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Background

South Africa has a water shortage as it is speculated that the demand for water is already equal to the supply. The limited water supplies are further contaminated with mine water and poorly treated sewage. Acid mine water is widely debated in the media. Furthermore, salinity and metal content of surface and ground water are increasing. Water users downstream of the pollution source are affected by poor water quality and their health is at risk if exposed to high metal concentrations over time.

Acid mine drainage (AMD) has for many years been a major environmental challenge associated with the mining industry. In the Western Basin, AMD decants uncontrolled at a flow-rate of 10 to 60 Mℓ/d. This water (with a pH of 3.2, containing iron/Fe(II), free acid, manganese and uranium) is detrimental to the environment and the health of humans and animals, is unsuitable for irrigation and threatens the stability of the dolomitic rock at the Cradle of Humankind, World Heritage Site. In the Central Basin, the water was at a depth of 540 m below the decant level at the time of writing and is rising at an average daily rate of 0.7 m.

Formation of acid mine water

Mine water typically contains four main components: free acid, iron/Fe(II), several heavy metals and salts (Maree, 2012). The formation of AMD can be attributed to the convergence of the following events:

  • Dissolution of limestone/dolomite up to its solubility level in natural, ingress water;
  • Pyrite oxidation by bacterial action as a result of oxygen-rich ingress water passing through broken pyrite-containing rock within the mine environment and producing acidity, iron/Fe(II), sulphates and other salts;
  • Partial neutralisation of free acid due to natural alkalinity contained in the mined and broken rock media; and
  • Reciprocating contact of pyrites-rich rock with water and oxygen when the water level fluctuates as a result of water being pumped out at a constant rate, whilst the water recharge varies with seasonal rainfall.

High Calcium Neutralisation (HCN) limestone

High Calcium Neutralisation (HCN) limestone is well suited for the treatment of Acid mine drainage (AMD) as it has the lowest cost per unit alkalinity. With very skilled and experienced staff and consultants, we offer a premium product for pre-treatment. HCN Lime can be used at various treatment plants throughout South Africa, as it is a preferred limestone neutraliser.

HCN Lime is a limestone that is produced by selective mining, optically sorting and milling to an ultra-fine powder. With a state-of-the-art laboratory on site, samples are collected and tested on an on-going basis to ensure that every load complies with the required standard. The chemical composition and fineness of the product makes it an ideal limestone for treatment of AMD and Flue-gas desulfurisation (FGD).

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