Abstract
Several thousand tons of plastic are produced globally for pharmaceutical blister packages every year, leading to an expected consumption of over 2.8 million tons by 2026. Comprising a complex multilayer structure, blisters cannot be recycled in conventional recycling processes, leading to a loss of aluminium and valuable polymers during incineration and landfilling. As a promising secondary source of aluminium, new recycling strategies need to be developed to selectively separate the different layers. In this study, three types of blister packaging materials consisting of 13–68% (w/w) aluminium were investigated regarding aluminium and polymer recovery by using biogenic sulfuric acid for bioleaching. Waste elemental sulfur from biogas desulfurisation was assessed for biogenic sulfuric acid production by the two sulfur-oxidizing bacteria Acidithiobacillus thiooxidans and Acidithiobacillus caldus and compared to commercial elemental sulfur. For biogenic sulfur, higher sulfate production yield (320 mM), lower pH-value (pH = 0.56) and complete sulfur oxidation within 14 days was observed when compared to commercial sulfur. Application of a more concentrated biogenic acid (pH = 0.22) led to more effective and complete (∼100%) aluminium bioleaching up to 7.5% (w/v) blister waste within 7–9 days of incubation compared to 83% and 63% chemical leaching efficiency of transparent and white blisters using commercial sulfuric acid at the same pH, respectively. In addition, the plastic fraction after bioleaching was characterized and tested regarding re-processability. Results showed that sulfur from a biological origin can be oxidized faster by bacteria and biogenic acid is more effective in aluminium bioleaching compared to commercial sulfuric acid. Furthermore, results indicated that the plastic material is suitable for re-processing making this process an economically and environmentally friendly treatment option.
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