Cadmium removal from soil by fulvic acid-aided hydroxyapatite nanofluid.

Mobile engineered nanoparticles have the potential for removing a variety of pollutants from contaminated soils. In this study, elution of soil cadmium (Cd) by nano hydroxyapatite (nHAP) suspension was investigated at different concentrations of fulvic acid (FA). The nHAP nanofluid (500 mg L-1) increased the elution rate of soil Cd by ∼4.34 times (from 0.64% to 2.78%) compared with nHAP-free background solution due to a ∼2 order of magnitude larger adsorption capacity of Cd on nHAP than on the experimental loamy soil. FA played an indispensable role in the efficient removal of Cd by nHAP from the soil. The elution rate of soil Cd increased from 2.78% to 3.31%, 4.37%, 5.45%, and 8.46% after adding 20, 100, 200, and 500 mg L-1 of FA to the nHAP nanofluid (500 mg L-1), respectively. This linear facilitation (i.e., addition of each 100 mg L-1 of FA increased Cd elution by ∼1%) is attributed to FA-enhanced nHAP mobility and FA-strengthened Cd transfer from soil to nHAP. This study suggests that flushing with the environment-friendly, cost-effective, and FA-containing nHAP nanofluid can effectively remove Cd from soil, given that leachate could be collected by subsurface drainage tiles.