Cyanide destruction

This section describes the treatment technologies currently in use to recover or remove wastewater pollutants normally found at coil coating facilities. The treatment processes can be divided into six categories recovery techniques, oil removal, dissolved inorganics removal, cyanide destruction, trace organics removal, and solids removal.5-14 Adoption of specific treatment processes will depend on the following ... 

Robbins, G.H. 1996. Historical development of the INCO S02/AIR cyanide destruction process. Canad. Mining Metall. Bull. 89 (1003) 63-69. 

Fig. 2(b) represents similar dependencies for technological solutions. Solutions were obtained by means of cyanidation of specified quantities of one metal (Au, Ag, Cu, Zn, curves l -6 ), or the ore concentrate containing all the above stated metals (curve 7 ). Figures prove that process of cyanide destruction is determined by the time of plasma action on the solution. For technological solutions, time of treatment required for complete destruction of cyanide ions depends on composition of the solution. The more complex is the composition, the longer time is required for complete degradation of cyanides. Character of the curves is changed as well. 

In the event of technological solutions, curves of cyanide destruction have horizontal sections which occurrence is caused by various speed of degradation of free cyanide and cyanide, combined in complex with metal. 

Ho et al. used a packed-bed reactor and a series of 316 stainless steel fiber an-ode/cathode pairs to decompose cyanide-containing effluent [41]. The cyanide destruction process was enhanced by the presence of metal ions, which led the authors to treat a copper cyanide effluent. The cyanide concentration was decreased from an initial concentration of 1400ppm to less than 20 ppm within a 4-20 h time period at an energy consumption of 5 -13 kW h/kg CN. At a CN/Cu ratio of 4.6 most of the copper was deposited on the cathode while some was converted to the divalent form and deposited on the anode surface as an oxide. 

In a related study, Lin et al. [42] used a bipolar arrangement of the same reactor and electrode system mentioned above to compare the performance of the two configurations. The bipolar design was shown to yield higher current efficiencies for cyanide destruction at the expense of a higher power consumption. Nonuniform copper deposition on various cathodes showed that the reactions were not occurring uniformly with the bipolar arrangement. 

The CE for the cyanide destruction process is obviously determined by the extent of the parallel reaction (7), a factor which becomes much more important as the cyanide levels drops to below 100 ppm [88]. Complete mineralization of the CN-by reaction (8) removes all traces of the offending species, but at the expense of considerably more charge consumption. It may be reasonable to stop the reaction at the CNO- stage, something which is quite feasible since reaction (8) occurs with more difficulty than (6) [89] at a potential of almost 0.5 V more anodic [87]. At a PH < 10, the cyanate ion hydrolyzes on its own according to the following reaction ... 

Use For textile and pulp bleaching, cyanide destruction, wastewater and sewage treatment, food processing, electronics industry. 

Since a slight excess of chlorine is usually employed to obtain cyanide destruction, the waste stream may still be quite toxic from the residual chlorine present. Dechlorination using sulfur dioxide can be used to reduce any residual chlorine to chloride, which removes the toxicity before discharge (Eq. 5.20). 

The high toxicity of [CN] makes it essential for cyanide-containing waste produced by industry to be treated. Several methods are used. For dilute solutions of cyanide, destruction using hypochlorite solution is common ... 

McGUl, S. L., and P. G. Comba 1990. A Review of Existing Cyanide Destruction Practices, U.S. Bureau of Mines, Reno Research Center, Nevada Mining Association, Nevada Department of Wildhfe, WUdUfe/ Mining Workshop, Reno, NV, March, pp. 11, 16, 29. 

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