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1 <br />I4, A 5 C I <br />i , 4. DATA EVALUATION: CYANIDE ANALYSIS <br />4.1 GENERAL COMMENTS <br />i , In order to be able to interpret the cyanide database in Table 1, it is essential to <br />understand the components which are determined by any of the cyanide analytical <br />methods. These general comments address the issues of metallo-cyanide chemistry <br />' in terms of analysis for cyanide. <br />Three values of cyanide are determined: <br />"free cyanide" (FCNI: this is made up solely of cyanide ions in solution and <br />hydrogen cyanide. These species are essentially <br />interchangeable as a function of pH value; <br />' weak acid dissociable cyanide (WAD CNI: the analysis will determine all <br />"free" cyanide (cyanide ions and hydrogen cyanidel, plus <br />metallo-cyanide complexes which ark dissociable <br />' (broken down to release their cyanidel by a weakly acid <br />analytical protocol (i.e., pH 4.5). The cyanide <br />complexes in these samples are with copper, zinc, <br />' chromium, nickel, manganese, and mercury, where <br />these are present in the samples; <br />total cyanide (TCN): this analysis determines all "free" cyarhide, all WAD <br />cyanide and the strongly bound metallo-cyanide <br />complexes with iron and cobalt. <br />Therefore total cyanide levels in these samples will exceed weak a6id dissociable <br />cyanide which itself will exceed, by some considerable margin due to the amount of <br />copper present in the samples, the free cyanide values in the samples. <br />It should be noted that the high pH of the samples ensures that the metal species <br />analyzed can only be in solution as metallo-cyanide complexes. At this pH value, <br />' these metals are essentially insoluble for of very low solubility) unless they are <br />complexed with cyanide. <br /> <br />~~ <br />' 4 <br />