Preparation And Adsorption Behavior Of Sugar Charcoal/Silica Gel Composite Adsorbent Towards Removal Of Cr(Ⅵ) From Water

Hexavalent chromium-containing wastewater (HCCWW) is harmful to human being health and natural environment, so it is necessary to treat HCCWW. In this paper, sugar charcoal/silica gel composite adsorbent is prepared by using silica gel as template, sucrose as carbon source and preserving template on the basis of overcoming the disadvantages of removing template. Adsorption is adopted and sugar charcoal/silica gel composite adsorbent is used to dispose simulating HCCWW. The results show that the adsorbent is recognized as a good adsorbent of hexavalent chromium from aqueous solutions.The static test is carried out according to the capacity of adsorbents removing chromium. Orthogonal experiment is exerted on the basis of many single factor experiments, and the optimum condition of preparation is obtained, which is the mass of sucrose, silica gel and sulfuric acid being 5 gram, 2 gram and 2.5 gram respectively with the mass of water being 25 gram ,as well as the heating temperature being 150°C. The adsorbent is charactered by absorbing iodin and methylene blue, the surface function groups and XRD.The adsorption rate of chromium is determined by pH, time of contact, temperature, dose of adsorbent, initial concentration of chromium and ionic intensity. Optimum pH of adsorption is 2.3, and the equilibrium time of contact is 20 hours. The adsorption rate of chromium in 34mg/L is 99 percent and the adsorption capacity is 10.2mg/g, when the dosage is 3.3g/L. The adsorption rate of chromium and total chromine will decrease with the existence of sodium chloride, sodium sulfate and sodium nitrate in solution.Equilibrium data fit to Langmuir adsorption isotherm and the relative parameters of Langmuir adsorption isotherm and adsorption thermodynamics are calculated. The adsorption process is controlled by aperture diffusion dynamics and the kinetic process can be described by the pseudo-second-order model.The mechanism mainly includes two aspects, adsorption and deoxidation. The function of adsorption is accomplished by complexation and electrostatic attraction; Deoxidation occurs on the condition of high acidity. It is removed by reacting with hydroxyl groups on the surface of sugar charcoal/silica gel composite adsorbent. Trivalent chromium generated is partly adsorbed. However, the removal rate of trivalent chromium is very low because of the existence of electrostatic repulsion.