Xu Zhi, Guo Zhao-Hui, Xu Rui, Xiao Xi-Yuan, Xie Hui-Min, Hu Yu-Lian
School of Metallurgy and Environment, Central South University, Changsha 410083, China.
Huan Jing Ke Xue. 2023 Feb 8;44(2):1051-1062. doi: 10.13227/j.hjkx.202203147.
Pyrolysis is an important technology to achieve the harmlessness and recycling of contaminated biomass. In this study, the effects of oxygen-controlled atmosphere on the component properties and heavy metal accumulation characteristics of contaminated rice straw biochar were studied. The results showed that low-oxygen pyrolysis could effectively produce biochar using contaminated rice straw and improve the stability of heavy metals in biochar. Under the nitrogen atmosphere, the yield of rice straw biochar was 29.4%-34.9%. The aromatization index (SUVA) of dissolved organic matter (DOM) increased first and then decreased with the increase in pyrolysis temperature, whereas the fluorescent components were mainly humic-like acid substances. Meanwhile, Ca mainly existed in the form of CaCO in biochar. Compared with the pure nitrogen condition, the biochar yield was reduced by 5.6%-13.5% and 14.9%-15.7% under the pyrolysis atmosphere containing 10% and 20% oxygen content, respectively. Ca existed in the form of CaO in biochar, which increased the pH value of the biochar by more than 0.5 units. The oxygen of the pyrolysis atmosphere accelerated the degradation of the lignin component, resulting in the gradual decrease in SUVA of DOM. With the increase in oxygen content in the pyrolysis atmosphere, humic-like acid substances in DOM were transformed into fulvic-like acid substances. Under the conditions of 400℃ and a 10% oxygen-containing atmosphere, the exchangeable fractions of Cu, Cd, Pb, Ni, and As in biochar were decreased by 5.2%, 3.7%, 1.7%, 0.8%, and 0.7%, respectively, indicating that heavy metals are transformed into more stable states. The results suggested that the higher biochar yield and heavy metal stability could be obtained by introducing a proper amount of nitrogen into the air (controlling the oxygen content of approximately 10%) for pyrolysis treatment of contaminated rice straw, providing an economic and feasible technology for the achievement of harmlessness and recovery of contaminated rice straw.
热解是实现污染生物质无害化和资源化回收的一项重要技术。本研究考察了控氧气氛对污染稻草生物炭的组分性质和重金属累积特性的影响。结果表明，低氧热解能够有效地利用污染稻草制备生物炭，并提高生物炭中重金属的稳定性。在氮气气氛下，稻草生物炭的产率为29.4% - 34.9%。溶解性有机物（DOM）的芳构化指数（SUVA）随热解温度的升高先增大后减小，且荧光组分主要为类腐殖酸物质。同时，Ca在生物炭中主要以CaCO的形式存在。与纯氮条件相比，在氧含量为10%和20%的热解气氛下，生物炭产率分别降低了5.6% - 13.5%和14.9% - 15.7%。Ca在生物炭中以CaO的形式存在，使生物炭的pH值升高了0.5个单位以上。热解气氛中的氧加速了木质素组分的降解，导致DOM的SUVA逐渐降低。随着热解气氛中氧含量的增加，DOM中的类腐殖酸物质转化为类富里酸物质。在400℃和10%含氧气氛条件下，生物炭中Cu、Cd、Pb、Ni和As的可交换态组分分别降低了5.2%、3.7%、1.7%、0.8%和0.7%，表明重金属转化为更稳定的形态。结果表明，向空气中引入适量氮气（控制氧含量约为10%）对污染稻草进行热解处理，可获得较高的生物炭产率和重金属稳定性，为实现污染稻草的无害化和回收提供了一种经济可行的技术。
