دانلود رایگان مقاله جذب پالادیم (II) یون کلسیم آلژینات مهره ژل در غلظت کلرید مختلف و pH

Abstract

A kinetic and thermodynamic study on the sorption ability of calcium alginate gel beads towards Pd(II) ion was made in aqueous solution at different pH and chloride concentrations. The experimental conditions adopted in the sorption experiments were established on the basis of a speciation study on the Pd2+-AA system in which all the side reactions, such as the hydrolysis of Pd(II), the protonation of alginate and the interactions of the ligand and the metal ion with ions of ionic medium were taken into account. In the pH range 2–5 and at chloride concentration in the range 0 6 CCl /mmol L1 6 10 the gel beads showed good sorption ability towards Pd(II) ion as confirmed by kinetic and thermodynamic data calculated by a pseudo second order equation and using Langmuir and Freundlich models. The comparison between qe values related to the kinetics of Pd(II) sorption and Ca(II) release in solution by gel beads indicated that the ion exchange is one of the main sorption mechanisms of the sorbent material. Similarities were found between the trends of sequestering (% PdAA species, pL0.5) and the sorption (qe, qmax) parameters as function of pH and chloride concentration. It confirms a close relation between the behaviour of alginate as sequestering agent for Pd(II) ion in aqueous solution and of calcium alginate gel beads as sorbent material for the removal of the metal ion.

5. Conclusions

On the basis of the results obtained the following conclusions can be made: 1. the speciation study carried out on the Pd2+-AA system gave evidence for the formation of a stable Pd(AA) species with logKPdAA = 9.124 in mixed NaClO4/NaCl medium, at I = 0.1 mol L1 and T = 25 C; 2. the sequestering ability of alginate towards Pd(II) ion has been evaluated by calculating the pL0.5 parameter, a semi-empirical parameter that represents the total ligand concentration necessary to sequestrate the 50% of trace metal ion present in solution. The sequestering ability of alginate changes by varying the pH and chloride concentration in solution with a maximum pL0.5 value of 6.28 found at pH = 2 and at CCl = 0; 3. a kinetic and thermodynamic study on the sorption capacity of Ca-AA gel beads towards Pd(II) ion was carried out in the pH range 2–5 and at different chloride concentrations. The experimental data were fitted with a pseudo second order kinetic equation and with Langmuir and Freundlich isotherms, respectively; 4. the experimental conditions to be adopted in the sorption study were chosen on the basis of the results of the speciation study on the Pd2+-AA system, assuming that the sequestering capability of the ligand in solution and the sorption capacity of its calcium salt gel beads towards Pd(II) ion are strictly correlated; 5. the good linear correlation and the similarities between the trends of binding/sequestering (pL0.5, % of PdAA) and sorption (qe, qmax) parameters as function of pH and chloride concentration confirm our T hypothesis about the analogous behaviour of alginate as ligand in aqueous solution and as sorbent gel material towards Pd(II) ion; 6. kinetic and thermodynamic studies on the sorption capacity of calcium alginate gel beads showed that in the pH and CCl ranges investigated CaAA is a good sorbent towards Pd(II) ion. The highest qmax values were found at pH = 2 and CCl = 0 mmol L1 and at pH = 3 and CCl = 2.5 mmol L1 . A fairly good palladium uptake was also found at pH = 5 and CCl = 0.01 mol L1 . Ackno.