The KNeW process was developed to solve the problem of removing dissolved cations and anions from acid mines drainage (AMD), thus producing excellent quality water at an affordable cost for inland agriculture.
AMD is caused by rainwater permeating through mine dumps which contain vast amounts of pyrite (iron sulfide). This Pyrite reacts with the oxygen from the air to form free sulfuric acid and a residual ugly rust coloured stain where it has been lying. This acidic solution flows down into mine workings and continues to eat away at the dolorites in the reefs underground, which then release a cocktail of elements, including heavy metals and radioactivity. This unpleasant mixture is pumped to the surface to allow underground mining to continue thus creating the “AMD” scourge that is being dealt with in some areas by neutralizing with lime. Neutralizing with lime is not a permanent solution as the product gypsum – which is usually stored in the mine area - will re-dissolve with time and convert back to being a sulfate source for renewed pollution. It is, also, unable to remove any of the sodium present and only partially reduces the sulfate level to 1200ppm – allowable limits are 200ppm.
South Africa uses 65% of its fresh water for this important activity. However, one of the worst pollutants for agriculture in irrigation water is its sodium content. Sodium attaches to clay particles in the soil and renders it impervious to water penetration and to oxygen ingress to keep the vital organic life in the soil alive. In most AMD the level of sodium is around 900ppm and with an average of the SA AMD flow at 350ML/day (Turton 2014). This equates to 115 000 tons of sodium per year being poured into our rivers. As 65% of this goes to irrigation that means that 75 000 tons per year of sodium is applied to our soils because of the AMD discharge – and this effect is cumulative.
In most countries of the world over 60% of all fresh water is used for irrigation –
South Africa uses 65% of its fresh water for this important activity.
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Reverse osmosis (RO) is able to remove all the dissolved solids but this process delivers excellent water at a very high price while creating a brine that has to be stored for ever – at the coast this is returned to the sea but inland this problem becomes severe.
Coal mines mostly produce a neutral effluent (NMD), which contains sodium sulfate and sodium chloride in large amounts. This effluent is created because the soil layer above all SA’s coal mines contains a high level of salt – said to have formed when the sea above the coal seam dried up millions of years ago. When the overburden is disturbed to remove the coal underneath, the salt is leached out by rainwater falling on it and this saline solution then runs down into the opencast or underground workings, from where it is pumped out into the nearest river. When this NMD is disposed of it will also contribute to the destruction of irrigated farmlands just as AMD does.
In the KNeW process, acidity is removed by neutralizing with Soda Ash. Thus, the usual large gypsum precipitate is avoided, and the minor quantities of heavy metal pollutants can be removed as a concentrate and rendered immobile by fixing in cement. This will ensure that they are never released again into the environment.
of the KNeW process
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Trailblazer Technologies was established in 2006 by two partners, who had just exited from long and exalted careers in the plant nutrition industry. Alastair Forsyth had built a substantial business in Ocean Agriculture (Pty) Ltd over 30 years, which was then a leading speciality plant nutrition business in sub-Saharan Africa...
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The KNeW process was developed to solve the problem of removing dissolved cations and anions from acid mines drainage (AMD) so producing good quality water at an affordable cost for inland agriculture.
When the ion exchange plant is run sequentially i.e. first through all the catex CSTR’s and then through the anex CSTR’s the level of free H⁺ in the final catex CSTR is high enough to interfere with the absorption of sodium ions which stops all the Na⁺ being removed from the aqueous phase.