Green Economy Journal Issue 39

Profile
A Sustainable
Post-Mining Future:
The Reuse Potential of AMD
By Tamsyn Grewar and Kerri du Preez (Biotechnology Division of Mintek)
Mining is a significant driver of the South African economy, however a lack of enforcement
of regulations has left a legacy of environmental and socio-economic impacts, including
uninhabitable land and acid mine drainage (AMD). The AMD produced from our gold
and coal mines contains abnormally high levels of sulphate with relatively low metal
concentrations, which is a uniquely South African problem.
In view of the anticipated number of mines due to close in the near
future, the impact of uncontrolled and untreated decant of acid water
on the environment and communities will be significant and severe,
including:
1. Serious and long-term consequences for community health
2. Contamination of natural water bodies
3. Unavoidable job losses
Currently, South Africa does not have a commercially available,
sustainable solution for the treatment of AMD. We need to look at finding
integrated solutions to solving the most immediate challenges around
AMD treatment, instead of trying to solve this problem in isolation. A truly
sustainable solution should address the Triple Bottom Line: Society, the
Environment and the Economy.
Innovators in the sustainability arena are proactively investigating
new ways of sharing resources between industries. Two of the largest
combined water users in South Africa are mining and agriculture, and a
strategic marriage of these two industries, at least in part, could make a
significant contribution to addressing the damage caused by our mining
legacy.
Over the past few years Mintek’s Biotechnology Division has been
developing a biological process for the treatment of AMD. Mintek’s
cloSURE TM technology employs biological sulphate reduction, facilitated
by a complex consortium of microbes. It has been developed as a low-cost,
low-maintenance technology for treatment of AMD, and is particularly
suitable for treating small point sources in remote locations that lack
services and infrastructure, such as mines after closure.
cloSURE TM takes a three-pronged approach to mine water treatment,
by removing metals, increasing pH and removing sulphate to below
limits required for safe discharge or reuse. It also produces relatively small
volumes of waste in comparison to current treatment alternatives, such as
high density sludge processes. The process overcomes the obstacle of high
substrate costs by utilising organic waste products, including cow manure.
cloSURE TM consists of a number of stages. AMD typically has a pH
between 2 and 3. Currently a partial neutralisation step is required, since
the sulphate reducing bacteria have a lower pH limit of around 5. However
the cloSURE group at Mintek is undertaking research to overcome this
issue so as to eliminate the pre-treatment step and the associated costs.
Mintek’s pilot plant located at a coal mine in Mpumalanga
The pre-neutralised AMD is then treated in two successive steps. Stage 1
employs anaerobic sulphate reduction, while Stage 2 facilitates aerobic
sulphide oxidation. Stage 1 does most of the heavy lifting in terms of water
treatment, by removing sulphates, metals and further neutralising the
effluent. Stage 2 is primarily a polishing step to remove excess sulphide and
any remaining metals of concern prior to re-use.
To date, the process has been piloted at a local coal mine treating 300L
of AMD a day. Preliminary data shows that the treated water would be
of a suitable quality to irrigate a number of hardy crops grown on the
Mpumalanga Highveld, including maize, wheat, potatoes and sorghum.
The next phase will demonstrate the treatment and re-use of the water in
irrigated crop trials with local partners.
The primary objective of the cloSURE TM process is to produce treated
water that is fit for re-use in irrigated agriculture. An alternative water
resource and rehabilitated mine land has the potential to create agriindustrial
hubs which would promote entrepreneurship, and employment
in local communities.
The broader vision of the project encompasses skills development and
new inclusive economies around mine water in the Mpumalanga region.
Such an approach to protect community health and water resources,
while promoting socio-economic development of affected communities,
has the potential to change the post-mining landscape of South Africa.
Green Economy Journal - GreenEconomyOnline
greeneconomy.media
9