Study On The Adsorption Of Organic Composite Hydroxy-aluminum Pillared Bentonite To Phosphate And Its Air Flotation Application Effect

Water eutrophication is a global environmental problem,and excessive phosphate is one of the key factors causing such problems.Adsorption dephosphorization method has attracted much attention because of its high economic benefits and good dephosphorization effect.As a cheap adsorption raw material,bentonite is often mentioned in the application research of phosphorus removal by adsorption.However,the difficulty of separation of powdered bentonite has always been the key factor limiting its further development and application.Therefore,the study of phosphorus removal by adsorption should not only pay attention to the effect of phosphorus removal by adsorbent,but also actively explore the good separation technology of adsorption materials,and air flotation process has a great advantage in the separation application of powder adsorption materials.In this paper,bentonite is pillared with hydroxyl-aluminum,and the pillared bentonite(Al₁₃-Bent)is organically modified with three ionic surfactants Cetylpyridine bromide（CPB）,Sodium dodecyl sulfonate（SDS）and Dodecyldimethyl betaine（BS）to prepare organic composite pillared bentonite(CPB-Al₁₃-Bent,SDS-Al₁₃-Bent,BS-Al₁₃-Bent).X-ray diffraction analysis（XRD）,Fourier infrared spectroscopy（FTIR）and total organic carbon determination（TOC）were used to characterize bentonite adsorbents and analyze their structural characteristics.Through adsorption experiments,the adsorption performance of three bentonite adsorbents for phosphate was investigated.Meanwhile,the effects of p H and coexisting ions on the adsorption of phosphate were investigated.Finally,the air flotation effect of SDS-Al₁₃-Bent and Al₁₃-Bent was compared through air flotation test.Combined with the adsorption experimental results,the applicability and development potential of CPB,SDS and BS modified bentonite-based adsorption materials were comprehensively analyzed,which could provide reference for the follow-up air flotation process research and engineering application of similar adsorption materials.The main conclusions of this study are as follows:（1）Organic composite pillared bentonites(CPB-Al₁₃-Bent,SDS-Al₁₃-Bent,BS-Al₁₃-Bent)were prepared by modifying Al₁₃-Bent with CPB,SDS and BS.And the prepared bentonite-based composites were characterized by XRD,FTIR and TOC.The results showed that the layer spacing of Al₁₃-Bent modified by CPB changes.The layer spacing of0.6CPB-Al₁₃-Bent was 0.078 nm higher than that of Al₁₃-Bent,and CPB was successfully inserted into the bentonite layer.The interlayer spacing of SDS-Al₁₃-Bent and BS-Al₁₃-Bent had not changed significantly,but new absorption peaks representing organic components appear in the FTIR spectrum,which indicated that SDS and BS were also successfully combined with Al₁₃-Bent through hydrophobic bonding.The TOC characterization results could also illustrate the above conclusions.（2）The phosphate adsorption properties of CPB-Al₁₃-Bent,BS-Al₁₃-Bent and SDS-Al₁₃-Bent were studied.The results showed that the optimal p H value for phosphate adsorption of CPB-Al₁₃-Bent,BS-Al₁₃-Bent and SDS-Al₁₃-Bent was 3,and the adsorption reaction had strong anti-interference ability of Cl^-,NO₃^-,SO₄^2-ions.Pseudo second-order kinetics and Elovich equations could better describe the entire adsorption process,adsorption process was affected by chemical effects.At the same time,the adsorption of CPB-Al₁₃-Bent,BS-Al₁₃-Bent and SDS-Al₁₃-Bent for phosphate conformed to Sips isothermal model.The maximum fitting adsorption capacities of 10%SDS-Al₁₃-Bent and 20%SDS-Al₁₃-Bent were34.47 mg·g^-1 and 29.25 mg·g^-1,respectively.SDS-Al₁₃-Bent had better phosphate adsorption properties.（3）The main mechanism of CPB-Al₁₃-Bent,BS-Al₁₃-Bent and SDS-Al₁₃-Bent on phosphate adsorption was ligand exchange and electrostatic attraction.CPB and BS affected the ligand exchange,which resulted in the decrease of the phosphate adsorption properties of CPB-Al₁₃-Bent and BS-Al₁₃-Bent.（4）The application effect of SDS-Al₁₃-Bent in air flotation is analyzed emphatically.The air-flotation test shows that SDS-Al₁₃-bent had the best air-flotation separation effect when the dissolved air pressure was 0.4 MPa and the reflux ratio was 30%.After air flotation treatment,the remaining solution was clear,and the average SS removal rates of10%SDS-Al₁₃-Bent and 20%SDS-All₁₃-Bent were 99.78%and 99.87%,respectively.The anionic surfactant SDS modification not only significantly improved the air flotation separation performance of hydrophilic powder adsorbents,which had little effect on the adsorption performance of the adsorbent inherent.The modification of anionic organic compounds has great potential in the application of bentonite adsorbents to air flotation.