Using alfalfa plants to harvest gold sounds ridiculous?sort of like using broccoli to dig for diamonds. But Jorge Gardea-Torresdey, chemistry department chairman at the University of Texas at El Paso, says alfalfa filtering is a potentially efficient and cost-effective way of retrieving gold nanoparticles. Best of all, the process is environmentally friendly.
The existing methods of producing gold nanoparticles, used for electrical contacts in nanoelectronic circuits, require expensive and toxic chemical processes. Gardea-Torresdey’s approach taps alfalfa’s natural ability (called phytoremediation) to extract minerals from the medium it’s growing in. Alfalfa planted in places where gold naturally accumulates, such as near gold mines, can retrieve significant amounts of the metal. “I think we can eventually get 20 percent of the weight of the plant in gold,” he says.
Gardea-Torresdey’s research dates back to his teenage years. Working in a mining laboratory near his home village of Parral in northern Mexico, Gardea-Torresdey became fascinated with the idea of using plants to suck up toxic mine tailings. Nearly 30 years later, Gardea-Torresdey started applying the same approach to harvesting useful metals?such as gold. He focused his efforts on alfalfa. “Alfalfa can pick up metal better than other plants,” he says. Experiments conducted with alfalfa grown in soil imported from Parral yielded positive results. Working with colleagues at the University of Texas at Austin and Stanford University, Gardea-Torresdey discovered that the gold stored inside the plant was nearly identical to gold particles produced through chemical processes. Getting the metal out of the alfalfa also proved to be easy. The gold is isolated and extracted by simply mashing up the plants and then spinning the goop inside a centrifuge.
Gardea-Torresdey admits that the technique still needs additional refinement and testing. But he’s hopeful that his process will eventually become the preferred method of extracting gold particles from soil. “That would be a dream come true,” he says.