-This study evaluates the recovery of heavy metals employing a spent catalyst from the hydrodesulfurization (HDS) of diesel, with no chemical, thermal or physical pretreatment, using the bacterial strain Acidithiobacillus thiooxidans FG-01. Direct and indirect bioleaching tests were carried out in Erlenmeyer flasks (500 mL). The influence of the pulp density and supplementation with elemental sulfur on the bioleaching were also investigated. The spent catalyst contained organochlorines, petroleum hydrocarbons and heavy metals in its composition. The best recovery results (26% Al, 26% V and 39% Mo) were achieved in the two-stage (indirect) bioprocess, with a pulp density of 50 g/L. It was not possible to recover Co, Cu and Ni (< 5%) under any of the conditions tested. The bacterial strain A. thiooxidans FG-01 was found to be a promising candidate for the recovery of Al, V and Mo using the crude spent HDS catalyst.
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.
This paper describes the use of an electrical impedance model to assess acute skin reactions to irritant over time. The applied method is noninvasive and quantitative and can detect the irritation before the visual signs. The results showed that the signs of acute irritation (oedema) were present until the second day after irritant application. The method is able to detect the initial phase of irritation and the assessment of regeneration time could be attained by a combination of more than one bioengineering methods.
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