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Strontium Sorption on Hematite at Elevated Temperatures

“…The excess of protons was evaluated from data in the range 2.7 Ͻ Ϫlog[H ϩ ] Ͻ 3.0 (16). The value of B in the suspension was found to be 2.0 Ϯ 0.1 mM independent of temperature.…”

“…Diluted HCl and NaOH solutions were prepared and standardized as described earlier (16). Solutions of SrCl 2 were prepared by dissolving weighed amounts of SrCl 2 ⅐ 6H 2 O (BDH Chemicals p.a.).…”

“…Formation constants given in Table 3 increase between 25 and 75°C. These temperature-dependent constants and the following van't Hoff equation can be used to evaluate reaction enthalpy and entropy for reactions [16] and [17]: log ␤ ϭ Ϫ⌬H/ 2.3RT ϩ ⌬S/ 2.3R.…”

“…Provided enthalpy and entropy are constant in the temperature range studied, a plot of log ␤ versus 1/T results in a straight line with slope Ϫ⌬H/ 2.3R and intercept ⌬S/ 2.3R. It should be noted that reactions [16] and [17] are not isocoulombic reactions and the assumption of the constance of ⌬H and ⌬S is not strict. However, we have assumed that in this quite narrow temperature range ⌬C p ϭ 0, and the van't Hoff equation, [21], can be used to determine ⌬H and ⌬S.…”

“…Indeed, from the data in Table 1, the enthalpy of OH Ϫ adsorption is calculated to be 54 kJ mol Ϫ1 . The sum of the enthalpies of Sr attachment to the surface (reaction [16]) and OH Ϫ adsorption (reaction [11]) (102 kJ mol Ϫ1 ) should give the enthalpy of formation of surface complex 'FeOSr ϩ to which the middle line in Fig. 3 with one proton released corresponds (109 kJ mol Ϫ1 ).…”