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‘Unique’ AMD solution a revenue earner rather than a cost

Trailblazer Technologies director John Bewsey discusses the unique aspects of its patented KNeW process for treating acid mine drainage.

21st March 2014

By: Chantelle Kotze

  

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Local chemical engineering technology company Trailblazer Technologies’ patented KNeW process for treating acid mine drainage (AMD) is unique in that it provides a return on investment, as opposed to being an added cost to the mining process, says Trailblazer Technologies director John Bewsey.

Unlike the existing processes used to clean AMD in South Africa, the KNeW process does not rely on the revenue from the sale of water for its economic justification.

The KNeW process, an acronym for the phrase ‘Potassium Nitrate ex Waste’, instead cleans AMD by removing all the dissolved salts and converts them into beneficial raw materials, which are saleable in the agriculture and industrial markets.

The sale of the end product covers all of the capital expense and operational costs, Bewsey reiterates.

Other benefits of the KNeW process is that it uses little power and creates much-needed jobs in the chemicals processing industry.

In the KNeW process, the polluted wastewater from mines is neutralised and filtered to remove coarse particles and precipitated heavy metals. The water is then pumped through an ion exchange battery to remove all the dissolved ions, leaving the water of any designed quality.

Besides the sale of the potassium nitrate derived from the nitric acid catex regenerant, other valuable and commercially pure products produced through the regeneration mixes from the ion exchange operation in the KNeW process include ammonium sulphate, dolomite and sodium chloride.

Viable End Use
The KNeW process, which aims to produce zero effluent, is one of the few processes available that can beneficially remove the worst and most difficult pollutant to deal with – sodium.

This is opposed to all of the other AMD treatment processes, which extract the pollution salts from the AMD, but produce valueless or troublesome brines and solids.

Bewsey says to partially or completely clean AMD for drinking purposes is misguided as State-owned utility Rand Water supplies over 4 100 Mℓ/d, which is enough for urban use, while the AMD arising across the mining area is estimated to be about 350 Mℓ/d, and should, instead, be used for irrigation purposes in agriculture.

Instead, he insists that it is most important that AMD be brought to a standard that is suitable for agriculture – agriculture water use accounts for 10 000 Mℓ/d, or 60% of South Africa’s water use – and be returned to the country’s water sources for irrigation purposes, rather than to be trying to supplement the lesser requirements of the urban user.

Bewsey points out that most of the research focus until now, has been on developing a process to remove the major dissolved ion – sulphate – in the gold mining areas of the Witwatersrand, along with iron and heavy metals such as manganese and chromium. However, little work has been directed towards the removal of dissolved sodium, which he believes is the most dangerous pollutant in gold mine effluent.

“The sodium cation causes more damage to soil than all the other dissolved solids combined and must, therefore, be removed from the environment,” he stresses.

“It poses a significant threat to the agricultural industry, as it is a ‘slow killer’ of soil because it attaches itself to the clay particles in the soil and is not readily removed.

Bewsey explains that when the sodium attaches itself to the clay particles, it causes the clay to swell, making the soil impervious to air and water.

Without water and oxygen in the soil, the agricultural yield drops quite drastically, which becomes a far more serious long-term problem than any other problem associated with AMD.

Bewsey highlights that it is, therefore, crucially important that any process used to treat AMD must completely remove the sodium, the toxic heavy metals and, where applicable, residual radio activity in the water.

He believes that it is a misdirection of effort to concentrate only on sulphate reduction or removal.

The KNeW process, was developed in 2010 and patented in 2011.

Edited by Martin Zhuwakinyu
Creamer Media Senior Deputy Editor

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