Physical and chemical regularities of zinc sulfide concentrate pressure leaching in the presence of lignosulfonate

Abstract

The study covers physical and chemical regularities of zinc sulfide concentrate oxygen pressure leaching in sulfuric acid. The effect of lignosulfonate concentration (CLSN = 0.2÷0.8 g/dm3), leaching time (τ = 20÷120 min), temperature (T = 393÷423 K), and oxygen partial pressure (РО2= 0.3÷0.7 MPa) on the degree of zinc and iron extraction into the solution and on the cake grain-size distribution was established. It was shown that lignosulfonate additive intensifies zinc and iron extraction into the solution. Maximum extraction of zinc and iron was 89 and 37 %, respectively, for 120 min of leaching at CLSN = 0.6÷0.8 g/dm3. The differential rate law with respect to lignosulfonate was 0.3 for sphalerite, and 0.9 for iron sulfides. A controversial influence of rising temperature on the process under investigation was found. Temperature elevation from 413 to 423 K leads to a decrease in zinc extraction by 3–4 % due to the formation of sulfur-sulfide aggregates over 150 μm in size. The calculated values of apparent activation energy (Еа) of sphalerite and iron sulfide leaching in the presence of lignosulfonate were 30 and 45 kJ/mole, respectively. It was found out that an increase in oxygen partial pressure from 0.3 to 0.5 MPa has a positive influence on leaching and increases extraction of zinc and iron by 22 and 27 %, respectively. However, an increase in oxygen partial pressure up to 0.7 MPa in the presence of lignosulfonate after 40 min of leaching led to a decrease in leaching rate, possibly as a result of lignosulfonate destruction. It was found that differential rate laws with respect to oxygen are 1.2 for sphalerite and 2.5 for iron sulfides.