Preparation and Characterization of a Novel Ca-Fe-Si-S Composite for the Simultaneous Stabilization of Heavy Metals in Arsenic Slag

In this work, a novel Ca-Fe-Si-S composite was prepared from thermal desorption residue through FeSO₄ impregnation-pyrolysis. The characteristics and modification process of the composite were specified through a series of analytical methods. And stabilization experiments were conducted to investigate the performance of prepared materials. The optimal Ca–Fe–Si–S composite was obtained at impregnation ratio of 10%, pyrolysis temperature of 900℃ and pyrolysis time of 60 min. The modification process included the dissolution of calcium hydroxide, the formation of gypsum and ferrous silicate, the dehydration of gypsum, the reduction decomposition of calcium sulfate, the decomposition of calcium carbonate and the solid reaction at high temperature. The obtained optimal Ca–Fe–Si–S composite was a multifunctional material mainly composed of high contents of Ca, Fe, Si, S, which corresponding to FeS, CaS, Ca₂SiO₄, Ca₃Al₂(SiO₄)₃, Ca₃Fe₂(SiO₄)₃, Ca₅(SiO₄)₂SO₄. The application of 5% optimal Ca–Fe–Si–S composite successfully lowed the leaching concentrations of As, Zn, Cu, Cd in arsenic slag to meet the discharging standard. Meanwhile, the non-specifically bound and specifically bound of As totally decreased by 3.72%, and the acid extractable species of Zn, Cu, Cd reduced by 11.20%, 29.37%, 2.76% respectively. The distribution of stable species for heavy metals significantly increased as united results of surface complexation, chemical precipitation and ion/anion exchange reactions between the prepared composite and heavy metals. The findings of this research provide an effective material for the simultaneous stabilization of multiple heavy metals.