Abstract: Four kinds of raw materials including sawdust, rice bran, rice straw and corn stalk were used to produce the biochars by pyrolysing at temperatures of 300, 400, 500, 600 and 700℃ under the protection of the nitrogen atmosphere and the adsorption characteristics of these biochars for Pb²⁺ and Cd²⁺ were investigated in detail. Experimental results show that the biochars produced at 700℃ are more effective than those produced at the other temperatures for all these raw materials to remove Pb²⁺ and Cd²⁺ from aqueous solutions, and the rice straw biochar (C700, i.e. the rice straw biochar obtained at 700℃) has the highest adsorption capacity among these biochars. The adsorption capacities of C700 for Pb²⁺ and Cd²⁺ are 126.58 and 60.61 mg/g, respectively. The composition of mineral phase, the surface morphology and the BET surface area of the biochars are analyzed by XRF, SEM and BET surface area analyzer. The XRD patterns of biochars after adsorption of heavy metal are analyzed, which illustrates that the Langmuir isotherm model fits the experimental data of Pb²⁺ and Cd²⁺ adsorption by these four kinds of biochars, and the XRD patterns suggest that carbonate, phosphate, silicate and/or sulfite containing Pb²⁺ or Cd²⁺ are present in these biochars after adsorption.

Key words: biochar, adsorption, Pb²⁺, Cd²⁺

摘要： 以木屑、米糠、稻杆、玉米秸杆为原料, 在300, 400, 500, 600和700℃下, 氮气保护的无氧气氛中热解制成生物炭, 探讨不同类型生物炭对水溶液中重金属Pb²⁺和Cd²⁺的吸附效果。研究发现, 对于4种生物质原料而言, 在700℃下制备的生物炭对水溶液中Pb²⁺和Cd²⁺的吸附效果均优于其他制备温度下获得的生物炭, 其中稻杆生物炭(700℃)吸附容量最高, 对Pb²⁺和Cd²⁺分别为126.58和60.61 mg/g。利用X射线荧光光谱、环境扫描电子显微镜、气体吸附仪等方法, 分析700℃下制取的4种生物炭的矿物相元素组成、表面形貌及其比表面积。采用X射线衍射法分析4种生物炭样品在吸附重金属后的矿物相特性, 分析其重金属吸附机理。结果表明, 4种生物炭对Pb²⁺和Cd²⁺的吸附均满足Langmuir等温吸附模型, 同时XRD分析显示Pb²⁺和Cd²⁺在生物炭表面以碳酸盐、磷酸盐、硅酸盐和亚硫酸盐形式存在。

关键词: 生物炭, 吸附, Pb²⁺, Cd²⁺