Recovering and reusing water, H2SO4, nickel and cobalt from gold mining wastewater using air-gap membrane distillation and solvent extraction

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Gold mining industry has attracted significant attention for its impact on the environment, encouraging a responsive interest in recovering valuable materials from gold mining wastewater. This study, aligned with the principles of the circular economy, aimed to explore the extraction of water, sulfuric acid, nickel, and cobalt from gold wastewater, employing air gap membrane distillation (AGMD), non-dispersive solvent extraction, and conventional solvent extraction. In the AGMD process, it was demonstrated that 69 % of the wastewater could be reclaimed in the form of high-quality distilled (6.6 ± 1.8 L/m2h). The reclaimed water played a pivotal role in the subsequent non-dispersive extraction stage, acting as a re-extraction agent. Hollow membrane contactors were employed in this stage, achieving a recovery rate of over 95 % for sulfuric acid from the concentrate, with high selectivity over iron (βFe = 488) and magnesium (βMg = 8011;). The acid-depleted stream was then subjected to conventional solvent extraction, wherein Cyanex 272 proved highly effective in extracting nickel, although with limited success in extracting cobalt. The previously used acid current was reintroduced as a re-extractant, demonstrating an 89.3 % re-extraction efficiency. In summary, this study conclusively demonstrated the feasibility of reintroducing water, sulfuric acid, and nickel into the economic cycle through the applied methods. The recovered materials were carefully examined for their potential applications, not only within the gold mining but also across various industrial sectors. This multifaceted approach aligns with the circular economy's objectives, fostering the efficient and sustainable reintroduction of recovered materials into economic processes.