Effects of key parameters in recycling of metals from petroleum refinery waste catalysts in bioleaching process

Abstract

Environmental laws concerning spent catalysts disposal have become increasingly more severe in recent years. Due to the toxic nature of spent catalysts, their disposal can pollute the environment. The recovery of heavy metals decreases the environmental impact of the waste catalysts and the recycled product can be further used for industrial purposes. Bio-hydrometallurgical approaches, such as bioleaching, appear to offer good prospects for recovering valuable metals from spent refinery catalysts. Currently, identifying and modifying the parameters that influenced the efficiency of bioleaching is important for industrial sector. The biological system can be further improved through optimizing the bioleaching parameters, such as the nutrient culture media, amount of oxygen and carbon dioxide, pH, temperature, inoculum, metal resistance of microorganisms, chemistry of solid waste, particle size of solid waste, solid liquid ratio, bioleaching period, size of substrate, shaking speed, and also the development of more effective bioleaching microorganisms. In our previous review (Asghari et al. in J Ind Eng Chem 19:1069–1081, 2013), information available in the literature on the bioleaching fundamentals of spent catalysts with a focus on recent developments was reviewed in detail. In this study, the effects of most important factors that influence an efficient bioleaching process of spent refinery catalysts with the hope that these valuable and useful data can help determine the most efficient process will be discussed. The details of metals recovery with a focus on the effects of different variables in the bioleaching such as reaction time, pulp density, initial pH, particle size, nutrient concentration, temperature and buffer will also be presented.