Fractionation Behavior of Metals (Al, Ni, V, and Mo)During Bioleaching and Chemical Leaching of Spent Petroleum Refinery Catalyst

摘要

We analyzed, for the first time, the different fractions of metals present in the spent catalyst and changes they undergone during bioleaching and chemical leaching. Before bioleaching, Al (83.9 %) was found mainly in the residual fraction of the pretreated spent catalyst. Ni (61.3 %) was mainly present in the exchangeable fraction exhibiting its high environmental mobility. V (58.5) and Mo (49.3 %) mainly existed in the oxidizable fraction suggesting that highly oxidizing conditions would liberate these metals from the spent catalyst. During bioleaching with Acidithiobacillus thiooxidans, almost complete solubilization of the exchangeable as well as of reducible fraction was observed. Due to strong acidic conditions, part of oxidizable fraction of these metals was also solubilized. Bioleaching also affected the fractionation of metals remaining in the treated spent catalyst. At the end of the process, most of the metals remaining in the spent catalyst were found in the more stable fractions ensuring the safe disposal of spent catalyst. The leaching yields and fractionation behavior of metals during chemical leaching was found to be identical. The results of the present study strongly suggest that bioleaching is an effective method for removing metals from the spent catalyst.