| Electronic plating, mining, tanning are the primary industries that pollute water with heavy metals in our country. However, for containing high concentrations of organics and salinities, existing multimeric complexes and multiple ions, chromium tanning wastewater has distinctive differences with other industry wastewater polluted by heavy metals. Chemical precipitation combining with adsorption, ion exchange, membrane separation technology are common treating methods for wastewater polluted by heavy metals, but conventional chemical precipitation can not meet our more and more stringent reduction emission standard for wastewater containing chromium. Furthermore, conventional adsorbents are difficult to deeply treating tanning wastewater with low cost, for their poor selectivity and stability. Therefore, it is urgent to develop a kind of adsorption material of high selectivity and stability to deeply treat wastewater from tanning industry.Tanning wastewater containing low concentration of chromium and much organics after alkaline precipitation was considered in this thesis. Mechanisms and precipitation behaviors between Cr(III) in solution, organics from different sources and neutral salt ions in tanning process were studied. Adsorption selectivity problems of Zr, Al, Ti metal oxides to Cr(III) were discussed and chemical tanning mechanisms of multiple metals were used for reference. Then adsorbents of Zr and Zr-Al composite oxides which had high selectivity to chromium were screened out. And they were recombined with nano montmorillonite(MMT) to prerpare porous adsorbent of metallic oxide MMT by gel casting method, so as to solve the problems of acid and alkaline unstable and powder easy lost.The main researches are listed as following:(1) Chief organic(OM) was identified through leather processing, and complexes of heteronuclear with polymers were fabricated by OM reacting with Cr(â…¢), Al, Zr and Cr respectively. GPC was employed to measure average molecular weight of organic chromium(OM-Cr). SEM-EDS, DTA-TG and FTIR were used to detect coprecipitation of OM and Cr(â…¢). HPCE and UV-Vis were adopted to check acting force between OM and Cr( â…¢). Collaborative precipitation of OM and Cr(â…¢) under different states were explored. Rules of collaborative precipitation between metal oxides and OM-Cr were discussed. The Multi carboxyl group of CA was the main factor that effected alkali stability of Cr(â…¢), and OM-Cr could be removed by adsorbing.(2) Metal oxides were prepared by alkaline precipitation and sintering. Then adsorption material of metal oxide/MMT was prepared by inserting MMT with metal oxides, which could efficiently and selectively adsorb Cr(â…¢). DTA-TG was employed to test metal deposits changes. XRD was used to detect components of metal oxides. TEM was adopted to observe micromorphology of adsorption materials. SEM-DES was employed to test microstructure and element change of adsorption materials. BET was adopted to measure specific surface area of adsorption materials. Metal oxides were screened out, which could efficiently and selectively adsorb Cr(â…¢). With MMT as carrier, adsorption material of Al2O3-ZrO2/MMT was prepared, which had large specific surface area, wide adapting range of pH, resistance of Na+ and Ca2+. The relationships between kinds and ratios of metal oxides, cationic, OM, pH and Al2O3-ZrO2/MMT were explored. Kinetics and thermodynamics of Cr( â…¢) adsorbing on Al2O3-ZrO2/MMT were also discussed.(3) Through regulating MMT interlayer spacing, modifying MMT with Zr irons, drying and sintering, composite material Al2O3-ZrO2/MMT was prepared which could maintain the stability of metal oxides. XRD was employed to test layer changes of MMT. SEM was adopted to observe morphology of Zr-MMT. BET was used to measure specific surface area of Zr-MMT. The effects of MMT kinds, dipping temperature, pH, sintering temperature on adsorptive properties of Zr-MMT were studied. The relationships between sintering temperature and composite material MMT layer spacing, material structure, adsorptive properties were explored. Kinetics and thermodynamics of Zr-MMT adsorbing Cr(â…¢) were considered. Through physical intercalation-chemical situ deposition and interlayer controlling of MMT, an adsorptive preparation method was established which could stably and efficiently combine Zr-MMT.(4) Molding material Zr-MMT was prepared by shaping its powder gel with polystyrene balls as pore-forming agent. XRD was employed to test interlayer structure and matter change of molding material. DTA-TG was used to obtain exhaust temperature of molding material. SEM was adopted to observe micromorphology of molding material. DES was employed to test element changes of molding material. TOC was used to detect affinity between molding material and OM. System Zeta potential was used to measure charge of molding material. BET was employed to measure specific surface area of MMT under different stages. The effects of OM, temperature, pH and cationic on adsorptive properties of molding material were discussed. Desorption reproducibility of molding material, stability of Zr ion, kinetics and thermodynamics were considered. The method of preparing molding OM-Cr powder by gel casting was established, which had a wide range of pH, resistance to Na+ and Ca2+, removal ability to OM-Cr.The problem of metal oxides instability was solved by physical inserting MMT and combing with chemical situ deposition method in this thesis. Porous molding absorbent material was prepared by gel casting method, which worked out the problem of powder losting with water in engineering application. Engineering material was developed, which could efficiently adsorb polymorphic chromium. It was also resistance to organics, neutral salts and suitable for treating tanning wastewater. Properties of prepared materials and adsorption mechanisms were verified. There is a better theoretical and actual guiding significance to deeply remove chromium. |
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