Effects of multivalent cations on low-rank coal solubilities in alkaline solutions and microbial cultures

Microorganisms are able to solubilize low-rank coals using the mechanism of base solubilization, but a pH values of ≤8. Pretreatment of coals with HCl under nonoxidizing conditions removes organically bound multivalent cations and results in an increase in the amounts of coal solubilized either by microorganisms or in alkaline buffers. These results indicate the importance of cations in the organic structure of coal and suggest that metal complexation and removal is another mechanism used by microorganisms to solubilize low-rank coals