Many industrial processes including the case hardening of steel, electroplating and ore refining can result in waste waters that contain toxic concentrations of cyanide. These may be destroyed by alkaline chlorination or direct electrolytic oxidation, but the former produces considerable volumes of sludge for disposal while the latter incurs high energy costs.

However, recent work by C. E. Byvik of the National Aeronautics and Space Administration’s Langley Research Center and A. Miles of Southern University has demonstrated another oxidation technique, and this is effective in reducing cyanide concentrations to levels which are significantly below those achieved by established methods (“Solar-Assisted Oxidation of Toxic Cyanide”, LAR-13171/TN, NTIS Tech. Notes, October 1985).

In their solar-assisted oxidation technique, oxygen-containing air is bubbled through the waste cyanide solution, in which platinised titania powder is suspended, while it is subjected to either artificial or natural sunlight. The platinised semiconducting powders can be recovered and reused, and the results suggest that the process could become an effective and inexpensive method of treating cyanide-containing industrial waste water.