Beneficiation of brass ashes

Slags formed during brass smelting contain a significant amount of metallic value. The glassy and oxidized portion of the ground slag, usually referred to as "brass ash", consists of compounds such as ZnO, ZnO·SiO₂, Cu-Zn, CuO, Cu and Zn/Cu/B oxide, and its colored-metal content may vary between 28÷52% Zn and 8÷16% Cu. These ashes are classified as harmful wastes, due to their high Zn content, and are considered to be secondary raw materials that should be treated accordingly, from an economical viewpoint. The aim of this experimental study is to investigate the possibilities of beneficiating brass ashes by treating it with H₂SO₄ or (NH₄)₂CO₃+ NH₄OH mixtures. Effects of temperature, air sparging and addition of oxidizing agents, such as MnO₂ and Fe₂(SO₄)₃, are investigated on copper and zinc leaching recovery. As a result of both acidic and alkaline leaching experiments, it is observed that more than 90% of Zn and more than 65% of Cu was leached out. Two separate process flow sheets are proposed for the possible treatment of brass ashes.