| Bentonite is a kind of clay mineral which is abundant in China.It is widely used in wastewater treatment because of its special layered structure and good cation exchange properties.However,the powdery bentonite has good water swelling and dispersibility,which makes it easy to form mud in aqueous solution and difficult to achieve solid-liquid separation,resulting in secondary pollution,which limits its application in wastewater treatment.In this paper,sodium bentonite from Anji County,Zhejiang Province was used as raw material and studied the preparation by different methods.The FT-IR,XRD,TGA-DTA,SEM and BET analysis methods were used to analyze the structure and performance of the prepared samples,and the influence factors and adsorption mechanism of the prepared adsorbent particles on the dye adsorption in waste water were studied systematically,and the optimal adsorption conditions were determined.The main achievements of this paper are as follows:?1?In this paper,three kinds of bentonite-based adsorbent particles were prepared by extrusion-sphericity method and sol-gel method.The optimum preparation conditions of bentonite particles?G1?are:Na2CO3 content is 5%,the roasting temperature of 500°C,the roasting time 50 min;The optimum preparation conditions of bentonite composite particles?G2?are:bentonite/fly ash ratio 8:2,Na2CO3 content is 3%,calcination temperature is 500°C,calcination time is 40 min;bentonite/fly ash composite particles?G3?optimal preparation conditions:sodium alginate mass fraction is 1%,CaCl2 mass fraction is 3%,the ratio of bentonite/fly ash is 10/10.?2?The bentonite modified by cetyltrimethylammonium bromide?CTAB?was used to prepare organic bentonite?P-OBT?.The XRD diffraction pattern showed that the d001 peak of the modified soil shifted to small angle with the increase of CTAB content.The corresponding inter-layer spacing(d001 value)of organic bentonite is increased to 2.31 nm when the CTAB content is increased to 27.7%.In the FT-IR spectrum,it can be observed that the modified bentonite has-CH2 and-CH3characteristic peaks.In summary,the cationic surfactant?CTAB?modification effect is obvious.The P-OBT was subjected to shape granulation by a sol-gel method to obtain spherical particles?G4?having good stability.?3?The removal effect of several bentonite-based adsorbent materials on dyes was discussed.When G1 adsorbed MB solution(50 mg·L-1),the removal rate was68.8%,and the adsorption amount was 1.86 mg·g-1.When G2 adsorbed MB solution(50 mg·L-1),the removal rate reached 93.86%,and the adsorption amount was 2.35mg·g-1.When G3 adsorbed MB solution(100 mg·L-1),the removal rate was 98.71%,and the adsorption amount was 32.38 mg·g-1.When G4 adsorbed MB solution(100mg·L-1),the removal rate was 92.12%,the adsorption amount was 59.55 mg·g-1 and When G4 adsorbed RhB solution(100 mg·L-1),the removal rate reached 81.25%,and the adsorption amount was 11.52 mg·g-1.?4?The adsorption isotherms of the adsorption process were analyzed.The results show that the adsorption of MB by G2 is in good agreement with the Langmuir isotherm model,indicating that the chemical reaction is involved in the adsorption of MB by G2;the adsorption of MB by G3 is very Good conformity to the Freundlich isotherm model,indicating that the adsorption of MB on the heterogeneous surface of the adsorbent involves multi-layer adsorption;the adsorption of MB by G4 is in good agreement with the Langmuir isotherm model and the adsorption process of Rh4 by G4 is more in line with the Freundlich isotherm model.?5?The thermodynamic parameters of the adsorption process were analyzed.The results show that the adsorption process of G2 on MB is a spontaneous endothermic process,in which the?H?value is 1.247 kJ·mol-1 is greater than zero,indicating that the temperature rise is favorable for adsorption.?S?is greater than zero,indicating that the chaotic degree of the whole system increases during the adsorption process;the adsorption process of G3 on MB is a spontaneous endothermic process,and the system chaos increases;the adsorption process of G4 on MB is a Spontaneous exothermic process,?S?is less than zero,indicating that the whole system is less chaotic during the adsorption process;when G4 adsorbed RhB at the 298k,?G?is greater than zero,indicating that the adsorption cannot proceed spontaneously,and additional energy is required to promote the reaction.As the temperature rises,?G?is less than zero,indicating that increasing the temperature is beneficial to adsorption.?H?is a positive value,indicating that the adsorption is an endothermic process.?6?The kinetics of the adsorption process was analyzed.The results showed that the adsorption behavior of G2,G3 and G4 on MB and the adsorption behavior of G4on RhB were consistent with the pseudo-second-kinetic model.Combined with XRD,FT-IR spectrum and thermodynamic analysis,it was proved that the adsorption process was the common result of physical adsorption,chemical adsorption and ion exchange.?7?Ethanol was used as desorption agent for desorption experiments.After 5consecutive adsorption-desorption,the removal rate of G3 on MB could still reach65.5%.This indicates that the adsorbent particles have good recycling performance. |
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