Monovalent Ion Exchange Kinetics of Hydrated Calcium-Alumino Layered Double Hydroxides

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• 作者：Guillermo Puerta-Falla ; Magdalena Balonis ; Gabriel FalzoneMathieu Bauchy ; Narayanan Neithalath ; Gaurav Sant
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2017
• 出版时间：January 11, 2017
• 年：2017
• 卷：56
• 期：1
• 页码：63-74
• 全文大小：742K
• ISSN：1520-5045

文摘

This study reveals ion exchange kinetics in hydrated calcium-alumino layered double hydroxides of the alumino-ferrite monosubstituent (AFm) subgroup. By careful analysis of solution phase (ion) concentrations and the solid phases, the rate of exchange of NOb>3b>^– for Cl^– ions from the interlayer positions is studied across a range of temperature, solution compositions, and solution conditions (i.e., static and convectively mixed). Ion exchange kinetics conform to an exponential first-order reaction that follows an Arrhenius formalism. The activation energy of ion exchange is 38.2 ± 4.6 kJ/mol for exchange occurring in the thermodynamically preferred (i.e., NOb>3b>^– for Cl^– ion exchange) direction and it is 1.8 times greater for the inverse less-preferred pathway. For ion exchange occurring in the favored direction NOb>3b>-AFm converts to Cl-AFm; whereas in the disfavored (less-favored) direction, the compositional change occurs in two steps with the formation of a Cl–NOb>3b>–AFm solid solution as an intermediate step; before Cl^– species are exhausted and NOb>3b>-AFm forms as the product. By comparison of ion exchange rates in static and mixed solutions, transport through the Nernst diffusion layer (NDL) is identified as the rate-limiting step in ion exchange kinetics.