Dong J. Kim

Bioleaching kinetics and multivariate analysis of spent petroleum catalyst dissolution using two acidophiles

Bioleaching studies were conducted to evaluate the recovery of metal values from waste petroleum catalyst using two different acidophilic microorganisms, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. Various leaching parameters such as contact time, pH, oxidant concentration, pulp densities, particle size, and temperature were studied in detail. Activation energy was evaluated from Arrhenius equation and values for Ni, V and Mo were calculated in case of both the acidophiles. In both cases, the dissolution kinetics of Mo was lower than those of V and Ni. The lower dissolution kinetics may have been due to the formation of a sulfur product layer, refractoriness of MoS(2) or both. Multivariate statistical data were presented to interpret the leaching data in the present case. The significance of the leaching parameters was derived through principle component analysis and multi linear regression analyses for both iron and sulfur oxidizing bacteria.

Dissolution kinetics of spent petroleum catalyst using sulfur oxidizing acidophilic microorganisms

Bioleaching studies of spent petroleum catalyst were carried out using sulfur oxidizing, Acidithiobacillus species. Leaching studies were carried out in two-stage, in the first stage bacteria were grown and culture filtrate was used in the second stage for leaching purpose. XRD analysis of spent petroleum catalyst showed oxides of V, Fe and Al and sulfides of Mo and Ni. The leaching kinetics followed dual rate, initial faster followed by slower rate and equilibrium could be achieved within 7 days. The leaching rate of Ni and V were high compared to Mo. The low Mo leaching rate may be either due to formation of impervious sulfur layer or refractoriness of sulfides or both. The leaching kinetics followed 1st order rate. Using leaching kinetics, rate equations for dissolution process for different metal ions were evaluated. The rate determining step observed to be pore diffusion controlled.

A novel process to treat spent petroleum catalyst using sulfur-oxidizing lithotrophs

A novel process was developed using sulfur-oxidizing bacteria to extract metal values like Ni, V and Mo from spent petroleum catalyst. Bacteria were grown in elemental sulfur media for five day and after filtering, the filtrate was used for leaching purpose. Effect of different parameters such as contact time, particle size, pulp density and lixiviant composition were studied to find out the extent of metal leaching during the leaching process. XRD analysis proved the existence of V in oxide form, Ni in sulfide form, Mo both in oxide as well as sulfide forms, and sulfur in elemental state only. In all the cases studied Ni and V showed higher leaching efficiency compared to Mo. The low Mo leaching rate may be either due to formation of impervious sulfur layer or refractoriness of sulfides or both. Leaching kinetics followed dual rate, initial faster followed by slower. Dissolution mechanism was explained on the basis of both surface and pore diffusion rate. The leaching kinetics followed 1st order reaction rate. Finally, multiple linear regression analysis was carried out to compare the observed and calculated leaching percentage values for three metals.

Bio-dissolution of Ni, V and Mo from spent petroleum catalyst using iron oxidizing bacteria

Bioleaching studies of spent petroleum catalyst containing Ni, V and Mo were carried out using iron oxidizing bacteria. Various leaching parameters such as Fe(II) concentration, pulp density, pH, temperature and particle size were studied to evaluate their effects on the leaching efficiency as well as the kinetics of dissolution. The percentage of leaching of Ni and V were higher than Mo. The leaching process followed a diffusion controlled model and the product layer was observed to be impervious due to formation of ammonium jarosite (NH4)Fe3(SO4)2(OH)6. Apart from this, the lower leaching efficiency of Mo was due to a hydrophobic coating of elemental sulfur over Mo matrix in the spent catalyst. The diffusivities of the attacking species for Ni, V and Mo were also calculated.