Recovery of Metals from Mine Wastes: The Effect of Biochar–Fe Composites in the Immobilization of Arsenic

Mine wastes are a major environmental problem of main mines activities. However, in recent years, related to the circular economy strategy, some of these wastes have been considered as secondary source of raw materials. Generally, metal’s content show low concentrations and their recovery made the development of cheap and sustainable technologies necessary. The main objective of the present research is to study the potential recovery of zinc from one mine waste (MW) originated in an old zinc/lead mine exploitation. Two biochar–Fe composites (BM–Fe and HM–Fe) were used as catalysts in the leaching of zinc and copper. Biochars were obtained by pyrolysis of pruning waste (BM–Fe) or hydrochar from pruning waste (HM–Fe), impregnated with 5 wt% ferric sulfate. The use of the two biochars did not improve the amount of zinc recovered, but was able to reduce, significantly, the arsenic leaching, promoting its immobilization in the final residue. Graphical Abstract: [Figure not available: see fulltext.]