Marek Kosmulski

Adsorption of cadmium on alumina and silica: analysis of the values of stability constants of surface complexes calculated for different parameters of triple layer model

The calculated values of stability constants of surface complexes formed by heavy metal ions depend on the assumed model of the electric double layer and its parameters. Using various parameters of the triple-layer model (TLM) (which fit the titration data almost equally well), one obtains stability constants in a range as wide as two orders of magnitude. On the other hand, the equilibrium constants of the surface reactions ue5fcAlue5f8Oue5f8Na + Cd2+ = ue5fcAlue5f8OCd+ + Na+ (log K = 7.4 at 15°C and log K = 7.1 at 35°C) and ue5fcAlue5f8Oue5f8Na + Cd2+ + Cl− + H+ = ue5fcAlue5f8OHCdCl+ + Na+ (log K = 15.7 at 15°C and 14.9 at 35°C) are not dependent on the TLM parameters. The surface complexes formed in these two reactions are used in a model which is able to explain cadmium adsorption from NaCl and NaClO4 solutions up to a concentration of 1 mol dm−3. Only one surface complex, ue5fcSiue5f8OCd+, is used in a model which explains the adsorption of cadmium on silica from the same electrolytes, and the equilibrium constant of the surface reaction ue5fcSiue5f8Oue5f8Na + Cd2+ = ue5fcSiue5f8OCd+ + Na+ (log K = −0.9 at 15°C and −1.0 at 35°C) is not dependent on the TLM parameters used in its calculation. The adsorption of cadmium at constant pH increases with temperature, but adsorption at a constant surface charge density is independent of temperature for both oxides.

Oxide/electrolyte interface: electric double layer in mixed solvent systems

Abstract The effects of an admixture of an organic cosolvent on 1:1 oxide/aqueous electrolyte systems, detected by means of potentiometric titrations, electrokinetic methods and radiotracer adsorption, are summarized and discussed in terms of the possible influence of the solvent composition on the structure of the electric double layer in such systems.

Standard enthalpies of ion adsorption onto oxides from aqueous solutions and mixed solvents

Adsorption of sodium from 0.001–0.1 M NaCl solutions in water and mixed solvents (aqueous methanol and dioxane up to 30%) on silica and alumina at given pH and ionic strength increases with the temperature. However, at given surface charge density and ionic strength, sodium adsorption in the above systems is practically independent of temperature over the range 15–35°C; thus the apparent positive (endothermic) enthalpy, calculated from iso-pH data, reflects the increase in the negative surface charge. This suggests that cation adsorption in the studied systems is purely electrostatic in character. In contrast, adsorption of Cl− ions on alumina at constant pH and ionic strength is independent of the temperature. This observation is in line with adsorption of various anions on goethite at high fractional surface coverage. Cobalt adsorption on silica and alumina in the presence of 0.1 M NaCl at constant surface charge density also increases with the temperature. Thus the tendency found for other (hydr)oxide—multivalent cation adsorption systems has been confirmed.

SURFACE CHARGE OF ANATASE AND ALUMINA IN MIXED SOLVENTS

Abstract Heavy water (up to 50%) does not affect the surface charge density of oxides. The absolute value of negative surface charge of anatase and alumina decreases, when water is replaced by dimethylsulfoxide (DMSO)–water mixtures. The relative decrease of the negative surface charge of these oxides in the presence of DMSO is independent of the nature and concentration of the supporting electrolyte. In contrast, the positive branch of the charging curves of alumina is insensitive to DMSO admixtures, and for anatase, the positive charge even increases when DMSO concentration increases. Dioxane causes a shift of the pzc of alumina to lower pH values, especially at low ionic strengths, but the effect of dioxane on the surface charge density is rather insignificant when alumina carries a high negative or high positive surface charge.

Effect of n-alcohols on the electric double layer formed on the surface of controlled pore glass

Abstract Common intersection point of potentiometric titration curves and isoelectric point for the controlled pore glass (CPG)-NaCl system are 3 and 2, respectively; i.e., they are similar to those found for silica. The negative surface charge of CPG is decreased when pure water is replaced by mixed solvents containing water and ethanol, 1-propanol, or 1-butanol. The same w/w concentrations of these alcohols lead to approximately equal decreases in the negative surface charges in the system CPG-NaCl solution for 0.01 and 0.001 M NaCl concentrations.

Adsorption of cesium on, and desorption from, controlled porous glasses

Cesium contained in aqueous solutions of different composition was adsorbed in columns packed with controlled porous glasses (CPG) and then removed by means of 1M HCl. Recovery of cesium in the eluate was studied as a function of the solution composition and the kind of CPG.

Lanthanides adsorption on controlled pore glass

Eu/III/ and Ce/III/ are adsorbed on controlled pore glass from neutral and basic solutions. The experiments have been carried out using 10−5M solutions of chlorides. For 0.1 M NaCl as a supporting electrolyte very low adsorption is observed below pH 6 and above pH 8 the adsorption curve has a plateau corresponding to over 90% of europium /or cerium/ adsorbed. At lower NaCl concentrations the above pH values shift towards lower values. Europium adsorbs considerably better than cerium and the best selectivity is observed at pH=7.

Influence of the Leaching Process on Adsorption Properties of Porous Glasses

Abstract Among numerous material used as ion exchangers, porous glasses show a high affinity toward cesium ions. This affinity depends on the pore diameter and the presence of an alkaliborate phase. Materials exhibiting extremely high selectivity of cesium adsorption are obtained from glass of 62.7% SiO2, 26.9% B2O3, 6.6% Na2O, and 3.5% Al2O3 by fast cooling of a crude glass mixture in water and then by leaching with water at 90°C for 1 to 4 h. The selectivity factor of cesium adsorption in relation to sodium exceeds 50.

Electric and sorption properties of controlled pore glasses

A series of controlled pore glasses (CPG) was made from the same raw glass by means of different chemical and thermal treatments. BET specific area, selectivity of cesium adsorption in relation to sodium, ionosorption capacity under dynamic conditions of these CPG were measured and potentiometric titrations carried out. σ0 vs. pH curves show i.e.p. and c.i.p. values similar to those for silica. KOH treatment leads to increase of BET specific surface but ionosorption capacity is decreased.