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 degrees C to 175 degrees 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 degrees C Between 125 degrees C and 175 degrees C, The dominant species are CuCl+ and CuCl20. At very high Cl-concentrations (5 M NaCl), CuCl+ is the dominant species at 25 degrees C and 75 degrees C, becoming CnCl(3)(-) and CuCl42- at 125 degrees C. However, between 125 degrees C and 175 degrees 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. (C) 2000 Elsevier Science B.V. All rights reserved.