Zinc recovery from steel-making wastes by acid pressure leaching and hematite precipitation

The hydrometallurgical extraction of zinc from EAF dust and steel-making sludge was studied. These materials were treated with sulphuric acid at elevated pressure using microwave heating. More than 92% of zinc can be leached out using 0.3 M acid solution at 260 °C. Fe(II) remained in solution while most of the Fe(III) was precipitated as hematite. The iron concentration in the leach liquor decreased markedly when hydrogen peroxide solution was added at the start of the experiment. In this case, zinc extraction reached almost 99%. The hydrolytic precipitation of ferric sulphate was investigated at 200 °C for a low iron concentration. The reaction was found to be first-order with respect to Fe(III), and the apparent rate constant was 0.01 min− 1.