Investigation of the Fate of Wastewater Phosphorus within the Processed Kimberlite Containment Area at BHP's EKATI~(TM) Diamond Mine

摘要

At the Ekati~(TM) diamond mine, located 300 km northeast of Yellowknife, wastewater consisiting of sewage from the housing facility, flow from the vehicle washing bay and wastewater from neighbouring worksites was previously collected, treated and discharged into a local lake. The discharge was observed to have negative impacts on the lake which included an increased algae growth and lowered dissolved oxygen levels in the lower portion of the lake as early as 1997. Part of the cause of this impact was believed to be increased phosphorus concentrations in the lake originating from the treated wastewater discharge. There was concern that the increased phosphorus levels may affect downstream lakes, in the form of eutrophication and decreased winter dissolved oxygen concentrations. To minimize the impact, BHP Diamonds Inc. relocated the discharge of treated wastewater to its processed kimberlite containment system. The purpose of this study was to understand the fate of phosphorus in the treated wastewater when added to the processed kimberlite containment area. The study involved conducting laboratory investigations to develop adsorption isotherms for phosphorus on the processed kimberlite. The phosphorus adsorption isotherms can be used to evaluate the fate of phosphate in the processed kimberlite containment area. The effects of parameters such as temperature, coagulant, and flocculent addition were determined. The quantity of phosphorus adsorbed per gram of kimberlite was found to be low. At a pH of 7.0, 0.5 kg of kimberlite is needed to reduce the concentration of phosphorus from 10 mg/L to 0.1 mg/L in a volume of 1L of wastewater (i.e. 0.2 mg phosphorus removed/g of dried kimberlite). Even though the kimberlite adsorption of phosphorus is low, there is more than adequate kimberlite available in the tailings to remove the phosphorus loading when the pH is 7.0.