Tired Rectorite / Humic Acid Microspheres And Its Effect On The Adsorption Of Heavy Metal Ions

Rectorite and humic acid are two kinds of low-cost adsorbents. They were prepared into rectorite/humic acid microspheres using PVA as immobilized material. The optimum conditions for the preparation were determined by orthogonal test, and the rectorite/humic acid microspheres were characterized. The results show that the optimum dosages are as follows: rectorite, 1%; humic acid, 4%; PVA, 7%; sodium alginate, 0.1%; calcium chloride, 0.5%. The microspheres are smooth and regular in appearance and have a great deal of pores inside. The mean diameter is 0.42 cm and specific surface area is 6.29 m2/g.Effects of microspheres dosage, shaking time and pH value on adsorption of Cr(Ⅵ), Cd(Ⅱ) and Pb(Ⅱ) were investigated. The results show that microspheres dosage and shaking time have obvious influence on adsorption of Cr(Ⅵ), Cd(Ⅱ) and Pb(Ⅱ). pH value has significant impact on adsorption of Cr(Ⅵ) but no apparent impact on adsorption of Cd(Ⅱ) and Pb(Ⅱ). For the adsorption of Cr(Ⅵ), Cd(Ⅱ) and Pb(Ⅱ), the optimum microspheres dosages are 0.02 g/mL, 0.025 g/mL and 0.01 g/mL, respectively. Under this condition, equilibrium was found to be attained within 2.5 h, 6 h and 2 h, and the removal rate can reach 98.39%, 98.10% and 96.05%, respectively. pH value of 1 is the optimum condition for adsorption of Cr(Ⅵ). It's no need to adjust pH value for adsorption of Cd(Ⅱ) and Pb(Ⅱ).The adsorption thermodynamics and kinetics of Cr(Ⅵ), Cd(Ⅱ) and Pb(Ⅱ) onto microspheres were evaluated. The isothermal adsorption law can well be described by Langmuir, Freundlich and Temkin model. The adsorption process is spontaneous, endothermic and out-of-order. The whole adsorption process is mainly controlled by entropies. The adsorption can be classified as chemical adsorption. The adsorption kinetics of Cr(Ⅵ) onto microspheres conforms to pseudo-first-order and pseudo-second-order equation. The adsorption kinetics of Cd(Ⅱ) and Pb(Ⅱ) onto microspheres both conforms to pseudo-second-order and Elovich model. The adsorption process is jointly controlled by inner and outer diffusion for all the three heavy metal ions.Under the conditions of coexistence of heavy metal ions, the order of adsorption capacity of microspheres is as follows: Cd(Ⅱ) > Cr(Ⅵ) > Pb(Ⅱ). Adsorption of heavy metal ions by microspheres caused by the combination of hydroxyls of humic acid with heavy metal. The microspheres can be reused after being regenerated by 1 mol/L NaCl solutions.