The kinetics of dissolution of synthetic covellite, chalcocite and digenite in dilute chloride solutions at ambient temperatures

Abstract

. (2011) The kinetics of dissolution of synthetic covellite, chalcocite and digenite in dilute chloride solutions at ambient temperatures. Hydrometallurgy, 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 MANUSCRIPTThe kinetics of dissolution of synthetic covellite, chalcocite and digenite in dilute chloride solutions at ambient temperatures. AbstractAn experimental study of the comparative kinetics of dissolution of various synthetic copper sulphides (covellite, chalcocite, digenite) in dilute chloride solutions has been carried out at ambient temperatures such as could be encountered in the heap leaching of secondary copper sulphide minerals.The dissolution of sized synthetic covellite particles was carried out in dilute HCl solutions containing known concentrations of copper(II) and iron(III) at controlled potentials. The results show that the rate of dissolution is similar at potentials of 600 and 650 mV, but is predictably less at a potential of 550 mV. The rate of dissolution is remarkably similar to that of chalcopyrite under similar conditions and is largely independent of Cl -and HCl concentration in the range 0.2 to 2.5 M and 0.1 to 1 M respectively. The effect of temperature is significant and an activation energy of 71.5 kJ mol -1 was derived which confirms a chemical or electrochemical rate-determining reaction on the mineral surface. A mineralogical study of the residue after leachingshows that most of the sulphur is associated with unreacted covellite and occurs as isolated globules on the surface with over 90% of the unreacted covellite surface free of sulphur.Dissolution of synthetic chalcocite and digenite is rapid compared with that of covellite under the same conditions. At a potential of 500 mV, the relatively rapid A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTinitial dissolution of chalcocite and digenite does not proceed beyond about 50% and 45% copper dissolution, respectively, as predicted from the thermodynamics. These results confirm the formation of a covellite-like phase as an intermediate which cannot be leached at a potential of 500 mV. An increase in the potential results in rapid dissolution of this "secondary covellite", relative to primary covellite. These results provide useful information for the conditions that should be used for the heap leaching of ores containing secondary copper sulphide minerals.

Study on the second stage of chalcocite leaching in column with redox potential control and its implications

“…The range of Eh was chosen based on heap bioleaching practices (Ruan et al, 2013), and the values set were greater than the rest potential of chalcocite reported at approximately 600 mV (Miki et al, 2011;Petersen and Dixon, 2003).…”

“…Oxidative dissolution of chalcocite by Fe 3+ , O 2 or Cu 2+ , either in a sulfate or chloride system, occurs in two distinct stages with the production of secondary covellite (Cu 1.0-1.2 S) as an intermediate (Bolorunduro, 1999;Cheng and Lawson, 1991a;Dutrizac and MacDonald, 1974;Mao and Peters, 1983;Mcdonald and Langer, 1983;Miki et al, 2011;Mulak and Niemiec, 1969;Petersen and Dixon, 2003;Ruan et al, 2013;Ruiz et al, 1998Ruiz et al, , 2007Senanayake, 2007Senanayake, , 2009Sullivan, 1930;Thomas et al, 1967):…”

“…The secondary covellite is more reactive than the primary mineral Lawson, 1991a, 1991b;King, 1966;Walsh and Rimstidt, 1986). Miki et al (2011) attributed this effect to the significantly increased surface area of the secondary covellite formed by the dissolution of approximately 50% of copper from chalcocite. The leaching rate of the second stage is more dependent on temperature compared with the first stage, with reported activation energies from 55 kJ/mol to 105 kJ/mol (Dutrizac and MacDonald, 1974;Petersen and Dixon, 2003).…”

“…The complicated chalcopyrite oxidation may be related to critical leaching conditions, particularly the solution Eh (Nicol et al, 2010;Velásquez-Yévenes et al, 2010a, 2010b. Unlike chalcopyrite, spontaneous oxidation in the second stage of chalcocite leaching occurs if the potential for the oxidant couple is greater than that for the oxidation of the secondary covellite (Miki et al, 2011). Chalcocite oxidation always follows the "polysulfide pathway".…”

The Development of Fine Microgram Powder Electrode System and Its Application in the Analysis of Chalcopyrite Leaching Behavior

“…However, the second peak at 0.529 V is lower than that of the covellite or chalcocite oxidation peaks. Miki et al [10] indicated that covellite, which is produced from chalcocite oxidation, is more easily oxidized than crystalline covellite. The second peak may be a covellite oxidation peak that is produced from chalcocite oxidation.…”