Preparation, Characterization Of Modified Bentonites And Their Application In The Sorption Removal Of Pollutants From Water

Bentonite is an inexpensive, abundant clay mineral, which has good sorptioncapacity and friendly to environment, so it can be used as the basis raw materials incheap bentonite products as adsorbents. The bentonite has some characters, such asspecial2-d space structure, sorption function on mineral surface, high cation exchangecapacity between layers, hole filter function and special nano structure effect. Thestructure between layer and surface properties of the bentonite can be controlled.Therefore, a series of high efficiency and multi-function bentonite complex adsorbentscan be prepared through the activation, modification or multi-modification processing.In this dissertation, cationic starch, hydroxyl aluminium and CTMAB agents arechosen as raw materials to prepare modified bentonites. A series of novel sorptivematerials with special structures and functions derived from bentonite was synthesizedand their performances on removing dyes, organic compounds, heavy metals andphosphorus in the water were studied at the same time. The relationship betweenstructure characteristics and properties of modified bentonites was explored by modernanalytical and testing technology. As the key points, the sorption mechanism, influencingfactors and laws of cationic starch bentonite (CS-bentonite) as adsorbents on dyes,organic pollutants, heavy metal ions, and phosphorus removal from water were studied.A system experimental investigation about the sorption mechanism, influencing factorsand laws of hydroxyl aluminium and CTMAB modified bentonite materials on dealingwith dye wastewater was made. These studies were tried to provide essential principlesand techniques of the functional modifications of bentonites and the applications onwastewater treatments. The innovative achievements can be summarized as follows:1. A novel sorptive material of quaternary ammonium cationic starch-bentonite wassynthesized. Quaternary ammonium cationic starch has a series of virtues such as abundance in resources, low price, biodegradability, non-toxicity and good specificationand was used as raw materials to prepare novel sorptive materials in this study. Thesurface topography, electrokinetic chemistry characteristics and layer spacing of theCS-bentonite synthesized had been changed. The specific surface area, Zeta potential andlayer spacing of the modified bentonite were increased from33.96m~2/g,-24.01mV and1.2.44nm to57.76m~2/g,-13.01mV and1.515nm, respectively. The structure ofCS-bentonite was characterized by TEM, SEM, IR, TG-DSC, etc, proving that theexfoliated layers of CS-bentonite were formed, the intercalation of cationic starch wassucceed, the flocculation characteristics were increased and the surface hydrophobicitywas enhanced. The experiment results of sorption stability showed that the desorptionrate of the novel CS-bentonite synthesized was low, meeting the requirements of thepractical application for treating wastewater. As a result, these results show the directionfor the research and development of the novel absorbents.2. The preparation technology, reaction mechanism, theoretical parameters andperformance features of activation of quaternary ammonium salt cationicstarch-bentonite complex sorption materials were comprehensive explored. Takingpolymer content as the main control index which impacts absorption ability, theorthogonal test was systematacially investigated. The optimum technology of preparationof the high performance starch-bentonite composite sorption materials had been explored:the starch initial concentration, reaction temperature, reaction time and reaction systempH value are7.0g/L,60℃,2.0hand7.0, respectively. The sorption dynamics betweenthe bentonite and cationic starch indicates that the cationic starch sorption is more fit tothe first-order kinetics law and the sorption isotherm is more fit to Langmuir model. Thermodynamics data shows that△G~θ＜0, indicates that sorption process is spontaneous,△S~θ＞0shows that the entropy of whole sorption system increases，0<△H~θ<63kJ/molindicates that the reaction is exothermic and warming is beneficial to the sorption ofbentonite for cationic starch. These research results have high academic and pragmaticimportance. Especially they have theoretical significance for development of neweconomic and stable adsorbents.3. The sorption mechanism and influencing factors of CS-bentonite materials sorbed wastewater pollutants, such as dyes (Methylene Blue and Congo Red), p-nitrophenol,Cr(Ⅵ) and phosphate had been studied systematically. The results show that cationicstarch-bentonite reacts with dye in water mainly by surface sorption and interlayerorganic phase partitioning; reacts with p-nitrophenol in water mainly by surface sorptionand interlayer organic phase partitioning; reacts with Cr(Ⅵ) mainly by surface sorptionand surface complexation; reacts with phosphate mainly by surface sorption. Thesorption isotherms of dye, p-nitrophenol and Cr(Ⅵ) reacting with the starch/bentoniteaccords with Langmiur isotherms model, but the isotherms of phosphate reacting withthe starch/bentonite accords with Freundlich isotherms model. All the sorption process ofthe four characteristic of pollutants accord with pseudo-second-order kinetic equationwhich suggests that the sorption process are complex, such as external liquid filmdiffusion, surface sorption and intraparticle diffusion. These studies of sorption ruleprovide the consultation basis for the development and utilization of starch-bentonite.4. The removal of dyes by hydroxy aluminum (Al-OH) and cetyl trimethylammonium bromide (CTMAB) modified bentonite was deeply studied. The sorptioneffects of hydroxy aluminum pillared bentonite on Acid Turquoise Blue A(ATBA), BasicViolet14(BV14) and Basic Green (BG) are better than sodium bentonite with muchmore than95%sorption efficiency; the sorption isotherms accords with Henry andLangmuir isotherms model, kinetic curves conform the proposed second-order kineticsmodel and the order of sorption capability is BG>BV14>ATBA。The sorption ratio ofCTMAB organic intercalation bentonite on Acid Blue25(AB25), Acid Blue29(AB29),Acid Turquoise Blue A(ATBA) and Acid Golden Yellow G (AGYG) dyes are more than95%, the four acid dyes’ sorption experiment data are in line with Freundlich isothermsmodel and proposed second-order kinetics equation, the order of sorption capability isATAB>AGYG>AB93>AB25.According to the studying the sorption effect of new adsorbent material—quaternaryammonium type Cationic starch-bentonite complexes on the wastewater dyes (MethyleneBlue and Congo Red), p-nitrophenol, Cr(Ⅵ) and phosphate, the sorption effect,mechanism, isotherms model and kinetic parameters were gotten; Opening up thesorption action mechanism and enriching the sorption effect theory in this research will have strong theoretical significance and application value. Study about sorption effect ofdyes on the Al-OH and CTMAB modified bentonites can provide more systematicresearch base for bentonite’s dye wastewater treatment.