Passive metalliferous mine water treatment with recycled concrete aggregate

Metal-impacted water is generated by most metal mine facilities, usually in perpetuity. Responsible and legal mining requires that when discharged this water must meet water quality standards that are protective of human health and the environment. However, active treatment at most mine sites is difficult and expensive to maintain, particularly after the cessation of operations. This paper reports the results of a decade-long project that has demonstrated a successful method of long-term passive treatment of metalliferous mine water using universally available recycled concrete aggregate as the treatment medium. The method is to pass the metalliferous water upward through a large bed of recycled concrete aggregate with particle size between 10 mm and 40 mm, retain the water in the bed for between 4 to 8 days, and discharge of the treated water into a surface pond above the recycled concrete aggregate bed. This provides long-term removal of toxic and deleterious metals from the mine water, particulate filtration to retain the removed metals in the treatment system at non-hazardous levels, and oxidation and polishing before final discharge. The long-term testing presented in this paper demonstrates that when the passive treatment facility conforms to this design specification there is always a retention time which achieves the desired treatment of metals.