Cyclones Improve Bauxite Process Efficiency for Aluminum Producer
An existing system at MAL involved Warman 6/4 pumps transporting material directly from the mill. While the pumps were performing well, Weir Mineral engi- neers recommended the introduction of two Cavex 500 CVX hydrocyclones to pro- vide greater efficiency to the system. The cyclones were subsequently installed in August 2010.
A major factor that limited the efficien- cy of the alumina production is the differ- ent 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, approx- imately 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 instal- lation of the two Cavex 500 CVX cyclones, which allowed for the automat- ic 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 elimi- nating waste, underpinning a more effi- cient system and increasing the overall system recovery.
The cyclones were installed at an angle of approximately 35° from horizon- tal 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 con- centration would be ~62% by weight solids. This underflow density also deter- mines 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 appli- cations in the mining and mineral pro- cessing industry, as their capacity for pro- viding closed circuit grinding classifica- tion for improved efficiency, reduced wear and higher throughput can benefit appli- cations by improved classification ahead of other process equipment such as flota- tion cells, magnetic separators, spirals, hindered settling classifiers, etc. Cavex cyclones, says Weir, also provide better dewatering and desliming efficiency, reducing product loss and improving prod- uct 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 entire- ly new feed geometry that substantially increases hydraulic capacity while mini- mizing localized wear on the feed cham- ber 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, offer- ing 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 clas- sification efficiency. In conventional cyclones slurry bursts into the cylinder with no flow control and the resulting tur- bulence is responsible for gouging the liner walls.
For grinding circuit applications, Weir says the cyclones increase circuit capac- ity 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.