Optimization of pilot bioleaching for enhanced metal recovery: scale-up bioreactor, comparative bio-oxidation analysis, and advancing the continuous pyrrhotite bioleaching process

Abstract

The Sudbury region’s long history of nickel (Ni) and copper (Cu) mining has led to significant tailings accumulation, deemed waste due to processing limitations of past technologies. These tailings still contain valuable minerals, but their maintenance poses high costs and environmental risks. Due to weathering, the sulphide minerals in the tailings generate acid, facilitated by indigenous microbes, and contaminating nearby water bodies and surrounding land. Increasing regulatory demands and environmental concerns necessitated long-term tailing management and remediation plans. Research has highlighted bioleaching as a promising technology for treating low-grade minerals and environmental cleanup. The microbial assisted process has been proven effective for gold, Cu, and cobalt (Co) extraction, and has shown potential for pyrrhotite (Po) contained in tailings but is short of larger-scale testing for industrial feasibility. This study developed pilot-scale bioreactors to bioleach Ni and Co from Po tailings, using three 50-liter reactors in both batch and continuous modes. Key investigations addressed particle homogeneity within the reactors, gas mass transfer, and cooling needs due to exothermic nature of the bioleaching reactions. Results showed effective metal solubilization and valuable operational data for scale-up and techno- economic analysis. The pilot tests compared the bioleaching performance with bench-scale systems, using BACOX technology with microbial consortia to solubilize arsenic from arsenopyrite and release gold. The pilot reactors improved arsenic, iron solubilization, and overall metal recovery, despite a longer microbial adaptation period required. The continuous bioleaching of Po tailings using the CanmetMINING process to set a benchmark for pH control was essential for efficient Ni and Co recovery while minimizing iron passivation. Adjusting particle size and pH control improved the outcomes, with Acidithiobacillus caldus and Sulfobacillus spp. identified as key bioleaching microbes. The process successfully solubilized up to 93.4% Ni and 95.4% Co, with iron levels reduced to 2.88% in the PLS. However, issues with slurry flow rates and pump blockages underscored the need for further optimization of the feed transfer systems. Key findings included the pilot reactor’s superior metal recovery and homogeneity and the importance of reduced particle size and pH control. Recommendations for industrial scale-up include pretreatment steps like grinding to ensure consistent particle size for efficient bioleaching.