PROBLEM TO BE SOLVED: To provide a new method for removing a fluoride ion, with which a large volume of wastewater is treated at a low cost.SOLUTION: In a method for removing a fluoride ion, an adsorbent which is obtained by cleaning a mandarin orange squeezed juice residue, having been treated by heating and drying, with water to remove a water-soluble organic material and a water-soluble calcium compound therefrom, and making a tetravalent zirconium ion and/or a tetravalent cerium ion be adsorbed and carried thereon, is immersed in an aqueous solution to be treated and the fluoride ion in the aqueous solution to be treated is adsorbed thereon and removed from the aqueous solution.【課題】低コストで大容量の排水を処理できる新規のフッ化物イオン除去方法を提供する。【解決手段】フッ化物イオン除去方法は、加熱・乾燥処理したミカン搾汁残渣を、水で洗浄して水溶性の有機物およびカルシウム化合物を取り除いた後、４価のジルコニウムイオンおよび／または４価のセリウムイオンを吸着・担持させて得られた吸着剤を、対象水溶液に浸漬して、当該対象水溶液中のフッ化物イオンを吸着・除去する。【選択図】図１
