To provide a method which is capable of removing uranium from by-products at the time of uranium production, i.e., magnesium fluoride slag contaminated with metallic uranium and uranium compd., recovering other components in an effectively utilizable manner and executing safe waste disposal.

The uranium fluoride compd. 11 contaminated with the metal uranium and uranium compd. is treated by digestion and is made into soluble potassium fluoride and insoluble magnesium hydroxide. Next, the solid phase and liquid phase 17 thereof are separated. The solid phase is dissolved in an acid by which the soln. of the metal salt is produced. The liquid phase is treated with lime to settle calcium fluoride. The potassium is returned to potassium hydroxide by conversion and is recalculated to the digestion reaction. The metal salt is separated and the uranium salt is removed from the magnesium salt. Consequently, the uranium contaminants are efficiently removed from the magnesium and the magnesium is recovered in such a manner that the effective recycling and safe disposal thereof are made possible. In addition, the calcium fluoride useful in various kinds of applications is produced.