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붕산의 결정화에 코발트가 미치는 영향
A Study on the Effect of Cobalt on the Crystallization of Boric Acid
HWAHAK KONGHAK, February 1987, 25(1), 35-44(10), NONE
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Abstract
붕산의 용해도가 온도에 민감한 성질을 이용하여 모의 방사성 핵종으로서 코발트를 포함하는 액체 붕산폐기물을 냉각을 이용한 CMSMPR 결정화기로써 결정화시킨 후 정상상태에서의 입도수지 모델을 통해 코발트가 붕산의 결정화 속도들에 미치는 영향을 고찰하였다.
붕산 수용액 내에 코발트가 존재하면, 순수 붕산의 결정화 속도들에 비해 핵생성 속도는 증가하고, 결정성장 속도는 감소하였으며 이 경우 코발트의 양이 증가함에 따라 이러한 현상은 더욱 커졌다. 코발트의 분배계수는 붕산의 결정성장 속도에는 무관하였으며 모의 폐액 내의 초기 코발트 농도가 증가함에 따라 그 값이 감소하였다.
또한 체류시간 및 초기 코발트 농도 변화에 따른 붕산의 핵생성 속도 및 결정성장 속도를 예측할 수 있는 실험식을 얻었으며, 본 실험 초기 코발트 농도 범위 내에서 결정화 속도들을 과포화도, 초기 코발트 농도 및 부유밀도에 관련시킨 결과 다음과 같은 상관식을 얻었다.
rm G=1.626 TIMES 10-4 it CDOT rm S1.726 it （ rm C'_i o）-0.032
rm Brm o=2.973 TIMES 109 it CDOT rm G1.149 it (rm C'_i o)0.086 rm M'_T it 1.015
붕산 수용액 내에 코발트가 존재하면, 순수 붕산의 결정화 속도들에 비해 핵생성 속도는 증가하고, 결정성장 속도는 감소하였으며 이 경우 코발트의 양이 증가함에 따라 이러한 현상은 더욱 커졌다. 코발트의 분배계수는 붕산의 결정성장 속도에는 무관하였으며 모의 폐액 내의 초기 코발트 농도가 증가함에 따라 그 값이 감소하였다.
또한 체류시간 및 초기 코발트 농도 변화에 따른 붕산의 핵생성 속도 및 결정성장 속도를 예측할 수 있는 실험식을 얻었으며, 본 실험 초기 코발트 농도 범위 내에서 결정화 속도들을 과포화도, 초기 코발트 농도 및 부유밀도에 관련시킨 결과 다음과 같은 상관식을 얻었다.
rm G=1.626 TIMES 10-4 it CDOT rm S1.726 it （ rm C'_i o）-0.032
rm Brm o=2.973 TIMES 109 it CDOT rm G1.149 it (rm C'_i o)0.086 rm M'_T it 1.015
Simulated liquid radwastes containing aqueous boric acid and cobalt as its pseudo-activity source were crystallized in the cooling CMSMPR crystallizer. Cobalt and boric acid concentration in the simulated solution and the flow rate of feed were varied at each run. The effects of cobalt on the growth and nucleation rate of boric acid were analyzed through the steady-state population balance with respect to boric acid.
The presence of cobalt in the boric acid solution resulted in the reduction of growth rates and the increase of nucleation rates of boric acid compared with the crystallization rates of pure boric acid solution. And the results showed that there was no habit modification of boric acid crystals in spite of the presence of Co（II）, and distribution coefficients for Co(II), defined as the ration of the Co(II) concentration in the boric acid crystals to that in the boric acid solution, were found to be less than unity.
Relationships permitting the prediction of nucleation and growth rates at various Co(II) concentration and/or residence time(i.e. flow rate)within this experimental ranges were obtained. And within the experimental range of initial Co(II) concentration kinetic relationships between crystallization rates of boric acid and supersaturation, Co(II) concentration, and suspension density were found as follows;
rm G~=~1.626 TIMES 10^-4 it CDOT rm S^1.726 it ( rm C'_i ^o)^-0.032
rm B^rm o=2.973TIMES 10^9 it CDOT rm G^1.149 it (rm C'_i ^o)^0.086 rm M'_T ^it 1.015
The presence of cobalt in the boric acid solution resulted in the reduction of growth rates and the increase of nucleation rates of boric acid compared with the crystallization rates of pure boric acid solution. And the results showed that there was no habit modification of boric acid crystals in spite of the presence of Co（II）, and distribution coefficients for Co(II), defined as the ration of the Co(II) concentration in the boric acid crystals to that in the boric acid solution, were found to be less than unity.
Relationships permitting the prediction of nucleation and growth rates at various Co(II) concentration and/or residence time(i.e. flow rate)within this experimental ranges were obtained. And within the experimental range of initial Co(II) concentration kinetic relationships between crystallization rates of boric acid and supersaturation, Co(II) concentration, and suspension density were found as follows;
rm G~=~1.626 TIMES 10^-4 it CDOT rm S^1.726 it ( rm C'_i ^o)^-0.032
rm B^rm o=2.973TIMES 10^9 it CDOT rm G^1.149 it (rm C'_i ^o)^0.086 rm M'_T ^it 1.015
