Granulated Preparation Of Bentonite Composites And Their Application In Dye Adsorption

With the development of industry,the water pollution problem caused by the increasingly serious discharge of domestic sewage and industrial wastewater poses a serious threat to the ecosystem and human health.So the effective treatment of water pollution becomes an increasingly urgent subject.With low price,rich reserves and other advantages,bentonite,a natural mineral,has been widely applied to wastewater treatment as a good absorbent.However,bentonite is easy to form emulsion by swelling and dispersing in water.The solid/liquid separation and recycling problem largely limits the industrial application of bentonite in powder form for wastewater treatment.To address this problem,three kinds of bentonite compositeswere prepared by different ways to synthesize bentonite in globular or bulk form.Among them,the novel approaches for preparation of bentonite composites by using paper fiber and PVA sponge as the carrier are proposed,respectively.The structure and properties of the composites were characterized by XRD,FT-IR,SEM and TGA-DTA.Meanwhile,the effect of them on the decoloring of dyes,absorption and desorption mechanism were studied.The results of this study provides basic experimental data and process basis for the application of bentonite in the treatment of dyeing wastewater.The main contents of this thesis are as follows:1)With nature bentonite as binder and organic bentonite as raw materials,the bentonite granules(G-BT)with certain stability were prepared by the method of blending and granulation.After coating with PVA,the more stable granules(PVA/G-BT)were obtained.With the paper fiber(P)as the skeleton and agar(A)as binder,the lightweight and porous bentonite granules(P-AB)were prepared by the non-traditional freeze-dried method(without vacuum).Then they were strengthened by PVA to obtain the bentonite granules(PVA/P-AB).A porous hybrid bulk adsorbent(PVA-CS/BT)was prepared by PVA sponge immobilizing chitosan/bentonite.2)The structure of the three bentonite composites was characterized by SEM.The results showed that PVA / G-BT granules were compact with less pores in the surface.With paper fiber skeleton structure,PVA/P-AB granules were fluffy and porous.PVA-CS / BT bulks were porous by immobilize the little CS / BT particles on PVA sponge skeleton.3)The effects of three kinds of bentonite composites on the removal of dyes were mainly discussed.According to the results,the removal efficiency of PVA / G-BT to 100 mg / L Congo red(CR)was more than 95%.The removal efficiency of PVA / P-AB to 600 mg / L CR was more than 95% and the maximum adsorption capacity wasas high as 429.9 mg/g,which was better than that of P-AB(60).With 95% removalefficiency in 80 min and 160.2 mg/g adsorption capacity for Methylene blue(MB),the adsorption properties of PVA-CS/BT for MB in absorption rate and removal efficiency was better than that of CS/BT granules.During five rounds of reuse,the removal efficiency of PVA / P-AB for CR and PVA-CS/BT for MB still reached to 94.11% and 64.60%,respectively.4)According to the model of adsorption isotherms and adsorption kinetics,the results indicated that PVA/G-BT and PVA/P-AB to CR adsorption isotherm followed Langmuir adsorption model,PVA-CS/BT to MB followed Freundlich model.All the adsorption behavior followed pseudo second order kinetic model well.Thermodynamic analysis suggested that all the adsorption was spontaneous endothermic process,to which increase of temperature was conducive.5)Weight loss rate study showed that three bentonite composites were stable in water to meet the use of bentonite granule or bulk for wastewater treatment.The comparison of solid-liquid separation suggested that the three bentonite composites well addressed the problem that the bentonite in powder form is difficult to be separated and recovered from treated water.