Complexation of Cu2+ in oxidized NaCl brines from 25°C to 175°C: results from in situ EXAFS spectroscopy

In order to understand the significance of Cu2+ transport in oxidized brines and in secondary enrichment processes, we studied the speciation of 0.1 M CuCl2 in 0, 2, and 5 M NaCl solutions from 25°C to 175°C using in situ EXAFS spectroscopy. No chloro-copper complexation is observed in solutions containing 0.2 and 2.2 M Cl at temperatures up to 75°C. Between 125°C and 175°C, the dominant species are CuCl+ and CuCl20. At very high Cl concentrations (5 M NaCl), CuCl+ is the dominant species at 25°C and 75°C, becoming CuCl3− and CuCl42− at 125°C. However, between 125°C and 175°C, there is a transition to only CuCl+ and CuCl20. This may result from the competitive ion-association of Na+ and Cl−. CuCl42− may be an important species in fluids associated with the formation of red-bed copper deposits.