Optimization of bioleaching process for arsenic extraction from abandoned mine soils by oxalic acid

Soils contaminated with heavy metals, such as arsenic (As), pose significant environmental risks and can cause serious ecological and health-related damage. Biological methods, such as bioleaching (organic acids), biosorption (lignocellulosic materials, microbial biofilms), and bioaccumulation (microbial biofilms), have shown potential for remediating of heavy metal pollution sites. However, research optimizing the bio-based solutions remains limited. This study aimed to optimize As leaching from two abandoned mine soils using oxalic acid (OA). Response surface methodology (RSM) with a second-order central composite design (CCD) was employed to determine the optimal conditions, focusing on OA concentration and soil weight. Additionally, OA production by the brown-rot fungus Antrodia albida was monitored, revealing significant synthesis under low pH conditions, with peak production observed on the eighth day of incubation. The bioleaching efficiency of fungal OA was compared with commercial OA, showing comparable As extraction rates exceeding 95% in both soil types. However, the extraction efficiency for other heavy metals varied: fungal OA was more effective for cadmium, nickel, and lead, whereas commercial OA demonstrated higher efficiency for chromium, copper, and zinc. These findings underscore the potential of fungal OA as a sustainable alternative for remediating soils contaminated with heavy metals, particularly in low-pH environments.