Thermal treatment of purified 2,5-furandicarboxylic acid (FDCA) for producing a carboxylic acid composition, the process comprising the steps of providing or producing a thermal treatment composition comprising a purified carboxylic acid composition and a water containing treatment solvent composition; subjecting the thermal treatment composition to an elevated temperature, wherein the FDCA is partially dissolved, and cooling the treated composition and separating at least a portion of the FDCA from the treated composition to obtain a carboxylic acid composition.