The sorption of > 93% of Hg(II) ions is achieved onto sunflower stem (50 mg/4.5 cm3) from deionized water (D.W.) in 10 minutes equilibration time between two phases. The kinetics of sorption follows Reichenberg, Lagergren and Morris-Weber equations. The first order rate constant of sorption computed from Lagergren equation is 0.28 ± 0.01 min-1. The sorption data obey Dubinin–Radushkevich (D–R) and Freundlich isotherms. The Freundlich sorption capacity KF = 13 ± 6 mmol g-1, 1/n = 0.68 ± 0.03 and D–R saturation capacity Cm = (2.9 ± 0.4)×102 μmol g-1, β = -0.0047 ± 0.0002 mol2 kJ-2 and mean free energy = 10.3 ± 0.2 kJ mol-1. The variation of sorption with temperature (293–318 K) gives ΔH = - 32 ± 2 kJ mol-1, ΔS = 123 ± 6 J mol-1 K-1, ΔG298K = - 4.30 ± 0.05 kJ mol-1. Ascorbate, Sr(II) and Y(III) enhance the sorption whereas disufite, iodide, Cd(II), bisulfite and thiocyanate suppress the sorption. Selectivity studies indicate that Hg(II) ions can be separated from I(I) and Cs(I) using sunflower stem column. The sorbent may be used as a scavenger for the preconcentration of Hg(II) ions from its very dilute solutions or treatment of industrial and municipal effluents containing Hg(II) ions. A possible mechanism of biosorption of Hg(II) ions onto the sunflower stem is suggested.
Sorption of Cd(II) ions on Haro river sand has been studied using radiotracer technique. The effects of pH and acid concentrations on the sorption were studied. The sorption increases with pH, reaches a maximum at pH7 and decreases at higher pH values. With acids, it was found that sorption decreases with increasing acid concentration, and for more oxidizing acids sorption was less. Kinetic studies indicate that mostly intra particle diffusion occurs with first order rate constant of 18.45 × 10−2 min−1. The sorption data follow the Freundlich and Dubinin–Radushkevich (D–R) isotherms. In addition to the radiotracer method, voltammetric technique was applied and the results by the two techniques are in good agreement. The sorption free energy value indicates that adsorption process is chemisorption. The effect of temperature was studied and values of ΔH, ΔS and ΔG for Cd(II) have been calculated which are 20.15 kJ mol−1, 74.04 J mol−1 K−1 and −1.754 kJ mol−1. Adsorption of Cd(II) on Haro river sand is endothermic, spontaneous and entropy driven. The effect of different anions and cations at different concentrations was studied. Levels of cadmium have been monitored in water and sediments.
The sorption of preheated selenium-thiocyanate complexes onto polyurethane (PUR) foam has been studied as a function of equilibration time (1–60 min), concentration of selenium (3.80 × 10−4 −4.39 × 10−3 M) and amount of PUR foam. Maximum sorption (> 98%) has been achieved from 0.5 M hydrochloric acid solution within 20 minutes using 7.25 mg/cm3 PUR foam in the presence of 3.75 × 10−2 M thiocyanate ions. The sorption data have been subjected to Langmuir, Freundlich and Dubinin-Radushkevich (D–R) isotherms. The Freundlich parameters 1/n = 0.25 ± 0.02 and of KF = 1.7 ± 0.2 mmole g−1, Langmuir constants M = 0.23 ± 0.01 mmole g−1 and of b = 23 ± 2 dm3 mmole−1 and of D-R constants, Cm = 0.82 ± 0.04 mmole g−1, β = −0.0032 ± 0.0002 mole2 kJ−2 and of E = 12.5 ± 0.2 kJ mole−1 have been evaluated. The kinetic data have been subjected to Morris-Weber, Lagergren and Reichenberg equations and rate constants of intraparticle transport and first order have been computed. Thermodynamic parameters of enthalpy, entropy and Gibbs free energy suggest the endothermic and spontaneous adsorption of Se(IV)-SCN complex onto PUR foam at higher temperature. The influence of common anions and cations on the accumulation of selenium-thiocyanate onto PUR foam has been carried out. The possible sorption mechanism has also been discussed.