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Coal petrography crucial to evaluate SA’s low-grade coal – SABS

15th March 2013

By: Yolandi Booyens

  

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Owing to the overexploitation of high-grade coals in South Africa’s main mining areas, coal petro- graphy has become crucial in evaluating low-grade coals and their byproducts, according to the South African Bureau of Standards (SABS).

The benefits of coal testing are acknowledged in the South African coal industry, as the quality of many coal products on the local market is lower than those on international markets.

In response to this, the SABS relaunched its petrography laboratory in August 2012 to offer testing services to the coal and minerals industry, which, it states, will stimulate foreign direct investment by renewing trust in the region’s capability to offer world-class services, such as mineral testing, to the mining industry.

The laboratory offers a strategic service to businesses across the Southern African mining region, particularly the Waterberg, in Limpopo, and the Botswana coalfields.

Coal petrography can assist South Africa’s coal industry in predicting the blending compatibility of coals, the effect of carbon content from heated and oxidised coals, flame stability, the rate of combustion, temperature distribution in a furnace and burn-out characteristics, SABS senior test officer and coal petro- grapher Vongani Chabalala tells Mining Weekly.

Coal testing assists not only in exploit- ing and beneficiating but also in allocating the right type of coal to the right process, such as coal for steam generation and coals for metallurgical processes, he explains.

“It also helps the producers and con- sumers of coal to know the total value of coal in relation to revenue.”

Chabalala, one of seven coal petro- graphers in Africa, completed a project aimed at determining the rank of Free State coal through reflectance and maceral analysis earlier this year.

The project started in August last year, with the results showing that the coal contained low reactive maceral (vitrinite and reactive semifusinite) and medium to high mineral matter. The reflectance analysis of the coal samples showed that Free State coal is medium-rank bituminous coal.

Meanwhile, Chabalala points out that the analysis of minerals through optical microscopy is critical to the understand- ing of the rock’s origin and in determining coal characteristics, including coke strength, which inevitably lends itself to prime-coal market end-users.

Petrography guarantees the highest standard possible for customers seeking coal testing services and coal certification.

The microscopic organic constituents of coal refer to the nature of organic matter found in coal. The constituents are reactive to inert particles, which determine the suitability of coal for specific process, Chabalala explains.

South African Coal

South African coals contain low levels of vitrinite and are rich in inertinite particles, with some of these particles being reactive.

The microscopic inorganic constituents refer to minerals such as clay, quartz and pyrite, which could indicate the ash level or impurities in coal. South African coals contain high levels of mineral matter, some of which are beneficiated before use.

Further, the country is rich in bituminous coal, Chabalala points out. “The rank (or maturity) of South African coal, however, varies from one region to another.”

Coals from Witbank, in Mpumalanga, comprise medium-rank bituminous coal that is used for steam generation, compared with medium-rank bituminous coking coals from Makhado, in the northern region of Limpopo, which have a slightly higher reflectance than Witbank coal.

Internationally, coal is the most widely used primary fuel, accounting for about 36% of the world’s electricity production. This situation is likely to remain unchanged until at least 2020.

“South Africa’s coal reserves are estimated at 53-billion tons and, at our current production rate, there should be almost 200 years of coal supply left,” Chabalala concludes.

Edited by Megan van Wyngaardt
Creamer Media Contributing Editor Online

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