A critical review of the thermodynamics of hydrogen cyanide and copper(I)–cyanide complexes in aqueous solution

Abstract

Kyle, J.H. and Hefter, G. (2015) A critical review of the thermodynamics of hydrogen cyanide and copper(I)-This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT2 AbstractDespite the importance of cyanide and of metal-cyanide complexes in gold hydrometallurgy, and the need for reliable thermodynamic data for modelling gold solution chemistry, no comprehensive critical overview of the thermodynamics of hydrogen/cyanide and metal/cyanide complex formation has appeared in the literature since that of Beck in 1987. In particular there has been little consideration of the values of the equilibrium constants (and related thermodynamic parameters) at the higher ionic strengths and non-standard temperatures more typical of hydrometallurgical processing. The copper(I)/cyanide system is of particular importance in gold hydrometallurgy as gold is often associated with copper sulfide minerals such as chalcopyrite, chalcocite, covellite and bornite, all of which except chalcopyrite are reasonably soluble in cyanide solutions due to the formation of copper(I)/cyanide complexes. This paper reviews the available thermodynamic data for the hydrogen/cyanide and copper(I)/cyanide systems in aqueous solution with special emphasis on measurements made at elevated ionic strengths and as a function of temperature. It has been found that, while reliable data are available at 25 o C and very low ionic strengths, the data for higher ionic strengths and temperatures are limited. An attempt has been made to rationalize the available data, and to point out areas where further careful measurements are desirable.

Investigation of complexation and solubility equilibria in the copper(I)/cyanide system at 25 °C

“…A preliminary mention of Solis' work has been made (Hefter et al, 1993) but his final results (Solis, 1995) have not been published. Akilan's data were cited, without experimental detail, as "unpublished" in our earlier review (Kyle and Hefter, 2015). These details are provided here for the first time.…”

“…However, almost all of those studies were made on dilute solutions (Kyle and Hefter, 2015;Beck, 1987;Lu et al, 2002). This is unfortunate because the formation constants obtained under such conditions do not adequately account for observed behaviour under hydrometallurgical conditions (Dai et al, 2010).…”

“…The limitations of the existing stability constant database for the Cu(I)/CN − system have been detailed recently by Kyle and Hefter (2015). These authors noted that little information was available on …”

Predicting Cyanide Consumption in Gold Leaching: A Kinetic and Thermodynamic Modeling Approach

“…As the leaching of the ore proceeds, the concentrations of the major species change and so does the ionic strength and, consequently, all the activity coefficients and conditional equilibrium constants [19,20]. To model the chemical speciation during the leaching process, it is necessary to quantify the formation of each significant species.…”

“…For the leaching of each mineral system, possible species were determined from relevant papers and the PHREEQC database [14,19,23]. The most significant of these species and their equilibrium constants are shown in Table 1.…”