The regularities of the reversible reaction of isomerization of ammonium thiocyanate (NH4NCS) into thiourea (NH2)(2)CS), and the reverse reaction, were analyzed. An ecologically clean and highly efficient method for the extraction, purification, separation, and production of isomers from the coal byproduct ammonium thiocyanate was developed based on the measured volatilities of NH4NCS and (NH2)(2)CS.