Produção de meio lixiviante por consórcio microbiano para recuperação de metais de baterias de íons de lítio

Abstract

This work arose from a problem: how can we transform the technological waste we accumulate into something valuable? To this end, we focused on cell phone batteries, which, when discarded, not only pollute the environment but also waste precious metals. Among the methods used is leaching - a process that uses an acidic medium to solubilize the metals in the solid sample. The current limitation of this method is the use of inorganic acids, which require infrastructure resistant to these reagents and are not biodegradable. There are leaching studies replacing inorganic acids with organic acids, which are biodegradable, with promising results. The proposal of this work was to produce a leaching medium, rich in organic acids, produced by fermentation using an anaerobic and heterotrophic microbial consortium. Organic acids can have the function of solubilizing metals, of being reducing agents and also chelating agents that contribute to improving metal recovery. In addition to organic acids, a medium with these characteristics can contain phenolic compounds that act as chelating agents. The methodology describes the procedures used in the research for the production of organic acids via anaerobic fermentation by microbial consortia. Initially, the microorganisms were maintained in a suitable synthetic medium, with lactose as a carbon source. The fermentation tests were conducted with two different consortia from industrial effluents, incubated under controlled conditions for 10 days. During this period, variables such as cell growth, lactose consumption, pH of the medium and production of organic acids (mainly lactic, butyric and propionic acids) were monitored. The analysis of these substances was performed by spectrophotometry (DNS) for sugars and high performance liquid chromatography (HPLC) for organic acids. The medium produced presented a higher concentration of lactic acid (approximately 13 g/L), followed by butyric acid and propionic acid. There are studies in the literature that achieved high recovery using lactic acid, which in this work was obtained in higher concentration in the produced medium, indicating the leaching potential of the produced medium. This technology allows the integration of an effluent treatment process into the leaching process, representing a reduction in the cost of raw materials, stages and minimization of environmental impacts.