Minerals processing perfection: Down to the grain

Despite best efforts, there is always a degree of coal lost during its processing.

These particles may be lost as dust, during transfer, or even afterwards in tailings.

While it may not seem like a major loss if a few stray particles are gone here and there, over the space of a month, or even a day, it can result in much lower product levels.

Over the space of a mine's life this can potentially result in huge tonnage levels that are simply lost.

And with the current prices of coal at their lowest all year, dropping from $115 per tonne in February down to $87 per tonne in July, coal is only a few dollars off the massive slump of the global financial crisis, which saw coal at $83 per tonne.

Now the CSIRO and BASF have collaborated together to improve coal recovery and reduce lost product rates.

According to BASF the two groups have created a process that improves the "recovery of coal particles that are otherwise lost to tailings, making coal production more efficient and potentially increasing reve­nues for coal producers".

The "new coal particles recovery process offers significant improvement in the recovery of difficult to float coal".

Froth floatation is a well recognised process for recovering fine coal, as coal itself is naturally hydrophobic.

Initially the CSIRO's Coal Grain Analysis tool identified that particles from certain coal types were difficult to recover from flotation methods.

After this it began a collaboration with BASF, which had created block copolymers, and found that introducing these copolymers as promoters to the fine coal slurry actually boosted yields "and has the potential to significantly increase the availability of saleable coal".

Neil Fitzmaurice, the head of BASF's Industry Group Mining Asia Pacific explained that "high quality coking coal is a key ingredient for steel production and critical for the development of the emerging economies of Asia.

"This new coal particle recovery process offers a significant improvement in the recovery of coal, maxi­mising yield and lowering production costs."

CSIRO research manager for coal preparation, Bruce Firth, added there are significant variations in different types of coal, adding that "we can determine the flotation response of specific coal types by the Coal Grain Analysis method, the introduction of BASF's chemical reagent into the process increases the attachment of particularly coal particles to flotation bubbles".

According to the CSIRO's laboratory studies and plant scale tests, the addition of block copolymers improves recovery for both fine and coarse coal particles.

The new process requires only minor modifications to existing industry methods, BASF adding that it is currently in the process of commercialising the flotation promotion agent.

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