Recycling of Cyanide Wastewater Applying Combined UV–Ozone Oxidation with a Titanium Dioxide Catalyst and Ion Exchange Resin Method

We investigated how to reuse water from cyanide wastewater by combining UV–ozone oxidation with a titanium dioxide (TiO2) catalyst and de-ionization by applying an ion exchange resin method. A TiO2 catalytic film was formed on the surface of quartz tubes by a novel sol-gel method. During UV–ozone oxidation with the TiO2 catalyst, cyanide ion (CN-) was oxidized to cyanate ion (OCN-) in a relatively short time without the application of any other chemicals. The processed water was smoothly de-ionized by an ion exchange resin method. The cyanate ion was decomposed into NH4+ and CO2 by hydrolysis under acidic conditions in a cation exchange resin column. Ammonium ion (NH4+) adsorbed to the cation exchange resin. The electric conductivity of the effluent from the ion exchange resin column was less than 1×10-1 mS m-1. This de-ionized water could be reused as rinsing water in the plating process. These experimental results suggested that toxic cyanide wastewater could be reused as de-ionized water.