Abstract
Efficient application of nanoscale zero-valent iron (nZVI) particles in remediation processes relies heavily on the ability to modify the surfaces of nZVI particles to enhance their stability and mobility in subsurface layers. We investigated the effect of sodium carboxy-methyl-cellulose (CMC) polymer stabilizer, pH, particle concentration, and flow rate on the transport of nZVI particles in sand columns. Breakthrough curves (BTCs) of nZVI particles indicated that the transport of nZVI particles was increased by the presence of CMC and by increasing the flow rate. The relative concentration (RC) of the eluted CMC–nZVI nanoparticles was larger at pH 9 as compared to RC at pH 7. This is mainly attributed to the increased nZVI particle stability at higher pH due to the increase in the electrostatic repulsion forces and the formation of larger energy barriers. nZVI particle deposition was larger at 0.1 cm min−1 flow due to the increased residence time, which increases the aggregation and settlement of particles. The amount of CMC–nZVI particles eluted from the sand columns was increased by 52% at the maximum flow rate of 1.0 cm min−1. Bare nZVI were mostly retained in the first millimeters of the soil column, and the amount eluted did not exceed 1.2% of the total amount added. Our results suggest that surface modification of nZVI particles was necessary to increase stability and enhance transport in sandy soil. Nevertheless, a proper flow rate, suitable for the intended remediation efforts, must be considered to minimize nZVI particle deposition and increase remediation efficiency.
Highlights
Interest in the application of nanoscale zero-valent iron particles in remediation of point-source polluted sites has grown dramatically in recent years [1,2]. nZVI are characterized by a large surface area, high reactivity, and possible mobility in the subsurface due to its small size
We investigated the effect of CMC polymer stabilizer, pH, nZVI particle concentration, and flow rate on the transport and deposition of nZVI particles in sand columns
CMC increased the zeta potential of nZVI particles by two fold as compared to that of bare nZVI particles. These findings were consistent with the DLVO calculations, which showed a greater increase in the electrical double layer repulsion forces in the presence of CMC
Summary
Interest in the application of nanoscale zero-valent iron (nZVI) particles in remediation of point-source polluted sites has grown dramatically in recent years [1,2]. nZVI are characterized by a large surface area, high reactivity, and possible mobility in the subsurface due to its small size. NZVI particles have been widely used in the remediation of a number of pollutants, including chlorinated organic compounds [3,4], heavy metals [5,6], and inorganic anions [7,8]. Despite their small size, nZVI particles traveling through porous media rapidly aggregate, forming larger-sized particles, increasing the possibility of settling and deposition of particles [9]. Despite the enhanced deliverability of surface-modified nZVI particles as compared to that of bare nZVI particles, transport of nZVI particles in the subsurface porous media could be limited by several other factors, such as solution chemistry (e.g., pH and ionic strength), collector grain size, and nZVI particle concentration [21]
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