A new plant features a unique process to minimise fines generation in the production of calcite and lime. It has been supplied to Umzimkhulu Industrial Holdings’ Rossmin open cast limestone mining operation at Port Shepstone, on the KwaZulu-Natal South Coast.
“The plant was designed and installed to only produce two sized products: 80mm +30mm and -30mm +10mm. The -10mm is a by-product,” explains Osborn product sales manager, Shane Beattie. The process is revolutionary in that a conventional crushing plant would be a jaw and cone configuration to crush down to a -80mm product from a run of mine (ROM) of 600mm.
“We supplied a modular 3042 jaw plant feeding into a modular 2340 jaw plant, then over a modular 6 x 20 triple deck screen, splitting the product into -80mm+30mm, -30mm+10mm and a -10mm +0mm. The primary reason for the two-stage jaw crushing process is to minimise the generation of fines (-10mm),” Shane explains, adding that this material cannot be used in the next stage and is a waste product.
Difficult to manage
He adds that their pioneering process is more effective than the conventional separation process at other plants, where all the ROM material is crushed to -1mm and smaller, then flotation is used to remove the impurities. “This process requires lots of water and waste that is more difficult to manage.”
Umzimkulu and Rossmin will only process the high grade material, up to 99% calcite, Shane says. “By only feeding the high grade -80+30mm to the Tertiary/Quaternary plant and, the next stage being dry, will produce a higher yield per ton crushed,” he notes. Since this stage is the most expensive part of the process, by only crushing the desired calcite, the operation will be able to dramatically reduce its cost per ton, and the capacity in this stage is utilised to its fullest potential.
Three years in the making
The company also supplied the mine’s next stage with its imported high frequency screens, to cut at -2+1.2mm, -1.2+0.8mm, -0.8+0.4mm and -0.4+0.075mm. “This is an extremely innovative process that enables us to screen out the -1.2mm fraction. This is then sent to an air classifier, which removes the -0.075mm from the -1.2mm.
“The -1.2+0.075mm fraction is then sent to the second 2624VM high frequency screen, a double deck 6’ x 24’ screen, to separate the -1.2+0.8mm, -0.8+0.4mm and -0.4mm +0.075mm fractions.”
The equipment supplied was transported to KZN in 22 loads, and the scope of Osborn’s contract included the supply, installation and commissioning of the primary plant. “This order has been some three years in the making. We devoted the necessary time to truly understanding our client’s requirements, and we are proud to have delivered a truly unique and optimal solution,” Shane concludes.