Copper recovery from PCBs by Acidithiobacillus ferrooxidans: toxicity of bioleached metals on biological activity

Abstract

The suitability and limits of bioleaching for copper recovery from printed circuits boards has been stated with new strategies and methodologies. The process has been tested using a continuous column reactor simulating those conditions found at industrial scale. The new strategy developed improved the kinetic reaction rate and overcomes transport limitations for the leaching solution, thus improving copper recoveries from 50 to 80% in only 6 h. This drastically reduced the time required by previous studies to achieve the same copper recovery. Inhibition effects of the biological process due to the release of metals from e-waste has been identified by means of microrespirometric monitoring tests. This systematic study allowed identifying that nickel, copper and aluminum impact the microorganisms’ activity, inactivating them in specific scenarios (depending on the concentration and the time exposed). Including the time exposure as variable, this work demonstrated that metal concentrations that have been reported as non-toxic to microorganisms, resulted toxic when the required leaching contact time was considered. Besides high iron concentrations also produce inhibitory effect on the microorganisms’ growth, despite being the energy source for their metabolism.