Adsorption of Cr(NH₃)₆³⁺ and Cr(en)₃³⁺ on Clay Minerals and the Characterization of Chromium by X-Ray Photoelectron Spectroscopy

Abstract

Abstract--The nature of Cr(NH3)63+ and Cr(en)33+ (en = ethylenediamine) adsorbed on chlorite, illite, and kaolinite has been studied by X-ray photoelectron spectroscopy (XPS). The interaction of the chromium complexes with the clays began at pH 3. During the 7-day interaction time the pH of the complex-clay suspension increased to 8 for illite and chlorite. For kaolinite the pH increased to about 3.6 with Cr(NH3)63+ and to 6.4 with Cr(en)33+. These pH changes appear to be associated with a clay-catalyzed hydrolysis of the chromium-amine complexes. XPS binding-energy data for adsorbed chromium indicate that the dominant species are chromium aqua complexes. Nitrogen/chromium atom ratios, calculated from the XPS photopeak intensities, are less than 6: l for complexes adsorbed on the clays, suggesting that chromium complexes are initially adsorbed but subsequently hydrolyze to produce aqua-chromium surface species.

Adsorption of fluoride on clay minerals and their mechanisms using X-ray photoelectron spectroscopy

“…For example, Koppleman et al studied the binding energy of Cu, Cr, and Co in the clay minerals' superficial layers through XPS under different pH levels and time durations. By comparing the results with the standard electron energies of these elements, they confirmed the definite element forms, effectively revealing the adsorption mechanism [17][18][19][20]. However, there is very little research on the fluoride binding morphology and binding energies of the superficial layers of clay minerals.…”

Methods for Speciation of Metals in Soils

“…These can reveal the oxidation state of the trace metal in molecules on the surfaces of particles. Also known as electron spectroscopy for chemical analysis (ESCA), the technique has been used in the trace analysis of metal species on fly ash particles, ferromanganese nodules, Pb adsorption on montmorillonite, Co(II) on MnO 2 , Cr( x ) 3+ species adsorbed on clays, silicate adsorption on gibbsite, cation exchange by layered silicates, metal precipitation, and phosphate absorption onto goethite (Counts et al, 1973; Czuha and Riggs, 1975; Koppelman and Dillard, 1975, 1978, 1980; Alvarez et al, 1976; Linton et al, 1976, 1983; Adams et al, 1977; Keyser et al, 1978; Adams and Evans, 1979; Bancroft et al, 1979; Murray and Dillard, 1979; Dillard et al, 1981, 1982, 1984; Cabaniss and Linton, 1984; Farmer and Linton, 1984; Martin and Smart, 1987; Martin et al, 1988; Turner, 1988; Soma et al, 1989; Vempati et al, 1990; Johnsson et al, 1992; Junta and Hochella, 1994; White and Peterson, 1996; Olazabal et al, 1997; Chang and Liu, 1998; Gier and Johns, 2000). Further progress will be made as X‐ray focused microprobes are utilized in conjunction with XPS.…”

Chromium speciation in a contaminated groundwater: redox processes and temporal variability

“…Cr(III) has very low solubility, and at pH values (6-10) encountered in groundwater, it precipitates forming Cr(OH) 3 or Cr x Fe 1−x (OH) 3 (Eary and Rai 1988). Both Cr(III) and Cr(VI) may adsorb onto clay minerals (James and Bartlett 1983), Fe(III) , Mn(IV) (Zachara et al 1987), and Al(III) oxides and hydroxides (Koppelman and Dillard 1980), although adsorption of Cr(VI) decreases with increase of pH (Fonseca et al 2009). Cr(III) may solubilized by complex formation with organic matter such as humic and fulvic acids (James and Bartlett 1983).…”