Modern Mining September 2020

processes

Cavex hydrocyclone. The specially designed radius tiles assist in main- taining the more rounded profile of the Cavex hydrocyclone in such applications. Gabriel highlights two case studies where these have been successfully applied. One is a major coal mine in Mpumalanga, South Africa, where the customer had previously employed older technology and Weir Minerals Africa retrofitted its Cavex ceramic tiled hydrocyclones onto that spe- cific cluster. The payback was only seven days. The original dewatering clas- sification circuit hydrocyclone cluster consisted of eight conven- tional cyclones, which delivered large amounts of oversize and grit in the overflow. This resulted in excess

Above: Production of the new Cavex 2 or CVD hydrocyclone in a cluster destined for a gold mine in West Africa. Right: Weir Minerals has experienced an increased demand for the Cavex dense media cyclone.

tile hydrocyclone proved its prow- ess was a DMS application at another coal mine in Mpumalanga. A competi- tor’s 610 mm cyclone typically had an operational life of only six months before being refur- bished. The short operational wear life was impacting the over- all performance of the plant. A site audit and review by Weir Minerals Africa revealed that the exist- ing cyclone was operating inefficiently and producing low yields. A Cavex 500CVXT20 DM hydrocyclone, made from mild steel and lined with 25 mm slip casted radius (92% alumina) ceramic tiles, was proposed. “Slip cast radius tiles are used on the feed chamber and cover to maintain the laminar spiral 360-degree scroll inlet profile of the hydrocyclone. This ensures increased efficiency, reduced turbulence and improved wear life,” explains Gabriel. Based on the washability analysis, the DM cyclone would need to treat two different coal types, grains and peas. The objective was to achieve a minimum of 72,2% mass yield for the peas type. Following the installation of the Cavex 500CVXT20 DM hydrocyclone, the client achieved higher separation efficiency through an average 15% yield increase. Additionally, an overall average of 75% yield for both coal types has been achieved,

grit entering the thickeners and the filters struggling to cope. Saleable ore was also lost to the overflow and eventually to the thickeners. Weir Minerals Africa proposed the removal of the existing conventional cyclones and retrofitting eight Cavex 500CVXT10 ceramic tiled (92% alu- mina) hydrocyclones in the existing cluster. The key performance indicators were to produce a finer cut and to yield a higher solids mass pull to the cyclone underflow. More importantly, one set of test work results with the Cavex hydrocyclones installed showed that an additional 35 tph of solids reported to the underflow when compared with the previously installed set of cyclones. Additionally, Cavex hydrocyclones produced a finer cut with an average d50c of 107 microns as compared with an average d50c of 210 microns pro- duced by the conventional cyclones. As a result, an increased solids loading of 24 t per cluster onto the spirals increased the saleable yield. Another ben- efit realised was the increased plant availability and reduced downtime achieved as a result of reduced solids volumes reporting to the overflow and eventu- ally the thickeners. “The installation of the Cavex hydrocyclones proved beneficial to the client. Since installation, the majority of the solids now report to the underflow, which results in increased saleable yield. More solids report to the spirals, reducing downtime, because the thickeners and filters can handle the existing volumes,” explains Gabriel. Another application where the Cavex ceramic

September 2020  MODERN MINING  9