METHOD FOR PRODUCING HIGH PURITY POTASSIUM FLUOTANTALATE CRYSTAL OR HIGH PURITY POTASSIUM FLUONIOBATE CRYSTAL, RECRYSTALLIZATION TANK USED FOR THE PRODUCTION METHOD AND POTASSIUM FLUOTANTALATE CRYSTAL OR POTASSIUM FLUONIOBATE CRYSTAL OBTAINED BY THE PRODUCTION METHOD

摘要

PROBLEM TO BE SOLVED: To obtain a product having a good crystal grain size distribution of high purity potassium fluotantalate crystals or high purity potassium fluoniobate crystals without using a physical grading means. SOLUTION: In the method for producing high purity potassium fluotantalate crystals or high purity potassium fluoniobate crystals, a recrystallization stage is provided with a first cooling stage where a saturated solution obtained by a dissolution stage, and whose solution temperature is 60 to 90 deg.C is cooled so that the solution temperature of the saturated solution reaches the range of 35 to 50 deg.C at a cooling rate of T deg.C/hr, and a second cooling stage where the saturated solution is cooled to a range where the solution temperature reaches 10 to 20 deg.C from the point of time at which the first cooling stage is finished at a cooling rate of [T-18] deg.C/hr to [T-1] deg.C/hr.