7.3
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Coal
7.3.1 |
Grootegeluk Mine
Waste Disposal: There are a number of discard dumps situated around the mine. The status of the various
discard dumps are as follows:
- Dump Nos. 1, 2 and 3: This consists of three separate discard dumps adjacent to each other. The dumps
were constructed using mainly open pit coarse discard and overburden. The dump covers an area of
approximately 76.1Ha and is approximately 60m high and was decommissioned in 1981. The dump has
been capped with sandy material and some vegetation established. The vegetation is sparse however
as a result of the spontaneous combustion taking place within the dump. The capping material is being
eroded away by wind and rainfall and this is allowing the spontaneous combustion to continue. The burning
taking place within the dump is being monitored by the Grootegeluk Mine.
- Dump No. 4: The current production of plant coarse discard is being disposed of on this dump via
a conveyor and spreader system. The discard is being placed via an upper and lower bench conveyor
system. Capping of the outer face of the lower bench system is being carried out using the sandy soil from
the borrow area in close proximity to the dump.
Currently 80% of the plant coarse discard is disposed of on the lower bench and 20% on the upper bench.
At the current rate of deposition of the plant coarse discard, the lower bench has a life of approximately
6.5 years while the upper bench has a life of about 27 years. Grootegeluk Mine intends to change the
deposition rates in about 2010 to 60% to the lower bench and 40% to the upper bench. The Mine is also
planning to move the lower bench conveyor to the in-pit disposal area in approximately 2011 and then the
upper bench conveyor system in 2021. After this date all plant and pit coarse discard will be disposed
of in the open pit. Dump No. 4 is approximately 60m high at present. Grootegeluk Mine is busy replacing
capping material to the lower bench in areas where the previous capping material has been eroded away.
Some areas on this dump are also burning and this is being monitored by the mine.
- Dump No. 5: This dump is still operational and is situated adjacent to dump No. 4. Originally plant discard
was placed at the base of this dump. Pit overburden is now being placed on the dump mechanically with
haul trucks and dozing and the discard is being covered. Burning within this dump is also occurring and
this is being addressed by the Mine by placing of the pit overburden to cover the discard. Storm water
management at the dump is also being investigated to try and prevent erosion of the cover material from
the dump. The dump is approximately 80m high and covers an area of approximately 551.7Ha when
combined with dump No. 4.
- Dump No. 6: This dump was decommissioned in 1987. The dump is approximately 50m high and covers
an area of approximately 87.8Ha. The dump consists mainly of pit overburden with some interburden
having been placed on the eastern side. The dump has been capped with material, however vegetation
establishment has not been implemented. Burning is taking place within the dump and this is being
addressed by Grootegeluk Mine by covering these areas with soil material to try and extinguish the burning
locations. An approved permitted domestic landfill waste site has been established on top of this dump
and is being used by the mine. Two effluent water/silt ponds are located at the toe of this dump to collect
the polluted storm water run off from the plant and to allow for the fine silts to settle out prior to removal.
The polluted water system is being efficiently managed by the mine and the ponds were dry at the time
of the inspection. The mine is also busy with a number of projects in order to better manage and control
all storm water run off from around the various areas at the plants and to use this water as part of the
process system, thereby reducing their requirement for potable water.
- Dump A: Dump A is situated adjacent to Dump Nos. 4 and 5. The dump is being constructed mechanically
using haul trucks and spreading with a dozer. The dump is being constructed with overburden material
from the pit. The dump is currently approximately 10 – 15m high.
- Renoster Dump (Dump B): This is a fairly new dump and is also referred to as Dump B. This dump is also
being constructed using haul trucks and loosely tipping the overburden discard over the side slopes at the
angle of repose. No formal compaction is being applied to the dump. This dump is approximately 40m high
at present and covers an area of approximately 54.6Ha.
- Tyre Dump: This dump has been partially decommissioned and was constructed with interburden and
overburden material from the pit as well as silt material from the de-silting operations. The dump is
approximately 15m high and was constructed with some underdrainage system. The dump has been
capped and rehabilitation test work is being carried out on this dump in order to try and establish the
requirements for the other dumps to be rehabilitated around the Grootegeluk Mine. This dump will need
to be removed in about 40 years time due to the proposed future mining operations at the Mine.
- Backfill Dump: The backfill dump is situated in the pit and commenced on a small scale in 2000. It is
currently being constructed using the interburden from the open pit and then covering with the overburden
from the pit excavations. A large amount of research has been carried out by the mine in order
to determine the optimum operating and placement conditions for the discard in order to try and eliminate
the spontaneous combustion problems associated with this type of work. The discard material is placed
in cells and covered with overburden material at present it is not susceptible to spontaneous combustion.
The cover material is being placed within a period of eight weeks to prevent combustion taking place.
As stated earlier, the mine propose to dispose of part of the plant discard to the Backfill Dump in 2011 and
after 2021 it is proposed that all discard being produced will be disposed of back into the pit. The mine
is actively pursuing the planning and programming to ensure that this can be achieved. Furthermore it is
also being proposed by the mine to mix some ash material from The Matimba Power Station with the
discard being placed into the cells in order to try and further reduce the spontaneous combustion problem.
An input dewatering return water dam and sump has also been prepared in the pit adjacent to the
backfilling operation in order to collect and store the polluted storm water run off water for re-use at
the Grootegeluk Mine.
Life of Mine Discard Tonnage: Currently Grootegeluk Mine produces some 18Mtpa of discard material from
the plant area. This discard is reactive and prone to spontaneous combustion and is being disposed of at
Dump No. 4 at present. There is also approximately 7.5Mtpa of interburden (pit discard) being produced
at the Grootegeluk Mine. This discard is also reactive and prone to spontaneous combustion. This discard is
currently being disposed of in the Backfill Dump in cells as part of the testing programme. At a later stage
Grootegeluk Mine proposes to add ash from the power station to coarse discard in order to try and reduce
the spontaneous combustion problem further. Grootegeluk Mine also currently produces some 13.5Mtpa
of overburden material from the pit workings which is non-reactive. This material is mainly being used to cover
the discard dumps.
Life of Discard Dumps: Based on the current production rate of plant coarse discard material it can be seen
that there is sufficient life on Dump No. 4 lower bench for the plant discard up to 2011, after which the lower
bench conveyor will be moved to the Backfill Dump in the pit for future disposal. Also the Dump No. 4 upper
bench has sufficient capacity for the balance of the plant coarse discard from 2011 to 2021, after which the
upper bench conveyor will also be moved to the Backfill Dump in the pit. From 2021 all the plant and pit coarse
discards will be disposed of in the cell system in the pit. The future planning and targets for the backfill
operations are well advanced to show that this is feasible for the life of the Mine.
Tailings Disposal:
The status of the various slimes dams are as follows:
- Dam Nos. 1 and 2: These ring dyke slimes dams have been consolidated into one operating dam. The fine
coal slimes is pumped to the dam and then deposited via an HDPE pipe around the dam. Holes have been
drilled into the HDPE distribution pipe to deposit the slimes using a spigot deposition method, which allows
for beaching and settlement of the suspended solids. Supernatant water then gravitates to the centrally
located penstock decant system for removal and pumping back to the plant. The solution trench around
Dam Nos. 1 and 2 is concrete lined, and overgrown in some areas. There are no paddocks around the
tailings dam to contain run-off of fine slime discard from the side slopes. Very little fine slime discard runoff
however was noted around the dam. Two step-ins have been constructed around the perimeter of the
consolidated dam. Two test panels for drying of the fine discard have been installed on the western flank
upper step-in of the dam by Jones and Wagener. Erosion gullies have occurred down the slope of the dam
in these areas where decant pipes have been installed. This will require some maintenance. The existing
penstock decant system and pipeline has shown signs of failure on three occasions in the past.
The last occurrence took place early in 2004. Following a camera inspection of the inlet structures
by Fraser Alexander Tailings (“FAT”) the dam operators, it was recommended to replace the system with
a new elevated penstock pipeline and inlet system. This new elevated penstock system is currently being
completed and comprises of a double inlet system on the dam with a steel outlet pipe to the outer edge
of the dam, which changes to a 500mm diameter HDPE pipe which conveys the decanted supernatant
water to the sump. Once the new penstock system becomes operational, the old penstock pipe will be
concrete grouted and the inlets sealed. Seepage was noted along the northern flank of the dam. This is
as a result of the under drainage pipes in this area being blocked and covered with slimes when Dam
No. 4 existed. This seepage must be monitored to ensure that erosion from the slopes of the dam do not
become excessive. The dam is equipped with piezometers which are monitored monthly by FAT.
- Dam No. 3: This slimes dam is currently being re-mined mechanically and the fine coal discard transported
to the plant for blending with the coal supplied to the Matimba. The re-mining of the fine coal discard
is taking place at the rate of 15.000ktpm. Once this dam has been re-mined, the Grootegeluk Mine intends
to convert the dam to a drying bed system whereby the fine coal discard will be deposited into paddocks
for drying and then re-mined for blending with the coal to Matimba on an ongoing basis. As part of this
operation, a conveyor system will be installed to convey the dried fine discard to a mixing plant prior
to conveying to the power station. Test work relating to the drying of the fine discard and the final design
of Dam No. 3 drying beds is currently in progress and is being carried out by Jones and Wagener.
It is proposed to implement this drying process during 2007. This system will result in no further slimes
dams being required at Grootegeluk Mine.
- Dam No. 5: This dam covers an area of 14.8Ha and has a top area of 13Ha at present. The maximum
height of the dam is approximately 3.5m. The dam is currently dormant, but could be used in the case
of an emergency. It is proposed by the mine to start re-mining the fine coal slimes discard in approximately
2007.
- Return Water Holding Facility and Sump: Decanted water from the slimes dams reports to the concrete
lined sump from where it is pumped back to the plant via a floating barge pump in the sump and pipelines.
Excess rain water from the solution trenches and area around Dams Nos. 1 and 2 report to a small earth
holding facility adjacent to the sump. This water drains into the sump or the Mamba Return Water Dam.
The sump and Mamba Return Water facilities are linked with a pipeline.
- Mamba Return Water Dam: The Mamba Return Water Dam was designed and constructed to contain
a 1-in-50 year 24-hour storm event from the slimes dams. The dam is lined with Hyson Cells filled with
concrete. The dam has been equipped with an inlet area on the southern side and a spillway on the
northern side. An under drainage system has been installed below the liner and seepage water is pumped
back into the dam.
Life of Mine Slimes Tonnage: The current remaining LoM at Grootegeluk Mine based on the current
production is approximately 50 years. This excludes the five undeveloped farms which are still available for
mining. With these additional farms the life of mine could extend to over 100 years. The current planned fine coal discard slimes production rate is 60ktpm (720ktpa). Modifications to the plant are being proposed. Once
these have been implemented (anticipated 2010) the amount of fine slimes discard will reduce to
approximately 45.833tpm (550ktpa). The current planned re-mining of fine coal discard from the tailings dams
is at the rate of 15.000tpm (180ktpa). This will increase to 45.833tpm (550ktpa) in 2010 when the cyclic
operated slimes dam is in operation.
Life of Tailings Dams: Based on the tailings dam annual monitoring report prepared by FAT in
November 2004, the planned slimes production rate is shown as 34,000tpm (408ktpa) while the actual
tonnage deposited was in the order of 80,400tpm (964.8ktpa). The top area of the dam is currently
approximately 818m x 515m = 421,270m2. This is based on the survey drawing provided by the mine.
The current rate of rise of the dam is therefore approximately 2.23m/yr. This is similar to the rate of rise given
by FAT in their annual report. The above indicates that the current tailings dams Nos. 1 and 2 have
a limited life (October 2006) at the current production rate of approximately 80,000tpm. The Grootegeluk Mine
is currently investigating alternative deposition options to resolve this problem.
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7.3.2 |
Leeuwpan Mine
Discard and Slimes: Leeuwpan Mine produces two principal sources of mine waste from the Leeuwpan
plant, namely coarse discard and slimes. Coarse discard is produced dry and is transported to the pit for
disposal. The method of disposal within the pit is dependent on the availability of tipping area. The primary
method involves tipping directly within the pit, where the material is placed, spread, levelled and compacted,
thus minimising the potential for spontaneous combustion. When availability in the pit is limited, end tipping
is used, however as lower placed densities are achieved the risk of spontaneous combustion is increased.
The spontaneous combustion has been effectively controlled through compaction and covering of the discard
with overburden. Slimes disposal facilities at Leeuwpan Mine included four slurry ponds where slimes were
deposited in these ponds hydraulically and allowed to settle out of suspension. The heights of these ponds
differ with a maximum height of about 3m. Penstock systems in these ponds allowed for supernatant water
to be decanted into the return water facility. The intention here was that fines, once dried would be removed
and sold to the brick making industry. The process had however been somewhat hampered by the inadequate
drying and consolidation of the slimes material. Consequently, and due to the inability of the additional
capacity to meet targets, Leeuwpan Mine has installed a filter process to dewater the slimes at the main plant
area. This advanced technology of the filter press allows the mine to re-use process water very efficiently and
enables direct disposal of the dried slimes with the coarse discard in the pit areas. Therefore the slurry ponds
are currently dormant with no future intention of slimes being deposited onto these ponds again.
Other Stockpiles: Dried slurry previously removed from the slurry ponds was stockpiled. Solution trenches
were constructed around these stockpiles capturing the storm run-off. The solution does not drain anywhere
and water is left to evaporate. Currently the mine plans to topsoil and grass these stockpiles in order
to rehabilitate them and to control dust. There are topcoal stockpiles located adjacent to the old plant, which
the mine plans to reprocess within the next two years. The discard material resulting from this process will
be placed within the Kenbar Pit.
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7.3.3 |
Tshikondeni Mine
The Tshikondeni Mine produces two principal sources of mine waste, namely coarse discard and tailings.
The mine currently operates two disposal facilities located adjacent to the plant and consists of and old
discard dump which was recently converted into a co-disposal facility and will operate this way for the
remainder of it’s safe operating life. The second co-disposal facility adjoins the old facility and has been
in operation since November 2003. The old facility is currently at the point of decommissioning and closure
and all the tonnage produced on the mine will then be discharged on the new operating facility towards the
end of 2005.
The tailings disposal facility is contained within the discard dump which is continuously raised during
construction to ensure adequate containment of the tailings discharge. The discard is transported
mechanically using vehicles and compacted in 150mm layers to reduce the risk of spontaneous combustion.
The tailings material is pumped into the tailings facility (containment area) via HDPE pipes from the plant in
slurry form and allowed to consolidate. The tonnage split between tailings and discard is currently in the
region of 16% tailings. Currently the tonnages are split between both the old and the new facilities. The old
facility has however nearly reached it’s safe maximum capacity. The new facility was formally designed and
constructed according to good practice and in-line with the industry norm and allowance was made for an
internal drainage system with effluent return infrastructure. The design was approved by all the necessary
authorities and it was agreed that the facility will reach a final closure elevation of 379mamsl. The internal
drainage system will control phreatic levels, increase the effluent return to the plant and create safe and stable
conditions. The seepage collected from these drains is channelled via an HDPE lined earth channel into a single HDPE lined pond (return water dam). From the return water dam the effluent is returned via pumps
located next to the facility back to the plant. The return water dam was constructed with a spillway and was
designed with a total capacity of 27,000m3 and includes an 800mm freebord as required by legislation.
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7.3.4 |
Arnot Colliery
The waste stream generated from the Arnot Colliery operation is discard. The slurry (fines) that is produced
is reprocessed in the plant, no fines are disposed of. The plant produces approximately 10,000 dry tonnes
of discard per month, which is disposed of in open cast voids. The discard is trucked to the open cast pits
and compacted to reduce the risk of spontaneous combustion of the discard. The cost of trucking the discard
is carried by Eyesizwe, while the placing and compacting cost is carried by Eskom. The mine indicated that
there had been no spontaneous combustion problems in the past and no spontaneous combustion problems
were evident on the day of inspection.
A model of the terrain has been developed and a volumetric assessment of the voids has been completed.
There are seven voids that could be utilised for discard disposal. The volumetric assessment indicated that
six voids would be utilised for the Eyesizwe LoM Plan. The capacity of the voids should be assessed on an
annual basis in order to determine whether there is any deviation from the LoM Plan in terms of discard
generated.
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7.3.5 |
Matla Colliery
The waste stream generated from the Matla operation is discard. The slurry (fines) that is produced
is pumped back to the storage stockpiles at the plant and reprocessed. The plant produces approximately
10,000 dry tonnes of discard per month, which is trucked and deposited onto Eskom ash dams. If no trucks
are available, a concrete bay is used to store any discard temporarily. Containment walls have been
constructed around the concrete bay area to contain any surface run off from the stockpile. A capacity
assessment of the ash dams should be undertaken to ensure that there is suitable storage space available
for the discard in terms of the LoM Plan. A deposition strategy and slope stability assessment must also
be undertaken as part of the assessment of the ash dams.
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7.3.6 |
New Clydesdale Colliery
The waste stream generated from the New Clydesdale operation is discard and slurry. The slurry is pumped
and disposed of in the underground workings, while the discard is trucked and disposed of in open cast voids.
The discard is compacted to reduce the risk of spontaneous combustion. The mine indicated that there had
been no spontaneous combustion problems in the past, and no spontaneous combustion problems were
evident on the day of inspection. At closure, a capping layer of material and grassing will be placed on the
discard area. The discard will be placed in a manner that will enable the area to be self-draining at closure.
The mine indicated that, as part of its five year LoM Plan, there are enough voids available to contain the
discard and that the potential for on-surface discard facilities is low. The capacity of the voids should be
assessed on an annual basis in order to determine whether there is any deviation from the LoM Plan in terms
of discard generated.
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