Pyrrhotite (Po) is an abundant iron sulphide mineral that occurs in nickel sulphide deposits, such as those in Sudbury, Ontario. Due to its low economic value and its high contribution to SO2 emissions produced during smelting, Po is rejected into the tailings during mineral processing. The rejection of Po can be accomplished in several ways, including by using chelating agents such as diethylenetriamine (DETA) as depressants in froth flotation. DETA can significantly improve nickel recovery and concentrate grades; however, it is challenging to manage in the tailings area. DETA, when used, forms stable chelates with Ni2+ and Cu2+ which cannot be precipitated with traditional lime treatment. Once in the tailings management area, DETA can desorb from Po solids upon dilution or with changes in temperature and/or pH. The species chelated with DETA can also change depending on the availability of the ions in solution. The use of DETA can, therefore, lead to concentrations of Ni2+ and Cu2+ in final effluent that exceed the regulated amounts. Due to the challenges with chelated metals in effluent, it is recommended that the chelating agents be removed from the tailings stream before it is deposited. Although DETA‐metal chelates are rarely discussed in the literature, some mitigation and degradation strategies investigated by industry are discussed in this review. DETA degradation methods are also discussed, with the primary focus being on biodegradation. DETA has generally been described as recalcitrant to biodegradation although there is evidence that proper acclimation should allow bacteria to develop DETA degradation pathways.

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