Abstract

In the actual mining scenario, copper bioleaching, mainly raw mined material known as Run-of-Mine (ROM) copper bioleaching, is the best alternative for the extraction from marginal resources that are not currently considered part of the profitable reserves because of the cost as-sociated with leading technologies in copper extraction. It is foreseen that bioleaching will play a complementary role in either concentration - as it does in Minera Escondida Ltd. (MEL) - or chloride main leaching plants. In that way, it will be possible to maximize mine with installed solvent-extraction and electrowinning capacities that have not been used since the depletion of oxide ores. One of the main obstacles for widening bioleaching technology applications is the lack of knowledge about the key events and the attributes of the technology's critical events at the industrial level and mainly at ROM copper bioleaching industrial operations. It is relevant to assess the bed environment where the bacteria-mineral interaction occurs to learn about the limiting factors determining the leaching rate. Thus, and due to the inability to accurately determine in situ key variables, their indirect assessment was evaluated by means of the quantification of microbial metabolic associated responses. Several candidate marker genes were selected to represent the predominant components of the microbial community inhabiting the industrial heap and the metabolisms involved in microbial responses to changes in the heap environment that affects the process performance. Oxygen reduction, CO2 and N2 fixation/uptake, iron and sulfur oxidation, and response to osmotic stress were the metabolisms selected regarding research results previously reported in the system. After that, qPCR primers for each candidate gene were designed and validated. The expression profile of the selected genes vs. environmental key variables in pure cultures, column-leaching tests, and the industrial bioleaching heap was defined. We presented the results obtained from the industrial validation of the marker genes selected for assessing CO2 and N2 availability, osmotic stress response, as well as ferrous iron and sulfur oxidation activity in the bioleaching heap process of MEL. We demonstrated that molecular markers are useful for assessing limiting factors like nutrients and air supply and the impact of the quality of recycled solutions. We also learned about the attributes of variables like CO2, ammonium, and sulfate levels that affect the industrial ROM scale operation