Phosphate Minerals and Applications of Phosphate Solubilizing Microorganisms for Extraction of Critical Minerals and Rare Earth Elements

The key energy transition industries are reliant on critical minerals including but not limited to rare earth elements (REEs), copper (Cu), and lithium (Li). Furthermore, the ongoing COVID-19 pandemic, geopolitical conflicts, and climate change have exposed major bottlenecks in the security of global critical minerals and food supply chains. On the one hand, the major host minerals for REEs are primary and secondary phosphate minerals such as monazite and xenotime. On the other hand, phosphate and potash used in fertilizers are essential to improve the resilience of agricultural soils in a changing climate. Phosphate solubilizing microorganisms (PSMs) are often reported to be a major contributing factor for plant and soil nutrition by making insoluble phosphate into more soluble forms. Recent progress in understanding the molecular mechanisms of REEs solubilization from REEs-containing phosphate mineral, monazite, has suggested that in addition to protonation and complexation mechanisms either through organic acids production in heterotrophs or biogenic sulfuric acid in acidophiles, bacterial attachment has a pivotal role in bioleaching systems. This chapter highlights the recent application of PSMs for the bioleaching of critical minerals and emphasizes the significance of microbial function to narrow down potential microorganisms and associated dissolution pathways of these metals.