PURPOSE: To continuously, efficiently and stably obtain EDTA crystals having a large crystal grain diameter and crystal shape close to sphere, by providing a sensor for an interface of suspended crystals in the upper part of a crystallization tank and connectedly driving the detector with a crystal taking out valve at the bottom of the tank.
CONSTITUTION: Free acid (H4Y) of ethylenediaminetetraacetic acid (EDTA) as a seed crystal is filled in a crystallization tank 2 and an EDTA solution 1 and a circulating solution 10 at ≤3pH are fed from the bottom into the tank 2. The crystals 3 are fluidized in upward streams to grow the grain diameter and the interface of suspended crystals slowly rising with the growth is detected with a sensor 12 provided in the upper part of the crystallization tank 2. When the interface is raised to a given position, a taking out valve 14 for the grown crystals is connectedly operated to take out and recover H4Y crystals having ≥1.1mm average grain diameter. An ultrasonic sensor, photosensor, etc., preferably ≥370nm light wavelength, etc., is used as the sensor for the interface.
SATO HITOSHI
SUMIYOSHI MORIYUKI
