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.