A combined chemical-biotechnological treatment of coal fly ash (CFA)

Abstract

Enormous quantities of coal fly ash (> 7 × 10 5 tons) are produced annually by coal-fired power plants in Israel, creating a severe ecological problem. Small amounts of toxic metals (e.g. As, Cd, Pb, V) are released upon suspending the ash in aqueous solutions. For safe disposal of the ash, a rapid and efficient process has been developed to remove the toxic elements and simultaneously recover valuable elements contained in the ash (Al ~ 16% and Ti ~ 1%). The rapid leaching pretreatment of 30% (w/v) ash loads was performed in a 300 1 air-lift reactor using sulfuric acid to dissolve the toxic and valuable elements (> 98% and 25%, respectively). The residual ash ceased to release detectable amounts of toxic elements in aqueous solution. The leached elements were fractionated and concentrated by a stepwise pH increase that enabled selective precipitation of Ti at pH 2.05 (~ 99%), Al at pH 6.5 (~ 98%) and toxic elements at pH 8.5 (~98%). The precipitation at pH 2.05 was coupled with a novel biomagnetic separation that employed Rhodococcus GIN-1 bacterium (NCIMB 40340) adsorbed on magnetite to enrich the titanium. Three cycles of the biomagnetic separation procedure enabled an overall 70-fold enrichment of titanium from the starting precipitate.