The Scotsman

Scientists Sitting On A Goldmine With Plants That Absorb Precious Metals

Money may not grow on trees, but scientists believe they could soon be harvesting crops of gold by encouraging plants to "mine" precious metals.

Scientists in New Zealand have induced plants to take up gold from ores found in the soil by absorbing it through their roots.

Professor Robert Brooks and Chris Anderson, who headed the team from Massey University, said the process could be used to extract gold and other precious metals, such as palladium, a silvery-white metal used to make jewellery.

According to Prof Brooks, current gold prices mean the amount salvaged from each plant could make the technique financially viable, as long as soil with a rich enough supply of ore can be found.

Researchers from the Institute of Natural Resources planted rapid-growing Indian mustard on mining ground in New Zealand.

By treating the soil with ammonium thiocyanate, a chemical often used in mining operations to make gold soluble, they found the plants could soak up and store the metal in their foliage.

The plants were then cut, burned and the ash was analysed. According to the findings, published in the scientific journal Nature yesterday, about 17 micrograms of dry-weight gold was extracted from the plant ash of each crop harvested -enough to make the process financially worthwhile at the current gold price of about $ 300 (GBP 180) per ounce.

"We believe this is the first evidence of significant gold uptake by any plant. As well as the economic ramifications this technology may have, this ability to make a 'crop of gold' opens up the way for the phytoextraction of other noble metals," Prof Brooks said yesterday.

He said the team now plans to cut costs by using fewer chemicals in the biological mining process.

Prof Brooks added that more money could be saved by selling off the energy produced by burning the plants, a method which is already used in the sugar beet industry.

Plants that naturally absorb quantities of heavy metals and toxins from the soil, such as lead and nickel, are increasingly used by some American companies to clean pollutants from the ground and abandoned industrial sites.

The idea is simply to fill an area with metal-absorbing plants, wait and then cleanse the land by harvesting and burning the crop. New Jersey-based Phyto-Tech is at the forefront of developing and marketing the technique, known as phytoremediation, and has worked on sites including Chernobyl.

In the UK, British Nuclear Fuels Ltd is investigating the feasibility of the process .

Elsewhere, scientists have made plants more efficient at removing poisons from the soil by genetic manipulation. At the University of Georgia, a molecular biologist, Rich Meagher, has turned a cousin of the common cabbage into a mean mercury extractor by giving it a shorter life span. The new, improved plant can be harvested up to seven times a year and reaches a height of up to 40cm, allowing it to absorb more mercury.

Scientists in Indiana are attempting to alter plant DNA to increase absorption rates.

Professor Peter Goldsburgh, at Purdue University, has claimed phytoremediation is the way ahead for purging toxic urban wastelands.