Temperature and pH Effect on the Sorption of Divalent Metal Ions by Silica Gel

The sorption of Zn2+, Ni2+ and Cd2+ ions by silica gel was studied as a function of ion concentration, pH and temperature. An increase in all three parameters led to an increase in the extent of sorption for all the metal cations studied. The selectivity of the solid was observed to be in the order Zn2+ > Ni2+ > Cd2+. Sorption of the metal cations was accompanied by the release of H+ ions into the bulk phase. On average two moles of H+ ions were released per mole of metal cation sorbed. The sorption data fitted the linear forms of both the Kurbatov and Langmuir adsorption equations. The values of the binding constants were used to estimate the apparent thermodynamic parameters, ΔH and ΔS, for the adsorption process. FT-IR spectroscopic studies also showed that the uptake of metal cations by the silica gel occurred via a cation-exchange process.

Sorption of Metal Ions on a Mixed Oxide [0.5 M SiO2:0.5 M Fe(OH)3]

The sorption of Zn2+, Ni2+, Cd2+, Ca2+ and Mg2+ ions on to a mixed oxide of iron and silicon was found to increase with increasing temperature, concentration and pH of the system. The selectivity of this mixed oxide was Cd2+ ≥ Zn2+ ≥ Ni2+ > Ca2+ > Mg2+, indicating that the mixed oxide was more selective as an exchanger towards Cd2+ ions relative to its components, SiO2 and Fe(OH)3. The sorption data fitted the linear forms of the Kurbatov and Langmuir adsorption equations. The sorption of metal cations was accompanied by the release of H+ ions to the bulk phase. On average 1 mol H+ was released for every cation sorbed. The values of the binding constants were used to estimate the apparent thermodynamic parameters, ΔH and ΔS. The phenomenon of enthalpy/entropy compensation showed that the adsorption of metal ions by the mixed oxide occurred typically through a cation-exchange mechanism.

Cation-Exchange Properties of CrPO4

Alkali metal ion exchange (Li+, Na+ and K+) on chromium phosphate (CrPO4) was studied potentiometrically as a function of temperature and metal ion concentration. The shift in the potentiometric titration curves corresponding to the exchange of alkali metal cations increased with increasing pH and concentration of the metal ions, while the opposite results were obtained by increasing the temperature of the system. The affinity of the exchanger for alkali metal ions was also found to be in the order Li+ > Na+ > K+. The data were employed to evaluate the apparent deprotonation constants of CrPO4 and the corresponding thermodynamic parameters ΔH0, ΔS0 and ΔG0.

Cation exchange removal of Cd from aqueous solution by NiO

Detailed adsorption experiments of Cd from aqueous solution on NiO were conducted under batch process with different concentrations of Cd, time and temperature of the suspension. The solution pH is found to play a decisive role in the metal ions precipitation, surface dissolution and adsorption of metal ions onto the NiO. Preliminary adsorption experiments show that the selectivity of NiO towards different divalent metal ions follows the trend Pb>Zn>Co>Cd, which is related to their first hydrolysis equilibrium constant. The exchange between the proton from the NiO surface and the metal from solution is responsible for the adsorption. The cation/exchange mechanism essentially remains the same for Pb, Zn, Co and Cd ions. The sorption of Cd on NiO particles is described by the modified Langmuir adsorption isotherms. The isosteric heat of adsorption (ΔH) indicates the endothermic nature of the cation exchange process. Spectroscopic analyses provide evidence that Cd is chemisorbed onto the surface of NiO.

Cation exchange removal of Pb from aqueous solution by sorption onto NiO

This paper reports NiO as a novel and an efficient adsorbent for the removal of Pb from aqueous solutions. In the present investigation, Pb adsorption experiments on NiO were conducted on aqueous solution at different initial Pb concentration, pH of the solution and adsorption temperature. The mechanism of adsorption was observed to be an ion exchange between the surface proton and Pb in aqueous solution. Experimental data were best described by the Langmuir isotherms. The surface structure of the NiO before and after adsorption of Pb was analyzed by using FTIR spectroscopy, scanning electron microscopy (SEM) coupled with energy dispersive X-ray analyses (EDX).

Phosphate/sulphate exchange studies on Amberlite IRA-400

The sorption behaviour of phosphate on strong basic anion exchanger, Amberlite IRA-400 (SO4(2-) form) is studied as a function of pH (3-11) at two different initial concentration ranges (0.161 - 0.807 mmol l(-1), 3.874 - 6.134 mmol l(-1)) at 25 degrees C. The stiochiometry of the exchange reactions is observed to be dependent upon concentration and pH of the solutions. It is suggested that the sorption of phosphate takes place initially as PO4(3-) followed by HPO4(2-)/H2PO4(-). The data obtained is explained with the help of a modified Langmuir and mass law action equations.

Temperature effect on phosphate sorption by iron hydroxide

The ion exchange sorption of phosphate on Fe(OH)3 is studied as a function of temperature (25-55 degrees C) and concentration (1.49-3.23 mmol l(-1)). The mechanism of sorption is observed to be the exchange of OH- anions from the adsorbent surface by those of H2PO4- and HPO4(2-) from the aqueous solution. An equation developed in the Langmuir formalism is used to explain the ion exchange sorption of phosphate on Fe(OH)3. The isosteric heat of sorption illustrates that the uptake of phosphate on Fe(OH)3 takes place through an anion exchange process, involving both the phosphate anions H2PO4- and HPO4(2-). Further, at higher temperature the solid prefers the HPO4(2-) anions forming a binuclear bridging complex.

Selective removal of Pb2+ by AlPO4

Aluminium(III) phosphate was observed to have a very high selectivity towards Pb2+ ions. Under similar conditions, the sorption capacities of the exchanger were observed to follow the order: Pb2+ > Zn2+ > Ni2+ > Co2+. The potentiometric titration data were used to determine the deprotonation constants (pKa) of AlPO4, which were dependent upon the temperature and nature of the metal cations present in the aqueous phase. Different physical methods i.e. FTIR, EPM and the wet chemical analyses were used to investigate the uptake mechanism of Pb2+ by the solid, which showed that no new solid phases were present in the solid residue after sorption of Pb2+ at pH 5. The exchange between protons from the surfaceand Pb2+ from solutions was found to be responsible for Pb2+ sorption by aluminum(III) phosphate.

The Sorption of Divalent Metal Ions on AlPO4

The sorption of Cu(2+), Pb(2+), Ni(2+), and Cd(2+) ions on the aluminum(III) phosphate was observed to increase with increases in the concentration, temperature, and pH of the system. The apparent dissociation (pK(a)), binding (pK(b)) and exchange (pK(ex)) constants of aluminum(III) phosphate were evaluated and found to be dependent upon the temperature and nature of the metal cations. The values of the dissociation constants (pK(a)) followed the order Pb(2+)<Cu(2+)<Cd(2+)<Ni(2+)<K(+), opposite to the values of the binding constants and selectivity shown by the solid. Ion exchange between protons from the surface and metal cations from aqueous solution was found to be responsible for the metal ions sorption by AlPO(4). The values of the dissociation (pK(a)) and exchange (pK(ex)) constants were used to estimate the corresponding apparent thermodynamic parameters (DeltaH(o)(diss), DeltaS(o)(diss) and DeltaH(o)(exch), DeltaS(o)(exch)). The values of DeltaH(o)(diss) and DeltaH(o)(exch) were found to be positive, which showed that both the dissociation and exchange processes were endothermic in nature. The DeltaS(o)(diss) and DeltaS(o)(exch) were also found to be positive, which showed that both the deprotonation and exchange processes on the AlPO(4) were entropy driven and spontaneous.

Temperature Effect on the Surface Charge Properties of gamma-Al2O3

A comprehensive study of the surface properties of the gamma-Al2O3 in KNO3 as a function of temperature was undertaken potentiometrically. Surface charge, ionization and complexation constants, and PZC were calculated from the potentiometric titration data in the temperature range 293-333 K. A difference between the PZC and CIP was observed as a result of the adsorption of NO-<INF POS="STACK">3 ions. A simple graphical procedure based on the mass action law was used to determine the number of surface sites and equilibrium constants. Thermodynamic parameters, which showed a decrease in the role of nitrate NO-<INF POS="STACK">3 ion in the charging mechanism of gamma-Al2O3, were also evaluated, whereas that of K+ ion increased with the increase in temperature. Copyright 1998 Academic Press.