PURPOSE: To produce both of thiourea which has high additional value and high purity rhodan salt by adding amine to an aq. soln. of thiourea and unreacted NH4SCN prepared by dissolving transition reaction product of NH4 SCN in water and bringing the nonreacted NH4SCN into contact with an aq. soln. of alkali material.

CONSTITUTION: Process (A); NH4SCN obtained from an aq. soln. containing NH4SCN such as waste water of desulfurized gas from coke oven is heated and dissolved to have a part of NH4SCN to transit to thiourea. Process (B); the above product is dissolved in water and brought into contact with amine, particularly comprising dicyclohexylamine to precipitate the addition product of NH4SCN and amine from which NH3 is removed. Process (C); The addition product is separated. Process (D); the addition product is brought into contact with an aq. soln. of alkali material such as NH3 to dissociate the addition product into rhodan salt and the original amine. Process (E); Thiourea is isolated from the filtrate containing thiourea in the process (C). Thus, rhodan salt and thiourea are both obtained from NH4SCN.