Theoretical Calculation of Equilibrium Cadmium Isotope Fractionation Factors between Cadmium-bearing sulfides and aqueous solutions

Abstract

7 In this study, the equilibrium isotope fractionation factors between Cd-bearing 8 aqueous solutions and minerals were predicted. The theoretical method used to calculate 9 the Cd isotope fractionation factors is the first-principle quantum chemistry method (Cd: 10 LANL2DZ, other atoms: 6-311+G(d, P)). Reduced partition function ratios (RPFRs) of 11 Cd-bearing minerals (Greenockite and Sphalerite) were modeled by the method of the 12 volume variable cluster model (VVCM). The theoretical method of “water-droplet 13 method” is used to simulate the solvation effect of different Cd-bearing aqueous solutions. 14 The results show that, in most cases, the Cd-bearing aqueous solutions are enriched in 15 114 Cd relative to Greenockite. The Cd isotope fractionation factors between Cd-bearing 16 aqueous solutions and Greenockite are in the range of 0.433- 0.083 (100℃) . And the Cd 17 isotope fractionations between different Cd-bearing species are believed to be widespread. 18 Cd isotope fractionation factors between different reservoirs are of great theoretical 19 significance to many geochemical processes such as surficial geochemical process and 20 ore-forming process. These theoretical parameters are studied systematically and 21 carefully in this study. 22