Esther M. Gabor (Zwingenberg / DE), Marc Gauert (Zwingenberg / DE), Alexandra Levesque (La Chaux de Fonds / CH), Andreas Blatter (La Chaux de Fonds / CH)
The challenges posed by climate change and the scarcity of resources call for new, sustainable production processes. In the field of precious metal recovery, research into the use of cyanogenic microorganisms has been ongoing for decades, however, without reaching sufficient technical maturity. At BRAIN Biotech, we have isolated a novel Pseudomonas strain (Pseudomonas metallosolvens) that exhibits particularly high metal tolerance, robustness and productivity in biocyanide synthesis, while being BSL-1 classified. This allows it to be used in industrial processes for the extraction of precious metals. Employing design of experiment (DOE) approaches, both the cultivation and extraction conditions for precious metals were optimized and a storage-stable formulation of the cells was developed for use as industrial starter cultures in dedicated recycling processes. Targeted bioprocess development has made it possible to scale up biocyanidation from laboratory scale to pilot scale (2 x 750 L) and to implement processing of gold-bearing ashes with promising results. Various influencing variables were taken into account, ranging from composition and physico-chemical accessibility of precious metals in different material classes to biologically relevant parameters such as oxygen transfer rate, pH, temperature and the effect of shear forces. Thanks to the interdisciplinary collaboration between chemists, microbiologists and process engineers, it was possible to scale up this complex process of biocyanidation to a relevant scale and to set up a mobile pilot demonstrator for further process development.