Ozonation cyanide removal

Introduce chemical oxidation process for cyanide removal using ozone. 

This is a process mainly used in power plants for destruction of cyanides using chlorine, hypochlorite salts, or ozone. The process removal efficiency is about 99.6% [12-19]. 

The use of ozone os on oxidant for industrial wastes containing cyanides and other reducible toxic substances appears worthy of careful investigation. The oxidation of simple cyanides by ozone is rapid and complete. Mass transfer controls the absorption. The use of packed towers or sieve plate towers is indicated, and the maintenance of a pH of at least 9.0 is recommended. The destruction of cyanates and cyanide complexes is slower than the cyanide oxidation. These substances are destroyed if sufficient contact time and proper pH control are maintained so that these slower reactions can take place. The use of redox potential to control the degree of oxidation appears promising. Proper interpretation of the redox potential of the treated waste will give an excellent indication of the effectiveness of the treatment and the degree of removal of cyanide and cyanate. 

Appendix B3 shows the typical performance data of ozonation process, for cyanide reduction. Percentage removal in the range of 51-97% was reported by the US EPA. 

Treatment of Electroplating Wastewater. Toxic cyanide ions are the major pollutant in electroplating wastewater. They must be removed before discharge of the wastewater. As shown in Eqs. (3) and (4), ozone can oxidize free cyanide ion rapidly to less toxic cyanate ion, which then slowly hydrolyzes to nitrogen and ammonia. The reaction equations are as follows " ... 

The major application of electrochemical ozone cells is in the oxidation of water-based species (in order to provide sterilization) and the oxidation of industrial process liquors containing cyanides or organicSte.g. phenols, dyes and pesticides, In such applications it is environmentally more desirable than CI2 or OCl" treatment (Chapter 7) as the latter chemicals may leave a range of undesirable species. Ozone treatments may be advantageously coupled with ultraviolet treatments in order to remove certain persistent chemicals (such as certain pesticides or polychlorinated biphenyls). In the case of sterilization of potable water the cells are likely to remain small modular designs (Fig. 5,15(b)). While the O3 required is very dependent on inlet-water quality, a cell of 100 cm anode area may service up to KKK) m day of water at the 1 mg dm O3 dose level... 

The tests demonstrate that upon varying content of phenols in the used water the ozonation is one of the most promising methods for their removal. The ozonation was foimd to be applicable for the decomposition of rhodanide in neutral and weak acid medium in the temperature range of 9-25°C. The ozone consiunption in this case is 2 mg/mg. The ozone uptake for the oxidation of the cyanide ion (CN ) is 1.8 mg/mg. 

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