Total cyanide is a term used to indicate, in terms of NaCN (or KCN), all the cyanogen existing in the form of simple cyanides, hydrocyanic acid, and the double cyanide of zinc.
Procedure. Measure 25 cc of clear cyanide solution, add 10 cc of caustic soda-potassium iodide solution, and titrate with standard AgNO3 solution to the first permanent yellow opalescence.
Standard AgNO3 solution (see free cyanide above)
Caustic Soda (NaOH)-Potassium Iodide (KI) solution. Dissolve 4 grams NaOH and 1 gram KI in 100 cc of water.
Determination of Total Cyanide by Distillation
Twenty-five cubic centimeters of cyanide solution is transferred to a 250-cc Claissen distilling flask leading to two 500-cc Erlenmeyer flasks connected in series. The first of these is placed in an ice bath. Each flask contains 150 cc of 2 per cent NaOH solution. Fifty cubic centimeters of dilute HCl (1 part 1.16 specific gravity acid to 4 parts water) is added to the Claissen flask through a separatory funnel. The contents of the Claissen flask are then boiled vigorously for about 6 min., after which the stopcock of the separatory funnel is opened to prevent “sucking back” and the flame removed. The contents of the Erlenmeyer flasks are then combined and agitated vigorously for about 1 min. with about 1 gram of litharge to precipitate any small amounts of soluble sulphide present. The solution is then filtered and washed, and the combined filtrate and washings titrated with silver nitrate, using KI as an indicator.
ANALYSIS OF CYANIDE SOLUTIONS
Those concerned with ore testing and plant control are principally interested in the determination of certain component parts of the working solutions that are critical for the proper functioning of the cyanide process.
These include especially the free cyanide, protective alkalinity, oxygen content, and reducing power of the cyanide solutions. In special cases it is also desirable to determine the precious-metal content of the solutions and the quantities of various cyanogen compounds that are formed during ore treatment, such as ferrocyanides, thiocyanates, and base-metal cyanides. While the analysis of gold precipitates and gold bullion is of importance to mill operators, the reader is referred to other sources of information on the subject.