纳米水铁矿在土壤中的稳定性及其与砷的协同迁移机制

Ferrihydrite nanoparticles offers a promising approach for arsenic (As) remediation, but the spent ferrihydrite nanoparticles with elevated As content could arouse safety concerns because of its high reactivity and mobility. However, there are little information of transport of nano ferrihydrite, and the fate of As(V)-treated ferrihydrite nanoparticles in soils. In this project, we will investigate As sorption and desorption mechanisms using batch equilibrium experiments under geochemical conditions. The stability of ferrihydrite nanoparticles in soils will be studied to measure the suspension particle size and the concentration of nanoparticles. We will test the transport of ferrihydrite nanoparticles in soil columns and their co-transport with As in saturated homogeneous soil columns coupled the advanced optical spectrum technologies. Then the correlation between the properties of soil and the mobility of nanoparticles can be revealed. The results will give the changes in the structure and characteristics of the nanoparticles in soils, and its influence on the binding of As. Furthermore, we also observe the distribution of colloid-As bound to achieve the transportation mechanisms of As in soils based X-ray Absorption Fine Structure (XAFS). The observation of this project will be conductive to understanding the effect of nanoparticles on As transport in soils, and also shed light on the future remediation of As-contaminated soil.

纳米水铁矿可用于土壤或地下水中砷的原位固定，但由于颗粒尺寸小，传输能力强，为与吸附在其表面的砷的协同迁移提供了可能性，引起潜在污染，目前关于纳米水铁矿进入土壤后的迁移转化及与砷的协同迁移机制尚不明确。本项目拟通过批量平衡吸附实验，测定不同环境因素下砷在纳米水铁矿的吸附、解吸过程，探讨其反应机理和界面反应机制；通过土壤悬浮性实验了解纳米水铁矿在各种土壤中的稳定性，主要监测纳米水铁矿粒径和浓度等的变化；模拟土柱实验，结合先进光谱技术，研究纳米水铁矿在土壤中迁移能力及与砷的协同归趋，揭示土壤理化性质与纳米材料迁移的相关性，弄清纳米水铁矿进入土壤后自身结构及特性的变化，探讨该变化所引起的与砷结合机制的改变，并通过观察流出液中胶体态砷微观分子特征，了解砷在土壤中的迁移机制。其研究结果有助于阐明纳米材料对环境中砷迁移的影响，为今后砷污染土壤修复提供理论支持。

纳米材料可用于土壤或地下水中砷的原位固定，但由于颗粒尺寸小，传输能力强，为与吸附在其表面的砷的协同迁移提供了可能性，关于纳米水铁矿进入土壤后的迁移转化及与砷的协同迁移机制尚不明确。通过吸附动力学、吸附热力学和吸附解吸实验，研究了两种晶型纳米水铁矿对As(V)的吸附性能。结果表明，As(V)在2-线和6-线水铁矿表面的吸附可用二级动力学方程拟合，其化学反应速率K2分别为0.077和0.031 g·(mg·h)-1。2-线水铁矿由于其无定形形态，对As(V)的吸附效果优于6-线水铁矿。热力学吸附过程符合Langmuir等温方程，吸附反应为放热反应，温度升高，吸附量增加，6-Line水铁矿对As(V)的解吸率大于2-Line水铁矿；选择腐植酸（HA）、黄腐酸（FA）和鸡粪提取的可溶性有机质（DOM），通过四组模拟土柱实验，发现HA抑制了As(V)的迁移，而加入FA和DOM后As(V)在土壤中的移动性显著增强。通过土壤悬浮性实验可知随着时间的延长，纳米颗粒沉积，粒径逐渐增大，稳定后每种土壤粒径和zeta电位等均有显著差异，pH值、有机质，土壤铁氧化物含量和溶液组成均影响纳米材料的稳定性。纳米水铁矿在土壤中的穿透曲线均不对称，出现了滞后效应，但此过程是可逆的，吸附在表面的颗粒会释放，受土壤理化性质的影响显著，穿过砷污染土壤时，对砷的迁移有影响，与纳米材料在土壤中的沉积作用相关。本研究结果有助于阐明纳米材料对环境中砷迁移的影响，为今后砷污染土壤修复提供理论支持。