In her presentation to the Southern African Institute of Mining and Metallurgy (SAIMM) diamond conference in Johannesburg in 2018, Boitumelo Zimba, a senior process engineer at Weir Minerals Africa, said the company’s hydrocyclones had improved plant efficiencies and produced 40% more tonnage than the mine’s target.
“As the Cavex hydrocyclone was tried and tested in hard rock mining and coal classification, the Cavex 360° laminar spiral inlet profile was used as a basis for the development of a dense medium cyclone,” said Zimba. “Individual casting patterns were developed and produced in order to fabricate the Cavex dense medium hard chrome cyclone with the exact laminar spiral feed chamber that exists when moulded out of rubber.”
Zimba noted, that the customer required a solution that could offer at least six months wear-life, and a probable error of separation (Ep) of no greater than 0.08 at a cut density of 3.1 t/m3. She explained that the lower the Ep – or probable error of separation – the more efficient the separation. Ep is defined as half the difference between the density at which 75% is recovered to sinks, and that at which 25% is recovered to sinks.
“Tracer tests were used to monitor the efficiency of the separation achieved by the Cavex hydrocyclones to ensure all of these requirements were met.
“Ep values achieved were 0,042 for the 4.0 mm tracer tests and 0,035 for the 8.0 mm tracer tests, which were below the set maximum target of 0,08 from the mine,” Zimba added. “This highlighted the benefits and improved efficiencies of the Cavex laminar spiral feed inlet.”
According to Zimba, the unique design of the laminar spiral inlet geometry delivers sharper separation and maximises capacity while delivering a longer wear-life than conventional involute or tangential feed inlet designs.
By providing a natural flow path into the hydrocyclone body the design allows the feed stream to blend smoothly with the rotating slurry inside the chamber, reducing turbulence and improving separation efficiency.
Another vital factor, Zimba notes, is the Cavex inlet design with its 360° scroll. “This design was proven through extensive computational fluid dynamics (CFD) analysis as well as Weir’s multiple installations to date,” he assures.
Initially, the hydrocyclones were commissioned to treat only fines at the diamond plant: the -8 to +1 mm material. Later however, the mine decided to run a combined DMS, after which the full DMS size range of -20 to +1 mm was treated through all the fines DMS hydrocyclones.
“The customer’s tracer tests on the Cavex hydrocyclones showed that cut points of 3.08 t/m3 were achieved for both the 4.0 mm and 8.0 mm tracers,” Zimba says. “This was within the performance levels of 3,1 t/m3 that the customer had specified.”
Weir Minerals also conducts ongoing research and development on methods to minimise turbulence on assembled caste components. “Combining our cone and spigot components in the hard metal range is an important contribution to the reduction in turbulence,” Zimba explains.
The Cavex hydrocyclones are designed with a variety of inlet sizes to accommodate a wide top size at specified medium-to-ore ratios. The inlet sizes range from 0.2 to 0.33 as a function of the hydrocyclone diameter.
To prolong life and efficiency, the hydrocyclones can also be manufactured with different materials. Cavex CVXA hydrocyclones are hard-wearing and are cast in 27% chromium iron for maximum abrasion resistance. In addition, components are designed for ease of maintenance, with all surfaces joined with a layer of epoxy cement.
“Future work will include the investigation of various alloys to combat high wear rates on some of the hydrocyclone components, in particular the vortex finder and the cone sections,” Zimba concludes. “This will allow longer operation and plant stability.”