N. Rehana

Selectivity reversal and dimerization of chromate in the exchanger Amberlite IRA-400

Abstract Chromate sorption on the strong basic anion exchanger, Amberlite IRA-400 is studied as function of pH (2–11), temperature (20–40°C) and different initial concentrations (1.030–15.449 mmol/l). The sorption increases with the decrease in pH and increase in temperature. The ratios of chloride released/chromate sorbed are determined, which are found to decrease with the decrease in pH of the solution, while the effect of temperature on mole ratios is negligible. It is suggested that the chromate sorption takes place initially as CrO 4 2− followed by HCrO 4 − . The differential isosteric heats of adsorption, Δ H , are also computed which show the process to be endothermic in nature. IR spectra of chromate sorption on the chloride form of the resins have been studied as a function of pH at 20°C. These spectra reveal the dimerization of HCrO 4 − to Cr 2 O 7 2− at lower pH inside the exchanger.

Selective Removal of Chromates by Macroporous Exchanger Amberlyst A-21

Sorption studies of chromate on weakly basic macroporous anion exchanger Amberlyst A-21 were performed as a function of pH (2 - 9), temperature (20 - 40 °C) and concentration (0.4 - 80 mmol.l−1). Chromate sorption was observed to decrease with the increase in initial pH of the solution, with a sorption maxima at pH 2 and increased with the increase in temperature. The changes in pH and in the ratio of chloride ions released to chromate ions sorbed suggested that the anion exchange process was accompanied by hydrolysis and Donnan invasion. The FTIR spectra and isosteric heat of sorption besides showing the hydrolysis / Donnan invasion of resin under different experimental conditions of concentration, pH and temperature also showed the dimerization of the chromate species inside the resin phase.

Temperature Effect on Phosphate Sorption by Iron Hydroxide

Abstract The ion exchange sorption of phosphate on Fe(OH)3 is studied as a function of temperature (25–55°C) and concentration (1.49–3.23 mmol1‐1). The mechanism of sorption is observed to be the exchange of OH anions from the adsorbent surface by those of H2FO4 ‐ 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.

Chromate Anion Adsorption on Iron Hydroxide

Chromate anion adsorption on iron hydroxide was studied as a function of pH (3–9) and temperature (20–40°C). The adsorption of chromate anion was found to decrease with increasing pH and increase with increasing temperature. The data were explained with the help of the Kurbatov and modified Langmuir equations. The small effect of temperature indicated that chromate anion adsorption on iron hydroxide occurred through a mechanism involving outer - surface sphere complexation.

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 °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 ION EXCHANGE SORPTION OF PHOSPHATE

ABSTRACT Phosphate sorption on the strong basic anion exchanger Amberlite IRA-400 (Cl− form) is studied as a function of temperature ( 25°C–50°C), at two initial pH values (5 and 9 ) in the concentration range 120–190 ppm. Chloride released/phosphate sorbed ratios increase with the increase both in temperature and pH and decrease with the increase in the concentration of solution. It is suggested that phosphate sorption takes place initially as HPO4 2− followed by H2PO4 −. The data is explained with the help of a modified Langmuir and mass law action equations. Various thermodynamic parameters (ΔG°,ΔH° and ΔS°) are presented. The differential isosteric heat of adsorption, is computed at different temperatures, showing the sorption of phosphate to be endothermic on the anion exchanger Amberlite IRA-400.

Selective removal of Pb2+ by AlPO4

Abstract 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 physico‐chemical 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 surface and Pb2+ from solutions was found to be responsible for Pb2+sorption by aluminum(III) phosphate.

Exchange of some divalent metal cations and their effect on the dissociation of iron(III) phosphate

Potentiometric titrations of iron(III) phosphate have shown an apparently weak monobasic acid behaviour towards alkali, alkaline earth and divalent transition metal ions. The selectivity sequence and dissociation of the exchanger was found to increase in the order Cu2+ > Zn2+ > Ni2+ > Ca2+ > K+. The dissociation constants of iron(III) phosphate have been determined from Potentiometric titration data in the temperature range 303–323 K. In addition, the exchange of Cu2+, Zn2+ and Co2+ on iron(III) phosphate and the effect of these ions on dissociation were also studied as a function of concentration, temperature and solution pH value. The thermodynamic parameters ΔH0, ΔS0 and ΔG0 for the dissociation of iron(III) phosphate are also presented.

Cation-Exchange Properties of Aluminium(III) Phosphate

Potentiometric titrations of aluminium(III) phosphate have been performed in the presence of aqueous electrolyte solutions containing Cu2+, Zn2+, Ni2+ and K+ ions as a function of the concentration of the latter, the pH and the temperature. The sorption of Zn2+ ions has also been studied and the data for metal ion sorption shown to correlate with the Potentiometric titration data, indicating that the process responsible for metal ion uptake is ion exchange. The pKa value of the exchanger and its thermodynamic parameters have been evaluated.

Counter ion effect on phosphate sorption

Abstract Phosphate sorption on the strong basic anion exchanger Amberlite IRA‐400 as a function of the counter ion is presented. The sorption is found to decrease in the order OH>C1>Br> I. Counter ion released / phosphate sorbed ratios indicete that at low concentrations the resin mostly prefers the doubly charged UPO4 2−. The data is explained with the help of a modified Langmuir and mass law action equations.