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

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 (Feþ3), proton (Hþ) and sulphate ions (SO4 ) 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 Feþ3 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. [doi:10.2320/matertrans.MER2008187]