| With the development of modern industrial and agricultural,large numbers of various pollutants, such as heavy metal ions(Cr, Pb, Hg and Ni, etc.) and toxic organic pollutants(phenolic compounds, etc.), were produced into the water, which caused serious damage to the aquatic environment. In various wastewater treatment methods, due to the process of the adsorption method is simple, easy to operate and environmentally friendly, it is the most practical method of sewage treatment. The core technology of sewage treatment is the sorbent materials. The most common adsorbent material is activated carbon adsorbent, however, there is a high cost of raw materials and high energy consumption problems for their preparation. Therefore, finding effective ways of lower-cost adsorbent material's preparation process has become a hot topic in the field of water treatment materials. Agriculture and forestry waste biomass such as waste wood chips, fruit dander, straw, etc., their main constituent is wood cellulose, containing-COOH,-OH,-NH2 and other active groups and having a certain pore structure, which have the capability of adsorbing heavy metal ions and organic pollutants. It is considered as a great potential of raw material used for preparing low-cost adsorbent material. The actual application of wastewater treatment found that these hard shell material's adsorption capacity is weak because of their insufficient active ingredients and pore structure inconspicuous, which results in poor absorption properties and unsatisfactory absorption effect of processing when it applied directly. Such biomass residue shell needs to be modified to improve its adsorption properties and enhance its capabilities of contaminant removal. In this paper, The Guizhou Hezhang walnut shell as raw material was used to prepare the modified walnut shells biological adsorption materials by phosphate modification. In order to improve its capacity of adsorb pollutants and improve the efficiency of water treatment, further treatment with sodium alginate polymer compounded modification also was used to prepare the modified walnut shell/alginate composites biomaterials. The series of prepared adsorbent material was applied to deal with the simulation wastewater containing Cr(VI) and phenol experiments. The main contents and results of the paper are as follows: Preparation of MWS. After the pretreatment of raw materials of walnut shell, then the material was used phosphoric acid to activate the feedstock. The effects of impregnation ratio, activation temperature and activation time on the adsorption of modified products were studied. The best preparation process was determined by orthogonal test: impregnation ratio 1:3, activation temperature 120 C, activation time 90 min.2. Analysis of MWS characterization. Adoption TG/DSC, SEM, Boehm titration and IR analysis techniques was used to characterize the structure and physicochemical properties of MWS. The results showed that Phosphoric acid impregnation changed the pyrolysis process of the shell material, and accelerated the carbonization process. At the same time, the surface morphology of walnut shell changed, the pore structure increased, the surface area increased. MWS surface has a certain oxygen-containing reactive groups such as carboxyl analysis by Boehm titration, and IR spectra confirmed that, compared to the shell material, MWS oxygen containing active groups increased, that is modified to enhance the adsorption capacity of shell material.3. Application of MWS absorbing Cr(VI) and phenol for wastewater. The effects of initial pH, MWS dosage and treatment time on the removal of pollutants were studied through the static simulation of wastewater treatment process. Under the experimental conditions, the adsorption rate increased with the dosage and absorption time increase, Cr(VI) and phenol respectively suitable for the acidic and neutral conditions when removed, the adsorption rate respectively is 99.65% and 87.49%. Based on the study of the process of wastewater treatment, the adsorption kinetics theory was established. It was found that the pseudo two order kinetic equation could describe the adsorption process of MWS on two kinds of pollutants. Process of MWS absorption Cr(VI) fit into Langmuir isotherm, Qm and b increased with temperature increasing, showed that the process is an endothermic process and heating is conducive to the adsorption of Cr(VI); The absorption of phenol is suitable for Freundich isotherm equation, parameter K increases as the temperature decreases. It is indicated that the low temperature is beneficial to the adsorption of phenol on the test conditions.4. Preparation of MWS/SA. In order to improve the application effect of MWS adsorption materials and to solve the problem of the recovery of fine particles modified products.,Through the polymer material sodium alginate(SA) packet embedded MWS was prepared by composite adsorption material MWS/SA, composite process of sodium alginate concentration, curing agent(calcium chloride) concentration, MWS dosage, caused by pore forming agent NaCl content, curing temperature, curing time to determine. The optimum preparation process was determined by using orthogonal experiment to optimize the modification conditions: alginate concentration was 2%(m/v), MWS concentration was 22g/L, NaCl at a concentration of 30g/L, added dropwise to 1%(m/v) CaCl 2 solution at 25? to cure 3h.5. Analysis of MWS/SA characterization. The influence of chemical structure change on the adsorption properties of MWS/SA was analyzed by scanning electron microscope(SEM) and infrared spectroscopy(IR) analysis technique. The results confirmed that the surface structure of the composite material is more rough than the SA, which still can be seen the folds of the grid sheet inside, described alginate modification increased the absorption surface area to some extent; Comparative analysis of the infrared(IR) spectra MWS/SA and MWS, composite modified the MWS structure has changed, is introduced with carboxyl and hydroxyl groups of oxygen-containing groups, enhance the adsorption ability of material, can promote the adsorption removal of Cr(VI), phenol and other substances.6. Application of MWS/SA absorbing Cr(VI) and phenol for wastewater. Similar with former MWS applications experimental design, the effect of MWS/SA dosage, pH value and treatment time on the removal of pollutants from polluted materials was studied. Under the experimental conditions, with the dosage and adsorption time increase, the absorption rate increased. Under the acidic conditions The adsorption rate increased with the increase of MWS/SA dosage and treatment time, and The adsorption effect of Cr under acidic condition was better. Phenol was suitable for adsorption treatment under acidic and neutral conditions, the adsorption rates were 95.37% and 80.27%, respectively. Both sewage adsorbed kinetics process by MWS/SA can be expressed with Pseudosecond-order model. The absorption process of Cr(VI) by MWS/SA fit into Freundich isotherm and the parameter K increased with temperature increase, it is indicated that elevated temperature under experimental conditions is conducive to absorption Cr(VI), MWS/SA absorption of phenol is also fit into Freundich isotherm equation, K value decreases with increased temperature, It is indicated that the temperature rises will reduce adsorption capacity of the adsorbent. It was proved that the low temperature is beneficial for the adsorption of phenol on MWS/SA. |
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