Mechanochemical activation on selective leaching of arsenic from copper smelting flue dusts

Highlights: • Mechanochemical pre-treating activates ~20% un-leachable arsenic phases in CSFUs. • Mechanochemical processing saves materials and time for leaching. • Mechanical conversion produces more freely soluble arsenic species. • Decomposing of sulfate cakes promotes arsenic releasing. A novel application, including mechanochemical pre-treating and alkali leaching, for arsenic selective leaching from copper smelter flue dusts (CSFUs) was developed to overcome the disadvantages of hydrometallurgical methods. Compared with raw CSFU powders, the mechanical-activated ones showed higher maximum arsenic leaching efficiency (increased by ~20%), and lower apparent activation energy (decreased by ~7 kJ·mol⁻¹). Furthermore, this novel process only consumed half of alkali and sulfides and needed one-third of the leaching time to compare with the ones used in the traditional alkali leaching process. The promoting effect of mechanical force on arsenic leaching firstly relied on the physical property changes of CSFU powders, including a decrease of particle sizes and an increase of the specific surface. Secondly, mechanochemical force converted As⁵⁺ species into reduced phases (e.g. As₂O₃, NaAsO₂), and thio-arsenates (e.g. AsO₂S₂³⁻, AsO₃S³⁻), which could spur its leaching due to their stronger mobilities in the alkali solution within sulfides. Finally, mechanochemical activation could be facilitated to separate discrete soluble arsenic species or incorporated ones from sulfate minerals in the CSFUs. This work may have important implications for the development of new eco-friendly technologies for purifying arsenic-bearing materials.