| Biochar is produced by all kinds of biomass materials under the condition of anaerobic or limited oxygen pyrolysis(typically below 700oC). Biochar is solid carbon material. In recent years, it was paying more and more attention because of its simple preparation method, extensive preparation biomass source, and the obvious effects of heavy metal ions removal from aqueous solution. As one kind of powder solid carbon material, biochar was used to remove heavy metal ion in aqueous solution. But it was hard to separate from water after the adsorption and as a resultant to lead to secondary pollution. People using the magnetization method to solve this problem, but the adsorptive ability of modified magnetic biochar decreased sharply. Based on the knowledge, this study presents a simple method to solve these problems by modified magnetic biochar with the addition of chitosan. At the same time, the conventional physicochemical analysis methods and spectral characterization techniques were used to analyze the basic composition and the basic characteristic of the material. The adsorption behaviors of adsorbent material were discussed through the thermodynamics and kinetics data fitting of biochar, CC, C-Fe, and CC-Fe. The potential adsorption mechanism of heavy metals were discussed according to the analyses of scanning electron microscopy(SEM) and infrared spectrum before and after the adsorption of heavy metals. The main research contents and results are as follows:(1) Biochar adsorbent was produced with corn straw under different pyrolysis temperature. The characteristics of the biochar were analyzed. Among those biochars, BC700 removal ability of copper and cadmium was 117.63 mg/g、110.76 mg/g, respectively. The carbon content of corn straw biochar is gradually reduced with the increasing temperature, while the ash content increases as the temperature rises. Corn straw biochar specific surface area and total porous volume increase with the rising temperature, PH values also increase with the rising temperature; Surface morphology of biochar, with the increase of temperature, the multi-layer structure and space structure gradually improved. Surface functional groups of corn straw change with the increasing temperature. For example, C-C bond die down and aromatic C=C build up; Cellulose and hemicellulose of corn straw were decomposed gradually along with the rising temperature, finally they shape the amorphous structure of biochar.(2) The possibility of adsorption mechanism for biochar was simply certificated before and after the adsorption to heavy metals wih biochar. The emergence of biochar surfaces of refractory material could be seen through the scanning electron microscopy(SEM); Position changes obviously of aromatic C=O, O-H, and aromatic C=C in the infrared spectrum. The Cu2+ and Cd2+ removal by biochars seemed to be attributable to surface complexation and/or precipitation depending on the functional groups and this needs to be quantified further.(3) Using chitosan and magnetic iron to modified the highly efficient adsorption biochar(BC700) to develop a kind of high efficient adsorbent, which was easy to recycle. In addition, in order to realize the basic composition and the basic characteristics of materials, we uanalyze the structure and physicochemical properties of the the original biomass materials and modified biochar materials by physicochemical analysis method and spectral characterization techniques. Finally, we use thermodynamics and kinetics data of BC700 and CC-Fe to fit their adsorption behavior. The result was that they both fit first-order-kinetics equation for Cd2+ well and fit both first-order-kinetics and second-order kinetic equation for Cu2+ appropriately. |
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