COMPANY > WESTERN UTILITIES CORPORATION
 
 
WITWATERSRAND BASINS
The project initially focused on the Western Basin of the Witwatersrand Gold Reef, and was subsequently expanded to include the Central, Eastern and Far Western Basins of the Witwatersrand ore body to secure adequate water sources to facilitate economic sustainability.
     
   
 
 
Various studies were conducted on the basins to determine the recharge of water including:
  •  “A strategic management plant for the prevention of water ingress into the underground working of the Witwatersrand Basin” by the Council for Geoscience in June 2005,
  • “Derivation of a numerical model for a cumulative water balance for the Central Basin” by Ferret Mining and Environmental Services in September 2005,
  • “Environmental Impact Assessment of proposed discharge of treated mine water via the Tweelopies Spruit” by Harmony Gold in July 2006,
  • “An investigation into groundwater recharge derived from the Upper Klip River tributaries” by Garfield Krige in October 1999.
  • Golder and Associates conducted a study on groundwater for the Western and Central Basin on behalf of WUC in June 2008.

 
Factors influencing the water ingress or recharge into the basins is mainly from the following sources:
RAINFALL
The area is situated within the Highveld climatic region. The average rainfall in the area ranges from about 900mm on the eastern border to about 650mm in the west which falls exclusively during the summer months, but the streams flow year-round due to the fact that they flow through some of the most industrialised, developed and densely populated land in South Africa. The maximum falls occur in January with events up to 125 to 140 mm per thunderstorm. Due to the rainfall pattern in the area and the direct contribution to the void, causing seasonal fluctuation in the ingress, a fluctuation in pumping rates are experienced in each basin with higher recharge observed during the summer months.
STREAM BED LOSSES
The three important reef outcrops, the Main, Bird and Kimberley Reefs run in a relatively narrow band in an East-Westerly direction. In the Central Basin the reefs, were initially mined by trenching methods, which were subsequently backfilled, and this is now enhancing the seepage from the surface as estimate at by Krige (1999).
NATURAL AQUIFERS
Below a certain level and depending on the permeability of the rock, the ground becomes saturated with water. The upper surface of this zone of saturation is called the “water table” and consists of unsaturated ground. The saturated zone below the water table is called an aquifer and aquifers are huge storerooms of water (refer to figure below).

 
     
 
 
TECHNOLOGY PROCESS
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 – 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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