Thermodynamics and kinetics of fluoride removal from simulated zinc sulfate solution by La(III)-modified zeolite
(School of Metallurgy and Environment, Central South University, Changsha 410083, China)
Abstract: To understand the mechanism of fluoride removal from the simulated zinc sulfate solution by the La(III)-modified zeolite, the adsorbent was characterized by XRD, SEM and EDS. The effects of absorbent dose and contact time, the adsorption isotherms and the sorption kinetics were investigated. The experimental results were compatible with the Langmuir isotherm model. The theoretical maximum adsorption capacities are 20.83 and 23.04 mg/g at 303 and 313 K, respectively. And the physisorption is revealed using the Temkin isotherm model and the D-R isotherm model. The sorption process is more suitable by the pseudo-second-order kinetic models. Thermodynamic parameters such as standard free energy change (？GΘ<0 kJ/mol), standard enthalpy change (？HΘ=8.28 kJ/mol) and standard entropy change (？SΘ=0.030 kJ/(mol？K)) indicate the spontaneity of adsorption and endothermic physical sorption. Furthermore, the fluoride concentration in the industrial zinc sulfate solution decreases from 98.05 to 44.09 mg/L with the adsorbent dosage of 15 g/L.
Key words: La(III)-modified zeolite; fluoride removal; zinc sulfate solution; adsorption isotherm; kinetics