Swiss Tower Mills (STM) Minerals and its technology partner, Outotec, have won an order to provide a HIG1600 regrind mill for the Mutanda mine  plant in the Democratic Republic of Congo. 

Mutanda, a high-grade copper and cobalt producer with operations located in the province of Katanga in the DRC, is operated by Glencore Xstrata plc, which owns 54.5%. As of June, Mutanda copper output was at an annualized rate of 120 ktpa. 

STM’s scope of supply for the project includes the HIGmill, complete with control and drive system. The mill is intended to grind 118 mt/h of copper concentrate with a F80 of 212 µm to a P80 of 35 µm. According to SLTM, the HIGmill provides several unique advantages, such as a low specific grinding energy (SGE) value combined with high-power intensity, simple flow sheet with no recirculating loads, flexibility in process variables, and long maintenance intervals. Deliveries are scheduled for the first quarter of 2014; start-up is planned for autumn 2014.

Swiss Tower Mills Minerals said it is Outotec’s exclusive technology partner for high-intensity grinding mills.

The HIGmill comprises a mill body, shaft with grinding discs, shell mounted counter rings, gearbox and drive. The grinding chamber is filled up to 70% with grinding beads. Rotating discs stir the charge and grinding takes place between beads by attrition. The number of discs (grinding stages) depend on the application and can number up to 30. Feed slurry is pumped into the mill via its bottom connection. When the flow transfers upward, it passes all consecutive grinding stages. Final product discharges at open atmosphere at the top of the machine.

According to Outotec, the tall, narrow, vertical mill body arrangement allows grinding media to be evenly distributed and mineral particles remain in constant contact, significantly increasing grinding efficiency.

In a typical application, the circuit feed is pumped to a scalping cyclone upstream of the mill. The overflow by-passes the mill and the underflow is fed into the HIGmill. The pulp density of the mill feed is also controlled in the cyclone. The mill shaft speed is adjusted in order to generate the required energy to reach the target fineness. In typical cases, the process is single pass and no external classification is needed. The cyclone overflow and mill discharge are the circuit’s products.

The Outotec HIGmill comes in various drum diameters. The mill heights can be varied to optimize the media load and power input for specific applications. Chamber volumes range from 5 to 20,000 liters with corresponding drives from 5 to 5,000 kW. The HIGmill, said Outotec, is the only ultrafine grinding technology in commercial use that can use small size high-density grinding media in mill sizes above 3,000 kW.

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