Yes, it is possible to improve the sorption of rare earth metals through complexation with carboxylic acids. Carboxylic acids can form complexes with rare earth metals due to the presence of their carboxylate groups (-COO-), which can act as ligands. These complexes can enhance the affinity of the rare earth metals for sorption onto various materials, such as ion exchange resins, activated carbon, or other solid sorbents. The complexation can increase the stability of the metal ions in solution, making them more accessible for sorption processes.