Sodium-Zinc Exchange Selectivity on Wyoming Montmorillonite in Different Background Anion Solutions

摘要

The effect of background anion on cation exchange reactions, such as Na-Ca and Na-Cu exchange reac-tions, on montmorillonites has been studied, but the results are not always clear and discrepancies exist inthe literature. In this study, the exchange of zinc (Zn2+) for sodium (Na+) on Wyoming montmorillonitewas investigated at 298 .K using Cl-, ClO4-, NO-3, OAc-, and SO42- solution media at a constant totalmetal charge concentration of 0.0200 molc L-1. Results indicated that the clay CEC values were essentialsimilar for Cl-, ClO-4, NO-3 and SO42- solution media with an average CEC of 0.856 ±0.008 molc kg-1; inan OAc- solution the clay CEC was much higher than that in other anion media. The specific adsorption ofZn (SAZn), as defined by the extraction of Zn using 0.05 mol L-1 Na2-EDTA, was different in the variousbackground solutions. The highest value for SAZn was 0.359±0.0350 molc kg-1, which occurred in OAc-solution. There was essentially no difference in the total apparent adsorbed metals (the sum of adsorbedequivalents of Na and Zn per kilogram of clay, Q) among the various background solutions. The average Q forall anion media was 0.807±0.011 mole kg-1 and was independent of exchanger composition. Experimentalresults indicated that there were no significant monovalent cation complexes such as ZnCl+ or ZnNO3+ thatwere adsorbed by montmorillonite. The Na-Zn exchange isotherms indicated that there was an adsorptionpreference for Zn over Na on Wyoming montmorillonite.

机译：研究了背景阴离子对阳离子交换反应（如Na-Ca和Na-Cu交换反应）对蒙脱土的影响，但结果并不总是很清楚，文献中也存在差异。在这项研究中，使用Cl-，ClO4-，NO-3，OAc-和SO42-溶液介质以恒定的总金属电荷浓度在298.K下研究了怀俄明州蒙脱石上锌（Zn2 +）与钠（Na +）的交换。 0.0200摩尔L-1。结果表明，粘土CEC值对于Cl-，ClO-4，NO-3和SO42-溶液介质基本相似，平均CEC为0.856±0.008 molc kg-1。在OAc-溶液中，粘土CEC远远高于其他阴离子介质。如使用0.05 mol L-1 Na2-EDTA萃取锌所定义的，锌的特定吸附（SAZn）在各种背景溶液中是不同的。 SAZn的最高值为0.359±0.0350 molc kg-1，出现在OAc溶液中。在各种背景溶液中，总的表观吸附金属（每千克粘土中Na和Zn的吸附当量之和，Q）基本没有差异。所有阴离子介质的平均Q为0.807±0.011摩尔kg-1，与交换剂组成无关。实验结果表明，蒙脱石不会吸附明显的单价阳离子络合物，如ZnCl +或ZnNO3 +。 Na-Zn交换等温线表明，怀俄明州蒙脱土上Zn的吸附优先于Na。

Sodium-Zinc Exchange Selectivity on Wyoming Montmorillonite in Different Background Anion Solutions

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