ASSESSMENT OF METAL RECOVERY FROM RAW SPENT HYDRODESULFURIZATION CATALYST THROUGH BIOLEACHING AND CHEMICAL LEACHING

Abstract

The aim of this work is to evaluate the recovery of metals from a spent catalyst of diesel hydrodesulfurization (HDS), without any chemical, thermal, or physical pre-treatment, using the Acidithiobacillus thiooxidans FG-01 strain and chemical leaching. The spent catalyst is a hazardous waste due to the presence of organochlorine compounds, petroleum hydrocarbons, and heavy metals. Chemical leaching tests were performed with solutions of citric acid (20 g L-1), oxalic acid (20 g L-1), citric and oxalic acid mixture (1:1, 20 g L-1), and sulfuric acid (10 g L-1). The best results of metals recovery through chemical reaction were obtained when using the inorganic acid solution. The two-step bioleaching assays were conducted in 500 mL Erlenmeyer flasks, with a pulp density of 27.5 g L-1, and a sulfuric acid concentration of 20 g L-1. There were no differences between chemical and microbial leaching results. The A. thiooxidans FG-01 is a promising strain due to the recovery of Al (~65%), V (~25%), and Mo (~25%) from the raw solid residue.