October 19, 2005
SIUC plant biologist Stephen Ebbs picked for project 'Down Under'
Stephen D. Ebbs
Stephen D. Ebbs, an associate professor in the Department of Plant Biology, left for the Southern Hemisphere earlier this month to work with a team of scientists studying ways to extract gold from waste rock using plants. The work in gold phytomining and phytoremediation has both financial and environmental applications. A team of scientists from the University of Melbourne specially selected Ebbs, who is an expert in the transport of metal cyanides and metal cyanide degradation. The funding for Ebbs' visiting professorship is coming from that university.
"Much of my professional career has been spent working in phytoremediation. This work provides another aspect of this field for me to pursue," Ebbs explained from on location in Australia. "The gold phytomining is a related concept, using plants to selectively remove a metal of interest from the growth media. Except this time we plan to recover (the gold) for commercial purposes."
Ebbs' team will work with simple leftover rock that contains gold. Studying ways of using plants to recover the gold from mine tailings, which are typically contaminated with cyanide, also is a goal of the study, however.
Cyanide selectively binds with gold. Today, mine operators typically spray a cyanide solution on a pile of waste rock and wait for the gold to bind with the cyanide. Workers then recover the gold from the solution, but must find a way to dispose of the poisonous substances left behind. This so-called "heap leach" method creates a large volume of toxic waste.
"Gold phytomining is envisioned as either an alternative to this approach or a way of recovering more gold from the waste rock or tailings after this heap leaching is completed," Ebbs said. "The accumulated gold in plants has been studied for more than 100 years and techniques for recovering this gold are known. The technology of gold phytomining is an attempt to improve on this natural phenomenon."
The plant of choice in this case is the eucalyptus tree, a plant native to the Australian continent and perhaps best known as the favorite food of the koala bear. The team chose eucalyptus for several reasons, Ebbs said. One of the parameters of the study is to use plant species native to the area where the gold mine is located. Also, eucalyptus is a cyanogenic plant, producing cyanogenic compounds as part of its normal metabolism.
The technique involves establishing plants and irrigating them with a cyanide solution to make the gold soluble, thereby introducing it into the plant roots. After a set period of time, the team will harvest the plants and recover the gold from the leaf tissue. Ebbs said studies indicate a surprising amount of gold – sometimes greater than 100 parts per million – can be recovered.
"Our goal is to learn enough about the ways plants accomplish the transport of gold cyanide to improve gold accumulation," he said.
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