Process for producing a carboxylic acid composition comprising 2,5-furandicarboxylic acid, the process comprising the steps: a) providing or producing a crude carboxylic acid composition comprising 2,5-furandicarboxylic acid and 5-formyl-2-furancarboxylic acid; b) purifying the crude carboxylic acid composition to produce a purified carboxylic acid composition comprising 2,5-furandicarboxylic acid, wherein the purifying comprises at least one step selected from the group consisting of: - hydrogenating at least a portion of the 5-formyl-2-furancarboxylic acid; - oxidizing at least a portion of the 5-formyl-2-furancarboxylic acid; - recrystallization of at least a portion of the 2,5-furandicarboxylic acid; and - hydrolyzing of dialkyl ester of 2,5-furandicarboxylic acid; c) providing or producing a treatment solvent composition comprising more than 95 % by weight of water, with respect to the weight of the treatment solvent composition; d) providing or producing a thermal treatment composition comprising the purified carboxylic acid composition and the treatment solvent composition; e) subjecting the thermal treatment composition to an elevated temperature in the range of 140 to 200 °C for a time in the range of 5 to 240 min, wherein the percentage of dissolved 2,5-furandicarboxylic acid, relative to the total amount of 2,5-furandicarboxylic acid, is in the range of 10 to 80% to obtain a treated composition; and f) cooling the treated composition to a temperature in the range of 20 to 80 °C and separating at least a portion of the 2,5-furandicarboxylic acid from the treated composition to obtain a carboxylic acid composition and a treatment mother liquor comprising water. a) providing or producing a crude carboxylic acid composition comprising 2,5-furandicarboxylic acid and 5-formyl-2-furancarboxylic acid; b) purifying the crude carboxylic acid composition to produce a purified carboxylic acid composition comprising 2,5-furandicarboxylic acid, wherein the purifying comprises at least one step selected from the group consisting of: - hydrogenating at least a portion of the 5-formyl-2-furancarboxylic acid; - oxidizing at least a portion of the 5-formyl-2-furancarboxylic acid; - recrystallization of at least a portion of the 2,5-furandicarboxylic acid; and - hydrolyzing of dialkyl ester of 2,5-furandicarboxylic acid; - hydrogenating at least a portion of the 5-formyl-2-furancarboxylic acid; - oxidizing at least a portion of the 5-formyl-2-furancarboxylic acid; - recrystallization of at least a portion of the 2,5-furandicarboxylic acid; and - hydrolyzing of dialkyl ester of 2,5-furandicarboxylic acid; c) providing or producing a treatment solvent composition comprising more than 95 % by weight of water, with respect to the weight of the treatment solvent composition; d) providing or producing a thermal treatment composition comprising the purified carboxylic acid composition and the treatment solvent composition; e) subjecting the thermal treatment composition to an elevated temperature in the range of 140 to 200 °C for a time in the range of 5 to 240 min, wherein the percentage of dissolved 2,5-furandicarboxylic acid, relative to the total amount of 2,5-furandicarboxylic acid, is in the range of 10 to 80% to obtain a treated composition; and f) cooling the treated composition to a temperature in the range of 20 to 80 °C and separating at least a portion of the 2,5-furandicarboxylic acid from the treated composition to obtain a carboxylic acid composition and a treatment mother liquor comprising water.