Sodium‐Copper Exchange on Wyoming Montmorillonite in Chloride, Perchlorate, Nitrate, and Sulfate Solutions

Abstract

AbstractThe effect of anions on the Na‐Cu exchange reactions on montmorillonites is not well understood and discrepancies exist in the literature. This study was conducted to examine the role of anions on the Na‐Cu exchange reaction on Wyoming montmorillonite. The copper exchange capacity (CuEC) and Na‐Cu exchange reactions on Wyoming montmorillonite were studied in Cl−, ClO−4, NO−3, and SO2−4 solution media at a constant total metal charge concentration of 0.0200 molc L−1. We found that the values of CuEC were similar in Cl−, ClO−4, NO−3, and SO2−4 electrolyte media, and the quantity of Cu extracted by Na2‐EDTA solution was only 1.0 to 1.2% of the CuEC and was not affected by anions. The apparent adsorbed metal charge, Q, and Vanselow selectivity coefficients, Kv, were determined across a wide range of exchanger phase composition, with Cu2+ occupying 30 to 95% of the charge sites. We found that the values of Q increased with Cu saturation in each of the anionic media, and the increase was not affected by anions. The increase in Q was attributed to decrease in negative adsorption of anions. We observed that Kv was independent of exchanger composition in each of the four anionic media. The values of Kv in the SO−4 medium were lower than those in other anionic media because of the complexation reaction between Cu2+ and SO2−4. The data showed that Cu2+ ions were not specifically adsorbed under our experimental conditions and that the exchanger phase behaved as an ideal mixture. It was concluded that no detectable monovalent complexes such as CuCl+ and CuNO+3 were adsorbed on Wyoming montmorillonite in the Na‐Cu exchange reaction.