Other
Scientific paper
May 1973
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1973gecoa..37.1277l&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 37, Issue 5, pp.1277-1293
Other
17
Scientific paper
Sorption of Co, Zn, Ca and Na by -MnO 2 was studied at 24.0 ± 0.5° C and pH 4. During the sorption of Co and Zn, Mn was released to the solution phase; however, Mn release was not detected during the sorption of Ca and Na. On the basis of crystal field theory, it is proposed that Zn may interchange with Mn 2+ in the -MnO 2 structure, whereas Co may interchange with both Mn 2+ and Mn 3+ . It is suggested that the interchangeable Mn 2+ and Mn 3+ sites were in the disordered layers in the -MnO 2 structure. Sorption of Co, Zn and Ca at pH 4 fitted single-site Langmuir isotherm expressions at all Ca concentrations, but only at concentrations greater than 10 -4 M for Co and Zn. Mn release by -MnO 2 at pH 4 during Co and Zn sorption also fitted single-site Langmuir isotherms. An expression for the case of multisite Langmuir sorption was derived and applied to the cases of Co and Zn sorption and to the case of Mn release during Co sorption. The data of these cases were used to calculate statistically the coefficients of multiple regression equations from which the sum of the capacities of all sites in each case were obtained. From all of these derived capacities, it is proposed that there was only one site where Ca interchanged with surface bound H. Zn was postulated to interchange not only with these bound H sites, but also with another site where it interchanged with structural Mn 2+ . Co was postulated to interchange with both of these sites, and additionally, with a third site where it interchanged with structural Mn 3+ . Using a pH-stat set at pH 4, it was determined that approximately 2 moles of H were released per mole of Co or Zn sorbed at bound H sites.
Burau R. G.
Loganathan P.
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