Preparation Of Attapulgite-Carbon Composite Based On Spent Bleaching Earth And Its Adsorption Effects On Heavy Metals And Antibiotics

With the industrialion and scale of livestock and aquaculture in China,residued heavy metals and antibiotics are often detected in the water,which harm to aquatic ecological environment and human health.As a common method to remove heavy metals and antibiotics from water,adsorption has been widely used because of its good effect,low cost and wide source of raw materials.Spent bleaching earth,as common solid wastes produced by making oil,contains20%-40%residual oil and may cause resources wasting and even secondary pollution if not properly disposed.In this study,carbon materials have been prepared based on the utilization of spent bleaching earth,which not only reduces the solid wastes pollution,but also further solves some environmental problems,achieving"waste to waste".In this study,attapulgite-carbon composites A&Cs（A&C300,A&C500,A&C700）were prepared by pyrolyzing spent bleaching earth under different high temperatures and limited oxygen.HPA/Cs（HPA/C-300,HPA/C-500,HPA/C-700）were prepared by modifying A&Cs with H₃PO₄.A&C500,A&C700 and HPA/C-300 with good adsorption effect were selected as adsorbents,and its basic properties and structural characteristics were analyzed and characterized.Tetracycline（TC）,Copper（Ⅱ）and enrofloxacin（ENR）,which are common pollutants in livestock and poultry wastewater,were used as target pollutants to analyze the adsorption influencing factors,effects and mechanism of the materials.The main results are shown as follows:（1）By SEM-EDS,BET,FTIR,XPS and XRD analysis,it found out that with the pyrolysis temperature rising,specific surface area and the degree of structural chaos of A&Cs increased,while the abundance of functional groups and the mass ratio of O/C decreased.After H₃PO₄ modification,rod-like structure was found on the surface of HPA/C-300,and the hydrophobicity of HPA/C-300 was enhancd,specific surface area and total pore volume improved,and types and number of functional groups increasd.（2）The removal effects and the adsorption mechanism of TC and Cu（Ⅱ）by A&C500 and A&C700 in the single polluted system have been compared and analyzed.The results showed that p H and the concentration of Na⁺have a significant effect on Cu（Ⅱ）but little effect on TC adsorbed by A&C500 and A&C700.According to the adsorption fitting models and thermodynamic analysis,the adsorption of TC and Cu（Ⅱ）by A&C500 and A&C700were spontaneous and endothermic which were dominated by chemical adsorption.The Q_m（the maximum adsorption capacity）of TC by A&C500 and A&C700 separately was 47.76mg·g^-1 and 43.37 mg·g^-1.And The Q_m for Cu（Ⅱ）was 16.73 mg·g^-1 and 22.50 mg·g^-1,respectively.The main adsorption mechanisms of A&C500 and A&C700 for TC included hydrogen bonding,π-πEDA interaction and hydrophobicity,while the main adsorption mechanisms of Cu（Ⅱ）contained ion exchange,electrostatic interaction,coordination and pore filling.（3）Through the above experiments,A&C500 as adsorbent was selected to explore its adsorption capacity and mechanism in the binary system of TC and Cu（Ⅱ）.The results showed that the adsorption capacity of TC and Cu（Ⅱ）by A&C500 in the binary pollution system was higher than that of in the single pollution system.In the binary pollution system,with the increasing of co-existing Cu（Ⅱ）concentration,the adsorption capacity of TC increased firstly and then decreased,and the maximum theoretical adsorption capacity of TC reached at 76.98 mg·g^-1.The adsorption capacity of Cu（Ⅱ）also increased and then decreased with coexisting TC concentration rising,and the maximum Cu（Ⅱ）adsorption capacity was 34.13 mg·g^-1.Through models fitting,XPS and FTIR analyzing,hydrogen bond,electrostatic interaction,ion exchange,coordination andπ-πEDA were the adsorption mechanisms of TC and Cu（Ⅱ）by A&C500 in binary pollution system.（4）H₃PO₄ modification can effectively improve the adsorption effects of HPA/C-300 for ENR.After H₃PO₄ modification,the adsorption capacity of enrofloxacin by HPA/C-300reached 66.79 mg·g^-1,which was 1.74 times that of A&C300 under the same conditions.The adsorption of ENR by HPA/C-300 was spontaneous and endothermic,and it was chemical adsorption.The adsorption mechanisms concludedπ-πEDA interaction,hydrophobic interaction,hydrogen bonding and pore filling.