Wang, X., H. Zhang, L. Wang, J. Chen, S. Xu, H. Hou, Y. Shi, J. Zhang, M. Ma, et al.
Science of the Total Environment 668:32-39(2019)

Stabilization technologies are not well developed for As in realgar tailings that are Fe-deficient and rich in Ca and S. Stabilization of tailings by adding ferrous sulfate was pilot tested to evaluate As transformation during stabilization.. Si, As, Ca, and S were the predominant elements in the raw realgar tailings with a low content of Fe, and realgar and pharmacolite were the main As-bearing minerals. After the ferrous sulfate treatment, the As leaching concentration of realgar tailings decreased from 135 mg/L to below the Chinese regulatory limit (2.5 mg/L). Based on the results of leaching tests, sequential extraction analysis, XRD, SEM-EDS, XPS, and thermodynamic modeling, the investigators concluded that ferrous sulfate addition enhanced the transformation of Ca-As and S-As species to more stable Fe-As species. The dissolution of pharmacolite was facilitated by H⁺ and SO₄^2- derived from the hydrolysis and oxidation of ferrous sulfate. Oxidation of realgar could be promoted by reactive oxygen species (ROSs) from Fe(II) oxygenation.