Insight into mineralizer modified and tailored scorodite crystal characteristics and leachability for arsenic-rich smelter wastewater stabilization

Abstract

Arsenic-rich non-ferrous smelter wastewater has the potential to cause harm to the environment and human health. The use of mineralizer modified and tailored scorodite crystals, a secondary As-bearing mineral, is considered to be the most promising strategy for arsenic stabilization. In this work, firstly, the mechanisms influencing the scorodite crystal characteristics for arsenic stabilization were investigated, and the results indicated that the scorodite stability was greatly influenced by the scorodite crystal shape and particle size. The crystal shape changes that the scorodite solids undergo during the aging period were observed, from a laminar structure to a polyhedron to a standard octahedral structure, and meanwhile, the As-concentration decreased from 10.2 mg L⁻¹ to 3.7 mg L⁻¹, with the relative particle size value (RPS) increasing from 1.50 to 2.64. Secondly, the addition of a mineralizer to further improve the scorodite crystal stability was investigated. It was meaningful to observe that the lowest As-concentration of 0.39 mg L⁻¹ could be attained when trace NaF was employed, and it was of great significance to apply this strategy for the disposal of As and F-containing wastewater due to the electrostatic interaction between scorodite and sodium fluoride. However, the scorodite crystal stability was weakened when other mineralizers (Na₂SiO₃·9H₂O and Al(NO₃)₃·9H₂O) were added. This indicated that these mineralizers play different roles in influencing the crystal phase, shapes and sizes of the solid precipitate (mainly scorodite). Finally, the mechanisms of the scorodite crystal evolution and the arsenic leachability characteristics were analyzed. In conclusion, the addition of appropriate mineralizers is a potentially effective strategy for the control of crystal growth, and could be used in the disposal and stabilization of arsenic-rich non-ferrous effluents.