| Opal is a kind of natural silica mesoporous materials. The adsorption property of the order of organic dyestuff and heavy metal wastewater was investigated with the opal as an initial adsorbent material. Specifically we use the opal to decolorize the crystal violet(CV) dyestuff wastewater first, then the opal-dye sludge was calcined under a low temperature for thermosetting carbon treatment to change the surface properties of the raw opal adsorbent material, after that the new getted solid material was used for the recovery and enrichment of heavy metals from aqueous solutions. Therefore, a new continuous adsorbent material was prepared and the crystal structure, morphology, specific surface area and pore size distribution of adsorbent material were characterized byscanning electron microscopy (SEM), BET, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), the point of zero charge (pHpzc) and other means. The experimental results show that:(1) The thermal treatment of opal at300,400,500,700℃increased the pHpzc value from6.6to7.4and lead to a decrease in the adsorption capacities of CV dye, demonstrating the significance of the silanol functional groups spread over the surface of opal.(2) The purification of CV onto opal adsorbent material were studied as a function of initial pH, functional group in adsorbents, initial concentration, sorbent dosage, contact time and temperature. The external mass transfer model, intra-particle diffusion kinetics, pseudo-first-order and pseudo-second-order models were used to fit the experimental data of kinetics. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms were applied to fit the adsorption isotherm models. Additionally, the adsorption mechanism was discussed by comparing the pHpzc figures and FTIR spectra before and after calcination/adsorptioa The characterization figures showed that the opal surface hydroxyl groups decreased gradually and the opal structure composition undergone some changes with the increase of heat treatment temperature. The equilibrium adsorption data fitted well to the Freundlich model and the kinetic data conformed to the pseudo-second-order model. Intra-particle diffusion was not the sole rate-controlling factor. The maximum adsorption capacity of CV onto opal was found to be101.13mg/g at30℃, pH7.2, initial concentration150mg/L, sorbent dosage0.8g/L. The average free energy (E<8kJ/mol) and activation energy (Ea) of13.85kJ/mol indicated that the adsorption of CV onto opal was a physisorption. Thermodynamic parameters (△G(?),△H(?) and△S(?)) were evaluated and revealed that the adsorption process was spontaneous and endothermic in nature. (3) Moreover, the opal-CV sludge was reutilized after calcination at250℃(O-CV-250) for the removal of heavy metals from aqueous solution. The O-CV-250not only had a maximum adsorption capacity of Pb(H) of20.92mg/g while had almost no adsorption of Ni(Ⅱ) and Cr(Ⅵ) but also increased the adsorption capacities from14.86mg/g to20.92mg/g compared to the raw opal. The kinetic data conformed to the pseudo-second-order model. The adsorption process was controlled by both diffusion and chemical reaction. Recycling use of O-CV-250was conducted and almost above70%removal rate was still attained after5times cycle used for the15mg/L Pb(H) solution.(4) This paper proposes a new method for preparing carbon-silicon continuous adsorption agent, which not only avoided the secondary pollution caused by the opal-dye sludge to the environment and put into practice the environmental reclamation green concept of "treatment of wastes with processes of wastes against one another", but also showed the selective recovery and enrichment property for Pb(H), and the adsorbent can be reused with great sorbent activity. |
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