:: Mintek Commissions new Grinding Roll for Comminution Research

As part of its research into more cost-effective comminution technologies, Mintek, specialists in minerals and metallurgical technology and beneficiation, has commissioned a pilot-scale high pressure grinding roll (HPGR).

The unit, supplied by Polysius, is powered by dual 11 kW motors and can operate at pressures up to 200 bar, with a nominal throughput of between 0.5 and 2 t/h.

The HPGR is a relatively new technology, which became commercially available in the mid-1980s. Initially adopted by the cement industry for replacing a conventional ball mill for fine grinding, it is now also commonly used in iron ore processing, for grinding primary ore as well as in pellet feed preparation, and for processing diamond ores. Adoption by the non-ferrous metals sector has been slower, but in recent years a number of precious- and base-metal producers have evaluated the HPGR, particularly for ores that are not ideally suited for semi-autogenous grinding. The technology is now viewed as having the potential to impact comminution technology to the same extent as autogenous and semi-autogenous grinding.

The HPGR uses the principle of interparticle crushing between two counter-rotating rolls, one of which is fixed and the other "floating" by means of hydraulic pressure. The almost pure compressive forces generate a high proportion of fines, along with extensive micro-cracking in the larger particles.

"As well as being more energy-efficient than conventional technology, the HPGR results in a product with very favourable characteristics for further downstream processing" explained Jan Lagendijk, Mintek's Chief Engineer: Comminution Services. "A HPGR in place of secondary or tertiary crushers can increase the capacity of a ball mill considerably. Further major benefits are that the fines produced may result in better liberation, while the micro-cracking in the coarser product particles may result in improved mineral and metal recovery in downstream processes such as flotation and leaching."

"The HPGR test work at Mintek will initially focus on PGM ore processing, and later be extended to other commodities", said Agit Singh, Manager of Mintek’s Mineral Processing Division. "We will be running extensive trials on different ore types to look at the possibility of reducing the specific energy consumption in comminution circuits. In addition, using the HPGR in conjunction with our other facilities, we will investigate the effect of the process on downstream unit operations such as dense-media separation, flotation, and leaching.”