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Some Interface Electrochemical Properties of Kaolinite
Author(s) -
Jiao YanNi,
Hou WanGuo
Publication year - 2007
Publication title -
chinese journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.28
H-Index - 41
eISSN - 1614-7065
pISSN - 1001-604X
DOI - 10.1002/cjoc.200790140
Subject(s) - chemistry , kaolinite , potentiometric titration , electrolyte , point of zero charge , electrochemistry , analytical chemistry (journal) , titration , inorganic chemistry , equilibrium constant , electrode , mineralogy , aqueous solution , chromatography
The interface electrochemical properties of clay were theoretically analyzed to obtain some relationships among point of zero net charge (PZNC), point of zero net proton charge (PZNPC), intrinsic surface reaction equilibrium constants ( K in 1‐p K model, K int a1 and K int a2 in 2‐p K model, * K int Na and * K int NO 3in inert electrolyte chemical binding model) and structural negative charge density ( σ st ) of clay, and some interface electrochemical parameters of kaolinite were measured. The following main conclusions were obtained. For clay possessing structural negative charges, the PZNC independent of electrolyte concentration ( c ) should exist just as amphoteric solid without structural charges such as oxides or hydroxides. A common intersection point (CIP) should appear among the potentiometric (or acid‐base) titration curves at different c and the pH at the CIP should be pH PZNC . A CIP among potentiometric titration curves at different c for kaolinite was observed, and the value of pH PZNC of kaolinite was 2.16. The values of pH PZNPC were decreased with increasing c , which arises from the presence of structural negative charges of kaolinite. In addition, it was observed that a good linear relationship existed between pH PZNPC and lg c . According to the values of pH PZNC and σ st measured, the intrinsic surface reaction equilibrium constants, p K and p K int a1 and p K int a2 of 1‐p K and 2‐p K models could be directly calculated for clay, and the values of p K , p K int a1 and p K int a2 for kaolinite were 2.93, 1.90 and 3.97, respectively. These experimental values of p K int a1 and p K int a2 for kaolinite are obviously lower than those optimized with fitting programs in literatures, which maybe arises from the introduction of a type of permanent negatively charged sites in the models of literatures. An interesting result obtained in this study is that the inert electrolyte chemical binding does not exist for kaolinite, which also arises from the presence of structural negative charges.