Effect of Potassium Carbonate Addition Rate on Surface Characteristics of Corn Stalk Derived Biochar

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the National Natural Science Foundation of China (No.41271331)

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    【Objective】In recent years, biochar as an environment- friendly material has been arousing more and more attention the world over. The use of biochar as an adsorbent has been proved to be an effective way in managing polluted soil and water. Ordinary biochar is quite low in specific surface area and underdeveloped in internal pore structure, which greatly affects adsorption efficiency of the biochar. Therefore, usually biochar needs activating for higher adsorption capacity. In this study, effect of the amendment of potassium carbonate on surface properties of biochar was studied. 【Method】Activated biochar was prepared under 600℃ from corn stalk amended with potassium carbonate at a varying ratio (stalk/potassium carbonate in mass=1:1, 2:1 and 4:1). Potassium carbonate was prepared into solutions according to the impregnation ratio, 0.60 mol L-1, 1.2 mol L-1 and 2.4 mol L-1 in concentration, separately, and added into corn stalk at a rate of 3 ml per gram of corn stalk in preparation of activated biochar. The biochars prepared in such a way were labeled as KBC-1-600, KBC-2-600 and KBC-4-600 separately;the biochar prepared without the amendment of potassium carbonate was labeled as BC600, non-activated biochar. Basic properties of the biochars, BC (corn stalk biochar) and KBC (potassium carbonate activated biochar) were characterized, with infrared spectrum, surface functional groups, specific surface area, pore size distribution and adsorption kinetics. Naphthalene, as a typical small-sized molecule persistent pollutant (POPs), was selected as adsorbate to evaluate adsorption capacity of KBC and BC. Naphthalene adsorption capacities of KBC and BC and affinities of KBC and BC to naphthalene were analyzed, and prospect of the application of activated carbon was discussed. The pseudo first-order kinetic model, second-order kinetics model and intraparticle diffusion model were used to analyze dynamic process of the adsorption.【Result】With increasing potassium carbonate amendment rate, aromaticity of the biochars increased. When the impregnation ratio was increased from 4:1 to 2:1, hydrophilicity and polarity of the biochars improved, but when the impregnation ratio was further increased from 2:1 to 1:1, hydrophilicity and polarity of the biochars decreased, instead. Potassium carbonate amendment increased specific surface area of the biochards, with KBC-2-600 in particular reaching up to 566 m2 g-1, whereas specific surface area of the ordinary biochar (BC600) was only 86.8 m2 g-1; The KBC600 series of biochars were significantly higher or on average 16 and 4 times higher respectively than BC600 in mesopore volume and micropore volume, and also higher in mesoporosity. The amendment altered the number of functional groups and their saturation on the surface of biochar. KBC was lower than BC in total of functional groups at 1 256 cm-1~3 414 cm-1. With the increasing amendment rate of potassium carbonate, the ester C=O disappeared, reducing hydrogen bond forming capacity, and unsaturated C-O-C increased, enhancing aromaticity and non-polarity. Alteration of the cellulosic cleavage process caused by potassium carbonate is considered to be the main cause triggering changes in functional groups on the surface of the biochar. Kinetic analysis shows that the adsorption of naphthalene onto BC600 and KBC-4-600 could be described by the pseudo-second-order kinetic model. The adsorption process involved simultaneously external surface adsorption and intraparticle diffusion; After activation by potassium carbonate, adsorption capacity of the biochar improved significantly. The fitting of intraparticle diffusion model demonstrates that KBC gets more complicated in internal pore structure.【Conclusion】The amendment of potassium carbonate contributes significantly to improvement of surface active sites and pore complexity of the biochar, thus enhancing its adsorption capacity of nonpolar aromatic pollutants. The potassium carbonate activated biochar has well-developed pore structure, and hence a great potential to be used as highly-efficient adsorbent in remedying polluted soils in future.

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ZHU Ling, WANG Yueying, Lü Yizhong. Effect of Potassium Carbonate Addition Rate on Surface Characteristics of Corn Stalk Derived Biochar[J]. Acta Pedologica Sinica,2017,54(6):1508-1517.

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  • Received:February 16,2017
  • Revised:April 18,2017
  • Adopted:May 05,2017
  • Online: June 26,2017
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