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Colloquium on Depressants
30 July, 2002
Cape Town, South Africa

The third Annual Colloquium of the UCT Depressant Research Facility took place in the UCT's Department of Chemical Engineering. Convened by Dr Dee Bradshaw, the Manager of the Facility, the colloquium attracted 52 delegates and participants, including 13 representatives of industrial depressant users, and 15 manufacturers, with the balance made up from UCT and other researchers, mainly from the Mineral Processing Research Unit [MPRU].

Polymeric depressants, derived variously from: starches; plant fibres, especially cotton; and the guar bean, are important reagents in the flotation of ores to recover nickel and copper and, especially, the platinum group metals [PGMs].

The Facility was established in 1999, with the MPRU, by the main PGM producers, namely Anglo Platinum, Impala Platinum, and Lonmin, who, as Members fund the ongoing research programmes. They have since been joined in this by the international mining group Rio Tinto, and the Canadian nickel producer Falconbridge.

Other work is undertaken for individual companies, principally the depressant manufacturing companies, many of them South African, but including, notably the Dutch AKZO and North American Cytec companies, both being represented at the Colloquium.

The eight technical presentations covered all aspects of the recent and current work being undertaken within the Facility. They addressed three main issues, namely: the influence of changes in depressant characteristics on overall flotation performance; the behaviour, and response to depressants, of specific mineral; and novel methodologies and tools for testing and the evaluation of results. The colloquium was concluded by a review and discussion session led by Associate Professor Peter Harris.

Depressants worth more than a row of Beans

A major event, which led to the setting up of the Depressant Research Facility originally, was the closure, in 1998, of the only local manufacturing plant for guar-based depressants. With properties differing markedly from the other depressant categories, they had long enjoyed a unique role in the flotation of PGMs. Indeed so fundamental was their role, that most users subsequently found it necessary to fall back upon substitute guar-containing products manufactures overseas.

The guar bean is a traditional peasant crop, with the bulk of the worlds supply coming from the Indian subcontinent, where supply, and the price, are subject to the vagaries of the monsoon climate. The food industry is a far bigger user of guar products than the minerals business; guar gum is a valuable stabiliser for ice-cream, amongst other things. In this application price is not an issue the food market is not price sensitive, the flotation application is. A series of bad harvests in the nineties, and the weak Rand, pushed the raw material price out of reach of the South African industry, and led to the closure of manufacture here.

At the same time efforts were being made to grow guar beans in Africa, and especially in southern Africa. It was reasoned that the chances of major crop failure, simultaneously, in two continents, should be reduced and this should smooth the supply to world markets, so limiting price fluctuations. Equally important, a home grown source of raw material would remove the exposure to exchange rate movements.

Thanks to the efforts of one man, Neil Ferrans of APX Guar, this local growing programme has gone from strength to strength. Trial quantities of depressant manufactured from his material have been evaluated by the Depressant Research Facility and shown to be as good as the previous commercial product. As a result the Colloquium provided the occasion for a landmark statement from local depressant supplier ChemQuest African Products. Speaking on their behalf, Chris Pretorius announced a merger between African Products and APX Guar which will lead to the resumption of full scale production of guar-based depressants in South Africa. With continued development by the Depressant Research Facility there seems to be no reason why this should not develop into a product range for international consumption.

Dee Bradshaw, University of Cape Town, South Africa. Email: db@chemeng.uct.ac.za




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