Adsorption of Hg2+ ions onto thiourea -modified Fe3O4/chitosan micorsperes

The Fe3O4/chitosan magnetic microparticles were prepared by the inverse phase suspension method and modified with thiourea (TMCS) as an adsorbent for removal Hg2+ from the water solution. The effects of pH values and temperature, the adsorption isotherms and kinetics were investigated. The results show that TMCS has a spherical form and the diameter of 80 μm~250 μm. The adsorption capacity of Hg2+ increases with pH values increasing but decreases with temperature. The negative values of enthalpy (ΔH0=-12.93 kJ/mol) indicated that the adsorption process is exothermic whereas the negatives values of Gibbs free energy (ΔG0=-16.41 kJ/mol~-17.22 kJ/mol ) suggested that the adsorption reaction is spontaneous. The adsorption equilibrium data were fitted well with Langmuir isotherms with the maximum adsorption capacity of 2.69 mmol/g. The adsorption kinetics followed the mechanism of the pseudo-second-order equation, evidencing chemical sorption as the rate-limiting step. The saturated TMCS could be desorbed by 0.01 mol/L ethylenediaminetetraacetic acid (EDTA) with the desorption efficiency of 91%.