Parameters influencing the microbial oxidation activity in the industrial bioleaching heap at Escondida mine, Chile

摘要

The oxidative activity of the microbial population in the industrial Run-Of-Mine (ROM) bioleaching heap is an important factor affecting the dissolution rate of sulfide minerals. The oxidative activity in Pregnant Leach Solutions (PLS) of each leaching strip of the Escondida industrial heap is monitored monthly and differences in oxidation time and oxidation profiles have been observed. In addition, a huge amount of information has been generated from the system including periodical monitoring of microbiological and physicochemical parameters. Previously, the application of a data mining technique ( decision trees) determined that changes observed in oxidation rates of PLS were related to the Most Probable Number ( MPN) of Fe-oxidizing microorganisms and some members of the population determined by quantitative Real Time-PCR ( qPCR). Based on those results, it was postulated that the availability of substrate would be the determinant factor of the MPN and of the number of cells of those members of the microbial community. The goal of this work was to explore the data ( microbiological and physicochemical data) including mineralogical characteristics of the ores loaded in the heap, as a new parameter for the analysis. For that purpose another data mining technique, "clustering" , was applied. Three different groups of strips were distinguished, being copper and iron sulfide mineral contents and lithology the most relevant factors selected by the segmentation algorithm used. The results showed that there is a good coincidence between the three groups defined and the metallurgical performance of the corresponding strips in terms of copper recovery and with the bacterial community composition and activity. Not the ore content alone but the ore content together with lithology—considered as the responsible for particle size distribution in the dumped mineral—are determinant of the microbial substrate availability. Those results allowed us to conclude that there is a direct relationship between ore substrate availability, microbial activity and copper recovery. That kind of information should be considered in defining models to describe and to predict copper recovery in industrial bioleaching ROM processes.