Conical spacers that can be retrofitted to its proprietary IsaMills, or incorporated in new mills, are said to be particularly effective the finer the regrind product required. The spacers have been commercialised, but Glencore Technology says tests on pyrite concentrate showed 12.7% to 21.5% reductions in specific energy draw in gold recovery with the P80 size ranging from 22um to 15um. The greater the fine grinding duty the higher the savings recorded, it claims.

Glencore says the conical spacers have no adverse effect on particle size distribution.

Fine grinding to P80 sizes as low as 7um is becoming increasingly important as mines treat ores with smaller liberation sizes.

Glencore Technology's popular IsaMill is 25 years old this year, with the first mills still working at Mount Isa and McArthur River in Australia.

The unit's technology manager, Virginia Lawson said the IsaMill had demonstrated it was more energy and metallurgically efficient than standard ball and tower mills when grinding metalliferous concentrates to smaller sizes.

"These specific energy savings offer the potential for a significant reduction in the operating costs of fine grinding," she said.

The spacers were best suited to sites with relatively fine grind size targets and high specific energy consumptions, she said.