A new minerals processing technique using freezing to treat and recycle wastewater has been developed.
The method, developed in Finland by Lappeenranta University of Technology (LUT), has been designed specifically for the mining industry in an effort to cut back the usage of potable water in operations and allowing for the recycling of more water, according to Science Daily.
Researchers have created a system of freezing waste water to purify it following the formation of a cleaner ice layer.
This clean layer of ice can then be removed from the rest of the wastewater, leaving the remaining wastewater more concentrated.
This method also cuts down on energy usage as the freezing of water — or crystallisation — requires several times less energy than evaporation.
The more energy efficient method then only needs the removal of the cleaner layer to retain potable water.
“In practice, this method could be used by leaving wastewater from mines to freeze in special pools under the open sky, after which the cleaner part could be removed by breaking the ice,” LUT stated.
“After that the ice would be taken away using a machine designed for that purpose to another pool where the treated waste water would be recycled, or undergo further treatment using membrane filtration, for example, for the needs of various processes. Recycling water from the industrial process would reduce the amount of fresh water that is used.”
While this method is not likely to have many practical applications in the Australian mining industry, LUT chemical technology researchers have developed additional equipment for the method including ‘winter simulators’.
“The simulator has been used to study the growth rate of the layer of ice that emerges, and the degree of purity when salt solutions of different concentrations are used. Last winter researchers also took samples on the ice of Lake Saimaa,” researchers said.
"We took samples of both the lake water and the ice and we examined the amount of impurities that they contained. The result was that the lake water contained about ten times more impurities than the ice. Another finding in the research was that the slower the layer of ice grows, the cleaner the ice is. Therefore, the purity of the ice is directly dependent on its rate of growth," Chemtech and LUT professor Marjatta Louhi-Kultanen, who specialised in the study of crystallisation, explained.
Louhi-Kultanen went on to say “future research will be aimed at an extensive examination of different types of waste water pools and the purity of their layers of ice and the implementation of freezing experiments with waste water samples in mining areas”.
Further research into the process will be carried out of over the next three years.