In order to protect wildlife, nature and people it is absolutely essential to treat cyanide containing effluents prior to discharge.
The oxidation and detoxification of cyanide containing waste waters can be achieved by introducing a variety ofdifferent treatment agents including chlorine gas, sodium hypochlorite and hydrogen peroxide, where the most commonly used chemicals are chlorine gas and sodium hypochlorite. The main disadvantages of the detoxification agents listed above are high operating costs, the associated bulk handling, and storage of highly toxic and dangerous chemicals on-site. This in itself poses an additional environmental risk alone that needs to be managed at high costs.
An alternative and also environmental safe oxidation agent is Ozone, being one of nature’s most powerful oxidants.Ozone is easy to produce on-site and on-demand. Ozone can be easily applied to any industrial waters, wastewaters and air treatment processes. During the treatment process Ozone itself disintegrates and does not generate harmful byproducts. It just turns back to oxygen. Therefore ozone provides not only an environmentally friendly,but also a cost effective alternative to halogenated oxidants (i.e. chlorine, sodium hypochlorite), absorption techniques (i.e. activated carbon) or separation processes (i.e. reverse osmosis).
Chemistry of the Ozone Oxidation Process of Cyanide containing Waste Waters
The cyanide oxidation process can be described by two main chemical reaction pathways as highlighted below:
The first step is the oxidation of cyanide to cyanate (see reaction 1).
CN + O3 -----> CNO + O2 (1)
The second reaction (2) shows the reaction, where cyanate is hydrolyzed and oxidized in the presence of excess ozone to bicarbonate, nitrogen and oxygen:
2CNO + 3O3 + H2O ----> 2HCO3 + N2 +3O2 (2)
The total reaction time for the entire oxidation process of cyanide ranges typically between 10 to 30 minutes.