Mechanism of gold dissolving in alkaline thiourea solution

  • Chai Li-yuang  (柴立元)
  • Wang Yun-yan  (王云燕)Email author


Reaction mechanism of gold dissolving in alkaline thiourea solution was studied by electrochemical methods, such as cyclic voltammetry, chronopotentiometry, AC impedance, linear sweep voltammetry. Apparent activation energy of anodic process of gold electrode dissolving in alkaline thiourea solution is 14.91 kJ/mol. Rate determining step is the process of gold thiourea complex diffusing away from electrode surface to solution. The results of AC impedance and chronopotentiometry indicate that thiourea adsorbs on gold electrode surface before dissolving in solution. There does not exist proceeding chemical reactions. Formamidine disulfide, the decomposed product of thiourea, does not participate the process of gold dissolution and thiourea complex. Species with electro-activity produced in the process of electrode reaction adsorbs on the electrode surface. In alkaline thiourea solution, gold dissolving mechanism undergoes the following courses: adsorption of thiourea on electrode surface; charge transfer from gold atom to thiourea molecule; Au[SC(NH2)2]ads+ receiving a thiourea molecule and forming stable Au[SC(NH2)2]2+; and then Au[SC(NH2)2]2+ diffusing away from the electrode surface to solution, the last step is the rate-determining one.

Key words

gold alkaline thiourea dissolution mechanism 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. [1]
    GRONEWALD T. Potential application of thiourea in the processing of gold[J]. J S African Inst M&M, 1977, 77(11): 217–223.Google Scholar
  2. [2]
    ORGUL S, ALTALAY U. Reaction chemistry of gold leaching in thiourea solution for a Turkish gold ore[J]. Hydrometallurgy, 2002, 67(1/3): 71–77.CrossRefGoogle Scholar
  3. [3]
    DENG T L, LIAO M X, WANG M H, et al. Enhancement of gold extraction from biooxidation residues using an acidic sodium sulphite-thiourea system[J]. Mineral Engineering, 2001, 14(2): 263–268.CrossRefGoogle Scholar
  4. [4]
    KUMAR V, MURTHY D S R, RAO K V. Extraction of gold from an Indian low-grade refractory gold ore through physical beneficiation and thiorea leaching[J]. Hydrometallurgy, 2003, 68(1/3): 125–130.Google Scholar
  5. [5]
    GONEN N. Leaching of finely disseminated gold ore with cyanide and thiourea solutions[J]. Hydrometallurgy, 2003, 69(1/3) 169–176.CrossRefGoogle Scholar
  6. [6]
    SENANAYAKE G. Gold leaching in non-cyanide lixiviant systems: Critical issues on fundamentals and applications[J]. Minerals Engineering, 2004, 17(6): 785–801.CrossRefGoogle Scholar
  7. [7]
    SENANAYAKE G.. Analysis of reaction kinetics, speciation and mechanism of gold leaching and thiosulfate oxidation by ammoniacal copper(II) solutions[J]. Hydrometallurgy, 2004, 75(1/4): 55–75.CrossRefGoogle Scholar
  8. [8]
    UBALDINI S, FORNARI P, Massidda R, et al. Innovative thiourea gold leaching process[J]. Hydrometallurgy, 1998, 48(1): 113–124.CrossRefGoogle Scholar
  9. [9]
    NINAE M, OBOSO A. TAKENAKA Y, et al. Synergistic extraction of gold from sulfuric acid solution containing thiourea[J]. Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 1991, 55(8): 867–873.CrossRefGoogle Scholar
  10. [10]
    GASPAR V, MEJEROVICH A S, MERETUKOV M A. et al. Practical application of potential-pH diagrams for Au-CS(NH2)2-H2O and Ag-SC(NH2)2-H2O systems for leaching gold and silver with acidic thiourea solution[J]. Hydrometallurgy, 1994, 34(3): 369–381.CrossRefGoogle Scholar
  11. [11]
    CHANDRA I, JEFFREY M I. An electrochemical study of the effect of additives and electrolyte on the dissolution of gold in thiosulfate solutions[J]. Hydrometallurgy, 2004, 73(3/4): 305–312.CrossRefGoogle Scholar
  12. [12]
    HUANG Zi-qing. Theory Introduction to Electrolyte Solutions[M]. Beijing: Science Press, 1983: 84–86. (in Chinese)Google Scholar
  13. [13]
    BARD A J, PARSONS R, JORDAN J. Standard Potentials in Aqueous Solution[M]. International Union of Pure and Applied Chemistry. New York: Basel Press, 1985: 287–321.Google Scholar
  14. [14]
    HU Yu-de, CHEN Bai-zhen. Investigating Methods of Metallurgical Electrochemistry[M]. Changsha: Central South University of Technology Press, 1990. (in Chinese)Google Scholar
  15. [15]
    CAO Chu-nan. Electrochemical Principles of Corrosion[M]. Beijing: Chemical Industry Press, 1985: 252–261. (in Chinese)Google Scholar
  16. [16]
    BARDER A J, FUKNA L R. Principle and Application of Electrochemistry Technique[M]. GU Lin-ying, LÜ Ming-xiang, SONG Shi-zhe, et al translate. Beijing: Chemical Industry Press, 1986: 615. (in Chinese)Google Scholar

Copyright information

© Central South University Press, Sole distributor outside Mainland China: Springer 2007

Authors and Affiliations

  • Chai Li-yuang  (柴立元)
    • 1
  • Wang Yun-yan  (王云燕)
    • 1
    Email author
  1. 1.School of Metallurgical Science and EngineeringCentral South UniversityChangshaChina

Personalised recommendations