Checking gold fever

"TAKE the gold, but check the pollution": this is the new refrain, born of desperation, that the Brazilian government is directing at the thousands of gold-diggers who have reduced the Amazon basin to an expanse of infertile muck. The only way that the government can spare the Amazon river the greedy depredations of the gold panhandlers is to virtually gift them new technology. A joint European and Brazilian research programme, funded by the European Commission, claims to have developed a technology that will increase the miners' gold yield and at the same time cut down pollution. It will leave the river free of the mercury that is dumped into it after the gold has been leached.

"We are appealing to the self-interest of the prospectors," says Paul Docx of Imperial College Consultants, the firm managing the L1.2 billion project. What he offers are two simple devices which the prospectors will hopefully find hard to resist. At present, they extract the precious metal by flushing the river sediment, rich in gold, down a sloping sluice. The mercury held in the troughs separates the gold from the sediment and combines with it, forming a thick, viscous amalgam. The problem is that at least half the mercury is barfed into the river along with the sediment. The gold is retrieved by heating the amalgam and letting the mercury burn off, polluting the air.

Imperial College Consultants offers a "gravity trap" which can be fitted at the bottom of the sluice. The trap contains a series of slats that slow the water flow. Any gold, mercury or amalgam settles. A second device prevents the release of mercury vapour into the air. The amalgam is boiled in a sealed crucible and the mercury is recovered in a condenser attached to it. What should attract the prospectors, most of them too poor to afford mining apparatus, is that the device is surprisingly cheap: each costs just L30 to build and can easily be carved out of scrap metal. The researchers vouch that the two devices used together can save 95 per cent of the mercury, and some of the gold, that is usually lost.

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