Carbon nanoparticles such graphene, carbon nanotubes, and carbon dots offer the potential to improve environmental treatment technologies due to their unique properties such as low toxicity and high metal sorption capacity. However, there are no studies on facilitated transport and remobilization of pre-sorbed metals by carbon dot (CD) nanoparticles in quartz sand columns. Here, we investigate the effects of solution ionic strength (IS; 1, 100 and 200 mM NaCl) and pH (Chen et al., 2017; Chen et al., 2010; Cornell and Schwertmann, 2006), initial CD concentration (200, 400, 600 and 800 mg L−1), and clay content (10, 20 and 30%w kaolinite) in quartz sand columns on the transport, retention and remobilization of Cu and Pb in saturated (upward flow) quartz porous media. Batch sorption experiments were employed to underpin the findings of the column transport experiments. Both CD and quartz adsorbed Cu and Pb from water, but adsorption was higher on CD than quartz. Co-transport experiment demonstrated the CD-facilitated transport of Cu and Pb. Sequential transport experiments (first three phases) demonstrated the retention of Cu and Pb in the quartz column, with higher retention of Pb compared to Cu. The Cu and Pb retention was attributed to their sorption on the quartz grains and precipitation under the experimental conditions investigated in this study. Cu retention increased with the increase in ionic strength, pH and clay content. Pb was nearly totally retained in the quartz column at all experimental conditions. The subsequent injection of CD resulted in Cu and Pb remobilization to different extents, except in the presence of high kaolinite concentration. CD is most efficient in remobilizing Cu and Pb at 400 mg L−1 CD concentration and under low ionic strength (ca. 1–100 mM), low pH (ca. 6) and in the absence of clays. Deviation from these conditions results in reduced remobilization of Cu and Pb.
