Raman study on the speciation of copper cyanide complexes in highly salinesolutions

Previous studies have established that the following three copper(I)-cyanid e complexes form in aqueous solution: [Cu(CN)(2)](-), [Cu(CN)(3)](2-) and [ Cu(CN)(4)](3-). The distribution of these complexes in solution at equilibr ium is highly dependent upon the CN/Cu molar ratio. The speciation of coppe r cyanide complexes in highly saline solutions is of interest to Australian mining companies because of the unusually highly saline process water used on the goldfields of Western Australia (ca. 200 g/l total dissolved solids ). This study has used the vibrational technique of Raman spectroscopy to d etermine the effect of highly saline water on the equilibrium distribution of copper cyanide complexes in solution for various CN/Cu molar ratios. For the first time it has been shown that in highly saline solutions the equil ibrium distribution of copper cyanide complexes changes significantly. It h as been established that [Cu(CN)(3)](2-) predominantly forms in highly sali ne solutions for CN/Cu molar ratios of 2.2 to 2.5, where previously it has been shown that both [Cu(CN)(2)](-) and [Cu(CN)(3)](2-) exist in non-saline solutions. Furthermore, in saline solutions containing an excess of cyanid e (ca. 200 mg/l) only [Cu(CN)(4)](3-) exists in solution and the formation of [Cu(CN)(3)](2-) has not been observed. This phenomenon has been used to explain the increased selectivity of ion exchange resins for gold cyanide i n highly saline solutions. (C) 1999 Elsevier Science B.V. All rights reserv ed.