Neptunium(V) reduction by humic substances of varying functionality

The time dependence of the reduction of Np(V) to Np(IV) by humic substances of varying functionality has been studied under anaerobic conditions between pH 3.5 and pH 9.0. Synthetic humic acids with pronounced redox functionality were studied in comparison to natural humic substances. For Np redox speciation in solution solvent extraction, NIR absorption spectroscopy and ultrafiltration were applied. Exemplary, the application of a synthetic HA is shown for the study of the Np(IV) sorption onto kaolinite in the presence of HA.