Department of Civil Engineering, Queen's University, Kingston, ON K7L 3N6, Canada.
Environmental Sciences Group, Department of Chemistry and Chemical Engineering, Royal Military College of Canada, Kingston, ON K7K 7B4, Canada.
Sci Total Environ. 2023 Aug 25;888:164188. doi: 10.1016/j.scitotenv.2023.164188. Epub 2023 May 16.
Ball milling has emerged as a promising destructive technique for treating per- and polyfluoroalkyl substances (PFAS)-impacted soils. Environmental media properties such as reactive species generated upon ball milling and particle size are postulated to influence the effectiveness of the technology. In this study, four media types amended with perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) were planetary ball milled to investigate destruction, fluoride recovery without additional co-milling reagents and the relationship between PFOA and PFOS destruction, particle size during milling, and electron generation. Silica sand, nepheline syenite sand, calcite and marble were sieved to achieve similar initial particle sizes (6/35 distribution), amended with PFOA and PFOS, and milled for 4 h. Particle size analysis was conducted throughout milling and 2,2-diphenyl-1-picrylhydrazyl (DPPH•) was used as a radical scavenger to assess electron generation from the four media types. Particle size reduction was observed to be positively correlated to PFOA and PFOS destruction and DPPH• neutralization (demonstrating electron generation by milling) in silica sand and nepheline syenite sand. Milling of a fine fraction (< 500 μm) of silica sand revealed less destruction compared to the 6/35 distribution suggesting the ability to fracture grains in silicate media is integral to PFOA and PFOS destruction. DPPH• neutralization was demonstrated in all four amended media types, confirming silicate sands and calcium carbonates generate electrons as a reactive species during ball milling. Fluoride loss as a function of milling time was observed in all amended media types. A sodium fluoride (NaF) spiked was used to quantify fluoride loss in the media independent of PFAS. A method was developed using the NaF-amended media fluoride concentrations to estimate the total fluorine liberated from PFOA and PFOS by ball milling. Estimates produced suggest complete recovery of theoretical fluorine yield is obtained. Data from this study was used to propose a reductive destruction mechanism for PFOA and PFOS.
球磨已成为一种很有前途的破坏性技术，可用于处理受全氟和多氟烷基物质（PFAS）影响的土壤。据推测，球磨过程中产生的反应性物种和颗粒大小等环境介质特性会影响该技术的效果。在这项研究中，将四种添加了全氟辛酸（PFOA）和全氟辛烷磺酸（PFOS）的介质进行行星式球磨，以研究破坏、无需额外共磨试剂的氟化物回收以及 PFOA 和 PFOS 破坏、磨矿过程中的颗粒大小和电子生成之间的关系。将硅砂、霞石正长岩砂、方解石和大理石筛分至相似的初始粒径（6/35 分布），添加 PFOA 和 PFOS，并研磨 4 小时。在整个研磨过程中进行颗粒大小分析，并使用 2,2-二苯基-1-苦基肼（DPPH•）作为自由基清除剂来评估四种介质类型产生的电子。观察到粒径减小与 PFOA 和 PFOS 破坏以及 DPPH•中和（通过研磨产生电子）呈正相关，在硅砂和霞石正长岩砂中。与 6/35 分布相比，细粒（<500μm）硅砂的研磨破坏程度较低，这表明在硅酸盐介质中碎裂颗粒的能力是 PFOA 和 PFOS 破坏的关键。在所有添加的介质类型中均证明了 DPPH•中和，证实硅酸盐砂和碳酸钙在球磨过程中作为反应性物种产生电子。在所有添加的介质类型中都观察到氟化物随研磨时间的损失。添加了氟化钠（NaF）以定量测量介质中独立于 PFAS 的氟化物损失。开发了一种使用添加 NaF 的介质氟化物浓度的方法来估计球磨过程中从 PFOA 和 PFOS 释放的总氟。估计表明，理论氟产量的完全回收是可以实现的。本研究的数据用于提出 PFOA 和 PFOS 的还原破坏机制。
