Lead enrichments montmorillonites

The results of the quantitative analysis of montmorillonite samples obtained with different Ca-montmorillonite/lead ion ratio and pH are shown in Table 2.14 for the surfaces with even lead distribution. The chemical composition of lead enrichments is shown in Table 2.15. 

The SEM picture shows two types of particles (1) lead enrichments without montmorillonite, and (2) montmorillonite particles with lead enrichment on it. The montmorillonite particles are much larger, their size can reach 10 pm, and their elemental SEM maps show even distributions of Al, Si, Mg, Fe, Ca, and O only the distribution of Pb shows spots with higher concentration (white spots in Figure 2.29). 

Lead enrichments can be detected only when the system contains both lead ions and montmorillonite. However, they cannot be observed on mica flakes immersed... 

Of course, only the weakly adsorbed lead enrichments can be transferred onto the surface of mica. The presence of other, more strongly adsorbed, lead enrichments on montmorillonite cannot be excluded. 

The precipitation and colloid formation of different metal oxide hydroxides is known in soils when the concentration of the ions reaches the value of stability products. In this case, the precipitation can be explained by the thermodynamic properties of the bulk solution. In the lead ion/calcium-montmorillonite system, however, the production of lead enrichments cannot be explained by the... 

In the first row of Table 2.14, the average composition of calcium-montmoril-lonite is given. In the second row, the mean composition of lead-montmorillonite, where lead concentration is even (no enrichments), is provided. The atomic percent of lead in lead-montmorillonite is about equal, within the experimental error of 5% to 10%, of the atomic percent of calcium in calcium-montmorillonite. Since the interlayer cation of the original montmorillonite is calcium ion, lead ions can completely exchange calcium ions. 

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