Impact of sulfate supplement on bioleaching of iron from fly ash residue using isolated Acidithiobacillus ferrooxidans strain: A Box-Behnken process optimisation

Abstract

Fly ash, a residue from coal combustion contains significant iron content (10-40%), has potential applications in various fields. Present study investigated the impact of sulfate on bioleaching of iron from fly ash, using a novel Acidithiobacillus ferrooxidans strain. Iron dissolution obtained was 95.5 mg/L with 100 rpm shake flask speed, 3% pulp density, pH 3.0, and 5.5 g/L sulphate supplement, compared to 74.5 mg/L without sulphate over 15 days. The study employed Box-Behnken design for Design of Experiments. Variables ranged from 50 rpm – 150 rpm for shake flask speed, 2.5 – 3.5 for pH, 1% – 5% for pulp density, and 1.0 g/L – 10 g/L for sulfate concentration. In the experiment with sulfate supplement, the concentration of sulfate was treated as a variable parameter, as opposed to the pulp density, while taking into account other relevant characteristics. Iron dissolution was taken as a response. Pulp density and sulfate concentration significantly affected iron dissolution. A quadratic regression model was fit and an ANOVA was performed. According to the model, sulfate concentration has a positive linear influence with sulfate supplement, while for no sulfate supplement, shake flask speed and pulp density have a positive effect on the bioleaching of iron from fly ash. © 2025 Korean Society of Environmental Engineers.