Study of the surface charge of a Porous Clay Heterostructure (PCH) and its adsorption capacity of alkaline metals

A Porous Clay Heterostructure (PCH) was prepared by chemical modification of a natural clay, by intercalation of a cationic surfactant. Its surface charge properties as well as its adsorption capacity for alkali metals were studied using a potentiometric titration method. The PCH developed a pH-dependent charge (σ_H), probably due to the presence of amphoteric silanol groups (SiO₂) coming from the pillars of silica interlayered during the pillared process. The PCH presented a region of zero charge in the range of pH of 4.0 to 7.7. The σ_H acquired by the PCH was adjusted with good correlation to the electric double layer model of Gouy-Chapman (r ² = 0.9925). The surface charge conferred the PCH ion exchange capacity for the studied metals (Li, Na, K, Rb and Cs) at high pH values (10 < pH), in comparable quantities (3.5 to 6 meq/g) to some Dowex resins. The results of this study suggest that PCH could have applications in the recovery of toxic metals from waste waters.