| In order to utilize comprehensively tea resources and increase economic value of tea plants to promote the development of tea industry, at the same time, considering the situation of water eutrophication, this paper performed a systematic study on the preparation of tea seed shells adsorbent.After pretreatment with acid and alkali, the tea seed shells were accessed tertiary amine groups on the cellulose backbone to obtain a weakly basic anion adsorbent by using epichlorohydrin as the etherifying agent and dimethylamine as the modifier agent. The removal of H2PO4- was used to examine the effect of material dosage, reaction temperature and time on the modification.The result of single factor experiment indicated that the removal rate of H2PO4- was increasing gradually with the amount of epichlorohydrin and it was reached maximal with 30mL, while the removal rate was going down. The removal rate was going up with the reaction temperature at the first stage, from 60℃ to 100℃. At the first stage, the removal rate was going up with time during 3h and then it was stable. Similarly, the removal rate of H2PO4- was increasing by use of more dimethylamine and it was reached maximal with 40mL, then it was stable. At the second stage, the removal rate was increasing with the reaction temperature,the maximal rate was reached at the point of 60℃ and then is was going down, the removal rate was going up with time during 5h and then it was stable.Through orthogonal test, the optimum modification condition was as follows:30mL of the amount of epichlorohydrin and 100℃ of the reaction temperature and 2.5h of time at the first stage.40mL of the amount of dimethylamine and 65℃ of the reaction temperature and 5.5h of time at the second stage.The composition, morphology and structure of the modified products were characterized by Leaf infrared spectroscopy, scanning electron microscopyand automatic specific surface area and porosity analyzer. The results showed that the morphology of tea seed shells has changed greatly, lignin and hemicellulose were removed and cellulose backbone was retained after modification.The affecting factors of the adsorption including the initial concentration of H2PO4-and the pH value and the adsorption temperature and time were studied in ways of static adsorption using H2PO4- as the adsorbate. The optimal combination conditions of the adsorption has been screened through the second orthogonal rotating experiment design.The equation was as follow:Y=2.0743+0.1593X1 - 0.1134X2+0.6222X3 -0.0592X32.The result showed that the effect of the pH value (Xi) and the adsorption temperature (X2) and the initial concentration of H2PO4-(X3) on the adsorption capacity was significant and addressed as X3>X1>X2. The optimum conditions of the adsorption wsa as follows:10 of the pH value,0℃ of the adsorption temperature and 50mg-L-’of the initial concentration ofH2PO4-. The maximum adsorption capacity of H2PO4- could reach to 3.9817mg·g-1.The static adsorption process of H2PO4- follows Langmuir adsorption isotherm equations and Freundlich adsorption isotherm equations.Form the adsorption kinetics and thermodynamics, it can be concluded that chemical adsorption is predominant for the adsorption of H2PO4- on the adsorbent. The adsorption rate is controlled by surface diffusion process and intra-particle diffusion process, and the intra-particle diffusion process plays a more significant role than surface diffusion process during the adsorption process.Compared to the unmodified tea seed shell, the adsorption capacity of the adsorbent has been greatly increased after being modified. And the adsorbent shows greater advantage on the adsorption of low concentrations H2PO4- when compared to activated carbon. Desorption and regeneration experiments show that the adsorbent has such advantages as easy regeneration and reusability. |
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