Selectivity of Na-Montmorillonite versus Concentration of Two Competitive Bivalent Cations (Cu²⁺, Pb²⁺): Quantitative XRD Investigation

Table 2

Structural parameters deduced from quantitative XRD analysis. Exch.cation: exchangeable cations, Z_n: coordinates of the exchangeable cations (i.e., the origin of these coordinates was placed on the plane of surface Oxygen atoms [27]), 𝑍_H2O(Å): coordinate of the water molecule sheets, M: the number of layers per stack W_A, W_B: abundances of the different types of layers.

Sample	Layer Thickness (Å)	Exch.Cation	Zn (Å)	𝑍H2O (Å)	WA WB	Character	M
10^−2 N	12.4–15.4	Pb^2+	9.8	9.8	0.91	Interstratified	6
	12.4	Cu^2+	11.2	9.4–13.7	0.09	Homogeneous
10^−3 N	12.3	Na^+	9.5	9.5	0.96	Homogeneous	8
	12.4–15.4	Pb^2+	11.4	9.4–13.7	0.04	Interstratified
10^−4 N	12.4	Na^+	9.8	9.8	1.00	Homogeneous	8