| 摘要 |
PROBLEM TO BE SOLVED: To perform stable and effective stripping and crystallization in respect to variation in boron concentration of solvent by measuring pH of stripping agent after contact with solvent and controlling the fed quantity of the stripping agent according to the value thereof. SOLUTION: A pipeline for feeding stripping agent after stripping to a crystallizer 3 from a backward extractor 1 is provided with a pH meter 5 to measure pH. Based on this result, the operation of a pump P2 for feeding stripping agent to a backward extractor 1 from the extractor 2 is controlled. Since when pH of the stripping agent after stripping is lower than the predetermined pH value, boron concentration in the solvent is high and the stripping agent quantity runs short, the fed quantity of the stripping agent to the backward extractor 1 is increased. On the contrary, since when pH of the stripping agent after stripping is higher than the predetermined pH value, boron concentration in the solvent is low and the quantity of the stripping agent becomes excessive, by increasing or decreasing the fed quantity of the stripping agent to the stripping, pH of the stripping agent after stripping is kept at a suitable pH value.
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