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TECHNOLOGY PROCESS
Water Sewage & Effluent [ September 2008]
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Zero-effluent discharge: heavy metals and
sulphates are removed through chemical precipitation; waste is
recovered as by-products through a pyro-metallurgical process.
Pilot process
The pilot process could be simplified as follows:
1. Entry point: Raw water enters the SAVMIN (Mintek) and Gypslim
(CSIR) plants.
2. Technology selection: The two plants are running in parallel
to test the process that delivers the most effective and viable
treatment results. Only one technology will be selected for the
commercialisation of the plant. They both produce SANAS Class 2
(industrial-type) water and a sludge by-product.
3. Pyro-metallurgical process: The sludge by-product is treated
through a pyro-metallurgical process in the by-product recovery
plant (also a CSIR technology).
4. Recovery and reuse - Gypslim: Through Gypslim technology, CaO,
CaS and BaCO3 is recovered and reused in the process.
5. Recovery and reuse - SAVMIN: Through the SAVMIN process,
Al(OH)3 is recovered and reused in the process.
6. By-product recovery plant: The by-product recovery plant will
produce metal sulphides, H2SO4 and high-grade precipitated
CaCO3.
The project's first phase entails the pumping of raw water from
the Western Basin to a water-treatment plant. The area for this
plant still needs to be determined. Eventually, the expansion
phase of the project will encompass the pumping of raw water
from the Western, Central and Eastern basins to a collection
infrastructure site and then to the water-treatment plant.
According to Schoeman, the plant will make use of a chemical
precipitation process that has the capability to remove heavy
metals and sulphates from the contaminated water.
The project ran three pilot plants at the Harmony No 8 shaft,
which is located near Randfontein, to demonstrate and test the
viability of the available technologies.
The SAVMIN plant - a Mintek patent Ð that has been
operational since April 5 2008 treats 4 m3/hour of AMD to
industrial standard.
The Gypslim plant (CSIR technology) has been in operation
since March 5 2008 and processes 1 m3/hour of AMD to industrial
standard.
The by-product recovery plant, also developed by the CSIR,
operational since March 10 2008, processes and isolates
by-products produced by the SAVMIN and Gypslim processes through
a pyro-metallurgical process. The SAVMIN and Gypslim plants were
benchmarked against each other to determine the most feasible
treatment results. The Gyplim technology was finally selected as
the treatment solution for the final commercial plant.
Both plants had been taken into a 30% engineering study and
subsequently a detailed technological agreement will be signed
with the selected party. The selected technology will now be
developed into a 10% engineering study and bankable feasibility.
The by-product recovery plant, however, will be a definite in
the process. According to Schoeman WUC's objective is to create
a "zero effluent discharge plant". The by-product plant will
convert various by-products back into raw materials by reusing
them in the process or selling them to the market, thereby
reducing the overall processing costs of the plant. "We do not
want to generate another tailings dam," Schoeman said. "All
waste streams will be converted into something useful. This is
the objective." A no-waste policy further adds to the
sustainability of WUC's water treatment project. It is a
visionary scheme that will provide a sustainable case study once
it gets off the ground. |
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