The potential effects of alkaline mill effluent on tailings management facility water quality and implications for closure

Lime is commonly used as a depressant for flotation of non-ferrous ore such as molybdenum and copper. Addition of lime during the flotation process increases the alkalinity and pH of mill effluent, consequently reducing dissolved concentrations of some metals such as cadmium, copper, manganese, nickel, lead, and zinc by metal hydroxide precipitation and co-precipitation. This process is also the basis of lime treatment, which is the most common type of treatment for mine-influenced water. Bench scale tests showed that lime addition in the mill circuit can reduce concentrations of cadmium in tailings slurry and supernatant. The tests indicate that coprecipitation and adsorption interactions are critically important in this system. This is further supported by water quality data from an operating mine site. Neglecting to account for metal hydroxide formation, co-precipitation, and adsorption interactions enabled by cycling water through the mill can cause model predictions for the operations period to overestimate dissolved concentrations of some constituents in tailings management facilities (TMFs). Similarly, using operations phase TMF water quality to inform post-closure predictions could result in underestimation of dissolved concentrations since improvements in TMF water quality due to the mill process are unlikely to persist after closure.Non UBCUnreviewedOthe