炭酸カルシウムの反応晶析における溶液のイオン組成とゼータ電位の変化  [in Japanese] Change in Zeta Potential of Calcium Carbonate during Reactive Crystallization  [in Japanese]

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Abstract

<p>結晶のゼータ電位は,結晶表面にどのイオンが優先的に吸着しているか反映する値であり,晶析における結晶の成長過程を理解するうえで有用な情報をもたらす.しかし,測定者や測定方法により値が大きく異なるため,結果の理解が困難となっている.本研究では,水酸化カルシウム水溶液と炭酸ガスを用いた炭酸カルシウムの反応晶析において,反応中の炭酸カルシウム結晶のゼータ電位の変化を溶液のイオン組成の点から考察した.また,高分子電解質ポリアクリル酸(PAA: Polyacrylate acid)を母液に加えた場合の添加の影響についても検討した.PAA無添加の場合は,生成した炭酸カルシウムのゼータ電位は正の値を示し反応中大きな変化を示した.このプラスの電荷は結晶表面へのCa<sup>2+</sup>の吸着を反映したものと考えられえる.反応中のゼータ電位は,反応初期は約+70 mVの値を示し中和反応の進行にともない減少し,中和点付近で約+15 mVの極少を示した後,緩やかに上昇する変化を示した.この変化を反応中の母液のイオン組成の変化と比較した結果,ゼータ電位の変化は母液中のCa<sup>2+</sup>の濃度変化を反映して変化することが明らかになり,結晶表面の電位決定イオンはCa<sup>2+</sup>でありその吸着平衡の変化はゼータ電位の変化により把握できることが示された.同様のゼータ電位の測定をPAAの存在下の反応晶析で行った結果,結晶のゼータ電位はマイナスの値を示し,結晶表面へのPAAもしくはPAAとCa<sup>2+</sup>の錯体の吸着が示唆された.これらの結果より,ゼータ電位が,結晶表面のイオンの吸着状態の状態を反映し,その反応晶析中の変化のモニタリングに有効な指標であることが明らかになった.</p>

<p>The change in zeta potential of CaCO<sub>3</sub> crystal during reactive crystallization was studied. In the reactive crystallization with Ca(OH)<sub>2</sub> solution and CO<sub>2</sub> gas, the zeta potential had a positive value, suggesting that Ca<sup>2+</sup> was adsorbed on the surface of crystal. In the early stage of the reaction, the zeta potential of CaCO<sub>3</sub> crystal was about +70 mV and decreased during the reaction. At the neutralization point, the zeta potential showed a minimum value of about +15 mV, after which it increased slowly. This dynamic change in the zeta potential during the reaction may reflect the change in the equilibrium between ions in the mother liquor and those on the crystal surface. To confirm this assumption, the zeta potential of the crystal sampled at the neutralization point was measured in mother liquors with various ionic compositions. The results showed that the change in zeta potential of the crystal reflects the change in the equilibrium at the crystal surface. The same measurement was conducted in the reaction with in the presence of polyacrylate acid (PAA) as polymeric additive. The zeta potential had a negative value, which suggests that PAA was adsorbed on the surface of crystal, and showed a dynamic change during the reaction. These results demonstrated that the change in zeta potential during the crystallization process reflects the change in the equilibrium between ions in the mother liquor and those on the crystal surface, information which will be useful for controlling crystallization processes.</p>

Journal

  • KAGAKU KOGAKU RONBUNSHU

    KAGAKU KOGAKU RONBUNSHU 44(1), 29-34, 2018

    The Society of Chemical Engineers, Japan

Codes

  • NII Article ID (NAID)
    130006316128
  • NII NACSIS-CAT ID (NCID)
    AN00037234
  • Text Lang
    JPN
  • ISSN
    0386-216X
  • NDL Article ID
    028935986
  • NDL Call No.
    Z17-725
  • Data Source
    NDL  J-STAGE 
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