This work investigated a bioleaching process to remove V, Ni and Cu from fuel-oil ash (FOA) using Acidithiobacillus thiooxidans. Adaptation of the bacterium to tolerate up to 4% (w/v) of the FOA particles suspended in the culture medium was carried out. The response surface methodology (RSM) based on a statistical analysis was used to optimize the initial sulfur concentration, initial pH and ash concentration in shake flask cultures first. Maximum V recovery (96.4%), Ni recovery (100%) and Cu recovery (99.2%) at the ash concentration of 1%, initial sulfur of 9 g L1 and initial pH of 1 were achieved. Risk assessments of FOA before and after bioleaching using the toxicity characteristic leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP) and total threshold limit concentration (TTLC) were evaluated. The results indicated that the bioleaching process detoxified FOA and the bioleached solid residue was well within the regulatory limits for disposal. In order to scale up the bioleaching process, some experiments were also performed in a bubble column bioreactor. The changes in growth characteristics in the bioleaching process were also studied. Maximum recoveries for V, Ni and Cu were 77.6%, 89.7% and 65.7%, respectively at an ash concentration of 1% after eight days of incubation. These recovery rates were lower than those for shake flasks, but they suggested that this process could be operated in a bioreactor after optimizing the bioreactor operating conditions.
