Thermophilic bioleaching of spent petroleum refinery catalyst using Sulfolobus metallicus

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 mm 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 10(6) to 10(8) cells mL(-1) showed a luxuriant growth performance of the microorganisms in the experiments in iron free modified Kelly medium.