The hydrolysis of UO22+, NdIII , CeIII and CeIV cations, induced by thermal decomposition of urea, was studied. Moreover, we investigated binary mixtures of uranyl and the lanthanides, as well as ternary mixtures of uranyl and both lanthanides using CeIII or CeIV. The impact of the urea content and the temperature on the reaction kinetics and the formed precipitate was evaluated and the results are in depth discussed in our article, some results are also summarised in this presentation. Uranyl ions precipitated as ammonium diuranate (ADU) with different stoichiometry under the applied conditions. NdIII and CeIII cations showed a comparable pH evolution during hydrolysis and LnCO3OH products were identified, whereas CeIV hydrolysed at a lower pH and formed nanocrystalline CeO2. Depending on the urea content, a partial co-precipitation was observed for mixtures of UO22+ and NdIII. The products of CeIII and CeIV hydrolysis were also identified in the precipitates of binary uranyl and cerium mixtures. For ternary U/Nd/Ce mixtures, a simultaneous precipitation of NdIII and CeIII and a partial incorporation of the Ln phase into the ADU phase was observed, whereas the presence of CeIV/CeO2 resulted in three individual phases. The precipitation reaction was followed by monitoring the pH evolution and the metal concentration in the supernatant, applying UV/Vis and ICP-MS. The formed precipitates were characterised by XRD and SEM. The data accrued during the study are part of this data set. Please note that the provision of this dataset is based on a voluntary basis. You are welcome to use the data from this set in your work. If you do so and publish resulting findings, please cite our work as required by the license.