Alternative to ball milling

GRINDING technology has taken a major step forward with the first successful commissioning of a 3 MW M10,000 IsaMill in a mainstream coarse grinding duty for Anglo Platinum in South Africa, according to Xstrata Technology.

GRINDING technology has taken a major step forward with the first successful commissioning of a 3 MW M10,000 IsaMill in a mainstream coarse grinding duty for Anglo Platinum in South Africa, according to Xstrata Technology.

This follows the installation of the first M10,000 IsaMill in a concentrate regrind, “UFG” duty at Anglo Platinum’s Western Limb Tailings Retreatment Project in 2003.

The scale up from the 1.1 MW M3000 IsaMill was a joint development between Anglo Platinum, Xstrata Technology and Netzsch Feinmahltechnik of Germany.

The new installation is at Anglo’s Potgietersrust PPL-C concentrator in Limpopo, Republic of South Africa. Chris Rule, Head of Concentrator Technology with Anglo Platinum said the IsaMill offers a real alternative to ball or tower milling in secondary and tertiary applications and enables a “step change” in metallurgical recoveries through better liberation.

“The energy efficiency, flotation improvement from inert grinding, and small installation footprint are all pluses, but the competitive capital and operating costs, in addition to the downstream recovery improvement are the primary project drivers.

“IsaMills can be used to design simpler grinding circuits that more specifically meet the liberation needs of each ore’s mineralogy. It is still early days, but so far the results are very promising,” Rule said.

The IsaMill was initially developed to increase the economics and metallurgy of ultra fine grinding of intermediate flotation concentrates.

The significance of the PPL-C installation is that it is the first IsaMill to be installed in a coarse, mainstream grinding application as a ball mill alternative, the company said.

Unlike other grinding mills, the IsaMill does not need to be closed circuited with hydrocyclones to produce a narrow particle size distribution for flotation, according to Xstrata.

The PPL-C IsaMill treats 250 – 300 t/h of feed to scavenger flotation.

Rule said that the mill, which was commissioned in December 2006, had achieved its metallurgical design objectives — grinding more efficiently than a ball mill, in a much smaller plant footprint, and with significant processing benefit from the inert grinding media.

The grinding media is 3.5 mm Maggoteaux Keramax MT1 ceramic beads.

The mill feed is PGM bearing Platreef ore with a variable and complex mineralogical character and is also an extremely hard and abrasive ore with maximum Bond BMWi > 30 kWh/t.

Following on the success of this first application, Anglo Platinum will be commissioning a further four 3 MW M10,000 IsaMills for mainstream coarse grinding in the last quarter of 2007, two more at Potgietersrust and two at the Waterval UG2 concentrator in Rustenberg.

The combination of efficient grinding, improved flotation chemistry and short equipment delivery time is expected to yield more applications.

Lindsay Clark, Business Manager — Mineral Processing with Xstrata Technology said the mainstream grinding applications at Anglo Platinum marked a turning point in grinding technology.

“The IsaMill is a step change in technology, fundamentally different from conventional grinding,” he said.

“The advantages that are well established for ultra fine grinding, have now been extended to a coarser size range currently dominated by conventional grinding methods.

“The industry has been searching for a step change in grinding efficiency for decades — we think it is here now with the IsaMill and Anglo Platinum is pioneering that process,” he said.

Key contacts:

Lindsay Clark

Mineral Processing Business Manager Xstrata Technology

LClark@xstratatech.com.au

Xstrata Queensland Support Centre

supportcentre@xstrata.com.au

To keep up to date with Australian Mining, subscribe to our free email newsletters delivered straight to your inbox. Click here.