The evaluation of zinc and/or copper sulfuric acid leaching from brass ashes

This study investigated sulfuric acid leaching of Zn and/or Cu from brass ashes. The material consists of a heterogeneous powder containing ZnO, CuO, SiO2, Zn2SiO4, Zn, and Cu as main phases. Due to the strong exothermic behavior exhibited by changing operating conditions (L/S ratio = 3-6 mL/g, pH 1-5), temperature with time behavior was monitored to determine the heat released by leaching reactions. Eh-pH diagrams were drawn to identify regions to leach Zn selectively or simultaneously with Cu. A rich-Zn liquor (62 g/L) with low Cu (0.97 g/L) content was obtained using L/S ratio 3 mL/g and pH 5; a second leaching stage at pH 5 resulted in a liquor with only 10.2 g/L of Zn and 1.5 g/L of Cu. The low efficiency was attributed to the predominance of the refractory Zn2SiO4 phase. To increase leaching yield of Zn and Cu, the leaching residue was leached at pH 1 and L/S ratio = 3 mL/g, resulting in a liquor containing 90.5 g/L Zn and 14.4 g/L Cu. Quartz was refractory to H2SO4 in all tests, and silica gel formation was not observed. The acquired liquors must be submitted to adequate treatment to produce purified Zn and Cu solutions.