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<br />C~w~ <br />CN- + SO, + O, + HZO -> OCN- + HzSO. <br />Cyanate Is not stable and readily hydrdyzes to carbonate and ammonium bns as fellows: <br />OCN- + 2Hs0 -> CO,~' + NH~* <br />~ Under alkaline condRions, the carbonate Ion precipitates as calcium carbonate and the ammonium <br />r1°~ I ion is cornerted tc ammonia. <br />WeaMycomplexed metal cyanide complexes Induding zinc, nickel, and copper are oxidized by <br />sulfur dioxide and oxygen to form cyanate (as shown above) and metal hydroxides. For example, <br />copper cyanide complexes (in this case tricyanocuprate) are decomposed as follows: <br /> <br />~~r <br />Y~~S LUd.~^ ~ Ui <br />t~ ,Ir. <br />2Cu' + SOZ + Oz + 2H* ---> 2Cu" + H,SO. <br /> <br />~ Va Analogously, nickel and zinc cyanide compounds also are oxidized by sulfur dioxide and oxygen <br />to form their metal hydroxides (NI(OH), and Zn(OH)z, respectively). Copper, nickel, and zinc <br />hydroxides will precipitate as very insduf~le slid compounds. <br />In the INCO SOZ/Air process, iron cyanide removal is initiated by reduction of ferricyanide to <br />ferrocyanide according to the fdlowing reaction: <br />2Fe(CN)e~ + SOZ + 20H" ---> 2Fe(CN)e+ + HzSO. <br />Ferrocyanide then forms a metallo-ferrocyanide complex which is precipitated with available metal <br />ions (i.e., zinc, copper, and nickel): <br />2MZ* + Fe(CN); " + 7H2O ----> MZFe(CN)8~7Hz0 <br />where: M" = ZnZ', NiZ*, or CuZ' <br />25301/RN0610.RPT INCO SOZ/Air Technical Revision Page 2 <br />June 16, 1992 San Luis Mine <br />