Removal of Cu and Sb from waste acid process of copper smelters for minimizing waste generation

The demand for waste minimization in copper smelters has been attracting widespread interest, particularly in the recent global trend towards ESG (environmental, social governance) standards. The typical waste acid process of primary copper smelters is composed of hydrometallurgical technologies such as valuable Cu recovery by single-stage sulfide precipitation followed by a couple of neutralization steps to remove impurities (including H₂SO₄ and Sb). In this study, a two-stage sulfide precipitation technique capable of removing > 99% of Sb as Sb₂S₃ and Sb₂O₃ was introduced prior to the neutralization with the goal of minimizing the generation of large volume of Sb(OH)₃ with CaSO₄ as waste. Moreover, SO₂ in waste acid was identified as the primary cause for the low efficiency of Sb removal by single-stage sulfide precipitation. In addition, an alternative neutralization method facilitated with a slurry mixing technique under optimum pH ≤ 2.5 was introduced in order to valorize the waste neutralization cake as salable gypsum. The phenomena of changing gypsum particle morphology with pH were elucidated by establishing a gypsum particle settling mechanism, which is associated with drag force and inter-particular force. The technical feasibility of the proposed methods was preliminarily assessed on a laboratory scale and verified on a pilot scale.