Extracting silver from used X-ray film.

Approximately one-fifth of the silver used each year worldwide ends up in X-ray film, according to Haruo Ishikawa, a professor in the Chemical Engineering Department of Japan's University of Osaka Prefecture. After X-ray film is developed and fixed, it holds about two percent by weight of silver in its emulsion layers, which are made of gelatin.

The most common current process to recover silver from used X-ray film is to burn the film in a furnace and retrieve the precious metal from the ashes. However, this method is "rather expensive because of the cost of maintaining the furnace and treating the soot and foul-smelling smoke. Furthermore ... recovery and purity of silver are low and the re-use of the polyester film is impossible."

For an inexpensive and efficient alternative, Ishikawa and his colleagues...