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Superplants Mine Profits from Metal-Rich Soils COLLEGE PARK, Maryland, March 8, 2002 (ENS) - When Scott Angle began to investigate the potential for safely remediating contaminated soil, back in 1994, he had no idea that his effort would be the basis for an entirely new method of mining. Angle, associate dean and associate director of the University of Maryland's Agricultural Experiment Station, found that a unique group of plants called hyperaccumulators can extract metals from the soil.
The plants must be able to tolerate and survive high levels of heavy metals in soils - zinc, cadmium, and nickel. These small, slow growing plants concentrate the metal in their shoot tissue. The plant shoots are then harvested and, through smelting, dried and burned for energy production. The ash is then processed to recover the metal. One such plant is alpine pennycress, Thlaspi caerulescens, a wild perennial herb found on zinc and nickel rich soils in many countries. This plant occurs in alpine areas of Central Europe as well as in the Rocky Mountains. Most varieties grow eight to 12 inches high and have small, white flowers. In 1998, Angle's findings were the impetus for the formation of a new University of Maryland start-up company, Viridian Environmental, to which the technology is exclusively licensed. Based in Houston, Texas, Viridian is funding the phytomining research and development in the amount of $1 million over five years. The goal is to show that phytomining is commercially feasible The U.S. Department of Agriculture (USDA) has signed a cooperative research and development agreement with Viridian. Angle is involved, and so is Viridian plant breeder Yin-Ming Li, Richard Roseberg at Oregon State University, and Alan Baker at the University of Sheffield, United Kingdom.
Agronomist Rufus Chaney of the USDA's Agricultural Research Service first hit upon the idea of using plants to selectively remove and recycle excessive soil metals in 1983. He explains how phytomining takes the process one step farther than remediation to extraction of the metals. "The crops would be grown as hay. The plants would be cut and baled after they'd taken in enough minerals." "Then they'd be burned and the ash sold as ore," Chaney says. "Ashes of alpine pennycress grown on a high zinc soil in Pennsylvania yielded 30 to 40 percent zinc, which is as high as high grade ore. Electricity generated by the burning could partially offset biomining costs." Chaney, working with Angle and Baker, selected several species of plants in the Alyssum genus, known as hyperaccumulators of nickel and cobalt. Soil and plant management practices were identified that allowed the selected genotypes to accumulate more than 2.5 percent nickel in their shoots. The sale of the metals recovered through this phytomining process has a potential profit of several hundred dollars per acre, says Angle, who notes there are millions of suitable acres worldwide from which to extract the metals. v In numerous countries, says Viridian president Jay Nelkin, "acres of land remain barren and infertile due to abnormally high concentrations of heavy metals that are toxic to most forms of plant life."
Phytomining creates a win-win scenario - the inexpensive cleansing of contaminated soil and the production of a valuable cash crop. Plants that accumulate metal can return an economic profit from waste rock. To date nickel, thallium, gold, platinum and palladium appear to be likely candidates for phytomining. Phytomining on contaminated soils containing these minerals is more lucrative than growing traditional crops on the same land, an Agricultural Research Service analysis has shown. Harvests from pastures or forests grown on such land would fetch about $50 to $100 per hectare per year. A phytomining crop growing on the same land would produce an annual 400 kilograms of nickel per hectare, worth more than $2,000 even at today's depressed market price for nickel. After selling the byproduct energy, the annual per-hectare value of a phytomining crop exceeds $3,000. The new plant mining process is environmentally friendly in nature. Unlike conventional soil mining techniques such as gold mining which uses toxic cyanide to remove the metal from its ore, this technology causes little or no damage to the environment. During the process, the soil is covered with foliage, reducing erosion and runoff losses. Copyright Environment News Service (ENS) 2002. All rights reserved. |
Alpine pennycress removes excess metals
from soil. (Photo by Keith Weller courtesy 
Rufus Chaney examines the roots of a metal
accumulating Thlaspi plant in a growth chamber. (Photo by Keith
Weller courtesy USDA)
Leaves of Thlaspi caerulescens can accumulate
levels of zinc and cadmium many times higher than leaves of most other
plants. (Photo by Scott Bauer courtesy USDA)