The Effect of Aeration and Stirring on Metal Recovery from Printed Circuit Boards

Abstract

The present research was aimed at studying the bioleaching processes used to mobilize non-ferrous metals (Cu, Ni, Zn and Al) from waste printed circuit boards (PCBs) with biologically generated ferric iron-containing sulphuric acid solutions. The used bacterial strains Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans were recovered from an acidic mine drainage. These bacteria were sub-cultured and acclimated in medium containing PCBs. Biologically oxidized Fe 3+ from Fe 2+ in presence of A. ferrooxidans caused the mobilization of metals. This study evaluated the influence of three different conditions on Cu, Zn, Ni and Al bioleaching from PCBs by metal-adapted mixed bacterial culture of Acidithiobacillus ferrooxidans and A. thiooxidans. The experimental results demonstrate, that aeration and stirring had pronounced effect on copper, nickel and zinc bioleaching. It was revealed that the highest Zn (76%) and Cu (40%) recovery was obtained under combined conditions of both stirring and aeration. For nickel recovery (63%) aeration was found to be the most effective. On the other hand, no investigated condition was effective for Al bioleaching. The pH changes in all three different conditions during bioleaching were very similar and on day 7 reached pH over 2. It is concluded, that mixed bacterial culture of A. ferrooxidans and A. thiooxidans were able to grow in the presence of electronic waste. The results also pointed out the importance of Fe 3+ on Cu, Zn and Ni recovery. Our experiments confirmed significant influence of different conditions on ferric ions concentration. Aeration had the most pronounced effect on the rapidly increase of Fe 3+ concentrations after 12th day and reached the highest concentrations at the end of experiment.