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In this attempt recovery of heavy metals from a hydrocracking spent catalyst was studied in a slurry bubble column bioreactor using Acidithiobacillus thiooxidans. Firstly adaptation of microorganisms to a spent catalyst was performed in a shaking flask. In the next stage the experiments were done accordance with a central composite design to find the optimal conditions; the three factors of particle size, pulp density, and aeration rate were chosen for examination. A full quadratic as well as two reduced cubic models were established to identify the relationship between the percentage of metals recovered and the variables. The optimal values of variables were a pulp density of 0.9% (w/v), particle size of 60.7 μm, and aeration rate of 209 ml/min to obtain simultaneous maximum recovery of three metals. The results showed that at optimal conditions maximum extraction of 87% ± 5.5% Mo, 37% ± 2.6% Ni and 15% ± 1.3% Al were achieved after only 7 days of batch processing in the bioreactor. The recovery of these metals can decrease the environmental impact of the waste catalysts and according to the results of this research slurry bubble columns, due to decrease the time of bioleaching process, can be further used for industrial purposes. [ABSTRACT FROM AUTHOR]

Abstract: This study was designed to compare one-step, two-step and spent medium bioleaching of spent catalyst by adapted Aspergillus niger in batch cultures. Aspergillus niger, which was adapted to heavy metal ions, Ni, Mo, Fe, and W, was grown in medium containing up to 5% (w/v) of spent catalyst. The main lixiviant in bioleaching was gluconic acid, which was produced at all pulp densities in the one-step bioleaching process. Gluconic acid was also produced in the two-step bioleaching process when the spent catalyst was present at pulp densities greater than 1% (w/v). In the spent medium leaching, however, the primary agent was citric acid. The pulp density of the spent catalyst was varied, and this resulted in different amounts of solubilized metals. A total of 3% (w/v) spent catalyst generally produced maximum extraction yields in the one-step bioleaching process; the amounts of leached metals were 100% of W, 77.8% of Fe, 90.9% of Mo, 65.8% of Ni, and 14.2% of Al. The highest concentration of gluconic acid in this condition demonstrated that it was the primary bioleaching agent. Compared with chemical leaching at 1% pulp density, the fungus was more efficient at the leaching of W, Al, Mo, and Fe and equally efficient in the extraction of Ni. [Copyright &y& Elsevier]

Abstract: This study was focused on the heavy metal (Ni, Co, Mo, V, Mn, Fe, W and Zn) tolerance of fungi strains Aspergillus niger, Aspergillus foetidus and Penicillium simplicissimum. Aspergillus niger was exposed to a mixture of Mo, V and Mn at a mass ratio of 1:2:6 as approximately present in the spent refinery processing catalyst. This study highlights the adaptation of fungi strains to Tungsten and Vanadium to high concentration. The effect of different metals and metal concentration on different strains of fungi was evaluated. Results showed that Ni was one of the most toxic metals for strains of Aspergillus and Penicillium. Aspergillus foetidus was the least tolerant, in particular for Ni, Co and Zn. In this work, Aspergillus niger, Aspergillus foetidus and Penicillium simplicissimum showed higher tolerance towards Mo and V, and the three fungi have a good potential for the bioleaching of spent refinery processing catalysts that contain Mo and V. The main objective of this study is to identify the best strain, based on tolerance development, for the spent refinery processing catalyst. [Copyright &y& Elsevier]

Abstract: Adaptation of Penicillium simplicissimum with different heavy metals present in a spent hydrocracking catalyst, as well as one-step, two-step, and spent medium bioleaching of the spent catalyst by the adapted fungus, was examined in batch cultures. Adaptation experiments with the single metal ions Ni, Mo, Fe, and W showed that the fungus could tolerate up to 1500mg/L Ni, 8000mg/L Mo, 3000mg/L Fe, and 8000mg/L W. In the presence of multi-metals, the fungus was able to tolerate up to 300mg/L Ni, 200mg/L Mo, 150mg/L Fe and 2500mg/L W. A total of 3% (w/v) spent catalyst generally gave the maximum extraction yields in the two-step bioleaching process (100% of W, 100% of Fe, 92.7% of Mo, 66.43% of Ni, and 25% of Al). The main lixiviant in the bioleaching was shown to be gluconic acid. The red pigment produced by the fungus could also possibly act as an agent in Al leaching. [ABSTRACT FROM AUTHOR]

In this article, bioleaching of computer printed circuit boards (CPCBs) was examined using Aspergillus niger with one-step, two-step, and spent-medium bioleaching methods. Four effective parameters were optimized using response surface methodology (RSM) to achieve maximum recovery of Cu and Ni. Under optimal conditions – pH of 5.15, pulp density of 10 g/l, 1E+007 spores of A.niger , and 4.5 days for the sample adding time − 97% and 74% of Cu and Ni were recovered, respectively. Two-step bioleaching and spent medium bioleaching were respectively identified as the best methods for maximizing Cu and Ni recovery. Fungi deteriorate the sample mainly by it is chemical action like producing acids. Surface morphology results confirmed the metabolites produced by the fungus—corrosive chemicals—eroded the particles of the e-waste sample during the bioleaching time. The mapping and energy dispersive X-ray (EDAX) of the initial sample and the processed sample validated that bioleaching was quite effective. The overall results indicate that Cu and Ni from e-waste can be recovered through the bioleaching process using A. niger. The addition time (day) of the sample to the solution plays an important role in metal recovery using A. niger. Acid production by the fungi increases the metal recovery, while biocrystallization of heavy metals decreases the recovery. This paper proved the great potential of the biohydrometallurgical route mediate by Aspergillus niger strain for recovering heavy metals from electronic wastes under defined optimal condition, two-step process, 30 ° C , and shaking rate of 130rpm. Unlabelled Image • Bioleaching of computer printed circuit boards using Aspergillus niger was studied. • pH, number of spores, the sample adding time, and pulp density were optimized using RSM. • The highest metal recovery yields were obtained in two-step bioleaching method. • Under the optimal conditions Cu and Ni were recovered 97% and 74% respectively. [ABSTRACT FROM AUTHOR]