Recycling of Water from Cyanide Waste Water by Ozone Oxidation Combined with UV Radiation and Ion Exchange Metho d

Abstract

In order to reuse water from cyanide waste water, the copper cyanide waste water is oxidized using ozone with ultraviolet (UV) radiation. The waste water processed by ozone oxidation is passed through a cation exchange resin column and then an anion exchange resin column. The advantage of the process of cyanide oxidation by ozone is that, unlike the conventional chlorination method, it does not produce salts or chloride, which would have to be removed later to reuse the water, because excess ozone decomposes merely into oxygen.
At the process of the ozone oxidation combined with UV radiation, cyanide ion (CN^-) was oxidized to cyanate ion (CNO^-) in a short time without addition of any other chemical. The reaction rate was about three times as fast as the oxidation reaction by ozone without UV radiation. At the process of cation exchange, sodium cation of sodium cyanate was replaced by H⁺. The cyanate ion is decomposed into CO₂ and NH₄⁺ by hydrolysis under acidic conditions. Ammonium ion was absorbed by the cation exchange resin.
The e lectric conductivity of the effluent from the anion exchange column was smaller than 10/μS/cm. No cyanideds, cyanate ion or copper ion were detected in the effuent. This deionized water can be reused as rinsing water in the plating processes.
On the basis of this experiments, we devised a practical recycling system where water of toxic cyanide waste water can be reused as deionized water in the plating processes. Saturated ion exchange resins, the only by-products of the system, are regenerated at a separated place on an industrial scale. This recycling system will reduce a burden on the earth environment and could possibly create economical effect at the process of production.