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1 <br />A 5 C I <br />4. DATA EVALUATION: CYANIDE ANALYSIS <br />4.1 GENERAL COMMENTS <br />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-cyahide chemistry <br />in terms of analysis for cyanide. <br />' Three values of cyanide are determined: <br />• "free cyanide" (FCN): 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 are dissociable <br />' (broken down to release their cyanide) 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 (TCNI: this analysis determines all "free" cyanide, all WAD <br />cyanide and the strongly bound nnetallo-cyanide <br />' complexes with iron and cobalt. <br />Therefore total cyanide levels in these samples will exceed weak 8cid dissociable <br />t 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 (or of very low solubility) unless they are <br />' complexed with cyanide. <br /> <br /> <br />4 <br />1 <br />