Sorption of metal ions on clay minerals. 2: Mechanism of Co sorption on hectorite at high and low ionic strength and impact on the sorbent stability

Journal Article · Wed Dec 15 04:00:00 EST 1999 · Journal of Colloid and Interface Science

DOI:https://doi.org/10.1006/jcis.1999.6538· OSTI ID:20013632

Schlegel, M L; Charlet, L; Manceau, A

The mechanism of Co uptake from aqueous solution onto hectorite (a magnesian smectite) and its impact on the stability of this clay mineral were investigated as a function of Co concentration (TotCo = 20 to 200 {micro}M, 0.3 M NaNO{sub 3}) and ionic strength (0.3 and 0.01 M NaNO{sub 3}, TotCo = 100 {micro}M) by combining kinetics measurements and Co K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The morphology of the sorbent phase was characterized by atomic force microscopy (AFM) and consists of lath-type particles bounded by large basal planes and layer edges. Time-dependent isotherms for Co uptake at high ionic strength indicated the existence of several sorption mechanisms having distinct equilibration times. The dissolution of hectorite was monitored before and after Co addition. Spectral simulations revealed the occurrence of {approximately} 2 Mg and {approximately} 2 Si neighboring cations at interatomic distances characteristic of edge-sharing linkages between Co and Mg octahedra and corner-sharing linkages between Co octahedra and Si tetrahedra, respectively. This local structure is characteristic of inner sphere mononuclear surface complexes at layer edges of hectorite platelets. The occurrence of these complexes even at low ionic strength apparently conflicts with kinetics results, as exchangeable divalent cations are known to form outer sphere surface complexes. To clarify this issue, the amount of Co adsorbed on exchange sites was calculated from the solute Co concentration, assuming that cation exchange was always at equilibrium. These calculations showed that sorbed Co was transferred within 48 h from exchange sites to edge sorption sites.

• Research Organization: Univ. of Grenoble (FR)
• OSTI ID: 20013632
• Journal Information: Journal of Colloid and Interface Science, Journal Name: Journal of Colloid and Interface Science Journal Issue: 2 Vol. 220; ISSN 0021-9797; ISSN JCISA5
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
AQUEOUS SOLUTIONS
CHEMICAL REACTION KINETICS
COBALT
MONTMORILLONITE
SORPTION
SORPTIVE PROPERTIES