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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.

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Dioxoneptunium(V) / Carbonate complexation / Solubilities / Alkali metal dioxoneptuniumcarbonates SummaryTo determine how the formation constants of dioxoneptunium(V) carbonate complexes change with temperature, we have measured the equilibrium concentration of 237 Np in aqueous solution over hydrated NaNp0 2 C0 3 and Na 3 Np0 2 -(C0 3 ) 2 at 30, 50 and 75 °C. Solutions having a wide range of carbonate concentrations, a constant sodium ion concentration of 1.0 mol · dm -3 , and approximately constant ionic strength (NaC10 4 ) were contacted with the solids for 2-4 weeks. In some cases mixtures of NaNp0 2 C0 3 and Na 3 Np0 2 (CC>3)2 were also used. At 30°C the observed solubility behaviour of NaNp0 2 C0 3 was similar to that reported in the literature for 25°C, whereas, at higher temperatures, the solubility minimum is less pronounced and appears to be shifted to higher carbonate concentrations. A limited number of similar measurements were done by equilibrating hydrated KNp0 2 C0 3 with K 2 C0 3 /KC1 aqueous solutions.Powder X-ray diffraction data indicate that, at the higher temperatures, hydrated NaNp0 2 C0 3 is gradually converted to solids with higher ratios of sodium and carbonate to neptunium, such as hydrated Na 3 Np0 2 (C0 3 ) 2 . Conversely, if the concentration of added carbonate is low, hydrated Na 3 Np0 2 (C0 3 ) 2 readily loses Na 2 C0 3 to the solution. The data are interpreted in terms of the relative stabilities of the sodium dioxoneptunium(V) carbonate solids and the temperature dependence of the stability constants of complexes of Np0 2 with carbonate. Interconversion of the solids is slow in both the sodium and potassium dioxoneptunium(V) carbonate systems.

PARAM H . TEWARI and ALLAY B. CAMPBELL. Can. J. Chem. 57,188 (1979). The dissolution of iron from carbon steel in aqueous H,S solutions has been studied as a function of time and temperature at 0.1 MPa H,S pressure using the rotating disc technique. The iron sulfide film formed on the disc surface has been identified by X-ray diffraction analysis. The solubility and dissolution rate of synthesized mackinawite, FeS,,_,,, have also been determined to help establish the mechanism of release of iron from carbon steel corroding in aqueous H2S solutions.The rate data have been analysed by an equation for a joint chemical and transport controlled process. At 22°C and 0.1 MPa H2S, the maximum rate of release of Fez+, obtained by extrapolating the data to infinite rotation speed, is 7.4 i 0.5 ~m o l / m 2 s. This is similar to the dissolution rate determined for synthesized mackinawite powders, but is 20 times faster than the rate of dissolution for troilite and more than 1000 times faster than the dissolution rates for pyrrhotite and pyrite. Thus, troilite and iron sulfide phases that form subsequently are not major contributors to Fe2+ release during the corrosion of carbon steel.At 22'C the diffusion coefficient for the FeSH+ ion is (1.4 i 0.2) x 1 0 m2/s and the activation energy of the diffusion process is 25 i 7 kJ/mol. The chemical reaction occurring at the surface has a n activation energy of 77 +_ 14 kJ,'mol.It is concluded that the release of iron from corroding carbon steel is governed by the dissolution rate of mackinawite, the initial corrosion product. This dissolution is controlled by the chemical reaction between mackinawite and H + and by the transport of the complexed FeSH' from the interface to the bulk solution.PARAM H . TEWARI et ALLAK B. CAMPBELL. Can. J. Chem. 57, 188 (1979). Faisant appel a la technique du disque rotatif, on a etudie la mise en solution du fer d'aciers au carbone dans des solutions aqueuses de H2S en fonction du temps et de la temperature, a une pression de 0.1 MPa de H,S. Gr2ce a une analyse par diffraction de rayons-)<, on a identifie le film de sulfure de fer qui se forme a la surface du disque. On a aussi determine la solu- jusqu'a une vitesse de rotation infinie est egal a 7.4 + 0.5 ynlol/mz s. Cette valeur est semblable au taux de dissolution determine pour des poudres de mackinawite rnais elle est 20 fois plus rapide que celle determinee pour la dissolution de la troilite et plus de 1000 fois plus grande que les valeurs correspondantes pour la pyrrhotite et la pyrite. Donc les phases du troilite et de sulfure de fer qui se forment subsequemment ne contribuent pas d'une f a~o n importante a la mise en liberte du Fe2+ au cours de la corrosion des aciers au charbon.A 22"C, le coefficient de diffusion de I'ion FeSH+ est (1.4 + 0.2) x m2/s et I'energie d'activation du processus de diffusion est 25 +_ 7 kJ/mol. L'Cnergie d'activation de la reaction chimique se produisant a la surface est 77 i 14 kJ/mol.On en conclut que la mise en liberte du fer par un acier au charbon soumis a u...