Stabilization of available arsenic in arsenic-calcium residue (ACR) using a developed cost-effective composite Fe-based stabilizer

In this study, FeSO4·H2O, zero valent iron (ZVI), and MnO2 were combined to develop a composite Fe-based stabilizer (CFS) for the stabilization of arsenic-calcium residue (ACR). The simplex-centroid mixture design (SCMD) method was used to model and optimize the mixture proportion. The study was concluded that the optimum combination for high As stabilization performance and low cost of stabilizer was the mixture of 65.05, 10.00 and 24.95 wt% FeSO4·H2O, ZVI and MnO2 (optimum CFS). Further stabilization tests indicated that addition of 25% optimum CFS led to a pronounced decrease in the As leaching concentration from 162 to 0.645 mg/L, lower than the Chinese regulatory limit (1.2 mg/L). XRD, SEM-EDS, FTIR and XPS were applied to reveal the stabilization mechanism of As in ACR. Overall, CFS combined with H2SO4 achieved excellent As stabilization performance through a “release-oxidation-stabilization” process. The released H+ from H2SO4 ionization and Fe(Ⅱ) hydrolysis facilitated the available As release. FeSO4·H2O and Fe0 as the sources provided Fe(Ⅱ), which activated molecular O2 to generate reactive oxygen species (ROSs). Then ROSs and MnO2 act as oxidants to drive the oxidation of As(Ⅲ) synergistically. The available As was stabilized by Fe/Mn (hydr)oxides and Fe(Ⅲ) by adsorption complexation and precipitation, and form stable amorphous Fe/Mn-As species. This study provided important insights into the design of multi-component composite stabilizer for achieving the effective stabilization of As-bearing solid wastes.