Kinetics, equilibrium and thermodynamics of cerium removal by adsorption on low-rank coal

摘要

The removal of cerium ions on low-rank coal has been studied as a function of contact time, nature of electrolytes (HClO4, HCl, H2SO4 and HNO3), dose of adsorbent, metal ion concentration and temperature. The radiotracer technique was applied to examine the distribution of cerium (Ce3+) using a batch method. Maximum adsorption was found to be at pH 5, using 0.4 g of adsorbent for 4 mL of 5 mg L-1 cerium concentration with equilibration time of 25 min. The adsorption of cerium was decreased with the increase in the concentrations of all the mineral acids used. The kinetic data indicated an intraparticle diffusion process with adsorption being pseudo-second order. The examined rate constant K-2 was 25 g mg(-1) min(-1). The adsorption data obeyed the Langmuir, Freundlich and Dubinin-Radushkevich isotherm plots over the cerium concentration range of 7.137 x 10(-3) to 6.423 x 10(-4) mol L-1. The characteristic Freundlich constants, that is, 1 = 0.381 and K = 5.152 x 10(-2) m mol g(-1) whereas the Langmuir constants Q = 2.889 x 10(-3) m mol g(-1) and b = 14.072 x 10(3) dm(3) mol(-1) have been calculated for the adsorption system. The adsorption mean free energy from the Dubinin-Radushkevich isotherm is 12.987 kJ mol-1 indicating chemical adsorption of ion-exchange mechanism. The uptake of cerium was increased with the rise in temperature (283-333 K). Thermodynamic quantities, that is, Delta H, Delta G and Delta S have been computed and discussed for the system. Adsorbent was characterized by using scanning electron microscopy and Fourier transform infrared spectroscopy before and after the adsorption of cerium. Effect of coexistent ions on the adsorption of cerium has also been investigated. Removal of cerium from tap water sample shows that the proposed method is successfully applicable.