Uptake of Iodide by a Mixture of Metallic Copper and Cupric Compounds

Ability of copper/cupric compound mixtures to remove iodide from solution was investigated to predict sorption of radioactive iodine in the environment and to assess their use in a nuclear reprocessing method. Thermodynamic calculations were performed to study the stability of such mixtures in solution and to obtain equilibrium constants of Cu(0)/Cu(II)/I- and Cu(0)/Cu(II)/Cl- systems. Both calculations and experimental results showed that a Cu(0)/Cu3(OH)2(CO3)2 (azurite) mixture selectively uptakes iodide ions (initial concentrations: 10-2 and 10-1 M) in the presence of 10-1 M chloride ions. Reaction of iodide with copper powder and azurite crystal or copper plate and azurite powder have also been investigated, leading to precipitation of CuI onto massive copper phase. The different solids were separately analyzed by XPS and MEB-EDX, giving some insight in the uptake mechanism. It is proposed that soluble copper released by the cupric compound is reduced at the surface of metallic copper, leading to a preferential precipitation of CuI on copper surface.