Adsorption of Co²⁺ by Oxides from Aqueous Solution

Abstract

The adsorption of Co(II) by Fe3O4, Al2O3, and MnO2 has been studied as a function of Co(II) concentration, solution-pH, and temperature. It is observed that the adsorption of cobalt increases markedly with the solution pH between pH 5 and 7.5. Above pH 8 adsorption becomes increasingly masked by precipitation of Co(OH)2 and no resolution of these two contributions to the loss of Co(II) from solution is possible. A log θ/(1–θ) vs. pH plot is found to be linear between pH 5 and 7.5, where θ is the fraction of occupied adsorption sites. The presence of 0.1 m Ba2+ and Mg2+ in the solution does not seem to affect the hydrogen ion dependence of the adsorption of Co(II) on alumina.The adsorption results have been analyzed by the Langmuir adsorption isotherm over a wide range of Co(II) concentration (10−6–10−3 m). The adsorption of Co(II) is found to be an endothermic process and increases markedly with temperature between 30 and 100 °C. The heat of adsorption decreases with increasing surface coverage of the oxides. At saturation coverage, the heats of adsorption for Co(II) on Al2O3, MnO2, and Fe3O4 are −14.9, −14.3, and −6.3 kcal/mol, respectively. Hydrolysis of Co(II) is suggested as a possible mechanism for the marked dependence of adsorption on pH and temperature.

Molecular Structure and Binding Sites of Cobalt(II) Surface Complexes on Kaolinite from X-Ray Absorption Spectroscopy

“…They suggested a change from a dominantly aquo surface complex to a more hydroxide-like complex but one that is not identical to the solid hydroxide phase most likely to precipitate. Other XPS studies of Co(II) complexes on ~'-A1203 suggest a correlation between hydrolysis, adsorption, and the formation of aquo-type complexes at low pH and possible formation of a surface precipitate at high pH (Tewari et al, 1972;Tewari and Lee, 1975;Tewari and McIntyre, 1975). Cobalt and Ni sorption on hectorite and montmorillonite studied by XPS (Davison et al, 1991) supported previous results indicating the formation of a hydroxidelike species at high pH and no change in the binding energies of the sorbed species after successive washings, implying strong bonding of the cation to the surface.…”

Active carbon prepared from vegetable wastes for the treatment of Pb(II) in aqueous medium

“…al., 1991) and potentiometric titration (Parfitt et. al., 1983 andTewari, 1981). Both the methods provide the accurate values of pH zpc .…”

Biosorption of Co2+ ions by lichen Hypogymnia physodes from aqueous solutions

“…However quantification of the biosorption of Co 2+ ions is complicated by the fact that cobalt precipitates at pH higher than 8 and therefore it becomes difficult to distinguish between sorption and precipitation beyond pH 8. Based on the known hydrolysis constant it has been shown that up to pH 8, Co(II) exists mainly as non-hydrolyzed Co 2+ ion but at pH 10 [Co(OH)] + predominates (Tewari 1972;Khan 2003). Moreover, extreme pH values can damage the structure of the (bio)sorbent and therefore decrease metal uptake (Kuyucak & Volesky 1989).…”