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THE! 1 ;_ c _ _ <br />`5c:~~i~L1t~1~ !3`~ ~o~v 1~F/'~• NC-`f1L r ~ <br />L 1 .~. <br />CYANIDES <br />.~ <br />aqueous solution se or below pH 8.5 Since most natural <br />waters have a off at or below 5.5, these compounds are easily <br />capable of releasing free cyanide into the environment. Two <br />examples of free cysnide samples are the alkali cyanides potassium <br />cyanide {KCN} and sodium cyanide (NaCN). <br />FREE (or direct) CYANIDE - Readily soluble cyanide compounds <br />that are capable of liberating cyanide gas (HCN} from an <br />WEAK ACID DISSOCIABLE (W.A.D.) CYANIDE - Cyanide compounds that <br />are capable of releasing HCN gas at pH 4.5 with one hour of reflux <br />distillation. Weak acid dissociable cyanides include all free <br />cyanide compounds plus other metal cyanides such as cadmium and <br />nickel cyanide. The presence of alkali cyanides in a solution <br />affect the solubility of other metal cyanides. Note that iron <br />cyanide is excluded from the weak acid dissociable cyanide <br />classification. <br />TOTAL CYANIDE after Distillation -Compounds that are capable <br />of releasing HCN from a strongly acid solution with one hour of <br />reflux distillation. These include all free and peak acid dis- <br />sociable cyanide Compounds, plus other compounds such as iron <br />cyanide. It should be noted that cyanide complexes of cobalt, <br />gold, platinum, and palladium are not fully recovered by this <br />method. <br />Theoretically speaking <br />FREE CYANIDE < WEAK ACID DISSOCIABLE CYANID$ < TOTAL CYANIDE <br />Examples: <br />1. Far a solution of KGN, the free, weak acid dissociable and <br />total cyanide values would all be equal, within experimental <br />error. <br />2. For a solution that <br />100 mg/L iron cyanide, <br />cyanide would be equal, <br />than the other two. <br />ANALYTICAL CONDITIONS <br />contains 100 mglL sodium cyanide and <br />the free cyanide and weak acid dissociable <br />but the total cyanide would be much•larger <br />Free cyanide analysis does not include a distillation step to <br />remove interfering substances or to convert cyanide complexes <br />to more soluble forms. The accuracy of tDzis classification of <br />c~~~nide compounds is highl,r dzpender.c upon what other ions are <br />_.. vhe sample . <br />