To provide a method for separating a carbon component, a nitrogen component in a cyanamide form, and a calcium component each contained in nitrolime and co-producing carbon, an aqueous cyanamide solution or dicyandiamide, and calcium carbonate individually as three separate products, which method solves problems associated with a prior art technique that the calcium component and carbon component of nitrolime cannot be separated and the raw material is not effectively utilized upon producing an aqueous cyanamide solution or dicyandiamide from nitrolime.

An aqueous solution of cyanamide is prepared by treating nitrolime obtained by nitriding calcium carbide with an aqueous solution containing cyanamide, removing carbon which is an insoluble component, subsequently treating the clear liquid with carbon dioxide gas, and separating the calcium component by precipitating it as calcium carbonate. The cyanamide solution thus obtained is subjected to a polymerization reaction under an alkaline condition to obtain dicyandiamide. The method described above is capable of concurrently separating and co-producing the three components using nitrolime as a starting material.