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<br /> <br /> <br />ANALYTICAL -GENERAL <br />Cyanide Concentration Aliquot <br /> in Aliquot < mL > <br /> < ppm CNP > <br />0.2 - 16 10 <br />2 - 32 5 <br />10 - 160 1 <br />20 - 320 0.5 <br />50 - S00 0.2 <br />III Interferences <br />Thiocyanate, cyanate and thiosulfate ions have no adverse effects and can be <br />tolerated at levels normally occurring in gold mill effluents. Sulfide is a source of <br />interference, 0.1 mg S- being equivalent to 0.025 mg CN" If present, sulfde ions can be <br />readily removed by the addition of lead salts. However, it is unlikely shalt mill effluents <br />would contain sulfide at levels large enough to significantly interfere in the cyanide <br />determination. Sulfide particles which contact the picric acid reag4nt because of <br />improper filtering of a gold bearing slurry, will also cause the S- interference. <br />The method requires a close control of pH since it affects the colour intensity <br />produced by the cyanide-picric acid reaction. The most intense coloradop results at pH <br />9.0 - 9.5. For maximum sensitivity and a good reproducibility of analytical results, the <br />picric acid reagent solution should therefore be buffered. In the precept prrocedure a <br />mixture of sodium tetraborate and carbonate as well as DTPA itself serve this purpose. <br />DTPA is preferred to EDTA due to more favorable values of acid ionization constants and <br />stability constants of some metal chelates. <br />w~w~~m <br />7 <br />