Use of adapted Aspergillus niger in the bioleaching of spent refinery processing catalyst

Abstract

Spent refinery processing catalyst is listed as a hazardous waste; the toxicity characteristic leaching procedure (TCLP) extracts of the catalyst are found to contain heavy metals at concentrations exceeding the regulated levels. In the present investigation, Aspergillus niger was adapted to single metal ions Ni, Mo or Al (at 100-2000 mg/L in steps of 100 mg/L) and then to a mixture of Ni, Mo and Al (at a mass ratio of 1:2:6, as approximately present in the spent catalyst). Adaptation experiments with single metals showed that the fungus could tolerate up to 1000 mg/L Ni, 1200 mg/L Mo and 2000 mg/L Al. In the presence of a mixture of these metals, the fungus was able to tolerate up to 100 mg/L Ni, 200 mg/L Mo and 600 mg/L Al. One-step bioleaching experiments with 1 wt% spent catalyst (of particle size