Heavy metals recovery from spent catalyst using Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans

In this investigation, a spent processing catalyst from one of the oil refineries in Iran was initially characterized physically and chemically. Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans were used to mobilize aluminum, cobalt, molybdenum and nickel from hazardous spent catalysts. Bioleaching experiments were performed in batch cultures. The growth characteristics of the bacteria (pH, Eh, cell concentration and ferrous and ferric iron concentration) were determined during bioleaching along with the concentration of metal values extracted from the catalyst. The results obtained from Inductive coupled plasma-optical emission spectrometry (ICP-OES) showed that after the one-step bioleaching process using A. ferrooxidans, maximum removal efficiencies of 63%, 96%, 84% and 99% were achieved for Al, Co, Mo and Ni, respectively. However, the highest removal efficiencies using A. thiooxidans were 2.4%, 83%, 95% and 16% for Al, Co, Mo and Ni, respectively. By recovering such valuable metals, the recycled product can be further used for industrial purposes.