Surface properties and adsorption characteristics for selenate of magnetite-coated vermiculite

摘要

The surface properties and selenate adsorption of magnetite-coated vermiculite (Mag-Ver) were investigated and compared with those of pure magnetite and vermiculite. Compared to the average values of magnetite and vermiculite, the BET surface area, total pore volume, surface fractal dimension and hydroxyl density of Mag-Ver increased. The pH of point of zero net proton charge (pHpznpc) of vermiculite, magnetite and Mag-Ver appeared at 2.9, 8.3 and 6.2, respectively. At pH 5.0, the surface charge of vermiculite, magnetite and Mag-Ver was -0.541, 0.354 and 0.187 mmol/g, respectively, and that of Mag-Ver shifted to the positive side in comparison with vermiculite. The maximum adsorption capacity (q(max)) for selenate by the three samples followed the order of magnetite>Mag-Ver>vermiculite, and the q(max) of Mag-Ver was higher than the average value of magnetite and vermiculite. The adsorption data for selenate by magnetite and vermiculite could be well fitted by Langmuir model (R-2 = 0.987 and 0.992, respectively), and Freundlich model can describe the selenate adsorption by Mag-Ver (R-2 = 0.981).