The influence of biologically produced sulfide-containing solutions on nickel and cobalt precipitation reactions and particle settling properties

Wastewater from mining and metallurgical activities provides a potential profit source for recovering leftover but valuable metals such as nickel (Ni) and cobalt (Co). For this, sulfide precipitation is an attractive option, although the cost of providing chemical sulfide and the poor settling of metal sulfides discourage its application. As an alternative, sulfide-containing solution (i.e. biogenic sulfide) can be produced on site by sulfate reducing bacteria that can utilize sulfate present in the wastewater, thus reducing reagent and transportation costs. Additionally, the various components in biogenic 'sulfide', i.e., bacterial cells, cell by-products and exopolymer may enhance the settling properties of Ni and Co sulfide, thus improving metal recovery. In this project, the effect of using chemical sulfide and four biogenic sulfide-containing solutions for Ni and Co precipitation and settling was evaluated. The biogenic sulfide-containing solutions were obtained from four bioreactors fed with volatile fatty acids (VFA), leachate from fermentation of municipal solid waste, ethanol and lactate, respectively. The results showed that VFA-fed biogenic sulfide enhances the Ni precipitation reaction as compared with chemical sulfide, whereas Co was effectively precipitated from solution (> 98%) regardless of the sulfide source and metal concentration. Settling extent of both metal sulfides reached up to 80-90% in lactate-fed biogenic sulfide, while <20% of the precipitates settled by reaction with chemical sulfide. Phosphate was the main component affecting particle settling whereas acetate and sulfate exhibited a smaller influence. This research highlights the importance of the different components from the biogenic sulfide-containing solutions in the precipitation and settling of Ni and Co precipitates, demonstrating enhanced prospects of metal recovery through biological sulfate reduction process.