Anglo American has established an automated mineralogical technique that characterises the fine fraction of coal-bearing borehole samples to reveal their bulk mineralogy, particle characteristics and the theoretical density of the particles.By Siksha Bramdeo Currently, coal analysis involves washability tests, chemical analysis and optical microscopy. However, these methods are not able to produce detailed information on coal and its associated minerals. In the days when South Africa’s coal deposits were of a high grade, washability tests, chemical analysis and optical microscopy were adequate to characterise samples. These high grades have steadily been depleted, leaving lower grade deposits that are, of necessity, starting to drive coal analysis increasingly into the arena of fine coal beneficiation. At present South African coal resources are not only highly variable, but are also difficult to treat , and the industry is being compelled to evolve its analysis techniques, moving increasingly towards automated techniques to reveal the required information about coal and the impact of the associated minerals. Based on a method used in the platinum industry, in which mineralogy is applied to plant processes, our successful progress towards an alternative predictive coal analysis tool will advance the efficiency of future exploration and coal beneficiation activities in the industry. This new method is highly accurate and results in a more representative sample. Automated coal analysis of fine particles will ultimately make it possible to obtain rapid and detailed mineralogical information on a particle-by-particle basis. This accurate knowledge of the mineralogy of the coal being sampled will allow for a more predictable ash content and serve as an important value-add in terms of providing quality assurance that the coal being sold meets specific customer requirements.
Importantly, being able to access this detailed information will also impact the design of future mineral extraction plants, because deposits can be characterised ahead of mining, making it possible to optimise process design and plant efficiencies. A good knowledge of the coal will aid in the understanding of how minerals will behave in the end product — for example, a coking blend and the effects the inherent minerals will have in a blast furnace.While corresponding studies have been implemented around the world using different techniques, this application has been developed in collaboration with Eskom and is the first time that a QEMSCAN system has been used in this particular context. QEMSCAN is an abbreviation for Quantitative Evaluation of Minerals by SCANning electron microscopy and is an integrated automated mineralogy and petrography solution providing quantitative analysis of minerals, rocks and man-made materials. Anglo American is one of only three industry laboratories to apply this analysis method on coal samples. A highlight of this research project has included the development of a new approach to preparing coal samples for analysis. Research into the new analysis method is well advanced and requires verification on different coal types and plant products. It is important to note, however, that this new method will not replace the sink float processes of old, but will be complementary to washability testing. The new analysis method is a product of innovative and focused research by our dedicated team at Anglo American’s Technical Solutions Division. Anglo American’s Mining and Technology Division houses one of the world’s biggest mineralogical facilities. It is a leading provider of metallurgical and process research, as well as laboratory facilities, technical consulting and field services in support of the Group’s operations, projects, business units and corporate functions. The team is focused on delivering and implementing sustainable multidisciplinary techno-economic solutions across the entire mining value chain, through research, consulting and field services. Bramdeo heads up the research team focusing on this technique at Anglo American’s Mining and Technology Division.