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

Abstract

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 130mgL−1d−1 and the average dissolved sulfide concentration was 190mgL−1. Biogenic H2S facilitated the selective precipitation of Mo at pH2 with recoveries of 36–72%. Vanadium precipitation of 64–70% was achieved with NaOH at pH6. The purity indices of Mo and V precipitates were 0.97 and 0.90 at pH2 and pH6, respectively. Percent Ni and Co precipitations were only up to 23 and 16%, respectively at pH3.5, 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 biogenic H2S to selectively precipitate Mo at pH2 as sulfide and NaOH to precipitate V at pH6 as hydroxide/oxide could be a viable option for recovering these metals from spent catalysts leachate.