Bacterial-mediated recovery of copper from low-grade copper sulfide using fly ash and bacterial community dynamics

• Optimal fly ash dosage (0.8 g/L) significantly enhances copper recovery (79.87%) and bacterial concentration (7.08×10^7 cells/mL) in bioleaching of low-grade copper sulfides. • Fly ash addition promotes the growth of key leaching bacteria (Acidithiobacillus ferrooxidans, Acidibacillus ferrooxidans, Leptospirillum ferriphilum), reaching up to 99.81% of the total microbial community. • The formation of specific precipitates (Zn(Fe3(SO4)2(OH)6)2 and Mg(Fe3(SO4)2(OH)6)2) reduces toxic ion effects, enhancing bacterial proliferation and bioleaching efficiency. • Chloride and silver ions in fly ash act as catalysts, transforming the passivation layer from dense to porous, improving ore-lixiviant-bacteria contact and overall copper recovery.