Operational determinants and performance stratification in bioleaching of metals from solid waste matrices: A systematic review

This systematic review on bioleaching was conducted following PRISMA guidelines. Three electronic databases (PubMed, Web of Science, Scopus) were searched from inception to November 2025. Studies were included if they: (i) were primary experimental research; (ii) applied bacterial or fungal bioleaching to secondary resources; (iii) quantitatively reported maximum metal extraction efficiency; and (iv) reported at least two key operational parameters. Data were harmonized to standardized units (inoculum concentration to % v/v, pulp density to % w/v, temperature to °C, contact time to hours). A total of 30 studies met inclusion criteria and were subjected to quantitative synthesis using descriptive statistics, Pearson correlation, multiple linear regression, principal component analysis (PCA), and k-means clustering. The majority of studies (76.7%) reported extraction yields exceeding 90%, with an overall mean efficiency of 92.9% (SD = ±12.8%). Performance was highly substrate-dependent: lithium-ion battery materials achieved complete recovery (100.0% ± 0.0%), electronic waste (E-waste) showed high efficacy (96.6% ± 9.2%), while industrial residues exhibited lower and more variable extraction (77.1% ± 18.3%). Multivariate analysis identified three operational archetypes: (1) High-Intensity/Long-Cycle (thermophilic systems for refractory materials); (2) Alkaline-Adapted (fungal systems for high-pH wastes); and (3) Optimized Standard (mesophilic bacteria for conventional E-waste). Initial pH showed a significant negative correlation with extraction efficiency (r = -0.387, p = 0.032). Other key parameters including pulp density, temperature, contact time, and particle size demonstrated complex interrelationships rather than simple linear effects. Standardized reporting guidelines and scale-up studies are needed to bridge the gap between laboratory and industrial application.