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UCT RESEARCH REPORT '11
42
a research-led university with
a global reputation, innovation
is at UCT’s core. The university seeks
to stimulate the creation of knowledge
and ultimately the growth of the South
African economy by fostering business
development and job creation through the
commercialisation and implementation of
intellectual property (IP); thus transforming
society for the benefit of all.
From water management to the development of high-
tech medical devices, UCT’s research and innovation
is having a real and important impact on the lives of
people, by improving processes, boosting health care,
and developing the economy.
Putting a freeze on the
problem of waste
A case in point is water management. This is a field that
has become a very important, if not the most important,
sustainability issue within the global energy and mining
resources industries. In South Africa, for example, more
than R200 million will be needed just to halt acid mine
drainage, which is affecting the western, central and
eastern basins of the Witwatersrand goldfields area, as well
as water quality in the Vaal and Crocodile river systems.
The level of underground acidic water in the Johannesburg
region has also risen to within 500m of the surface and
more brine is produced than companies can recycle,
mainly through evaporation processes. Besides the fact that
these processes are highly energy intensive, they generate
non-recyclable waste materials, and this makes it a non-
sustainable solution from an ecological perspective.
The answer in the long run may lie in eutectic freeze
crystallisation (EFC) and the research conducted by the
Crystallization and Precipitation Research Unit under the
leadership of Professor Alison Lewis. “After five years
of intensive research on EFC, the unit is able to convert
polluted water into 99 percent re-usable material, that is,
water and chemical salts,” says Professor Lewis. These
results have been positively received by industry and in
March 2011 the Coaltech Resources Association – one of
the major funders of this research – announced its plans
to build a R10 million pilot plant, which would be able to
purify 1 000kL/day of brine.
Eutectic freeze crystallisation works on the principle that,
when a waste stream is cooled to a specific temperature,
ice as well as salt will crystallise out of the solution. The
ice, being less dense than the salt, floats to the top of
the crystalliser, while the denser salt sinks to the bottom,
along with waste materials, and thus the process of ice
crystallisation excludes most impurities, resulting in pure
water when melted.
A typical brine treatment scheme is shown in the flowsheet
below.
“A treatment process needs to focus on both the solid waste
component (salts) as well as the liquid component (water)
of the wastewater stream, and so we treat wastewater as
a resource. This is the only way a truly sustainable and
From the lab to the market:
cutting-edge innovation
Figure 6
Typical eutectic freeze crystalisation brine treatment scheme
Feed
Stage 1 at -0.5oC
preconcentration
Ice
Stage 2
at
-0.9oC
Stage 3
at
-1.4oC
Ice
Ca
2
SO
4
2H
2
O
98.0% pure
Na
2
SO
4
10H
2
O
96.4% pure
Ice
Waste
As