Challenges and opportunities in the application of bioinspired engineered nanomaterials for the recovery of metal ions from mining industry wastewater.

Heavy-metal-bearing wastewater is among the most formidable challenges the mining industry currently faces in maintaining its social license to operate. Amongst the technologies available for metal ion adsorption, bioinspired engineering nanomaterials have emerged as one which exhibits great promise. However, current processes used for the preparation of adsorbents (including nanoscale activated carbon and biochar) represent a source of adverse impacts on the environment. In contrast, the application of biogenic-nanoparticles, i.e., those derived from processes catalysed by microbiota, has received significant attention in the last few years. Coupled with this, the use of naturally occurring reagents is of major importance for the sustainability of this emerging industry. This paper analyses the life cycle assessment (LCA) of the synthesis of adsorbents derived from agricultural wastes. Moreover, rather than simply recovering the ecotoxic metals from wastewater, the potential to valorise dissolved metals into high-value metallic nanoparticle products is discussed. LCA analysis revealed that the adsorbent had some adverse impact on the environment. The agricultural wastes contributed 27.86% to global warming, 54.64% to ozone formation, 33.06% to fine particles, and 98.24% to marine eutrophication. Mining wastewater is an important, and largely currently unexploited, source of metal value. However, the often-low concentration of such metals dictates that their conversion into high-value products (such as engineered nanoparticles) is an important new research frontier. Within this the use of biosynthesis methods has emerged as having great potential due to a range of beneficial attributes, including low cost, high efficacy and/or environmental compatibility.