This paper presents the results obtained from coprecipitation experiments of uranyl solutions in the presence of metallic iron and/or its alteration phases in synthetic bentonitic-granitic composition water. Experiments were done under oxidising conditions at room temperature. The pH range covered was 7.4 – 8.8. Changes in the uranium concentrations and the characterisation of the secondary phases formed in the experiments were done using XRD and SEM-EDS and are presented herein.
Final uranium concentration values were in the range of 2·10−5 – 5·10−4 mol (kg of H2O)−1. In all cases, results from these experiments did not show evidence of a clear effect due to the presence of iron (metallic or previously corroded) on the uranium concentration. These data were similar to those obtained by coprecipitation in similar conditions but in absence of iron material. Boltwoodite was observed [K2(UO2)2(SiO3)2(OH)2·3H2O] in iron surface materials and characterized in all experiments. Based on the experimental data obtained (uranium concentration in solution and bulk solid phase characterisation) we propose the following surface-mediated reaction:
2 K+ + 2 H4SiO4 + 2 UO2 +2 + 3 H2O ⇔ K2(UO2)2(SiO3)2(OH)2·3H2O + 6 H+