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.