Hydrometallurgical separation of zinc and copper from waste brass ashes using solvent extraction with D2EHPA

A blend of brass ashes containing 48.0% of zinc and 16.6% of copper was processed through selective leaching with dilute H2SO4 and solvent extraction, using D2EHPA as the extracting agent in order to separate zinc and copper. Solvent extraction tests performed in bench and pilot scales were designed to evaluate the following operating parameters: time, pH, D2EHPA concentration, A/O ratio in the extraction step, and O/A ratio in the stripping step. Zinc present in the brass ashes was efficiently leached by H2SO4 (recovery of 91.9%), whereas only 8.6% of copper was leached, producing a liquor containing zinc (28.6g/L), copper (1.5g/L), calcium (0.45g/L), iron (0.43g/L), and chloride (0.22g/L), as well as fluoride, lead, nickel and cadmium, at levels below 0.01g/L. Zinc was selectively extracted over copper by solvent extraction with D2EHPA. A continuous solvent extraction run in pilot scale was carried out using 4 extraction stages (pH=2, A/O ratio=1) and 2 stripping stages (O/A ratio=2), where 91.8% of zinc extraction and 96.9% of zinc stripping were achieved. Iron extraction efficiency reached 85.9%, thus illustrating the need for its prior removal if required. The fluorine extraction was 29.9%, as compared to 10.4% for chlorine, whose respective extractions are related to the presence of iron and zinc in the liquor, as evidenced by species speciation analysis. A copper concentrate containing 42.2% was obtained in the leaching step.