Aggregates of nanoscale zero-valent iron (nZVI) are commonly encountered for nZVI in water, especially during practical applications using large quantities of nZVI. Herein, in situ characterization was performed to study the status of nZVI aggregates in aqueous solution. Specifically, the aggregates are studied for their structural and physical properties under typical hydrodynamic conditions corresponding to three widely used unit operations (mechanical mixing, gravitational settling, and compression) in large-scale applications of nZVI, via six techniques including non-intrusive image analysis and particle image velocimetry. The study shows that the aggregates consist of interconnecting chains of iron nanoparticles and are highly porous in structure. The bulk density of the aggregates in water is close to 1.05 g cm⁻³ for the uncompressed aggregates and can reach 1.27 g cm⁻³ after compression; the porosity of the aggregates is close to 99.2% for the uncompressed aggregates and decreases to 95.1% after compression. During mixing, the aggregates remain mostly at tens of microns at the commonly applied mixing intensity (e.g., G at 500–1500 s⁻¹); breakage of the aggregates occurs at more turbulent conditions but they remain at microscale. During settling, the aggregates of size ∼30–300 μm have a settling velocity of nearly 0.05–0.23 mm s⁻¹; the settling aggregates are also characterized for their structural parameters such as aspect ratio, spherical index and fractal dimension. Slurries of the compressed aggregates are shear-thin and have an apparent viscosity of 52–2.8 × 10⁴ mPa s⁻¹ at 1–1000 s⁻¹. The work provides information about the actual status of nZVI in water during its practical application. The acquired quantitative information about the aggregates offers guidance on the design and operation of the facilities using nZVI for environmental applications.

中文翻译：

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水中纳米级零价铁 (nZVI) 聚集体的原位表征：工程方面

纳米级零价铁 (nZVI) 的聚集体在水中经常遇到 nZVI，特别是在使用大量 nZVI 的实际应用中。在此，进行原位表征以研究水溶液中 nZVI 聚集体的状态。具体来说，研究了聚集体在典型流体动力学条件下的结构和物理特性，这些条件对应于 nZVI 大规模应用中的三种广泛使用的单元操作（机械混合、重力沉降和压缩），通过包括非侵入式图像分析和粒子图像测速在内的六种技术。研究表明，聚集体由相互连接的铁纳米粒子链组成，结构上是高度多孔的。未压缩的骨料在水中的体积密度接近1.05 g cm ^-3，压缩后可达1.27 g cm ^-3；未压缩骨料的孔隙率接近 99.2%，压缩后降至 95.1%。在混合过程中，在常用的混合强度下，骨料大部分保持在几十微米（例如，G在 500-1500 s ^-1); 聚集体的破坏发生在更湍流的条件下，但它们仍保持在微尺度。^{在沉降过程中，尺寸约为 30-300 μm 的聚集体具有接近 0.05-0.23 mm s -1}的沉降速度；沉降骨料的特征还在于它们的结构参数，如纵横比、球形指数和分形维数。压缩骨料的浆料剪切稀薄，在 1-1000 s ^-1时的表观粘度为 52-2.8 × 10 ⁴ mPa s ^-1。这项工作提供了有关 nZVI 在实际应用过程中在水中的实际状态的信息。获得的有关骨料的定量信息为使用 nZVI 进行环境应用的设施的设计和操作提供了指导。