Scrounging metal

US researchers have developed a technique that can not only help recover precious metals, such as gold, but also clean up waterways contaminated with toxic metals like lead, mercury and chromium. The method has been developed by scientists at the us department of energy's (doe) Pacific Northwest National Laboratory in Richland, Washington (Popular Science, Vol 254, No 3).

The technique relies on two key components. The first is a silicate ceramic that can take the form of a bead or powder. Each grain of the ceramic material that is 5-15 micrometres in diameter has a dense pattern of cylindrical pores.

The second component is called a monolayer, and is a single layer of densely packed molecules chemically tailored to bond with metallic contaminants.

The scientists at Richland have found a way to attach monolayers within the pores of the ceramic grains. In this, one end of the monolayer binds to the ceramic and the other end is left free to eat a target metal that is passing through a pore. The multitudinous pores provide a large surface area to trap metals.

In fact, a mere teaspoon of this material in powder form has the surface area of a football field, says Jun Liu, a staff scientist who directed the research. The ceramic can reduce the concentration of a targeted metal to well below what is required for drinking water standards, it was observed during field tests.

The molecule-lined ceramic grains can be used for mining. It may help recover precious metals like gold from water. The doe is considering using the technique for cleaning up water and soil at places where mercury concentration is high. It may also be useful for extracting mercury from hazardous wastes. If successful, the technique may be used for cleaning up other toxic metals as well.