Biomagnetic separation of titanium-rich fractions from coal fly ash and from precipitated acidic leachate of coal fly ash

The enormous amounts of coal fly ash produced by coal-fired power stations in Israel can be exploited as a source of aluminum (~17% w/w) and titanium (~1% w/w) by acidic leaching and extraction of Al and Ti coupled with removal of toxic metals from the ash. During such leaching, more than 30% of the aluminum and titanium contained in the ash, as well as most of the toxic metals, were released. At pH 2.05, pH-dependent re-precipitation of soluble material in the leachate yielded a titanium-rich fraction with a Ti/Al ratio greater than 1.0. Further titanium enrichment was achieved by biomagnetic separation procedure using the adhesive bacterium, Rhodococcus GIN-1 (NCIMB 40340), which adheres selectively to the Ti-containing material precipitated at pH 2.05. At a pH range of 2 to 9 the bacteria could be immobilized on magnetite particles and mediated the binding of magnetite to the precipitated Ti-containing material. Application of magnetic field enabled the isolation of a triple conjugate of bacteria, magnetite and titanium-rich material, in which titanium was enriched by about 5-fold. Vigorous mixing of the resuspended triple conjugate followed by a second magnetic separation enabled the isolation of a double conjugate of bacteria and Ti-rich material, from which most of the magnetite (>90%) had been detached. The Ti/Al ratio in the biomagnetically separated material was more than 100-fold higher than in the original ash (7 versus ~0.06 w/w).