Bioleaching of Valuable Metals from Spent Catalyst Using Metabolic Citiric Acid by <i>Aspergillus niger</i>

Abstract

Spent catalyst is listed as one of the hazardous wastes. Based on the toxicity characteristic shows that spent catalyst contains some heavy metals at concentration above the regulations limits. This situattion becomes an important issue in nowadays. In this research, fungus Aspergillus niger was investigated to produce weak organic acid (citric acid). Batch experiments were performed to compare the leaching efficiency from spent catalyst of pulp density (2% and 4%) and particle size (212 µm, 150 µm and 75 µm). Result showed that after direct bioleaching process, maximum recovery of valuable metal 24.94%, 7.42%, 1.09%, 3.51%, 4.87% and 1.66% were achieved for aluminum, calcium, iron, copper, silver and platinum respectively at 2% pulp density. Overall data shows that metal recovery at pulp density 2% are higher than 4% pulp density. The maximum recovery based on particle size shows that the smaller particle (75 µm) the higher metal recovery (Al, Ag and Pt) and for some metals was different such as Fe, Cu and Ca.