Established in 1995, MAL is a major European bauxite, alumina and aluminum processing company with its largest operations in Hungary. Bauxite extracted from its mines in Hungary and Serbia is converted to alumina at the Hungarian site, with the company producing 300,000 metric tons per year of alumina.
An existing system at MAL involved Warman 6/4 pumps transporting material directly from the mill. While the pumps were performing well, Weir Mineral engineers recommended the introduction of two Cavex 500 CVX hydrocyclones to provide greater efficiency to the system. The cyclones were subsequently installed in August 2010.
A major factor that limited the efficiency of the alumina production is the different composition of raw bauxite from Hungary and Serbia. The Serbian bauxite constitutes 30% of the raw material input and is substantially more abrasive than the Hungarian material. Consequently, approximately 31% of material that went through the mill process was larger than 90 microns and was unsuitable for the next stage in the alumina production process.
A simple solution involved the installation of the two Cavex 500 CVX cyclones, which allowed for the automatic separation and retrieval of the larger solids that could then be transported back into the mill process for further size reduction. This had the benefit of eliminating waste, underpinning a more efficient system and increasing the overall system recovery.
The cyclones were installed at an angle of approximately 35° from horizontal to coarsen the cut point and also to maintain a more stable underflow. Due to the size of the solids and the density of the liquor, the maximum underflow concentration would be ~62% by weight solids. This underflow density also determines the density of the overflow stream.
Weir reports that since installation, the cyclones have provided a high level of performance, achieving 1,200 g/l with an 80-mm spigot. Spigot service life has been approximately 700–800 hours.
According to Weir Minerals, Cavex cyclones are suited for many slurry applications in the mining and mineral processing industry, as their capacity for providing closed circuit grinding classification for improved efficiency, reduced wear and higher throughput can benefit applications by improved classification ahead of other process equipment such as flotation cells, magnetic separators, spirals, hindered settling classifiers, etc. Cavex cyclones, says Weir, also provide better dewatering and desliming efficiency, reducing product loss and improving product recovery. Featuring unique laminar spiral inlet geometry designed to deliver maximum efficiency, Weir claims the cyclones provide maximum capacity and longer wear life than conventional involute or tangential feed cyclone designs.
Not simply a cone modification, the Cavex cyclone is designed with an entirely new feed geometry that substantially increases hydraulic capacity while minimizing localized wear on the feed chamber and vortex finder. This design results in lower operating costs and fewer cyclones required for a given duty.
As Weir explains, the Cavex design’s laminar spiral inlet geometry provides a natural flow path into the cyclone, offering a unique shape that has no sharp edges, no square corners and allows the feed stream to blend smoothly with the rotating slurry inside the chamber. The result is reduced turbulence throughout the whole cyclone—allowing for more-even wear, longer life and improved classification efficiency. In conventional cyclones slurry bursts into the cylinder with no flow control and the resulting turbulence is responsible for gouging the liner walls.
For grinding circuit applications, Weir says the cyclones increase circuit capacity by minimizing the quantity of fines bypassing to the underflow stream. This effect is achieved by maximizing the air core diameter created within the rotating mass of fluid in the cyclone and has been proven in both laboratory testing and full scale plant operation.