• Acidified seawater increased copper extraction from chalcopyrite by an enriched microbial community from 13.1% to 62.1% compared with non-acidified seawater.
• Acidification enhances microbial community adaptability to high-salt conditions and maintains an optimal redox potential (360–410 mV) that favors chalcopyrite dissolution.
• Chloride ions at 580 mmol/L improve leaching kinetics by increasing porosity and noncrystallinity of elemental sulfur intermediates.
• This approach offers a sustainable alternative for bioleaching copper minerals in freshwater-scarce regions, utilizing seawater as a viable process water.