Formation of layered single- and double-metal hydroxide precipitates at the mineral/water interface: A multiple-scattering XAFS analysis

Journal Article · Wed Mar 15 04:00:00 EST 2000 · Journal of Colloid and Interface Science

DOI:https://doi.org/10.1006/jcis.1999.6638· OSTI ID:20050900

Scheinost, A C; Sparks, D L

Spectroscopic and microscopic studies have shown that Ni and Co sorption by clay minerals may proceed via formation of surface precipitates. Several studies employing X-ray absorption fine structure (XAFS) spectroscopy suggested the formation of turbostratic, a-type metal hydroxides, of layered double hydroxides (LDH) with Al-for-metal substitution, and of 1:1 or 2:1 phyllosilicates. Distinction of these phases is difficult because they have low crystallinity and/or a small mass compared to the sorbents, and because they have similar metal-metal distances in their hydroxide layers/sheets. Distinction of these phases is crucial, however, because they have substantially differing solubilities. In this paper the authors show that an XAFS beat pattern at about 8 {angstrom} {sup {minus}1} can be used as a fingerprint to unequivocally distinguish LDH from the {alpha}-type hydroxides and phyllosilicates. Full multiple-scattering simulations and experimental spectra of model compounds indicate that the beat pattern is due to focused multiple scattering at Me/Al ratios between 1 and 4(Me = Ni,Co). By applying the fingerprint method to new and to already published XAFS data on Ni and Co surface precipitates, the authors found that LDH preferentially forms in the presence of the Al-containing sorbents pyrophyllite, illite, kaolinite, gibbsite, and alumina above pH 7.0. However, {alpha}-type metal hydroxides form in the presence of the Al-free sorbents talc, silica, and rutile, and in the presence of the Al-containing clay minerals montmorillonite and vermiculite. The authors believe, that the high permanent charge of these latter minerals prevents or retards the release of Al. When Al is available, the formation of LDH seems to be thermodynamically and/or kinetically favored over the formation of {alpha}-type hydroxides.

• Research Organization: Univ. of Delaware, Newark, DE (US)
• OSTI ID: 20050900
• Journal Information: Journal of Colloid and Interface Science, Journal Name: Journal of Colloid and Interface Science Journal Issue: 2 Vol. 223; ISSN 0021-9797; ISSN JCISA5
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
COBALT HYDROXIDES
ENVIRONMENTAL TRANSPORT
NICKEL HYDROXIDES
PRECIPITATION
SURFACE PROPERTIES