Advances in ion chromatography for monitoring the gold cyanidation process

During the gold cyanidation process, cyanide can be lost from the leachate by various chemical routes. Since cyanide is generally the most expensive reagent in this process, it is becoming increasingly important to monitor these cyanide losses. The products of these cyanide losses include base metal cyanide complexes, thiocyanate and cyanate. The two most significant cyanicides in order of importance are sulfides and copper bearing minerals. The problems caused by cyanide soluble copper minerals are well known to the gold processing industry and have been reviewed by several authors (e.g. 1, 2). One particular facet of this problem concerns the effect of the CN:Cu mole ratio, R, on the gold leaching kinetics. In order to efficiently leach cupriferous ores, it is important that R is maintained at a level that allows sufficiently rapid leaching without excessive use of cyanide. An additional consideration when leaching cupriferous ores is the oxidation of cyanide by Cu(11) minerals, resulting in the formation of cyanate. Ion chromatography (IC) has been successfully used for the determination of cyanide, metal cyanide complexes, thiocyanate and cyanate in leachates. Most of the important metal-cyanide complexes and thiocyanate can be determined by reverse phase ion interaction chromatography (e.g. 3, 4, 5, 6). Cyanide and cyanate are both unretained in the separation of the metal cyanide complexes and are not detectable as their respective anions. However, it has been possible to determine cyanide in this separation by either precolumn derivatisation with Ag to form [Ag(CN)J (4) or post-column derivatisation with a selective colourimetric reaction to produce a visible dye (5) .There are no reactions suitable for the analogous pre or post column derivatisation of cyanate in the above separation of metal cyanide complexes. Cyanate has been determined separately on an anion exchange column (e.g. 7, 8, 9). This paper presents two new IC techniques that enable the rapid determination of cyanate concentration and R in samples containing large concentrations of Cu(I)-cyanide complexes. Other metal cyanide complexes, in addition to Cu(I), can also be determined in conjunction with R, while other anions such as chloride and sulfate can be determined in conjunction with cyanate. The main aim of this work has been to