Nickel Removal by Nymphaea alba Leaves and Effect of Leaves Treatment on the Sorption Capacity: A Kinetic and Thermodynamic Study

In this study, ability of Nymphaea alba (White Water lily) leaves to remove Ni2+ from aqueous solution was studied in the batch system. HCl, MgCl2, and CaCl2 chemical modification of N. alba leaves showed increasing sorption capacity of Ni2+ (24 mg/g; pH 6.5). Removal percentage of Ni2+ increased by adding more biomass. Increasing Ni2+ concentration up to 210 mg/L and temperature up to 35 degrees C caused higher biosorption capacity. However, higher Ni2+ concentrations and rising temperature had vice versa effect. The optimum agitation time was 90 min. The prolongation of the agitation period had no considerable effect on the biosorption capacity. The kinetics study of modified N. alba leaves revealed that Ni2+ sorption follows pseudo-second order kinetic model. Estimated parameters, the rate constant of second order biosorption (K-2) and biosorption capacity (q(e)), for this model at T = 293 K were 0.225 g/mg min and 17.42 mg/g, respectively. The experimental results were correlated reasonably well with Langmuir model (q(max) = 118 mg/g; b = 0.022 L/mg). The changes in Gibb's free energy (Delta G degrees), enthalpy (Delta H degrees) and entropy (Delta S degrees) of Ni2+ sorption by modified N. alba leaves were estimated as -1.726, 0.208, and 0.0018 KJ/mol K, respectively. Thermodynamic parameters revealed spontaneous, endothermic, and irreversible nature for Ni+2 sorption. XRF and FT-IR analysis results showed that N. alba leaves had different functional carboxyl and sulfhydryl groups responsible for the sorption process.