| In recent years, the environment have been inevitably contaminating by the antibiotic, which residues in the aquatic environment, it has attracted people’s attention.. In this study, bentonite/carbon composite adsorbent was prepared, which used grapefruit peel powder and bentonite as raw materials, and used for adsorption of tetracycline from wastewater. The effects of different preparation conditions, the modified methods and adsorption conditions on the adsorption properties of the adsorbent were investigated. Studied the adsorption isotherm model, kinetics, thermodynamics and the corresponding adsorption theory, the experimental results showed:(1) Studied the effects of calcination temperature, ratio of raw materials and calcination time, etc. on the adsorption performance of bentonite/carbon composite adsorbent,, and preparation conditions were:calcination temperature 300 ℃, ratio of raw materials 1:1, calcination time 3h, ZnCl2 dipping modification, stirring time lh, the adsorption rate and adsorption values were:93.38%,115.57mg/g. Examined the impact of adsorption conditions:adsorption time, adsorbent dosage, tetracycline initial concentration and adsorption temperature on the adsorption performance, adsorption conditions were:adsorption mixing time 30min, adsorbent dosage 0.02g, tetracycline initial concentration 100mg/L, the adsorption temperature was room temperature, the adsorption rate was 93.64%。(2) To simulate the Langmuir isothermal adsorption model, Freundlich isothermal adsorption model and Temkin isotherm model by the data of the experimental results, we can learn that the modified bentonite/carbon composite adsorbent adsorption with Freundlich isotherm equation fitting effect was reasonable. At the same time, judging by the value of the linear correlation coefficient, infer that the adsorption process of modified bentonite/carbon composite adsorbent adsorption of tetracycline under different temperatures fitting better to the Freundlich isotherm model, probably consistent with the assumption the Freundlich adsorption model, which belongs to chemical adsorption process dominated.(3) Fitted the experimental data to four kinetic models as:the first-order adsorption kinetics model, the secondary adsorption kinetics model, particle internal diffusion model and Elovich model, the results showed that the adsorption kinetics data was not suitable for first-order model, indicating that the adsorption process was not the result of a single factor. The degree of the secondary adsorption kinetics model fits relatively well, which proved adsorption kinetics was mainly controlled by the chemical reaction, rather than by the mass transfer process control, Elovich kinetic model fitting effect was reasonable, which means that the adsorption process in line with the two-stage adsorption theory. Internal diffusion model fitting results deviate from the experimental data, showed that internal diffusion in the process of modified bentonite/carbon composite adsorbent adsorption of tetracycline was not the adsorption speed control procedures.(4) Adsorption thermodynamics study showed:adsorption thermodynamic parameters obtained from thermodynamic calculations of the experimental data showed that AG was negative, indicated that the adsorption of modified bentonite/carbon composite adsorbent was a spontaneous reaction process; in addition, unlike the general adsorption reaction was tetracycline adsorption was increased with increasing temperature, the △H were positive, indicated that the reaction was endothermic, △S was changed small. This can be explained by solvent substitution theory, by the absolute value of AH and △G, can also determine the adsorption of modified bentonite/carbon composite adsorbent was a result of physical adsorption and chemisorption interaction, but chemisorption dominant.(5) Morphologies, specific surface area and microscope of modified bentonite/carbon composite adsorbent were analyzed by TG, SEM, BET, XRD and IR. |
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