Contribution of calorimetry to the understanding of competitive adsorption of calcium, strontium, barium, and cadmium onto 4A type zeolite from two-metal aqueous solutions

摘要: Abstract The contribution of isothermal titration calorimetry is discussed to elucidate the mechanism competitive adsorption free Ca2+, Sr2+, Ba2+, and Cd2+ cations onto 4A-type zeolite from aqueous solutions at 298 K. individual isotherms for these related enthalpy displacement curves were compared between single-metal two-metal systems. Separate dilution runs carried out under same experimental conditions provided evidence that phenomenon made no significant total cumulative effect. In light observations in present study, it postulated divalent exchanged with extra-framework sodium different crystallographic locations within structure. binding affinity surface was established decrease following order: Sr ≈ Ba > Cd > Ca, line increasing endothermic character process. ΔdplHcum values systems also theoretical ones obtained by summing up metal contributions as measured appropriate case Sr(II) + Cd(II) system, competition became noticeable above a amount adsorbed 1 mmol g−1, indicated great differences values. For Ba(II) Ca(II) systems, sequence site occupation found be modified result competition. effect particularly pronounced strontium which gave more exothermic displacement.