Revalorisation of Fine Recycled Concrete in Acid Mine Water Treatment: A Challenge to a Circular Economy

Currently, only 50% of concrete produced from construction and demolition waste is being recycled in Europe. This falls short of the European Union's target of 70% by 2020. Moreover, this figure only considers coarse fractions (>4 mm), as technical issues arise when using fine fractions. In pursuit of a complete circular life for recycled concrete, this investigation explores the potential use of fine fractions to enhance the physicochemical conditions and reduce the element concentration of acid mine drainage. Two trickling sets were prepared using a filter holder, with acidic waters passing through a layer of recycled concrete aggregates. Results revealed an immediate increase in water pH to neutral levels, a reduction in solution oxidation, and the complete, or near-complete retention, of potentially toxic elements by the substrate (with retention percentages of over 99.9% for Al and Fe, between 43.1% and 61.1% for S, over 91.1% for Zn, and over 99.1% for Cu). The experiment also showed a significant increase in Ca levels (tripling the initial value) and some Mg in the water, which could promote the subsequent precipitation of carbonates and the retention of trace metals. In summary, this study demonstrates the effectiveness of using recycled concrete aggregates in a laboratory setting. Further investigation is necessary to evaluate the feasibility of implementing this technique at the pilot scale.