An integrated sequential biological leaching process for enhanced recovery of metals from decoked spent petroleum refinery catalyst: A comparative study

• Decoking caused removal of entrained hydrocarbons and carbon from coked spent catalyst.
• Two-stage sequential bioleaching significantly enhanced the leaching yields of Ni and V.
• Integration of bioleaching with alkaline leaching remarkably improved recovery of Mo.
• Sequential processes led to the significant increment in leaching yields of metals as compared to single stage.

We report on the effectiveness of a two-stage sequential integrated bioleaching process for enhanced recovery of metals from decoked spent petroleum catalyst. Fourier transform-infrared spectra confirmed that decoking led to removal of entrained hydrocarbons and carbonaceous deposits from the raw spent catalyst. Several two-stage sequential leaching strategies (two-stage bioleaching, two-stage abiotic leaching, bioleaching followed by alkali leaching, alkali leaching followed by acid leaching, and two-stage alkali leaching) were evaluated in batch reactors. The results suggested that two-stage bioleaching (240 h) with Acidithiobacillus thiooxidans was the most effective strategy to recover Ni (79%) and V (90%). Whereas integrating bioleaching with alkaline leaching remarkably improved leaching yield of Mo (88%) in a shorter period of time (125 h). A mineral liberation analysis of the treated residue also confirmed that most of the Mo was leach out during second stage alkali leaching.

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