While other grinding require closed circuit cyclones and high recirculating loads the IsaMill™ achieves a much steeper product sizes distribution in only a single pass

Feed to the IsaMill™ passes through 8 consecutive grinding stages between the discs before it reaches the internal classifier. Other mills with just one grinding stage require closed circuit cyclones and high recirculating loads and still don’t produce product size distributions as steep as the IsaMill™.

The product separator is one of the key advantages of the IsaMill™ design. The 8 consecutive grinding chambers, and high tip speed of the separator means that the mill constantly delivers sharp sizing performance. There are no screens or trommels to fail or block, any particle that leaves the mill must escape the same centrifugal forces. A further advantage of this mechanism is that it allows the IsaMill™ to use a wide range of media type and size. Even if a portion of the media degrades early, it can exit the mill without blocking screens, with the remaining competent media retained for grinding. In contrast, mills closed by fine screens are limited to using only the most competent media.

Media Type

The type of media used in the IsaMill™ ranges from effectively ‘free’ media source including smelter slag and coarse SAG Mill product, to low cost locally available sands through to more expensive, high quality ceramics. The best choice for any application is simply a question of economics, taking into account cost and quality of local media, power efficiency and capital cost. While higher quality media is more expensive, it is usually more power efficient, reducing the installed power requirements and operating cost.

The patented internal product separator unique to the IsaMill™ retains all media inside the mill and negates the need to use screens and cyclones to retain media. IsaMill™ operations can take advantage of this feature which translates to an ability to use a low cost, but relatively low quality grinding media such as silica sand, river pebble, smelter slag or fine primary mill scats (autogenous milling). This means low media cost, with power efficiency still better than conventional grinding.

While natural sands and slags have a wide range of performance as media and need to be tested for competency, power efficiency and consumption rate before being selected there are also a number of standard natural medias are available (e.g. sand). Performance of these medias is well known and predictable. In general natural medias, due to their grain size, are restricted to fine grind sizes (e.g. below 25 microns). Coarser grinds favour the use of manufactured media, which can be produced to have a desired and reproducible size and strict quality control. Further, the high sphericity, roundness, surface smoothness and SG mean that much higher power efficiencies can be achieved than for natural media. The power efficiency of coarse IsaMilling™ with ceramic media is much higher than for conventional ball or Tower Milling.

Until recent years ceramic media had been uneconomic for grinding. This changed with the development of Keramax MT1™ grinding media by Magotteaux International in cooperation with Xstrata Technology. The unique properties of MT1™, including low friction, high SG and very low wear rates, mean it can achieve exceptionally high grinding efficiency and low cost for coarse feeds. The first industrial application combining Keramax MT1™ and IsaMill™ technology was commissioned in late 2005.

Xstrata Technology can conduct a test program to compare the performance and economics of alternative media.