It does so by extracting from industrial waste water the last traces of any rare - and increasingly valuable - metal.

"We leave only a microgramme per litre," said Steve van Zutphen, a Dutchman who founded Magpie Polymers last year with Frenchman Etienne Almoric.

"It's the equivalent of a sugar lump in an Olympic swimming pool," Almoric said.

Magpie Polymers operates from slightly shabby premises at a factory at Saint-Pierre-les-Nemours, 80km southeast of Paris. But it is at the leading edge of technology with a procedure developed at the prestigious Ecole Polytechnique in 2007.

The process is based on the use of tiny pellets of plastic resin through which waste water is pumped.

Gold, platinum, palladium and rhodium little by little stick to the pellets and are thus separated from the waste water. A single litre of this patented resin can treat 5m3 to 10m3 of waste water and recover 50g to 100g of precious metal, "equivalent to $3900 to $6500," Almoric said.

Cellphones, catalytic converters and countless other everyday products contain these precious metals. But once they are scrapped the problem lies in retrieving the precious metals.

"What is complicated is that the amounts are infinitesimal, and so hard to recover," said Van Zutphen.

Once they have been separated and crushed, some industrial waste products have to be dissolved with acid in water. Then the metals have to be recovered irrespective of whether they are valuable. Magpie will not name its chief clients but is active in "France, England, Belgium and Switzerland".