Mining Mirror March 2018 | Page 19

Mine excursion Coal samples that enter the lab as solid core samples are ground down to a fine dust to reveal its numerous qualities. In other cases, the coal sample is sent in and crushed to different sizes in the laboratory’s jaw crushers and then further analysed, beginning with the sink/float process. The core needs to be crushed to exactly the size that will enter the mine’s processing plant — the sample needs to be plant specific. According to Carstens, the standard size of coal is 25mm, but this is not always the case. “Most coal that is fed into plants in Mpumalanga is 25mm,” Carstens informs. After crushing the coal, during what is known as the pre-treatment phase, the samples are put through the sink/ float washability dense medium separation, where the coal is separated into different density fractions. “Here we separate the coal into different densities before we start preparing it for a range of tests, including moisture, ash, volatiles, calorific values, percentage sulphur, and many more. There are special instruments for each different test, and each fraction is tested individually,” Carstens explains. Through a series of analyses and tests, the original core sample that arrived at the laboratory wrapped in plastic, is reduced to only a fraction of the original size. The powder that emerges after this intensive process can best be described as a recorded history and a book about the future of a core sample, retrieved by a geologist in the field. Looks can be deceiving though, and no matter how insignificant the powder might appear, it tells a story and it is an indispensable aid to exploration companies. Carstens emphasises the importance of a good geologist. “When you do coal exploration, the key is to use a reputable and good geologist. If it is a greenfields project and there is no plant yet, the geologist is your most important asset. Anybody can drill a hole, extract coal, analyse it, and start mining. But it’s not that easy. You need to plan properly and to do that, you need a proper geologist. If you have an existing operation with a plant, the most important people are the geologists, plant operators, and plant designers. And it is critical that these people speak to each other and formulate a strategy and plan before they come to us,” Carstens advises. Although this highly skilled and experienced team at Bureau Veritas can tell you the difference between Waterberg coal and Mpumalanga coal, or coking and thermal coal, they cannot make recommendations, and it is up to the mining team to make the final decisions. A few hours in the laboratory with coal experts is probably not enough to decipher the true mysteries of coal. It is enough, though, to realise the limits of our own knowledge about this finite and inconspicuous resource, and that it takes more than just digging a hole to consider yourself a coal miner. b MARCH 2018 MINING MIRROR [17]