Increasing arsenic immobilization capacity of a binder prepared by arsenic-containing biohydrometallurgy waste: Effects of ferric/ferrous salts addition

The aim of this study was to improve the immobilization capacity of a binder prepared from As-containing biohydrometallurgy waste (BAW) on arsenic (As) by modifying it with ferric/ferrous salts. The study investigated the chemical fractions of As and its leaching characteristics. Results indicated that the addition of ferric/ferrous salts significantly reduced the mid acido-soluble fraction of As, resulting in decreased As leaching. Among the four ferric/ferrous salts studied, ferrous sulfate (FeS2) performed the best, with only 0.5 wt% of FeS2 achieving satisfactory results. The influence of ferric/ferrous salts on the strength development and reaction products were also investigated. Although the incorporation of ferric/ferrous salts reduced As leaching, it also decreased the early age compressive strength of BAW. Ferric salts had a more significant impact on the strength evolution. In addition, the mechanism of Fe species on As stability using density function theory calculation was explored. Results suggested that As species could be adsorbed on the surface of Fe species through strong covalent bonds. Overall, the study demonstrated that modifying BAW using ferric/ferrous salts could effectively reduce As leaching. However, the decrease in strength especially at the early ages must be taken into consideration when using this method.