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<br />20:5 <br />0~98A 8J28 <br />Cl'anidc Chemisn•v wrd 7rr~nunrn+ <br />• SulphiJz which gains access to the absorption solution may cause positive <br />or negative interference with colotrrirnctric procedures ut very low <br />concentrations. <br />• Thioq';matc is a major interl'crcnce to the tortl cyanide distillation method. <br />usually resuhine in high cyanide values: however. decompose[ion is not <br />predictable ;tad the mechanism is uncertain. <br />• Bisulphate appears ro be a primary nc_,utivu interl'crcncu with the potential <br />for some desrre of cyanide desu'ucunn. Residual bisulphate is an <br />interterence. <br />• Sulphur species interference may be minimized by the Following treutmen[s: <br />- sulphide precipitation from the sample <br />- distillation of smallest possible .s:rntplc <br />• sulphide precipitation from the absorption xolution <br />- increased levels of chlora+ttine-T in rlrc colourintetric prOCedure <br />2.5 CALCULATION OF A MASS BALANCI: <br />It is possible to check the validity of a series of cy;tnide analyzes by comple[ing a <br />mass balance, comparinc the various cyanide art<f metals levels obtained from the <br />analysis of [itz :;true solution. <br />The mass calculations arc prepared assuming that iron ix hound to six uyanide <br />molecules (i.e. Fe(CN)~). copper is bound to three c}•anide molecules (i.e. Cu(CN),). <br />nickel is bound to four cyanide malccutus (i.c. Ni(CN),), and zinc cyanide is <br />completely dissociated as free cyanide and thr free metal. Thexc are the Four main <br />metals in cyanidation solutions, ^Ithr,u_h other mcerls could be added to the <br />calculations (i.e. lead, silver or mercury) iC present in elevated coneentrations. Baxzd <br />upon the number ol'cyanidz molecu(es buunci to each metal. the weight ratio of each <br />metal to cvanide is as follows: <br />• Iron U.36 me Fe/tms CN' <br />• Copper Q82 mg Cu/mg CN <br />~ • Nickc! 0.56 rnu Vi/mg CN <br />I u <br />I~ , <br />~~ I <br />II <br />As an ex:unple as,unte a anal, ward and I'rec r~-aniJr analysis of the same volution <br />produced conccmr:uiuns of 30Q m;;//I. 175 mg/I ,out 12; m/I, respcctivcly. It should <br />.Snrirh unrl ,tluddrr ~? <br />