ToF–SIMS depth profiling analysis of the uptake of Ba2+ and Co2+ ions by natural kaolinite clay

Abstract

The sorption behavior of Ba 2+ and Co 2+ ions on a natural clay sample rich in kaolinite was studied using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Depth profiling at 10-Å steps was performed up to a 70-Å matrix depth of the clay prior to and following sorption. The results showed that Co 2+ is sorbed in slightly larger quantities than Ba 2+ , with significant numbers of ions fixed on the outermost surface of the clay. Depletion of the ions K + , Mg 2+ , and Ca 2+ from the clay lattice was observed to accompany enrichment with Co 2+ and Ba 2+ ions. The data obtained using X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) indicated insignificant structural and morphological changes in the lattice of the clay upon sorption of both Ba 2+ and Co 2+ ions. Analysis using energy dispersive X-ray spectroscopy (EDS) showed that the average atomic percentage (±S.D.) of Ba and Co on kaolinite surface were 0.49 ± 0.11 and 0.61 ± 0.19, respectively, indicating a limited uptake capacity of natural kaolinite for both ions.

Effect of magnesium carbonate on the uptake of aqueous zinc and lead ions by natural kaolinite and clinoptilolite

“…In a study of Pb 2+ and Zn 2+ retention by kaolinite at metal concentrations of 100 AM, it was shown that the adsorption data were fitted closely by a constant-capacitance surface complexation model, one involving electrostatic attraction between transition metal ions and the permanent, negatively charged sites on the silanol faces of kaolinite, while the other is an inner-sphere complex at the variable-charge surface hydroxyl groups situated at the crystal edges and on the aluminol faces (Ikhsan et al, 1999). Our previous studies on the adsorption of other divalent ions (Co 2+ and Ba 2+ ) by kaolinite using ToF-SIMS depth profiling have shown that the fixation of these ions is associated with a decrease in the initial amount of exchangeable cations of the kaolinite, but that the decrease did not quantitatively agree with the amount of adsorbed Co 2+ or Ba 2+ kaolinite (Shahwan et al, 2004). In summary, when discussing the adsorption mechanism by kaolinite, in addition to the exchange of exchangeable metal cations, protons of the OH 2 + and OH groups at the edges should also be taken into consideration.…”

Atomic spectrometry update. Environmental analysis

“…The authors pointed out that SIMS is able to reveal information on the sources of particles that is not possible with ICP-MS or TIMS. Shahwan et al 141 used TOF SIMS to study the sorption of Ba 21 and Co 21 on a kaolinite-rich clay. They reported that significant numbers of ions of these elements were sorbed on the clay surface and observed that enrichment of the clay with these ions resulted in depletion of Ca 21 , K 1 and Mg 21 .…”