Study On Adsorption Effect Of Cr(?) By Biochar Made By Wheat Straw Modified By Zinc Chloride

Biochar is a kind of carbon-rich solid pyrolyzed under anoxic or anaerobic conditions. The surface of biochar is loose and porous, and its specific surface area is very large, so that the biochar has high surface energy and strong adsorption ability. And also the sources of biochar are widely available, all of these characters let the biochar have great potential in adsorption of pollutants such as heavy metal Cr??? in waste water.In this paper the wheat straw were choosed as the material and Zinc Chloride as the modifier to prepare the biochar. The paper investigated the optimal conditions for the preparation of modified wheat straw biochar and the optimum conditions for the adsorption of Cr???, and studied the modified and original wheat straw biochar adsorption effect of Cr??? respectively. By using the methods of elementary analysis, the content of C, H, N, O elements of the wheat straw biochar were determinated. By SEM characterization, the structure of biochar can be observed. By the FTIR analysis, the functional groups on the surface of wheat straw biochar can be roughly analyzed. Through those above analysis, this thesis further discussed the adsorption mechanism of the sorption of Cr??? on wheat straw biochar. However, in actual production the dynamic adsorption is often used to simulate the Cr??? removal in wastewater, so the thesis researched the adsorption and desorption of Cr??? on the modified wheat straw biochar respectively to make sure the optimal conditions. The major results and conclusions are as follows:?1? The optimal conditions to prepare modified wheat straw biochar are: Zinc chloride solution mass concentration of 250 g·L^-1, impregnation ratio of 220%, activation temperature of 400? and activation time of 60 min. When theinitial concentration of Cr??? is 50 mg·L^-1, the optimum conditions for the adsorption of Cr??? on modified wheat straw biochar are: pH=1, adsorbent dosage of 0.8 g·L^-1, and the temperature of 30?.?2? Sorption of Cr??? on the wheat straw biochar before and after modification both fitted with the pseudo-second-order kinetic model, and their isothermal adsorption process can be described well with the Freundlich and Langmuir isotherm model. Therefore, we considered that the adsorption process mainly includes monolayer adsorption and chemical in dominating station.?3? The optimal conditions for dynamic adsorption are: pH=1, flow rate of 3ml·min^-1, temperature of 20? and Cr??? concentration of 50 mg·L^-1. Taking NaOH as desorbent, the optimal conditions for dynamic desorption are: flow rate of 1ml·min^-1, temperature of 40? and Cr??? concentration of 1 mol·L^-1.