Haragobinda Srichandan

Bench-scale batch bioleaching of spent petroleum catalyst using mesophilic iron and sulfur oxidizing acidophiles

Microbial leaching of a petroleum spent catalyst was carried out using mixed mesophilic iron and sulfur oxidizing acidophiles. Bench-scale batch stirred tank reactors with a working volume of 1 L were used in this study at 35 °C. The pulp density considered for the study was 10% (w/v), while the particle size of the spent catalyst was varied by 45–106, 106–212 and >212 μm. The leaching percentage of Ni from the spent catalyst was found to be highest (97–98%) with varying particle size. However, the leaching yield for rest of the metals like Al, Fe, V and Mo was 70–74%, 66–85%, 33–43% and 22–45%, respectively. Influence of particle size was predominant on the recovery of all metals except Ni. Assessment of the generation of the bioleach residue after bioleaching showed a weight loss of 54–62% due to the dissolution of the metal values from the spent catalyst. The mineralogical study conducted by X-ray diffraction and scanning electron microscopy supports the dissolution of metals from the spent catalyst. Jarosite mineral phase was the dominant mineral phase in the bioleach residue due to the dissolution of the oxidic and sulfidic mineral phases present in the feed spent catalyst.

Bioleaching of metals from spent refinery petroleum catalyst using moderately thermophilic bacteria: Effect of particle size

The present work investigated the leaching potential of moderately thermophilic bacteria in the recovery of metals from spent petroleum catalyst of varying particle sizes. The batch bioleaching experiments were conducted by employing a mixed consortium of moderate thermophilic bacteria at 45°C and by using five different particle sizes (from 45 to >2000 μm) of acetone-washed spent catalyst. The elemental mapping by FESEM confirmed the presence of Al, Ni, V and Mo along with sulfur in the spent catalyst. During bioleaching, Ni (92–97%) and V (81–91%) were leached in higher concentrations, whereas leaching yields of Al (23–38%) were found to be lowest in all particle sizes investigated. Decreasing the particle size from >2000 μm to 45–106 μm caused an increase in leaching yields of metals during initial hours. However, the final metals leaching yields were almost independent of particle sizes of catalyst. Leaching kinetics was observed to follow the diffusion-controlled model showing the linearity more close than the chemical control. The results of the present study suggested that bioleaching using moderate thermophilic bacteria was highly effective in removing the metals from spent catalyst. Moreover, bioleaching can be conducted using spent catalyst of higher particle size (>2000 μm), thus saving the grinding cost and making process attractive for larger scale application.

Optimization of two-step bioleaching of spent petroleum refinery catalyst by Acidithiobacillus thiooxidans using response surface methodology

A central composite design (CCD) combined with response surface methodology (RSM) was employed for maximizing bioleaching yields of metals (Al, Mo, Ni, and V) from as-received spent refinery catalyst using Acidithiobacillus thiooxidans. Three independent variables, namely initial pH, sulfur concentration, and pulp density were investigated. The pH was found to be the most influential parameter with leaching yields of metals varying inversely with pH. Analysis of variance (ANOVA) of the quadratic model indicated that the predicted values were in good agreement with experimental data. Under optimized conditions of 1.0% pulp density, 1.5% sulfur and pH 1.5, about 93% Ni, 44% Al, 34% Mo, and 94% V was leached from the spent refinery catalyst. Among all the metals, V had the highest maximum rate of leaching (Vmax) according to the Michaelis–Menten equation. The results of the study suggested that two-step bioleaching is efficient in leaching of metals from spent refinery catalyst. Moreover, the process can be conducted with as received spent refinery catalyst, thus making the process cost effective for large-scale applications.

Thermophilic bioleaching of spent petroleum refinery catalyst using Sulfolobus metallicus

Abstract The present investigation aimed to study the thermophilic bioleaching of spent catalyst with different size fractions in modified Kelly medium with and without iron supplement using Sulfolobus metallicus. The results obtained showed Ni and Al recovery ranging from 94 to 97% and 54 to 59% respectively, with a lower recovery of Mo and V. The difference in the leaching yield in iron free and iron supplemented growth medium at all size fractions did not show much difference stating iron free modified Kelly medium to be a suitable growth medium for bioleaching of spent catalyst. However, the leaching yield obtained from different size fractions also suggested that the particle size >212 μm could be conducive for leaching of desired metal values without any problem. The redox potential profile during the bioleaching experiments and planktonic cell count ranging from 106 to 108 cells mL−1 showed a luxuriant growth performance of the microorganisms in the experiments in iron free modified Kelly medium. La présente recherche avait pour but d’étudier la biolixiviation thermophile de catalyseur usé avec différentes fractions granulométriques dans un médium de Kelly modifié avec ou sans supplément de fer en utilisant Sulfolobus metallicus. Les résultats montrent que la récupération de Ni et d’Al variait de 94 à 97% et de 54 à 59%, respectivement, avec une plus faible récupération du Mo et du V. Le rendement de la lixiviation dans le médium de croissance avec ou sans supplément de fer dans toutes les fractions granulométriques n’a pas montré grand différence. Ceci indique que le médium de Kelly modifié sans fer est un médium de croissance approprié pour la biolixiviation de catalyseur usé. Cependant, le rendement de lixiviation obtenu à partir de différentes fractions granulométriques suggérait également qu’une taille de particule >212 micromètres pourrait conduire à la lixiviation de valeurs de métal désirées, sans problème. Le profil de potentiel redox lors des expériences de biolixiviation ainsi que le compte de cellules planctoniques de 106 à 108 cellules/mL montraient un rendement de croissance luxuriante des microorganismes des expériences dans le médium de Kelly modifié sans fer.

Studies on the effect of coal particle size on biodepyritization of high sulfur coal in batch bioreactor

Abstract The moderate thermophilic mix culture bacteria were used to depyritize the Illinois coal of varying particle sizes (-100 μm, 100-200 μm, +200 μm). Mineral libration analysis showed the presence of pyrite along with other minerals in coal. Microbial depyritization of coal was carried out in stirred tank batch reactors in presence of an iron-free 9K medium. The results indicate that microbial depyritization of coal using moderate thermophiles is an efficient process. Moreover, particle size of coal is an important parameter which affects the efficiency of microbial depyritization process. At the end of the experiment, a maximum of 75% pyrite and 66% of pyritic sulphur were removed from the median particle size. The XRD analysis showed the absence of pyrite mineral in the treated coal sample. A good mass balance was also obtained with net loss of mass ranging from 5-9% showing the feasibility of the process for large scale applications.