A novel approach for microbial activity assessment in bioleaching. Towards to a standardised fast starting up protocol

• Maximum potential bioleaching rate was determined by offline OUR measurement. • Offline OUR measurement allowed to monitor and control iron oxidising cultures. • Bioleaching performance was function of the iron oxidising activity of the inoculum. Biohydrometallurgy is a proven industrial method for extracting base metals from sulfidic ores with low-grade content and as a pre-treatment of Au ores. The lack of study of biological aspects related with microbial activity assessment makes it difficult to control and monitor these processes; and the multitude of experimental procedures described in the literature hinders cross-study comparisons among researchers. Experimental tools that allow a quick and reliable quantitative assessment of the iron oxidising capacity of the cells during the bioleaching process are needed. This work proposes monitoring microbial activity through a simple and reliable method based on the offline measurement of the Oxygen Uptake Rate (OUR). The methodology allows to quantify the microbial activity evolution of a growing culture under no-limiting conditions. By this methodology, the maximum potential bioleaching rate of the culture at any time is determined, assessing the occurrence of a biological or chemical limitation. The results obtained reveals that whether due to Fe 2+ or O 2 depletion, substrate availability significantly limits microbial activity. This aspect is key to assess a culture suitability for bioleaching bioreactor inoculation, preventing long lag phases. Furthermore, the methodology allows for quick disturbances correction, avoiding process shutdowns and enhances technological reliability of continuous bioleaching.