Spray freezing decontamination of tailings water at the Colomac Mine

Abstract

A field pilot scale experiment was conducted to evaluate the efficiency of spray freezing to remove dissolved chemicals from the tailings lake water at the Colomac Mine, NWT. Cores of the spray ice were then taken to the University of Alberta. The distribution of chemicals in the ice cores were determined, then a 1 m long core sample was thawed in a controlled manner to simulate thawing in the field to examine the concentrations of chemicals in the melt water as the columns thawed. For the pilot scale project approximately 30% of the water pumped was frozen, with the remaining water returned to the tailings pond as runoff. Analysis of the water collected from an ice core melted under controlled laboratory conditions showed dissolved chemical removal of 87–99% (depending on the chemical species) after 39% of the spray ice column had melted. Arsenic concentrations were reduced from approximately 19 μg/L to approximately 5 μg/l. Cyanide had 99.2% removal but still remained at a concentration of approximately 350 μg/L. Approximately 60% of the treated water released at the end of the melt contained only 1–17% of the dissolved species. This melt water at the end of thaw would only require minor further treatment, which may significantly reduce overall treatment costs.