摘 要
生物炭作为土壤添加剂不仅能够改善土壤环境，提高粮食产量，捕获温室气体,而且在消减污染物风险方面具有很好的应用前景。本文以普遍的水生植物芦苇的秸杆作为生物炭制备的生物质原料，在350℃、450℃、550℃和650℃下制备生物炭，利用SEM扫描电镜、EDS、红外光谱、拉曼光谱等方法对其进行表征。采用平行实验法分别探究生物炭不同添加量和不同的热解温度对污染土中有效态Cd的影响。主要结果如下：
不同温度下制备的生物炭物理化学性质不尽相同。其中，生物炭的产率、表面含氧官能团含量和稳定性顺序基本为350℃>450℃>550℃>650℃，而O/C、(O+N)/C、多孔性和比表面积等参数则为350℃<450℃<550℃，且550℃>650℃，生物炭的pH、灰分和芳构化程度等参数则为350℃<450℃<550℃<650℃。
不同热解温度下的芦苇秸秆生物炭对Cd的稳定能力大小呈现的规律为：450℃、550℃和650℃下制备的生物炭对Cd的稳定能力随着温度的升高而增强，但是450℃温度下制备的生物炭与350℃制备的相比，其稳定能力要比弱；生物炭的分别以0%、0.5%、1%和5%的添加量与Cd污染土混合后，发现：随着生物炭添加量地增加，土壤中有效态Cd含量降低，反应了对土壤中Cd的稳定效果逐渐增强。
对影响生物炭稳定效果的因素进行了探究。结合不同热解温度的生物炭稳定效果和相应的生物炭的表征特点，发现：450℃制备的生物炭由于其表面含氧官能团的减少而使其对Cd的稳定效果低于350℃制备的生物炭；550℃制备的生物炭因为生物炭的亲水性、极性、pH、孔的比表面积和多孔性均高于450℃制备的生物炭，使得550℃制备的生物炭的稳定效果高于450℃制备的生物炭；650℃制备的生物炭主要是因为pH高，导致650℃制备的生物炭的稳定效果高于550℃制备的生物炭。
结合生物炭的稳定性、产率、实用性和对Cd的稳定效果等因素进行分析，本研究确定最佳的生物炭制备温度为550℃，添加量为5%。
关键词：Cd污染土壤；生物炭；制备；稳定效果；表征
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ABSTRACT
Conditioning soil with biochar can not only improve the qualification of soil environment, increase food production, capture greenhouse gases, but also show great potential on the issue of eliminating pollutants from soil. In this paper, biochar, derived from reed straw generated at four different pyrolysis temperatures(referred as R350,R450,R550 and R650),were characterized by SEM, EDX, infrared spectroscopy(FTIR), Raman spectroscopy and some other methods. Additionally, the influence of the different supplementation and pyrolysis temperature of biochar on the available cadmium content of soil were also investigated by parallel experimental method.The main findings are as follows.
Biochars generated at different pyrolysis temperatures displayed distinct properties. The yield,the content of surface oxygen functional groups and stability of biochar prepared under different temperature varied in the following order: 350℃>450℃>550℃>650℃.The O/C value,(O+N)/C value, porosity and surface area of biochar prepared under different temperature varied in the following order: 350℃<450℃<550℃, and 550℃>650℃.The pH value, ash content, and the degree of aromatization of biochar prepared under different temperature varied in the following order: 350℃<450℃<550℃<650℃.
The stable ability to the cadmium content of soil of biochar generated at different temperature varied in the following order:the stable effect of the biochar generated at 450℃,550℃,650℃ gradually rise as the temperature is higher. But the stable effect of the biochar generated at 450℃ is lower than that is made at 350℃.And the more biochar is added into the soil, the lower available cadmium content of soil has, which means the better stable effect is.
It is also been explored about the factors that effect the stability of biochar. Combined the stable effect and the properties of biochar that is generated at different temperature, The conclusion has been analyzed. Firstly, The stable effect to the Cd in the soil of the biochar which is made by 450℃ is not so good as that is made by
350℃, because the biochar which is made by 450℃ has less oxygen function groups. Secondly, The biochar which is made by 550℃ has higher hydrophilic, polar, pH value, aperture, and porosity ,which makes its stable ablility stronger than that is made by 450℃. Thirdly, the higher pH value of the biochar which is made by 650℃ than that is made by 550℃, result in the better stable ability of the biochar which is made by 650℃.
To reach the optimal effect, it is summarized that the best temperature to generate biochar is 550 ℃, and the best proportion of biochar is 5% in this research, combined some elements like the stability, yield, application of biochar to analyse.
Keywords: Cd-contaminated soil; biochar; preparation; stable effect; characterization
第1章 绪论
1.1 土壤重金属污染
1.1.1 我国土壤重金属污染现状
土壤环境是人类赖以生活的重要资源，也是农业生态系统的基础，但同时也是环境污染物质的缓冲带。近年来，随着经济的发展，工农业现代化发展的同时带来的却是各种不可忽视的环境问题，污水灌溉、农药化肥残留、固废填埋渗漏、金属矿藏开采及冶炼等等问题屡见不鲜，使得大量的金属进入土壤中，导致土壤质量退化，对人们的身体健康、生态环境、和经济发展等造成影响。
1.1.2 土壤重金属污染的危害
现在各地区工业化现象严重，酸雨现象也越来越严重，而土壤中的酸性强时，金属以游离态存在，使重金属的毒性更大，并且更容易被植物吸收，严重影响农作物质量和收成，游离态的金属容易通过径流和淋洗作用污染地下水，上面的种种都会导致金属在生物链中的富集，并最终危害人的身心健康，威胁到整个生态平衡。
土壤中的重金属很难通过自然界自身的净化系统去除。但是我国目前受重金属污染的耕地面积已达到 2000万hm2，约占总耕地面积的 1/5[1]，修复重金属污染的土壤已成为现如今土壤环境研究的热点内容。
