SA’s role in advancing DMS coal processing Following the successful South African-hosted International Coal Preparation Congress (ICPC 2025) last year, MCA meets Ernst Bekker and Frikkie Enslin, who highlight South Africa's key role in advancing coal-processing technology.
Left: Multotec’s dense medium cyclones are the equipment of choice for coal preparation, iron ore upgrading, and the pre-concentration of diamonds, metalliferous, and industrial minerals. Right: The Chance dense-medium washing process, also known as the coal-washing sand flotation process, was the first commercial dense-medium washing process for coal.
A t the South African-hosted 21 st International Coal Preparation Congress (ICPC 2025) last year, the foremost international event for researchers and industry leaders in the coal preparation industry, Frikkie Enslin, Product Manager for Cyclones at Multotec; and Ernst Bekker, the company’s Cyclones Process Equipment Specialist in South Africa, presented a paper about South Africa’s role in advancing dense medium separation (DMS) technologies for the coal industry. Entitled ‘Beyond Bessemer: the past, pres- ent, and future of dense medium separation in the coal industry’, the paper traces the de- velopment and evolution of DMS equipment in the coal industry, beginning with Sir Henry Bessemer's 1858 patent. “This conference makes one appreciate the fact that we still need coal, and while many of those who need to hear this don't attend, it's a good networking opportunity to share future trends and identify core priorities for today’s coal industry, bringing people up to speed in terms of the latest developments,“ begins Multotec’s Ernst Bekker. Bessemer holds many patents in his name, including a lesser-known invention for a gravity-based process to concentrate miner- als. “In his laboratory, Bessemer noticed that he could manipulate the density of a liquid to control which particles float and which sink. As metallurgists, we are manipulators of natural properties, and his observation has assisted us for over 150 years in becoming better and better manipulators of dense media technologies for coal separation,” he adds.
handpicking, where workers, often young boys, would stand beside a table or a slow-moving belt and physically remove rocks, shale, and other impurities from lumps of coal on the line. With declining ore grades, smaller liberation sizes, shifts in economic scales, and new technolo- gies, however, hand sorting quickly fell out of practice. An early technology was simple jigging, in which a coal-and-rock mix in a basket was submerged in water and then shaken up and down. Higher-density material sinks faster than the lower-density coal, causing the coal to migrate to the top and the heavy impurities to the bottom of the heap. “More sophisticated jig washers are still a popular choice for coal beneficiation today, because of their relative simplicity and low operational costs. They are more efficient in treating coarser particle sizes, though, and lib- eration plays a major role in raising separation efficiency,” notes Frikkie Enslin. During the operation of early forms of jig washers, it was observed that a concentration of fine-grained heavy minerals formed a semi- stable suspension that behaved like a heavy fluid, causing low-density material to float, regardless of particle size. “This observation led to the deliberate inclu- sion of semi-suspended fines in the water used in jig washers. The concept was further devel- oped with the introduction of trough-and-cone washers, eventually leading to the emergence of the first commercial dense-medium wash - ing process, known as the Chance process or ‘sand flotation process of coal washing’,” Enslin explains. Chance's separator paved the way for the development of other processes using different separating media, such as the Conklin process
using fine magnetite and water, the de Vooys process employing finely ground barite (BaSO4) and loess (fine-grained silt), and the Wuensch process that used natural fine clay and slate. “In addition to these processes, attempts were made to commercialise the use of saturated salts and organic liquids as dense media, such as a saturated solution of calcium chloride (the Lessing process), and chlorinated hydrocarbons (the DuPont process). In the early 1930s, significant developments in dense medium technology took place in the Netherlands, with the enhancement of De Vooy’s process into the renowned Barvoys’ process, and the introduction of new methods by Tromp that used finely ground magnetite or pyrite. “The breakthrough in modern dense medium separation came from the work of Staatsmijnen in Linburg, where the first dense medium separator was installed in a commercial plant in 1937, sparking global interest in DMS methods. Developed in the mid-1900s, a key South African DMS invention was the Norwalt Washer, a bath-type washer with the feed in- troduced into the middle of the vessel. The bath was fitted with stirring arms, which whisked the floats off to the edge of the vessel whilst the sinks collected at the bottom. Scrapers at the bottom transport the sinks to an exit point into a sealed elevator, which continuously removes discarded material. “These are no longer used, but they were quite popular from the 1950s to the 1970s. So we in South Africa have long had clever people making significant contributions to global DMS development,” Ernst Bekker points out. “I've never seen one, but the literature and the people I spoke to suggest that this develop- ment pushed the boundaries of efficiency with
Early coal separation technologies In the early days, coal separation relied on
20 ¦ MechChem Africa • March-April 2026
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