LAUSR

Abstract Coal fly ash (CFA), a waste byproduct of thermal power plants, is a major dust pollution source and a resource bearing valuable metals, such as Al and Ce. Metal bioleaching from CFA can be cost-effective for disposal with significant economic and environmental benefits. The goal of this study was to evaluate the bioleaching of Al and Ce from CFA by meso-acidophilic Acidithiobacillus ferrooxidans with the addition of pyrite after CFA was activated by roasting with Na2CO3 at a mass ratio 1:0.22 (w/w) to quantitatively transform the principal Al-bearing minerals mullite and sillimanite into nepheline and Al2O3. Optimal leaching of Al (91.2% after 12 days of incubation) and Ce (63.4% after 8 days of incubation) was achieved at a mass ratio of pyrite to activated CFA (a-CFA) 1.5:1, pulp density 20 g/L, initial pH 1.75 and initial inoculum 2 × 108/ml. As pyrite was bioleached, the species S2−, S22− and Sn2− were transformed to S0 and then to SO42−, and pyrite was converted to Fe(III)-containing species. With the accumulation of jarosites and the dissolution of a-CFA, amorphous phases containing Al2SiO5, interconnected [SiO4]-[AlOn] units, and SiO2 gel, mineralogical phases containing beaverite and pyrophyllite were successively generated. These results indicated that the oxidation of pyrite driven by A. ferrooxidans significantly promoted the dissolution of a-CFA for metal extraction. Compared with metal bioleaching from CFA in previous studies, the route of activation combined with bioleaching has resulted in significant progress in metal recovery.