Metal Leaching from Spent Petroleum Catalyst by Acidophilic Bacteria in Presence of Pyrite

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This paper describes studies on the recovery of metals from spent hydro-processing catalyst using mixed acidophilic culture in presence of pyrite. This culture was initially grown in the 9K⁻ medium (absence of 9 g/L Fe(II)) where ferrous sulphate (FeSO₄) was replaced by pyrite, and then applied in this bioleaching study. Bacterial action on pyrite catalysed the formation of ferric ion (Fe⁺³), proton (H⁺) and sulphate ions (SO₄⁻²) in the solution which leached metals (Ni, Mo and V) from the spent catalyst. Experiments were conducted by varying the reaction time, amount of spent catalyst and pyrite, and temperature. After 7 days with 30 g/L of spent catalyst and 50 g/L of pyrite, the leaching of Ni, V and Mo into the solution was 85, 92 and 26%, respectively. With increasing spent catalyst loading, the extent of metal dissolution was decreased, probably due to the precipitation of Fe⁺³ as a residue. Under all conditions tested, Mo showed recovery due to its precipitation with leach residues as MoO₃ observed by applying EDAX and XRD techniques to the leach residues.