East Rand company The Wren Group is launching a hydrothermal
sulphate removal (HSR) process which, it believes, would be a
significantly more cost-effective method for the treatment of acid
mine drainage and industrial effluents compared to conventional
methods, such as reverse osmosis and electrodialysis.
Financial director Sarah Zipp says the process can provide potable
water at an operational cost of 80 cents to R1,60/m3; and a total
cost, over 20 years, including capital cost, of R1,80 to R2,60/m3
– the price touching the upper numbers if the mine water is
extremely contaminated.
These figures exclude costs asssale of used mineral grinding millociated with the pumping of water to
the surface, sludge-disposal costs and the benefits from the
possible sale of the anhydrite as by-product to the process. (One
example of anhydrite use is in cement production).
Various parties have shown interest, including the Water Research
Commission, the Department of Minerals and Energy (DME)aluminium sulphate powder producers and the
Chamber of Mines, as well as several gold- and coal-mining
companies.
Zipp reports the process’s biggest advantages not only to be
derived from the cost, but also from the absence of toxic
byproducts as a result of the process, as well as the water quality
produced meeting World Health Organisation and South African Bursample request letter for attending a seminareau
of Standards measures for potable water.
Essentially the process treats mine water that is high in sulphates
as a result of the mining process.
Sources of acid mine drainage include surface run-off from open-pit
mining, waste rock dumps from metal mining, and also tailings
deposits.
In the Wren process, the water is pretreated, raising the pH level
by adding lime, dropping out most, if not all, of the heavy metals
in the hydroxide form, explains Zipp.
Again the pH level is reduced, this time to neutral, following
which the water is taken through to a heat-exchanger and heated to
about 140 ˚C.
The water is run through a precipitation process, and injected with
steam to increase the temperature to 150 ˚C, following which
it is subjected to a liquid separation process, finally
precipitating out the calcium and sulphate in the anhydrite
form.
This internationally-patented process makes use of low-cost fuels
such as coal, and can be automated easily, explains Zipp.
She believes the possible market for a process such as this is
substantial. In the central and eastern basin of Gauteng alone the
mine water in need of treatment is estimated at 200 to 300
megalitres a day.
However, Zipp says Wren is not in a position to take the project
further without assistance.
„The next step forward would be the involvement of government and
private sector companies. „Ultimately, we envisage a joint-venture
company to be formed by all key participants, such as the mines,
technology suppliers, and other supply companies,“ she adds.
DME also has an interest, as this department has to take
responsibility for the many abandoned mines in the country.
Wren will construct the first pilot plant, to be operational early
next year, at ERPM gold-mine on the East Rand.