Microbial processes for sustainable metal recovery and surface engineering

Microbial manufacturing is emerging as a complementary method to traditional metal processing using microorganisms and their metabolites as functional agents for selective dissolution, recovery, surface modification, and protective mineral formation. This review critically evaluates microbial manufacturing with a focused emphasis on sustainable metal recovery and surface modification and finishing, integrating mechanisms, quantitative performance, process intensification, scale-up, and techno-economic and life-cycle considerations. The reviewed processes are classified into two manufacturing functions: subtractive processing consisting of microbial or biogenic dissolution for metal recovery and controlled surface removal and constructive processing including extracellular-polymeric-substance-mediated biomineralization and functional surface formation. Recent intensified systems exhibit significant application-specific performance. The novelty of this review lies in integrating microbial metal recovery and surface engineering within a unified manufacturing-oriented framework that links biological mechanisms to manufacturing functions, engineering performance indicators, process intensification, scale-up, and techno-economic and life-cycle considerations. Rather than evaluating microbial processes solely through extraction efficiency or biological activity, the review assesses their manufacturing relevance in terms of selectivity, productivity, surface integrity, dimensional control, resource consumption, downstream processing, and industrial translation. However, the fact that microbial digestion functions under gentle conditions does not imply that it is intrinsically viable. Aeration, stirring, nutrient demands, water usage, retention duration, downstream separation, contaminant management, and process recycling can significantly influence both economic and ecological outcomes. The main challenge encountered in the analysis is the translation from biological feasibility to manufacturing reliability, especially for throughput, high solid processing, dimensional control, coating durability, repeatability, and pilot scale validation. Hence, this review proposes a manufacturing-oriented reporting framework and staged translation roadmap connecting mechanistic validation, process intensification, continuous or recycle operation, product qualification, and integrated techno-economic and life-cycle assessment. To summarize, data suggest that hybrid manufacturing is the most feasible near-term pathway by combining microbial or cell-free biogenic functions with known physical, chemical, and downstream operations to achieve selectivity, process control, productivity, and circular utilization of resources.