Reductive removal of arsenic from waste acid containing high-acidity and arsenic levels through iodide and copper powder synergy

Large amounts of waste acids with high acidity and arsenic levels are produced during pyrometallurgy of nonferrous metal sulfide ores, in which the treatment of arsenic remains a problem. In this study, copper powder was used as a reducing agent and synergized with iodine ions to effectively remove arsenic from waste acids. The influences of stirring speed, copper powder particle size, sodium iodide/copper powder dosages, and reaction temperature on the removal efficiency of arsenic were investigated. The results showed almost complete removal of arsenic under the optimal conditions: 600 rpm stirring speed, copper powder particle size <15 μm, molar ratio I:As = 5, molar ratio Cu:As = 8, reaction temperature 40 °C, and reaction time 90 min. The kinetics studies indicated that arsenic removal was controlled by chemical reaction with apparent activation energy of 42.39 kJ·mol−1. The morphological and structural characterizations of dearsenization residues showed surface of copper particles with double covering-layers. The interior covering-layer constituted the formation region of As(0), the phases of which were As and As-Cu intermetallic compounds, while the main product formed in exterior covering-layer was identified as CuI.