:: IsaMill Set to Increase Minerals Processing Benefits

Brisbane-based Xstrata Technology is making its biggest IsaMill yet to work in combination with ceramic media for an Anglo Platinum mine in South Africa.

The new and larger M10000 mill will have a 3MW motor and use breakthrough Magotteaux Keramax MT1 ceramic grinding beads. IsaMill uses ceramic media with very high disc rotation speed to increase the probability and energy of particle/media collision.

Xstrata Technology senior process engineer Brenton Burford told Australian Mining magazine that the powerful combination of a larger mill and ceramic media will provide Anglo Platinum with a fantastic competitive advantage.

Over the past few years IsaMill, a high-intensity continuous grinding technology, has grown in size from the 1.1MW M3000 to the M10000. The first couple of M10000s featured a 2.6MW motor but they are now available with a 3MW motor.

Until fairly recently, IsaMill was used for ultrafine grinding. However, the development of the larger and more powerful mills extends its use to coarse grinding.

A horizontal high-speed stirred mill, IsaMill operates with high power intensities up to 300kW/m3 compared with a ball mill, which is about 20kW/m3. The higher speed allows the mill to process particles faster. A steep particle size distribution is produced in open circuit operation without the use of screens. The very high power intensity of the IsaMill allows small installations: a 3MW M10000 IsaMill has a volume of 10m³, containing about 7m³ of media.

Burford says in some circumstances the combination of larger mills and the use of ceramic media will mean an operation can get away with using only one mill where two were previously needed. This calls for less infrastructure and lower capital expenditure, which can potentially save an operation several million dollars.

Ceramic media, which is quite high in alumina and silica, has several key advantages over traditional steel, slag and sand.

MT1 grinding beads are quite hard and spherical so waste less energy in rounding particles. MT1 has low friction, high SG and low wear rates, which means it achieves high grinding efficiency at a lower cost for coarse feeds.

Burford says with media like steel, the outside is quite hard but the inside is softer so it wears a lot faster, whereas ceramic media has good mechanical integrity and maintains this characteristic as it wears. In addition, ceramic media does not chemically or electro-chemically impact on the downstream flotation process.

"When you use steel media, for instance, it produces ferric ions, which tends to interfere with the chemistry of the particles and creates a passivating layer; this makes the particles hard to float or leach," Burford says. "Reaction also takes place more quickly," he says. "I don’t think people realise until they operate a plant without steel media just how important the chemical aspect is of downstream processing."

Xstrata Technology’s most recently completed M10000 mill was built for the Kumtor gold mine in the former Soviet republic of Kyrgyzstan. Burford says in such isolated locations ceramic media comes into its own because mills usually consume far less ceramic media, depending on ore type. "The consumption of ceramic media is much better than sand so you don’t need to have as much on hand," he says.

Another big advantage of ceramic media, especially in these days of escalating fuel costs, is power savings. These can range up to 20% compared with many sands.

"Using MT1 is quite a cheap way of increasing your regrind capability. It also saves time with downstream processing by grinding to finer sizes and provides improvements in flotation and leaching afterwards," Burford says. "With metal prices the way they are today, it won’t take long for IsaMill installations to achieve payback."

Burford says IsaMill technology is not only suitable for greenfield sites. "Because of their compact size, IsaMills can also be retrofitted in most existing processing plants with no need for a larger layout," he says. Burford says replacing worn parts is quick and easy, and is performed without removing the shaft, gearbox or motor. Operating IsaMills have availabilities of over 98%.

By the end of this year, four IsaMill M10000s will be in operation around the world, with several more installations being designed for the following year.

This article appears in the May 2006 issue of Australian Mining magazine.