烟草废弃物生物炭元素组成及其重金属安全性研究

为明确热解温度对不同烟草废弃物生物炭中元素组成及重金属安全性的影响,以烟秆、烟梗及废弃烟叶为原材料,研究了2种热解温度(450℃和600℃)下制备生物炭的产率、元素组成、重金属(Cr、Ni、Cu、Zn、As、Cd和Pb)含量及其浸出毒性特征。结果表明,当热解温度从450℃升至600℃,各废弃物生物炭的产率降低,生物炭中的碳(C)含量升高,而氮(N)和氧(O)含量降低;其中烟梗炭的产率最高,烟秆炭的碳含量及烟叶炭的氮含量最高。随热解温度升高,各生物炭中Ni、Cu、Zn、As和Pb等重金属含量均呈不同程度升高,而烟叶炭中Cr及烟梗和烟叶炭中Cd含量在600℃热解温度下显著低于原材料中含量;随热解温度升高,烟梗炭的Cr、As元素和烟叶炭的Zn、As元素的相对富集系数(REF)下降,且由富集趋势(REF>1)转为挥发趋势(REF<1);烟叶炭的Ni、Cu元素则由挥发趋势转为富集趋势。各生物炭中重金属的沥滤浸出毒性(TCLP)均低于其原材料浸出液,生物炭浸出液中Cu、Cd和Pb含量随热解温度升高而降低,As含量呈相反趋势,各生物炭浸出液重金属含量均低于GB 5085.3-2007浸出毒性规定限量值,表明烟草废弃物生物炭的重金属浸出毒性较低,可以在农田中安全施用。

Elemental Composition and Heavy Metal Safety of Biochar from Different Tobacco Wastes

To clarify the effect of pyrolysis temperature on elemental composition and heavy metal safety of tobacco biochar,an experiment was conducted to study the effect of two pyrolysis temperatures (450℃ and 600℃) on biochar yield,elemental composition,heavy metal (Cr,Ni,Cu,Zn,As,Cd and Pb) contents and leaching toxicity,using tobacco waste (tobacco stalks,tobacco stems and discarded tobacco leaves) as raw materials.The results showed that as the pyrolysis temperature increased from 450℃ to 600℃,the yield of tobacco waste biochar gradually decreased;the carbon (C) content in biochar increased,and the nitrogen (N) and oxygen (O) contents decreased;The heavy metal contents of Cu,Zn,As,and Pb in tobacco biochar all increased in certain degree compared to those in the raw materials,while the content of Cr in tobacco leaf biochar and Cd content in tobacco stem and leaf biochar under 600℃ pyrolysis temperature were significantly lower than those in the raw materials.The relative enrichment factor (REF) of Cr and As in tobacco stem biochar and Zn,As in tobacco leaf biochar decreased with the increase of pyrolysis temperature.And the corresponding heavy metals in biochar changed from enrichment (REF>1) to volatilization (REF<1).However,Ni and Cu in tobacco leaf biochar changed from volatilization to enrichment.In addition,the toxicity characteristic leaching procedure (TCLP) of heavy metals in tobacco biochar were all lower than those in leaching solution of their raw materials.The contents of Cu,Cd and Pb in leaching solution of each tobacco biochar all decreased with the increase of pyrolysis temperature,but the content of As in them showed the opposite trend.The contents of heavy metals in the leaching solution of tobacco waste biochar were all lower than the limit value of leaching toxicity of solid waste in GB 5085.3-2007,which indicated that the leaching toxicity of heavy metals in tobacco waste biochar was very low.So,the tobacco waster biochar could be applied to farmland safely.