Microbial recovery of metals from spent coal liquefaction catalysts. Quarterly report, April--June, 1992

During April and May the authors began the rather laborious task of crushing each of the solvent-extracted catalyst samples for the determination of the effect of crushing on leaching rate and percent metal recovered. The crushing of these catalyst samples employed a ball mill and it took approximately 1 week to crush each sample. All catalyst samples, after crushing, were sieved to a particle size of >100 mesh. Samples of 10, and 40 mesh were also collected, but only the >100 mesh was subjected to bacterial leaching. These samples were tested using denitrifying bacteria for their ability to release Ni and Mo from these samples. The data are shown in the attached figures as well as comparisons for rates of Ni and Mo released in relation to catalyst solvent pretreatment. These data were obtained with citrate as a carbon and energy source for the microorganisms. It is quite clear that crushing the catalyst allows for a more rapid release of these metals from the catalyst samples, regardless of the organic solvent used to pretreat the catalyst. However, the effects of the different solvents are still evident, although not as striking, after the catalysts are crushed (see previous reports). There also still appears to be a greater ease in removing Mo over Ni, a case particularly prevalent if ethyl acetate, methanol or xylene is used as the pretreatment solvent. In any case, it appears that a variety of solvents will be useful and that an optimized system could yield >90% release and recovery of both Ni and Mo in as little as 10 days of treatment. Experimental data are enclosed