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...conducting innovative research for the Mining Industry! |
The Centre for Environmental Research in Minerals, Metals, and Materials |
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September, 2002.
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Growing Metals
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How Hyper-Accumulating Plants can Recover Toxic and Valuable Metals from Waste Dumps
Chris Anderson, Senior Research Associate, Department of Soil and Earth Sciences, Massey University, Palmerston North, New Zealand
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John A. Meech, Professor of Mining Engineering and Director of CERM3
Background CERM3 has entered into a Research Agreement with a group at Massey University in New Zealand to conduct a joint project into Phyto-Reclamation and Phyto-Mining. Massey is the leading research group in the world studying the use of hyper-accumulating plants to remove toxic metals and valuable metals from waste dumps and spent heap leach operations. The work is being done in Brazil at Cachoera, a contaminated informal gold mining town located 200 kilometers south of the mouth of the Amazon. The tailings dumps are highly contaminated with mercury and it is hoped that mercury and gold can be recovered into a particular plant species simultaneously.
Hundreds of plants naturally accumulate specific metals from the soil in which they grow; nickel, for instance, can accumulate in Berkheya coddii, a plant native to South Africa and it is now being extracted from a toxic waste dump at a nickel refinery in Johannesburg. This species has a maximum biomass of 22 t/ha and a maximum nickel content of over 1%. Professor Robert Brooks at Massey, who passed away in 2001, first coined the term "phytomining" in 1977. His book on the subject is available at Amazon.com. More recently, Viridian Resources of Houston have patented a process for the same type of application using allysum and INCO have entered into an agreement to test out their technique on contaminated soils near their Port Colborne nickel refinery. The market potential for this technology is simply incredible and many new companies in North America are springing up to take advantage of the new opportunities to recover metals from abandoned waste dumps and remediate highly-contaminated sites.
The nickel hyperaccumulator Berkheya coddii native to South Africa. Researchers in the United States have been able to "phyto-mine" lead from contaminated soil using EDTA and, more recently, Dr. Chris Anderson has developed a method to recover gold from waste dumps at levels approaching 100 ppm on a dry weight basis in canola. The gold is rendered soluble through the addition of a thio-sulfate solution to the dump for a short duration of time. The plant draws the metal out of the earth and incorporates it into its cells. A recent field trial on several hectares of tailings at an abandoned mine near Te Aroha in New Zealand's North Island has demonstrated success at growing a variety of canola (Brassica juncea) on material that previously was barren of plant growth. Production rates of a kilogram of gold from each hectare of tailings is indicated. Canola is a rapidly growing plant which matures within 3 months in tropical climates. When the plants reach their maximum weight, the thio-sulfate is added to the soil. Even small traces of gold become soluble for about 10 days. The plants soak up the gold, and as they begin to wither, they are harvested, dried and then, burned to extract the metal. There are enormous potential environmental benefits from this phenomena. Numerous artisanal mining operations around the world discharge mercury with gold tailings. After mining, the remaining population often live off these un-reclaimed land growing plants for food. Contamination is a major problem. By taking this induced hyperaccumulation process into the field at such sites, remediation of the land can be performed while gold production provides the support needed to live. As the dump becomes cleaned of its toxic metal and the gold quantity drops, the land can then be converted to productive farming activities providing sustainability for the region and a natural method for these people to transition their economy from mining to agriculture. For a detailed presentation on phyto-mining and phyto-reclamation, click here.
References
C.W.N. Anderson, R.R. Brooks, R.B. Stewart, R. Simcock, 1998. Harvesting a crop of gold in plants. Nature, 395, 553-554.
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Email: cerm3@mining.ubc.ca
Copyright © 2002 Centre for Environmental Research in Minerals, Metals, and Materials. All rights reserved.
Permission is given to reproduce all or any of the contained materials provided due credit is given to CERM3 as the source.
Revised: September 28, 2002.
