PURPOSE: To obtain a dehydration promoter containing a specified nonionic surfactant as the active component and capable of improving dehydration of a calcium carbonate slurry and of reducing clogging of a vacuum dehydrator.

CONSTITUTION: The promoter composed of a nonionic surfactant selected from (A) a polyoxyethylene alkylphenyl ether represented by formula I [R is H or a 1 to 18C alkyl; (n) is 4 to 80] and (B) a polyoxyethylene-polyoxypropylene condensed material expressed by formula II (Molecular weight of propylene oxide is 950 to 3850. Content of ethylene oxide is 10 to 80% based on the whole molecular weight) and having a dehydration-promoting effect is added to a calcium carbonate slurry discharged in a causticizing process of papermaking or pulpmaking or in a process for production of calcium carbonate. After stirring, a vacuum dehydration treatment is applied thereto so as to form a remarkably effectively dehydrated calcium carbonate cake. The dehydrated cake is dried under strong heating to obtain quicklime. This method can reduce clogging of a dehydrator and remarkably reduce the heat quantity consumed when drying the cake under strong heating in a kiln, etc.