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EIA under way for new tailings dam – Phoenix Platinum

1st February 2013

By: Samantha Herbst

Creamer Media Deputy Editor

  

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Precious metals miner Pan African Resources has started an environmental impact assessment (EIA) amid plans to construct a long-term offsite tailings dam for its Phoenix Platinum chrome tailings retreatment plant (CTRP) in the North West province.

This will enable Phoenix Platinum to bypass the current highly oxidised feed- stock material sourced from integrated ferrochrome producer International Ferro Metals (IFM) which, since January last year, has been supplying Phoenix Platinum with opencast oxide material that does not float properly and, therefore, negatively affects the platinum-group element (PGE) recoveries.
IFM initially started supplying Phoenix Platinum with a sulphide-rich feed source from its Lesedi underground operations in Buffelsfontein, north-west of Johannesburg, when the CTRP was completed in November 2011.

However, the ferrochrome producer cut back drastically on operations at Lesedi in January 2012, owing to financial consi- derations. As a result, it moved mining operations to its low-cost opencast oxidised ore section.

“The metallurgy of oxidised tailings negatively affects recovery and concen- trate grade, leading to poor PGE concentrate production,” says Pan African CEO Jan Nelson.

The chemical changes to the oxidised orebody – which has been exposed to rain and oxygen in the atmosphere – affect the flotation response and efficiency of the ore in several ways.

“The weathered and, thus, more friable ore results in excessive ultrafine material being generated during processing. This material becomes entrained in the froth and does not drain during the flotation process, resulting in lower-concentrate grades,” he says.

To achieve target concentrate grades, the float cells have to be operated at deeper froth depths and lower air inputs, resulting in reduced platinum-group element (PGE) recovery.

“Platinum-group metal (PGM) flotation is, essentially, a sulphide flotation process – the PGEs in the tailings are attached to or associated with metal sulphides,” explains Nelson.

He adds that, when these sulphides are oxidised, their float response is much poorer, requiring higher reagent reac- tions and resulting in lower achievable recoveries.

“The flotation process normally renders the silicate waste rock hydrophilic (attracted to water) and, thus, nonfloatable. However, the altered waste rock resulting from oxidation is more susceptible to becoming hydrophobic (repelled by water) and, thus, floatable,” he says.

The result is that silicate gangue – which sometimes creates ‘sticky froth’ – attaches to the concentrate in conventional flotation dynamics and PGEs then become extremely difficult to recover. Nelson explains that the net effect is a reduction in PGE recovery and concentrates grades.

He tells Mining Weekly that Phoenix Platinum will continue to accept IFM’s current arising tailings, as it is the main source of CTRP’s process water source.

“Replacing the IFM current arisings with tailings dam material will only be possible once we have constructed our long-term offsite tailings dam,” he says.

Meanwhile, the effect of last year’s PGM’s low basket price was noted by Phoenix Platinum and would have relieved some of the effects of the oxide-feed material, says Nelson.

Moreover, despite signing a five-year PGM concentrate agreement with platinum major Lonmin’s operating subsidiary, Western Platinum, he stresses that last year’s violent strikes at the miner’s Marikana mine had no material effect on the CTRP’s operations.

Phoenix Platinum is currently in a closed period and cannot yet disclose projected production for the 2012/13 financial year. The plant does, however, hope to reach a target of 1 000 oz/m during the following financial year.

Nelson tells Mining Weekly that the CTRP’s management still plans to double throughput at the plant to 40 000 t/m by 2014 at an estimated capital expenditure of R92- million, but adds that this depends on both the PGM and chrome markets.

“Phoenix Platinum is in a position to rapidly move ahead with the project at short notice,” he says, adding that construction of the expansion stream will take less than 12 months to complete.

Further, Nelson cannot disclose what became of the proposed tender for addi- tional chrome tailings as the matter is “under confidentiality”.

Being awarded this tender would allow Phoenix to operate at 40 000 t/m for the next 17 years.

The company did, however, tell Mining Weekly in December 2011 that the Phoenix upgrade would proceed regardless of the tender outcome and that Pan African would try to secure more chrome tailings from other sources.

Edited by Megan van Wyngaardt
Creamer Media Contributing Editor Online

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