Performance comparison of hydraulic and gravitation HybridICE filters in freeze desalination of mine waters

Abstract

HybridICE is an emerging freeze desalination technology for treating complex mine wastewaters. The technology works on the principle that growing ice crystals reject impurities during freezing. The bottleneck in the freeze desalination processes may be the separation of ice from the ice slurry generated in the freeze engine. Two types of HybridICE filter have been developed to effect ice separation from ice slurry. The two types differ in the design of the filter elements, mode of feeding the slurry into the filter, and the mechanism of separation of ice from the slurry. In both types of filter, an extruded continuous ice column is formed around the filtering element, which has some openings to allow excess concentrated process water to flow out of the filter. However, the driving force in the gravitation filter is buoyancy, while in the hydraulic filter the ice column is driven by the pressure generated from the flow of the slurry. Salt removal and ice yield from each of the filter types was evaluated when a solution of approximately 4% m/m NaCl solution, prepared by dissolving 25.1 kg of NaCl in 674 litres of water, was treated in a HybridICE freeze crystallisation pilot plant. The objective was to describe the operation of the two types of filter and compare their performance. Salt removal and ice yield were found to be higher with the gravitation filter than the hydraulic filter.

Keywords: freeze, desalination, filter, yield, salt removal, ice