Solvent Extraction of Gold(I) Directly from Alkaline Cyanide Solution with Dibutyl Sulfoxide and n -Octanol
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INTRODUCTION
AS an important member of the precious metal group, gold exists in an elementarily scattered state in nature. Usually, alkaline cyanide solution,[1] thiosulfate solution,[2] thiocyanate solution,[3] thiourea solution,[4] etc. are used for leaching gold from its mineral ore. Among these methods, cyanidization still predominates because of the high leaching efficiency and mature technology. Generally, following dissolution in the traditional cyanide solution, the extracted gold is recovered mainly by activated charcoal adsorption, displacement/reduction with zinc dust, or galvanic deposition.[5] However, these methods have several drawbacks, in that some of the gold product is lost, the processes are rather too long, and the purity of the gold produced is rather too low.[6] So it is essential to select novel and highly efficient methods to substitute the traditional procedures to directly extract gold from alkaline cyanide solution. Fortunately, liquid/liquid solvent extraction not only can overcome these problems but also has a number of advantages. It has been proposed as the most promising technology for gold cyanide processing especially with suitable extractants for separation of gold from alkaline cyanide solutions.[7–12] In summary, only a few applicable systems were used to directly extract gold from alkaline cyanide solutions, including amines, modified amines, guanidine, substituted guanidine, sulfoxide category materials, as well as crown ethers.[11,13–18] Of these systems, quaternary ammonium salts, such as CTAB (cetyltrimethylLU PAN, Ph.D. Student, and FENGWU WANG and XIA BAO, Professors, are with the Department of Chemistry and Chemical Engineering, Huainan Normal University, Anhui, Huainan 232001, P.R. China. Contact e-mail: [email protected] Manuscript submitted August 9, 2008. Article published online July 8, 2009. METALLURGICAL AND MATERIALS TRANSACTIONS B
ammonium bromide), are considered as the most promising agents to extract gold directly from alkaline cyanide solution. However, although Au(CN)–2 can be effectively extracted by water-soluble quaternary ammonium salts, it is very difficult to strip it out of the organic phase due to its’ strong interaction with Au(CN)–2,[8] which heavily restricts this technology being industrially applied for gold production. In the present work, the effectiveness of dibutyl sulfoxide and n-octanol for the extraction of gold from alkaline cyanide solutions was investigated. N-octanol was added in the organic phase to improve gold extraction efficiency. The stripping characteristics of gold loaded in the organic phase were also studied. This method could provide a potential technology for gold recovery from alkaline cyanide solution in industry.
II.
EXPERIMENTAL
A. Materials In this work, dibutyl sulfoxide (molecule structure (n-C4H9)2S = O, synthesized in the laboratory) was used as an extractant, which was diluted in CA grade kerosene provided by Shanghai Chemical Reagents Co. (Shanghai, China). All other chemical reagents including sodium thiosulfate, pot
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