Selective precipitation of metals from synthetic spent refinery catalyst leach liquor with biogenic H2S produced in a lactate-fed anaerobic baffled reactor

This work evaluated the feasibility of using biogenic H2S and NaOH to selectively precipitate molybdenum (Mo), nickel (Ni), cobalt (Co) and vanadium (V) from synthetic spent refinery catalyst leach liquor. A lactate-fed sulfate-reducing anaerobic baffled reactor (ABR) was operated at room temperature to generate the required H2S. The average sulfate reduction rate in the ABR was 130 mg L−1 d−1 and the average dissolved sulfide concentration was 190 mg L−1. Biogenic H2S facilitated the selective precipitation of Mo at pH 2 with recoveries of 36–72%. Vanadium precipitation of 64–70% was achieved with NaOH at pH 6. The purity indices of Mo and V precipitates were 0.97 and 0.90 at pH 2 and pH 6, respectively. Percent Ni and Co precipitations were only up to 23 and 16%, respectively at pH 3.5, and the purity indices of these metals were low due to their simultaneous precipitation. After the optimization of the Ni and Co precipitations, the mixed Ni–Co sulfide solids could be sold to smelters or hydrometallurgical processing to recover the metals. Moreover, using biogenicH2S to selectively precipitateMoat pH 2 as sulfide andNaOHto precipitate V at pH 6 as hydroxide/oxide could be a viable option for recovering these metals from spent catalysts leachate.