Catalin Florin Petre 1, 2 Abdelaaziz Azizi 1 Caroline Olsen 2 Abdelaziz Baçaoui 2 Faïçal Larachi 1 1 Department of Chemical Engineering, Laval University, Qubec, Canada 2 COREM Research Center, Qubec, Canada Original Paper Capillary electrophoretic analysis of sulfur and cyanicides speciation during cyanidation of gold complex sulfidic ores A capillary electrophoretic protocol for the separation and quantification of the most important species potentially liberated during the cyanidation of gold sulfide- rich ores was accomplished in this study. The separation of 11 ions: S 2 O 3 2 – , Cu(CN) 3 2 – , Fe(CN) 6 4 – , Fe(CN) 6 3 – , SCN – , Au(CN) 2 – , Ag(CN) 2 – , SO 4 2 – , OCN – , SO 3 2 – , and HS – was achieved using an indirect UV detection method. The robustness of the analytical protocol was tested by analyzing ions speciation during the cyanidation of two gold sulfide-rich ores. The 1-h cyanidation of the two ores released up to six complexes into solution: S 2 O 3 2 – , Cu(CN) 3 2 – , SCN – , Fe(CN) 6 4 – , OCN – , and SO 4 2 – . The mineralogy of the ore was found to influence directly the nature and the amount of the dissolved species. Conserving the cyanidation solution for 72 h after sampling resulted in 96% total sulfur recovery. These results allow us to conclude that the analytical protocol developed in this study can become very useful for the optimization of precious- metals cyanidation plants. Keywords: Capillary electrophoresis / Gold cyanidation / Metallo-cyanides / Sulfide minerals / Sul- fur / Received: July 23, 2008; revised: September 1, 2008; accepted: September 4, 2008 DOI 10.1002/jssc.200800416 1 Introduction The pioneering work of Kudryk and Kellogg [1] described the electrochemical nature of gold dissolution in aerated cyanide solutions, a practice used to extract gold from ores, concentrates, and calcines since the late 19th cen- tury [2]. The process was successfully applied for a variety of ores and found widespread application in the 1970s for ores containing as low as 1 ppm gold [3]. Generally, the cyanidation process involves the following opera- tions: dissolution of gold from ores by an alkali cyanide solution,concentration of gold in solution, electrowin- ing or cementation by adding zinc metal of the gold from the leach solution and the safe disposal of waste products [3]. All the above steps require analytical con- trol; therefore,there is need for a quick and efficient method that can separate and quantify the various ions consumed/formed in the cyanidation reactors. Generally the dissolution of gold in alkaline cyanide solutions can be represented by [2] 4 Au + 8 CN – + O 2 + 2 H 2 O fi 4 Au(CN) 2 – + 4 OH – (1) However,nowadays a large proportion ofthe proc- essed gold is recovered from sulfide ores. Since the sul- fide minerals are to some extent soluble in cyanide solu- tions [4],there will always be an important amount of sulfur species present in the leach solution, which makes the cyanidation processmore complex to optimize. These difficulties concomitantly reflect on gold leaching and on reagent consumption. During industrial cyanidation, it is generally believed that the presence ofsuch sulfur species results in an excess consumption of cyanide and oxygen. In addition, from the results of kinetic studies, it has been argued that sulfur species also affect directly the gold leaching (reaction 1) [5]. This can occur when the leached sulfide ions passivate the gold surface by forming a passive Au 2 S layer [5]. Furthermore, early studies on the dissolution of gold in cyanide solution in the presence of sulfide miner- als have shown that transition metal components, i.e., Cu, Fe, Zn, etc., significantly increase the consumption of both cyanide and oxygen [4]. As the only target of the cya- nidation process is generally the recovery of the precious metals (Au, Ag), the amount of free cyanide theoretically needed for the process can be calculated based on the sto- ichiometry of reaction 1. Cyanidation plants data revealed that the cyanide used for precious metals recov- ery is less than 1%, while the rest of consumed cyanide is Correspondence: Professor Faal Larachi, Department of Chem- ical Engineering, Laval University, Qubec, Canada G1V 0A6 E-mail: faical.larachi@gch.ulaval.ca Fax: 1-418-656-5993 i 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com 3902 C. F. Petre et al. J. Sep. Sci. 2008, 31, 3902 – 3910