Calcined limestone waste from soda prodn. was studied by IR spectroscopy, X-ray diffraction and thermogravimetry and used for pptn. of phosphate ions from aq. solns. At the waste-to-phosphate ratio 1:1 (by mass), the phosphate ion concn. was decreased from 100 mg/L down to 4-9 mg/L. After 2 yr. long storage of the limestone, it lost about 16% of the free lime.