The crushers were commissioned through a toll treatment mining company called African Star Minerals, a subsidiary of Firestone Diamonds.
The machines were built overseas and reassembled in South Africa by IMS Engineering at African Star Mineral’s Bontekoe mine for the Buffels Inland Complex (BIC) project.
Originally developed for the Japanese aggregates industry, the Kawasaki KPR1200S crushers are the first of their kind to operate in the South African mining indus- try.
The BIC is situated on South Africa’s West Coast, an area known for its difficult-to-treat diamond-bearing material.
IMS Engineering’s Johnny Minnaar says that using Kawasaki KPR1200S preferential jaw crushers at the secondary and tertiary crushing stages at the BIC, enables De Beers to feed a mixture of soft conglomerate material and hard competent pebble/quartz material to the plant, and to preferentially crush the soft diamond-bearing conglomerate material to fine particles, while opera- ting the crusher at a relatively large gap setting.
The barron hard pebbles/quartz remain uncrushed and these larger nondiamond-bearing particles are then removed from the circuit by means of screening, which, in turn, reduces the amount of material presented to the next stage of opera- tion.
This facilitates the recovery of diamonds from the gravel without damaging diamonds at the De Beers Consolidated Mining alluvial opera- tion.
The Kawasaki KPR1200S units are fed with material received from the mine as well as the dump. The secondary preferential jaw crusher is fed with primary jaw crusher product while the tertiary preferential jaw crusher is fed relatively fine material at a rate of about 60 t/h to 70 t/h.
Minnaar says using the Kawasaki KPR1200S preferential jaw crushers will have several advantages at the Bontekoe plant during both crushing stages and the downstream diamond recovery process.
Firstly, it requires less energy than conventional crushing equipment, as only the conglomerate material is crushed, thereby reducing operating costs.
Secondly, the hard pebble material is used as a preferential crushing medium which increases the rate of interparticle crushing, which, in turn, reduces the amount of wear on the liners for each tonnage processed.
Thirdly, the crushers are opera-ted at a large gap setting, thereby reducing the probability of diamond breakage. Most notably, employing such technology early on in the diamond-processing plant enables more efficient diamond liberation in a smaller and, therefore, less capital intensive dense-media separation (DMS) plant.
“The production benefits and cost-saving advantages of operating the Kawasaki preferential jaw crushers will certainly be felt at the BIC. The technology has been designed to reduce day-to-day operating costs as well as the capital investment required to build a DMS plant, two factors that determine the longevity, or continued running, of a mine that is considered to be a marginal opera-tion,” says Minnaar.
De Beers project manager for Buffels, Vince Modena, says that the Kawasaki KPR1200S is the only available technology expected to meet the processing requirements at the operation.
As it was originally established in the 1970s and subsequently closed owing to inefficient processing techniques, the availability of more sophisticated processing equipment has been central to the revival of the mine, a producer of one-million carats a year of high gem quality diamonds.
Kawasaki preferential milling technology is widely used in the Southern African diamond industry. In recent years, IMS Engineering and Earth Technica Company have together developed processing solu- tions using preferential milling for operations on and off the West Coast. The BIC project, however, is a first in the application of preferential jaw crushing in the industry.