Predicting the fate of diethylenetriamine in pyrrhotite tailings management

Abstract

Rejection of pyrrhotite (Po) during flotation of copper-nickel sulfide ores can increase the concentrate grade and decrease smelter SO2 emissions. Diethylenetriamine (DETA) is an effective reagent for Po depression during flotation. However, it forms stable complexes with nickel and copper that remain soluble at alkaline pH and cannot be removed from effluent by conventional wastewater treatment. In this study, sorption tests were used to predict the fate of DETA introduced to the tailings area under various conditions. It was found that warm temperature and low pH promoted adsorption. Upon dilution, however, DETA desorbed from the tailings solids in a process that was also promoted at warm temperature, as well as alkaline pH. The behavior of DETA was modeled in a theoretical tailings management area using the experimental sorption data along with geochemical modelling using OLI Studio software to 1) predict the concentration of DETA, Cu-DETA, and Ni-DETA in final effluent and 2) ascertain if copper and nickel concentrations would be expected to exceed regulated limits. The modeling predicts that copper exceedances in the effluent would occur 2–5 months after DETA addition began, depending on the season in which DETA addition began. Decreasing the DETA dose and the ore throughput in the mill (consequently reducing DETA load in the system) limit the likelihood of Cu exceedance in the effluent. However, the most practical method to limit Cu exceedance is to thicken the tailings before deposition to minimize dilution and desorption of DETA from the tailings. These results can be used to guide the development and assessment of a mitigation plan if DETA is used as a reagent in mineral processing.