不同温度生物炭酸化前后的表面特性及镉溶液吸附能力比较

Comparison of Surface Characteristics and Cadmium Solution Adsorption Capacity of Un-acidified or Acidified Bio-chars Prepared from Rice Straw under Different Temperatures

以稻秆为原料,在不同温度(300,400,500,600,700℃)条件下采用限氧控温炭化制备生物炭,用HCl和HF对其进行酸化处理,利用傅立叶变换红外光谱仪、比表面积和孔径测定仪现代分析手段对生物炭酸化前后的表面官能团、比表面积、孔径等特性进行比较,分析制备温度和生物炭表面特性之间的关系,探究制备所需生物炭的最佳温度条件。通过生物炭酸化处理和镉吸附实验结果,研究酸可溶矿物在生物炭吸附镉的贡献及制备温度对生物炭吸附镉能力的影响,为生物炭吸附水体中重金属镉提供科学依据。傅里叶红外分析表明,不同温度生物炭表面官能团存在一定的差异,主要表现为随制备温度升高,烷烃基缺失,甲基-CH3和亚甲基-CH2逐渐消失,形成了芳香环且芳香化程度增加。生物炭酸化后无机矿物Si O2吸收峰逐渐消失,官能团种类并没有发生变化,不同官能团随制备温度变化规律仍与酸化前生物炭一致。表面积及孔径分析结果表明,生物炭孔结构主要为中孔,随着热解温度的升高,比表面积和总孔容有所增大,在600℃达到最大;平均孔径随着制备温度升高而变小。生物炭酸化处理可以显著增大生物炭比表面积,总孔容也有所增加。生物炭酸化后充分去除了矿物质,孔隙结构未发生变化,孔结构仍为中孔,微孔表面积减小。镉吸附实验表明生物炭对镉具有较强的吸附能力,不同温度条件下镉吸附率均高于75%,且随温度升高而上升。生物炭经酸化处理后,镉吸附能力显著下降,这说明生物炭中的酸可溶矿物质在镉溶液的吸附过程中有重要作用。

In this paper, rice straw is used as the raw materials to be prepared for bio-chars by using oxygen limited cleavage methods under different pyrolysis temperatures included 300, 400, 500, 600, 700℃. And different bio-chars are acidified with hydrochloric acid and hydrofluoric acid. All kinds of characteristic indexes included surface functional groups, BET specific surface area and bore diameters of the different un-acidified or acidified bio-chars are detected and analyzed by using Fourier Transform Infrared Spectroscopy (FTIR), surface area and pore size analyzer and other modern analytical methods. For the sake of finding the best preparation temperature of the required bio-chars, we analyze the relationship between the preparation temperature and the surface properties of the bio-chars. In order to provide a scientific basis for bio-chars adsorption to the heavy metal pollution of cadmium in the water, we also study the contribution of the acid soluble minerals in bio-chars of cadmium adsorption and the influence of the preparation temperature to the ability of bio-char cadmium adsorption by using the results of bio-char acidification treatment and cadmium adsorption experiments. The results of FTIR indicate that there are some differences in the surface functional groups of the different bio-chars under different pyrolysis temperatures, which indicate that alkane deleted, methyl (-CH3) and methylene (-CH2) gradually disappeared, and aromatic nucleus formed and more aromatization increased by new aromatic compound with the increasing of pyrolysis temperature. In the different acidified bio-chars prepared from rice straw, the absorption peak of some inorganic minerals such as SiO2 gradually disappeared. There is no significance difference in the surface functional groups between acidified bio-chars and un-acidified bio-chars, and the regularity of different functional groups changed along with temperature in the different acidified bio-chars is the same as that of the different un-acidified bio-chars. The results of the BET specific surface area measurement and pore size analysis show that the main pore structure of rice straw bio-chars are mainly mesopore, and the specific surface area and total pore volume increase and the mean pore size decrease with the rising of pyrolysis temperature, the BET specific surface area increase at the maximum value under the pyrolysis temperature of 600℃. The BET specific surface and the total pore capacity in the rice straw bio-chars increase significantly after acidification. Acid soluble mineral in the bio-chars were removed, the pore structure did not change, are mainly mesopore but the micropore surface area decreased after acidification. The results of cadmium adsorption experiments show that all the bio-chars prepared from rice straw have high adsorption capacity and the cadmium adsorption rate of all the bio-chars prepared under different temperatures are above 75%, and the cadmium adsorption capacity of the bio-chars increase as temperature rising. But cadmium adsorption capacity of the acidified bio-chars decrease significantly. Acid soluble mineral in bio-chars may have an important influence on the adsorption of cadmium solution.