Facilitated Transport of Copper with Hydroxyapatite Nanoparticles in Saturated Sand

Abstract

Saturated packed column experiments were conducted to investigate the facilitated transport of Cu with hydroxyapatite nanoparticles (nHAP) at different pore water velocities (0.22–2.2 cm min −1 ), solution pH (6.2–9.0), and fraction of Fe oxide coating on grain surfaces (λ, 0–0.36). The facilitated transport of Cu by nHAP (nHAP-F Cu) was found to increase with decreasing nHAP retention and decreasing transport of dissolved Cu. In particular, nHAP-F Cu transport increased with pH (8.0, 8.5, and 9.0) and especially λ (0.07–0.36) but was less signifi cant than dissolved Cu transport at lower pH (6.2 and 7.0). The transport of dissolved Cu decreased with pH and λ because of increased Cu sorption or precipitation. The nHAP retention decreased with velocity, pH, and decreasing λ. Scanning electron microscope images revealed that nHAP retention at pH 7.0 was controlled by surface roughness and nHAP aggregation, whereas measured zeta potentials indicate that attachment of the nHAP occurred on the Fe oxide coated grains. The retention profi les of nHAP exhibited a hyperexponential shape, with greater retention in the section adjacent to the column inlet and rapidly decreasing retention with depth for all of the considered pH and λ conditions, but tended to become more exponential in shape at a higher velocity. These observations suggest that hyperexponential profi les are a general phenomenon of unfavorable attachment conditions that is sensitive to the hydrodynamics at the column inlet. Abbreviations: BTC, breakthrough curv e; CFT, colloid fi ltration theory; EDX, energy dispersive x-ray; IS, ionic strength; nHAP, hydroxyapatite nanoparticles; nHAP-F Cu, hydroxyapatite nanoparticle facilitated copper; PV, pore volume; RP, retention profi le; SEM, scanning electron microscopy.