Abida Kausar

Equilibrium, kinetic and thermodynamic studies on the removal of U(VI) by low cost agricultural waste

In this research, biosorption efficiency of different agro-wastes was evaluated with rice husk showing maximum biosorption capacity among the selected biosorbents. Optimization of native, SDS-treated and immobilized rice husk adsorption parameters including pH, biosorbent amount, contact time, initial U(VI) concentration and temperature for maximum U(VI) removal was investigated. Maximum biosorption capacity for native (29.56 mg g(-1)) and immobilized biomass (17.59 mg g(-1)) was observed at pH 4 while SDS-treated biomass showed maximum removal (28.08 mg g(-1)) at pH 5. The Langmuir sorption isotherm model correlated best with the U(IV) biosorption equilibrium data for the 10-100 mg L(-1) concentration range. The kinetics of the reaction followed pseudo-second order kinetic model. Thermodynamic parameters like free energy (ΔG(0)) and enthalpy (ΔH°) confirmed the spontaneous and exothermic nature of the process. Experiments to determine the regeneration capacity of the selected biosorbents and the effect of competing metal ions on biosorption capacity were also conducted. The biomass was characterized using scanning electron microscopy, surface area analysis, Fourier transformed infra-red spectroscopy and thermal gravimetric analysis. The study proved that rice husk has potential to treat uranium in wastewater.

Prediction of optimum equilibrium and kinetic models for U(VI) sorption onto rice husk: comparison of linear and nonlinear regression methods∗

AbstractThe use of empirical models in the research is a vital part of the inventions and investigations of civil and environmental engineering organizations. Linear regression is the most commonly used method for optimization and parameter estimation of different equilibrium and kinetic models for sorption. In addition, the usage of this analysis can be extended to a range of nonlinear error functions, subsequently in consent to broader mathematical approach to parameter estimation. The sorption behavior of U(VI) ions from aqueous solution was studied with untreated, treated, and immobilized rice husk by conducting batch-mode sorption experiments. The equilibrium experimental data were fitted to the Freundlich, Langmuir and Redlich–Peterson isotherms by linear and nonlinear regression methods. Kinetic modeling of U(VI) ions removal was also done using linear and nonlinear pseudo-first and second-order rate expressions. In the case of nonlinear regression method, six error functions, namely hybrid fractio...

POTASSIUM AND CALCIUM UPTAKE IN MASHBEAN UNDER LEAD AND CHROMIUM STRESS

Plants of two mashbean genotypes were exposed to 20 or 40 mg L−1 of lead (Pb) or chromium (Cr) along with controls in a completely randomized design (CRD). Application of both metals (lead and chromium) caused a significant reduction in all growth parameters as compared with control. In addition, severe inhibition in potassium (K+) and calcium (Ca2+) uptake was observed with the increasing concentration of both metals in the root medium. Chromium was more toxic in reducing both cations as compared to same dose of lead. Overall, Pb and Cr contents of the root, stem and leaves increased under both metal stresses. In addition, both metals mainly accumulated in the aerial plant parts (stem and leaves).