COMMINUTION AND CRUSHING
Installation of part of a New Generation DRC at oil sands customer in Canada
fulfils both the immediate and future needs for mining oil sands.”
The TRC 25.37 is designed for a sustained 17,000 t / h throughput capacity in all oil sands materials and the most frigid ambient conditions. The two units which commenced production in 2016 are detuned to the contracted 14,000 t / h capacity but can be fully realised with a simple change to the ratio of the apron feeder.“ For those mines not immediately requiring the implementation of a complete new crushing plant, the upgrade to the powerful New Generation TAKRAF TRC 25.34 DRC has proven to be an economically effective means to increase production through elimination of stalls and reduced maintenance downtime; as well as increased recovery through achieving a high crushing ratio, even in the most extreme winter conditions.”
This type of primary crusher upgrade typically requires a shutdown period of 22 to 30 days. Economically, the payback period is less than two winter seasons, says TAKRAF. Finally, TAKRAF is also working on solutions for copper ore, iron ore and bauxite mines, together with mines with difficult overburden; which will culminate in a New Generation range of Extreme Class machines for their hard ore types. using laboratory, bench-scale and pilot-scale equipment, that indicate that this technology can be used to float coarse sulphide middlings that cannot be recovered by conventional flotation machines. Recent data collected from pilot-scale tests conducted at a base metal concentrator indicate that this technology can float middlings particles as large as 850 microns in diameter containing as little as 1 % exposed hydrophobic mineral. As such, the crossover of this technology into the base metals industry has the potential to substantially reduce grinding costs and increase concentrator recovery / capacity through the use of split-feed circuitry. The split-feed concept, which is often used for upgrading industrial minerals, involves segregation of the feed into more than one size class followed by subsequent upgrading using mills / separators / reagents specifically optimised for each size class. An example split-feed circuit was developed that utilises two stages of classifying cyclones in conjunction with the HydroFloat separator. The circuit is designed to recover, recycle and regrind coarse middlings containing small amounts of valuable mineral while simultaneously rejecting coarse wellliberated siliceous gangue so that mill throughput can be increased. Coarse tailings also maximise water recovery from impoundments while reducing overall impoundment size. Simulation data conducted using well-known process models suggest that this approach can increase existing primary mill capacity by up to 25 % with only modest investments in new classifying and flotation equipment.
The shown simplified flowsheet includes a primary grinding mill, primary classifying cyclones, rougher-scavenger flotation banks, cleaner flotation columns and a middlings regrind mill. The availability of the HydroFloat technology allows the circuit to be modified as shown. In this case, the primary classifying cyclones are reconfigured to provide a substantially coarser size cut( eg D80 increased from 150 to 300 microns). This layout allows the underflow to be passed back to the primary mill, while the overflow is passed to a secondary set of classifying cyclones. The secondary cyclone bank produces a fine( eg minus 200 micron) overflow that is sufficiently liberated to be upgraded by the downstream conventional / column flotation circuit and a coarse( eg nominal 150 x 300 micron) underflow that is passed to the HydroFloat circuit. In this case, feed to the HydroFloat is reclassified using a CrossFlow separator to ensure near-complete removal of fines. The HydroFloat is then used as a highly efficient flotation separator to ensure that all particles containing valuable sulphide mineral report to the overflow concentrate, which is recycled back to the primary grinding mill for further size reduction and liberation. The HydroFlow at the underflow, which consists of coarse liberated gangue, is rejected as a throwaway product that is essentially free of valuable mineral. As such, the siliceous gangue tonnage rejected by the HydroFloat makes room for new feed tonnage in the primary grinding mill. IM
Increasing mill capacity through HydroFloat
The HydroFloat™ from the Eriez Flotation Division is an innovative fluidised-bed flotation cell that can substantially increase the upper particle size that can be successfully treated by flotation. An IMPC 2016 paper by Mankosa et al outlined recent studies that were conducted
Examples of( a) the simplified baseline flowsheet and( b) modified split-feed flowsheet incorporating the HydroFloat technology
MARCH 2017 | International Mining 69