Bioleaching process for silver recovery: Structural and rheological studies

In this work, we characterize the microstructurel and rheological properties of silver manganese mineral pulps during a bioleaching process in a continuous stirred-tank reactor (CSTR). Analysis of the dissolution kinetics of Manganese in the pulp during the bioleaching process reveals a dissolution level of 20-23% during 36-48 h. This percentage allows the extraction of large percentages of silver (Ag) during the cyanidation process, thus obtaining 64 wt% of Ag. The maximum value of viscosity attained in the medium (especially between 48 and 72 h) is an important parameter, since it may cause processing setbacks such as in-homogeneous agitation and increase in transport energy. Several factors contribute to the continuous change of viscosity in the media such as mineral wearing, the presence of the excreted bacterial exopolysaccharide (EPS), pH changes, particle size modifications due to mineral wear (plus corrosion) and changes in density of the medium. For this reason, it is of great importance to monitor the theological behavior of the mineral pulp during the bioleaching and cyanidation processes. The mineral pulp behaves as a weak gel as reported in linear viscoelastic measurements.