粉煤灰合成沸石对铬污染土壤中Cr(Ⅲ)的吸附稳定化效果及机制研究

Study on the stabilization effect and mechanism of the synthesized zeolite from fly ash on Cr(Ⅲ)in chromium contaminated soil

为解决Cr(Ⅲ)对土壤的污染问题,采用碱熔水热法制取粉煤灰合成沸石,研究沸石掺量、反应时间、水分质量分数、初始pH值和Cr(Ⅲ)初始质量比等因素对合成沸石吸附稳定化铬污染土壤中Cr(Ⅲ)效果的影响,建立吸附等温线模型和吸附动力学方程,并进行微观表征和吸附稳定化机制分析。结果表明,粉煤灰合成沸石对污染土中Cr(Ⅲ)有良好的吸附稳定化效果。当沸石掺量为15%、水分质量分数为26%、pH值为5~9时,对Cr(Ⅲ)进行稳定化修复效果好。Cr(Ⅲ)的毒性浸出随Cr(Ⅲ)初始质量比增加而增大,随反应时间延长先逐渐减小而后趋于稳定。动力学及热力学拟合结果表明,准二级动力学模型及Langmuir等温模型可以解释Cr(Ⅲ)在合成沸石上的吸附行为,其中影响吸附速率的主要因素为膜扩散。SEM、XRD等微观分析结果显示粉煤灰合成沸石后,其结构发生明显变化,比表面积增大,有利于对Cr(Ⅲ)吸附稳定化。合成沸石吸附稳定化污染土中Cr(Ⅲ)的机制是离子交换、静电引力、沉淀等物理及化学吸附作用综合的结果。

This paper takes the synthesized zeolite from fly ash as the research object,and discusses its stabilization effect and stabilization mechanism on Cr(Ⅲ)in contaminated soil.For solving the problem of Cr(Ⅲ)soil pollution,using mine solid waste fly ash as the raw material,the synthesized zeolite from fly ash is prepared by the alkali fusion hydrothermal method,and the stabilization effect of the synthesized zeolite from fly ash on Cr(Ⅲ)is studied.The research considers the influence of zeolite content,reaction time,water mass fraction,initial chromium mass ratio,and initial pH on Cr(Ⅲ)stabilization effect.Through adsorption kinetics and thermodynamic analysis,the adsorption kinetic equation and isothermal adsorption model are established.Finally,SEM and XRD are used for microanalysis,and further explain the mechanism of the synthesized zeolite from fly ash to stabilize Cr(Ⅲ)in contaminated soil.The results show that with the increase of adsorbent content,the leaching mass concentration of Cr(Ⅲ)gradually decreases,and reaches the optimum when the content is 15%.Moreover,the synthesized zeolite from fly ash shows similar adsorption properties to natural zeolite,realizing waste utilization.As the reaction time increased,the leaching mass concentration of Cr(Ⅲ)decreases significantly at first,and then stabilizes for a long time after 28 days,indicating that the synthetic zeolite has better long-term stability on Cr(Ⅲ).When the water mass fraction is 26%,it can achieve a better stabilization effect.With the increase of pH,it was beneficial to the stabilization of Cr(Ⅲ)by synthetic zeolite.When the pH is between 5-9,the stabilization effect is good and when the pH exceeds 6,there are both ion exchange and partial precipitation.Besides,when the initial chromium mass ratio is below 5000 mg/kg,the use of synthetic zeolite to stabilize Cr(Ⅲ)can completely meet environmental quality standards.The study of adsorption kinetics shows that the adsorption process follows the quasi-two-stage kinetic model,and film diffusion is the main rate-limiting step for synthetic zeolite adsorption of Cr(Ⅲ).The study of adsorption thermodynamics shows that the Langmuir isotherm adsorption model can clarify the adsorption isotherm well,with a maximum adsorption capacity of 22.5 mg/g.The characterization of SEM and XRD microscopic confirms that synthetic zeolite has better adsorption performance than fly ash.From the perspective of the stabilization mechanism,the stabilization on Cr(Ⅲ)in chromium-contaminated soil by synthetic zeolite is the result of physical and chemical adsorption such as ion exchange,electrostatic attraction,and precipitation.The whole study shows that the synthesized zeolite from fly ash can well adsorb and stabilize Cr(Ⅲ)in contaminated soil,and is an ideal stabilizing material for Cr(Ⅲ)contaminated soil.