Bioleaching is considered a sustainable and effective alternative to conventional micromachining and extracting processes for recovering valuable metals from electronic waste. Nevertheless, the industrial scaling-up of these applications is limited by several factors.
Among these factors, the use of free cells and low microbial density have been reported to reduce process efficiency. Recent research has therefore focused on bacterial immobilization on different support materials as a solution for increasing microbial density inside the bioreactor and protecting microorganisms from toxic compounds. Furthermore, biomass immobilization facilitates biomass replacement whenever required. The increasing amount of metals in the solution is also a factor to be controlled, as it can inhibit bacterial activity.
This study set out to assess the suitability of two hydrogels, polyvinyl alcohol (PVA) and biocellulose (BC) as support materials for Acidithiobacillus ferrooxidans (A. ferrooxidans) immobilisation, and to analyse the effectiveness of the active material generated for use in metal bioleaching processes. In addition, an assessment was conducted of the influence of the amount of dissolved copper (0-20 g Cu2+/L) on the time required for complete Fe2+ oxidation to Fe3+.
The two hydrogels tested, PVA and BC, were viable as support materials for A. ferrooxidans immobilisation. Both active materials successfully transformed all the Fe2+ contained in the nutrient medium to Fe3+. Nevertheless, BC was specifically selected for further studies because of its higher efficiency (shorter oxidation time needed for complete iron transformation), longer integrity maintenance, and higher resistance to dissolved copper up to 20 g Cu2+/L.