaolin > Ca(OH)2 based on the modified BCR results. TCLP results showed that using Ca(OH)2 and CaCO3 as amendments can significantly reduce the metal leachability in an acidic environment, while zeolite is effective for most of the heavy metals and metalloid. The results showed that the sediment of the Maozhou River was seriously polluted by a variety of heavy metals and metalloids. This study provided extensive information on the speciation of metals or metalloid and the effect of various amendments on metals and metalloid stabilization, which can be of vital importance for further remediation of metal/metalloid-polluted sediment.