Pakistan Research Repository





The sorptive potential of sunflower stem, a cheap agricultural waste abundantly available, has been exploited for Cr(III), Cd(II), Sb(III) and Hg(II) ions. The sorption of each toxic metal onto sunflower stem is optimized with respect to the nature of electrolytes (buffers of pH 1-10, acids and deionized water), amount of sorbent and sorbate, equilibration time between the two phases at fixed temperature. The sorption of metal ions onto the sorbent surface is monitored using radiotracer and batch technique as a function of a parameter keeping the rest constant in order to accumulate maximum amount of sorbate onto sunflower stem. The sorption data of Cr(III), Cd(II), Sb(III) and Hg (II) ions have been subjected to Langmuir, Freundlich and Dubinin-Redushkevich (D-R) isotherms. The sorption of each metal ion has followed all three models. The sorption capacity, intensity and energy of each sorbate have been estimated using regression analysis. The values of correlation coefficient γ of such analyses are close to unity. The sorption mean free energy evaluated from D-R isotherm ranges between 8.66-10.33 kJ mol-1. The kinetic data have been applied to Lagergren, Reichenberg and Morris Weber equations. The linear follow up of the sorption of Cr(III), Sb(III) and Hg (II) to Lagergren equation indicates first order sorption whereas the Reichenberg equation reflects the effectiveness of the diffusion of trace metal ions within sorbent particles. The linear follow up of kinetic data of the sorption of Cr(III) ions to the Morris-Weber equation indicates the partial intraparticle diffusion of Cr(III) ions. The variation of sorption as a function of temperature was carried out for all four sorbates. The thermodynamic coefficients ΔH, ΔS and ΔG have been evaluated using regression analysis. The negative values of ΔG for all metal ions studied indicate spontaneous nature and feasibility of the sorption. The negative values of ΔH for Cr(III) and Hg (II) ions show exothermic, while the positive values of ΔH of Cd(II) and Sb(III) ions represent the endothermic nature of the sorption respectively. The influence of common anions, cations and complexing agents on the sorption of sorbates has also been investigated. Bisulphate, Fe(III), molybdate, citrate, Fe(II) and Y(III) ions suppress the sorption of Cr(III) ions significantly. Fe(III). EDTA, Pb(II) and thiosulphate ions reduce the sorption of Cd(II) ions drastically, whereas, tartrate , dichromate, Ca(II) and Sn(II) impede sorption of Cd (II) ions. The sorption of Hg (II) ions is enhanced in the presence of ascorbate, Sr(II) and Y(III), whereas it is suppressed in the presence of disuphite, iodide, Cd(II), bisuphite and thiocyanate. Bismuthate, Sn(lI) and Fe (III) increase the sorption of Sb(III) ions whereas molybdate, chromate, iodate, sulphate, fluoride and thiocyanate reduce the same. The sorption of other elements from different groups of periodic table and oxidation states have been investigated under optimised conditions selected for each sorbate. This selectivity study indicates that Cr(III), Eu(III) and Tb(III) can be separated from I(I) and Tc(VII); Hg (II) and Tc(VII) ions from I(I) and Cs(I); Cd(II) and Eu(IIIl) ions from Cs (I) and Sb(III), Eu(III) and Sc(III) can be separated from Se(IV), Cs(I) and As(III) using sunflower stem column. The sorption potential of sunflower stem for the ions Cr(III), Cd(II), Sb(III) and Hg (II) have been evaluated and compared with other biosorbents in the relevant sections of result discussions. Its sorptive behaviour is better or comparable with other biosorbents. Based on the chemical composition of sunflower stem and functional groups present in the sorbent matrix, a possible mechanism of biosorption of ions of Cr(III), Cd(II), Sb(III) and Hg(II) ions onto the sunflower stem has been suggested. This cheaper and novel sorbent has potential applications in water decontamination, industrial water treatment and in pollution abatement, in analytical and environmental chemistry

Item Type:Thesis (PhD)
Uncontrolled Keywords:toxic metal ions, radiotracer technique, sunflower stem, sorption, chromium, mercury, agricultural waste, cadmium, sorption mechanism, sorbate
Subjects:Physical Sciences (f) > Chemistry(f2)
ID Code:2652
Deposited By:Mr. Javed Memon
Deposited On:18 Jul 2009 10:38
Last Modified:02 Aug 2010 11:43

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