| Abandoned agricultural and forestry biomasses such as corn straw and pine nut shell are produced in China each year, but its way of utilization for circulation is limited and low at present. There is important significance to realize the utilization of corn straw and pine nut shell biomass resources. In recent years, with the development of the industry, amount of untreated heavy metal ions from metallurgy, electroplating, chemical industry etc. is released into the waterbody. It will give the normal animals and plants direct or indirect damage. Dealing with wastewater containing heavy metal ions has important practical significance. Biochars produced by agricultural and forestry wastes have wide raw material sources and cost saving features, and have good treatment performance for wastewater. It has theoretical significance to choose the appropriate method of rational utilization of agricultural and forestry wastes to solve water pollution problems.Prepared of biochars as carbon materials at the temperature of 200℃ in this study. It selected the citric acid concentration of 1.5 mol·L-1, corn straw and pine nut shell as raw materials, certain ratio of solid to liquid to adsorp Cr(Ⅵ) in wastewater. Analysis of the structure and morphology of biochars and the adsorption properties are carried out, and to discuss the carbon desorption and adsorption mechanism.(1) Compared to biochars produced by direct hydro thermal carbonization, biochars produced by citric acid modified have better surface area, carbon content, total number of microspheres and the amount of oxygen-containing functional groups. Under the same conditions, the products of corn straw is better than those of pine nut shell.(2) Biochars prepared from corn straw and pine nut shell adsorb the Cr(Ⅵ) will be subjected to reaction time, substrate concentration, temperature, pH and other factors. At the stirring rate of 100 r·min-1, biochars can reach the adsorption equilibrium in 80 mins, the maximum adsorption capacity is 25.92 mg·g-1. With the more acidic, Cr(Ⅵ) adsorption of biochars increase. Under the initial concentration of 50.00 mg·L-1, the removal rate was 99.20% at pH 2.(3) Cr(Ⅵ) adsorption of biochars accompanied by physical adsorption and chemical adsorption, it consists the pseudo two order kinetic equation in the process of adsorption, the fitting degree of Langmuir and Freundich adsorption isotherm model are achieved. In a certain range with the increasing of temperature, the saturated adsorption amount of biochars increases. The raising the temperature is conducive to biochars’adsorption.(4) The biochars after adsorption can be desorped in fixed frequency microwave in 800W, absorbance of leaching solution is basicaly no changed. It can be inferred the sample almost no longer exist Cr(Ⅵ) after microwave detoxification. The samples of re-adsorption after desorption, are found the saturated adsorption amount have no obvious changing.This study has shown that the hydrothermal carbonization of biochars can not only improve the physical and chemical properties, but also can be better used in waste removal for wastewater containing Cr(Ⅵ). |
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