Rethinking gold mining wastewater treatment with an integrated process of membrane distillation and membrane contactors for minimal waste discard and resource recovery

Abstract

The generation of wastewater in the mining industry is followed by concerns about the environmental impacts derived from its incorrect disposal. This study intended to simultaneously treat and recover water for reuse, sulfuric acid, and copper from gold mining wastewater, from an innovative integrated system of membrane distillation (MD) and non-dispersive solvent extraction (NDSX). The performance of this system was compared when different polymeric membranes (namely polypropylene (PP), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE)) were tested. The PP membrane yielded better results in terms of distillate flux (0.67 ± 0.32 L/m2h), owing to its reduced thickness compared with the other membranes. However, the PTFE membrane demonstrated superior outcomes in terms of rejection efficiency, achieving values >99.2 %. The occurrence of fouling due to the organic phase was observed, requiring periodical cleaning protocols and the development of oleophobic membranes to reduce the fouling rate in MD. In the extraction and re-extraction processes the PTFE membrane outperformed in terms of extraction efficiency (recovery of 94.0 % for acid and 97.3 % for copper). The results were explained by its greater porosity and lower roughness, variables that directly impacted the mass transfer of sulfuric acid and copper across the membrane. The study, therefore, demonstrates potentiality in the recovery of high-quality water, sulfuric acid, and copper, clearing the path of technologies with the potential to lower the wastewater discarded from industrial facilities.