Sorption of Palladium Ion on Montmorillonite

The other example of the ion sorption on edge sites is the sorption of palladium ions (Nagy and Konya 2007) on montmorillonite. As known, palladium ions are hydrolyzed at such a low pH value where the lattice of clay minerals is destroyed. For this reason, during the preparation of palladium-montmorillonite, we have to avoid the hydrolysis of Pd(II) and the acidic destruction of the clay at the same time. We can do so by applying Pd(II) as positively charged complexes at neutral pH. For example, [Pd(NH3)2]2+ complexes can be prepared from metallic palladium as follows  

Similarly, the ethylene diamine complex of palladium ([Pd(en)2]2+) can be prepared. These positively charged complexes can be used for the study of interfacial reaction with montmorillonite. 

FIGURE 2.4 The dissolved quantity of sodium ion as a function of the sorbed palladium(II) ion. Complex [Pd(NH3)2]2+. 

To eliminate this effect of ammonium ions, [Pd(en)2]2+ can be used. The results again show that a basal spacing is 1.200 nm, characteristic of monovalent ions. Therefore, we can conclude that a significant portion of palladium ions are sorbed on the edge sites. 

The results of the thermal analytical studies of Pd-montmorillonite produced from [Pd(NH3)2]2+ and [Pd(en)2]2+ further demonstrate that palladium ions are sorbed on the edge sites. Pd-montmorillonite shows the usual thermal processes of montmorillonites, with two new exothermic reactions at 338°C and 548°C. At around 338°C (maximum) exothermic reaction, a slight weight loss of the sample is also observed in a wide temperature range. It may indicate the partial amorphization of bentonite. At 548°C, the reduction of Pd(II) to Pd(0) may happen. 

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