The challenge
From a sustainable development
perspective, Anglo American believes
in conducting business with an eye to
the needs of the future. This means
minimising the negative impacts of
operations on the environment and
local communities at all stages of the
mining cycle.
The disturbance of land is an
inevitable consequence of opencast
mining and once mineral resources
have been extracted, overlying spoils
are returned to the void. The affected
area must be restored to an agreed
land capability and land use at the
mine closure to limit the negative
impacts of operations on the
environment and local communities.
Conventional rehabilitation usually
focuses on the shaping of spoils to
facilitate free drainage, covering them
with sub- and topsoil, fertilising and
finally seeding. Rehabilitation backlogs
and sub-standard rehabilitation would
result in serious cost, environmental
and community implications – all of
which have a direct bearing on Anglo’s
core business and licence to mine.
Land rehabilitation is extremely
costly, which is why Anglo aims to
rehabilitate as much as possible of the
affected land during a mine’s
operational life. This generally results
in a better rehabilitation outcome,
reduces costs and post closure
liabilities.
The initiative was largely driven by
an industry, and in fact, global
shortage of topsoil, both in terms of
quantity and quality. Topsoil is a
complex micro-ecosystem and the
planet has little more than 3 ft of it
spread over its surface. According to
the UN, the rate of loss is
10 – 100 times faster than that of
replacement, which takes place over
hundreds of years. This poses a real
and significant threat to food
production for the world’s growing
population.
According to an article published in
Time Magazine
, a rough calculation of
current rates of soil degradation
suggests we have about 60 yr of
topsoil remaining. Some 40% of soil
used for agriculture around the world
is classed as either degraded or
seriously degraded. The latter means
that 70% of the topsoil, the layer
allowing plants to grow, has been
depleted.
The solution
Fungcoal breaks down and liquefies
coal that has been exposed to the
elements, helping to speed up the land
rehabilitation process. When
accompanied with other
microorganisms, the fungi generate
humic and fulvic acid-like substances:
natural soil organic fertilisers that are
regarded as the building blocks of soil
fertility and plant life.
Humic and fulvic acids have two
important properties. Firstly, they
promote soil microbe and plant growth
and, secondly, they significantly
alleviate the compaction or hardening
of rehabilitated soil – one of the
greatest rehabilitation challenges
facing the industry.
As discard coal is used as a medium
on which certain grass species need to
grow, its application significantly
reduces the need for topsoil, while at
the same time turning what is
regarded as waste into a useful
product. The technology has been
trialled at four of Anglo American’s
coal mines and has shown very
positive results, both on rehabilitated
mining pits and coal discard facilities.
Trial sites currently cover 30 ha.
The Fungcoal system involves the
identification of a suitable weathered
coal that can serve as a carbon source
to support microbial growth and be
readily broken down and converted
into humic and fulvic acid-like
substances by these microorganisms
(mainly fungi, but also bacteria). A
mixture of this weathered coal
material, coal degrading
microorganisms, grass seeds and
fertilisers are then applied to poorly
rehabilitated soil, or directly onto
opencast spoils or discard dumps.
Natural root growth promoting fungi
and bacteria are able to establish and
populate poorly rehabilitated soil.
Results
Since 2006, a number of trial patches
have been established on a range of
opencast rehabilitated land, as well as
discard facilities at the Kleinkopje,
Greenside, Landau and New Vaal coal
mines. Success has been dependent on
the procedure used (different types of
microorganisms, fertiliser regimes,
weathered coal source and content),
with some patches performing
extremely well, some performing
moderately and some failing. Figure 1
shows untreated land and Figure 2
shows treated land at Kromdraai in
South Africa.
Two principal types of trials have
been performed. One involves the
self-cladding of discard facilities –
applying the Fungcoal directly onto
discard without the use of any top- or
subsoil and without a weathered coal
substrate.
The other involves opencast
rehabilitated land with the aim of
improving the quality of existing
rehabilitation in terms of organic
content and decompaction of soil. The
aim is also to experiment with
establishing plant growth where
topsoil is scarce or absent.
Of the dump self-cladding trials,
one was a failure as the initial growth
of the first two seasons withered
during subsequent seasons and has
mostly died off. The other dump trials
were more successful, with one of the
earlier trial patches from 2006 being
very successful, showing soilification
of the discard material down to a
depth of 0.5 m in 2014.
The trials on opencast rehabilitated
and un-rehabilitated land have shown
similar results with some trial sites
being very successful, others less so.
Again, this has depended on the type
of weathered coal locally available and
on the other factors mentioned above.
It has been shown that the weathered
coal from the Kromdraai Section of
Landau coal mine is eminently suitable
for use in the Fungcoal system and this
weathered coal is associated with the
best results to date.
Apart from accelerating and
improving the quality of rehabilitation,
the application of Fungcoal – following
approval from the relevant regulators
– will have far-reaching cost benefits.
While these numbers cannot easily be
quantified in the product’s application
for opencast pits owing to variable
100
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World Coal
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August 2015
