Preparation, Characterization And Adsorption Behaviors Of The Inorganic Pillared Bentonites And Its Application In Wastewater Treatment

The natural bentonite was used as matrices to prepare the hydroxyl-Fe and hydroxyl-Fe-A1 bentonites in this study.The relationship between preparation conditions and adsorption behaviors in aqueous solution,the physical and chemical properties and micro-structure of the inorganic pillared bentonites were studied.The applications of the natural and pillared bentonites in organotin wastewater treatment were investigated.The factors affecting the adsorption behaviors of the inorganic pillared bentonites was determined using Cu-EDTA complex as adsorbate.The results show that(1)the OH/Fe mole ratio,the pillared reaction temperature and the ageing time are the dominating factors that affecting the adsorption capacity of the inorganic pillared bentonites was determined(2)the adsorption isotherms of the natural and pillared bentonites fit with Langmuir and Freundlich isotherm(3)the adsorption kinetics was found to follow the pseudo-second order kinetics equation(4)the intaparticle diffusion was determined as control step of the adsorption rate.The results also show that the adsorption capacity(qm)the hydroxyl-Fe pillared bentonites was found in the linear relationship with the OH/Fe mole ratio.,i.e.q_m=0.026+0.03385OH/Fe,where the intercept is the contribution given by the inborn adsorption site of bentonite and the slope which is in direct proportion to the stoichiometric coefficient is equal to the contribution given by the hydroxyl adsorption site of the pillared bentonite.This indicates that the hydroxyl group acted as the accessorial adsorption site of the pillared bentonites.The diffusion coefficients(D_iq)and the pseudo-second order equation constant(k)increased with the increase of OH/Fe mole ratio.The optimal ageing temperature was 60℃.The ageing time has insignificant effect on q_m,k and D_iq. The optimal aging time was found to be 24 hours.The increase of q_m,k and D_iqof the hydroxyl-Fe-A1 bentonite with decrease of Fe/A1 indicated that activity of the hydroxyl adsorption site was depended on different metal ion in the hydroxyl-Fe-A1 bentonite.It was found that the d₀₀₁value of the hydroxyl-Fe pillared bentonite increased with the increase of OH/Fe mole ratio,while the d₀₀₁value of the hydroxyl-Fe-A1 bentonite decreased with the increase of the Fe/A1 mole ratio.The pore structure was characterized as 'house of cards' which was formed by novel meso-microporous delaminated structure and pillared fragments.Therefore,the cylindrical model is the most suitable model to characterize the pore structure of the pillared bentonites.The mesopore size is ranged from 2 nm to 80 nm with average pore size of 3.9nm.The fractal dimension and the BET surface area of the pillared bentonites were higher than that of the natural bentonite.It was found that the maximum BET surface area and the fractal dimension of the pillared bentonite was 108.87m²/g and 2.500, respectively under the condition of OH/Fe=1.0.The fractal dimension of the hydroxyl-Fe-A1 bentonite decreased with the increase of Fe/A1 mole ratio.The structural developing model of the pillared bentonite was developed with the consideration of the original stage,the swelling stage,the pillared stage and the end stage during the swelling process,the pillared process,and the conformed process,respectively.The influences of the pillared effect on the physical and chemical properties of the pillared bentonite were suggested as the formation of the pillared effect,the new pore and surface area effect,the clogging effect and smoothing and sealing effect. It was revealed that the process of pillared reagent structured into the bentonite was not through ion exchange.The organotin was found as one of the environmental hormone.Unfortunately,to my knowledge,there is no treatment method has been studied.The application of the natural and pillared bentonites in organotin wastewater was investigated.The dose of the pillared bentonite for COD removal was 4.0 g/l under the initial COD concentration of 3250 mg/l.The results show that COD removal efficiency is 35.8%.While,The dose of the pillared bentonite for organic removal was 10.0 g/l under the initial organotin concentration of 10.79 mg/l.The results show that organotin removal efficiency is 78.8%.The optimal pH value is 9.0.The adsorption data was fitted well with the pseudo second order kinetics equation.The diffusion rate in adsorption process was found depended the multi-factors including the intaparticle diffusion. The adsorption data of total tin fitted both Langmuir isotherm and Freundlich isotherm while the adsorption data of COD was adequately fitted with both Henry isotherm and Freundlich isotherm.The adsorption capacity and adsorption affinity for organotin of the adsorbent exhibited the following the order:hydroxyl-Fe-A1 pillared bentonite,hydroxyl-Fe pillared bentonite and the natural bentonite.It was found that the organic matters in organotin wastewater were composed by organotin matter and no-organotin matter that fit with different adsorption isotherm.The results of XRD,FT-IR,TG-DTA and EDX indicated that the structure of hydroxyl-Fe pillared bentonite was more stable than that of the hydroxyl-Fe pillared bentonite. The results implied that the changes in structure of hydroxyl-Fe pillared bentonite were due to the fact that the iron in the hydroxyl-Fe pillared bentonite was reacted with the sulfur ion in the organotin wastewater.