热空气氧化改性生物炭对镉的吸附特性研究

Study on Adsorption Characteristics of Cadmium by Thermal Air Oxidation Modified Biochar

【目的】探究改性生物炭对重金属元素镉(Cd)的吸附机理,以期为治理Cd污染和改性生物炭工业化生产提供参考。【方法】以工业化生产的竹屑生物炭(BB)和烟杆生物炭(TB)为原料,在300℃的低温限氧条件下进行氧化改性30 min,冷却至室温后制成两种改性生物炭(分别记为BB300和TB300)。通过X射线衍射技术对改性前后的生物炭矿物组分进行分析,结合吸附实验对其吸附溶液中Cd^(2+)的吸附特征进行研究。【结果】BB300和TB300产率高,分别达70%和65%。4种生物炭(BB、BB300、TB和TB300)的饱和吸附量分别为7.57、15.97、120.48和166.67 mg/g, TB和TB300相较于BB和BB300,吸附性能更好,但改性效果较差。对比Langmuir吸附模型和Freundlich吸附模型,Langmuir吸附模型能更好的拟合四种生物炭的等温吸附过程,表明这4种生物炭表面具有有限的吸附位点,吸附机制主要是单分子层吸附。对比准一级动力学吸附模型和准二级动力学模型,4种生物炭对溶液中Cd^(2+)的吸附过程更符合准二级动力学吸附特征,物理吸附与化学吸附同时发生。对比吸附速率k;,氧化改性能提升吸附速率。改性生物炭混土材料吸附Cd^(2+)实验表明,改性生物炭对土壤Cd^(2+)的吸附特征更符合Langmuir吸附模型,改性生物炭加入土壤能提升土壤对Cd^(2+)的吸附能力,同时土壤的理化性质也影响生物炭的吸附能力,pH值较高和CEC更高的紫色土能吸附更多Cd^(2+)。生物炭添加量对土壤Cd^(2+)吸附有正向的影响。【结论】利用热空气氧化方法改性的生物炭产率较高且无化学试剂带入,具备工业化生产的前景。改性后的生物炭能够有效提升生物炭对Cd^(2+)的吸附能力,对土壤Cd污染具有较优的钝化能力,为提升生物炭钝化土壤重金属能力和规模化生产应用提供了参考。

【Objective】Explore the adsorption mechanism of the heavy metal element cadmium(Cd) by modified biochar, hoping to provide reference for the treatment of Cd pollution and the industrial production of modified biochar.【Method】Two kinds of modified biochar(BB300 and TB300) were made from bamboo biochar and tobacco charcoal, which were produced in industry, and then oxidized for 30 minutes under the condition of low temperature and oxygen limitation at 300 ℃ indoor.The components of biochar before and after modification were analyzed by X ray diffraction technology, and the adsorption characteristics of Cd^(2+) in the solution were studied by combining with the adsorption experiments.【Result】The yields of BB300 and TB300 were high, reaching 70% and 65%,respectively.The saturated adsorption capacities of the four types of biochar(BB,BB300,TB and TB300) were 7.57,15.97,120.48 and 166.67 mg/g, respectively.Compared with BB and BB300,TB and TB300 have better adsorption performance, but less promotion.Comparing the Langmuir adsorption model and the Freundlich adsorption model, the Langmuir adsorption model can better fit the isothermal adsorption process of the four biochars, indicating that the four biochars have limited adsorption sites on the surface, and the adsorption mechanism was mainly monolayer adsorption.Comparing the quasi-first-order kinetic adsorption model and the quasi-second-order kinetic model, the adsorption process of the four kinds of biochar on dissolved Cd^(2+) was more in line with the characteristics of the quasi-second-order kinetic adsorption, and physical adsorption and chemical adsorption occur simultaneously.Compared with the adsorption rate k;,the oxidation modification performance improves the adsorption rate.The adsorption of Cd^(2+) by modified biochar concrete materials showed that the adsorption characteristics of modified biochar on soil Cd^(2+) were more in line with the Langmuir adsorption model.The addition of modified biochar to soil can increase the adsorption capacity of soil to Cd^(2+),and the physical and chemical properties of soil also affect the adsorption capacity of biological carbon, purple soil with higher pH and higher CEC can adsorb more Cd^(2+).The amount of biochar had a positive effect on soil Cd^(2+) adsorption.【Conclusion】The biochar modified by the hot air oxidation method has a higher yield and no chemical reagents, which has the prospect of industrial production.The modified biochar can effectively improve the adsorption capacity of biochar for Cd^(2+),and has a better passivation ability for soil Cd pollution, which provides a reference for improving the ability of biochar to passivate heavy metals in the soil and large-scale production applications.