Release and transport of Pb(II) adsorbed on graphene oxide under alkaline conditions in a saturated sand column.

The use of graphene oxide (GO) adsorbents to remove Pb(II) from wastewater has attracted lots of attention, but the release of Pb(II) from Pb-laden GO in alkaline groundwater requires further investigation. The current research demonstrated that oxidative debris (OD) could be stripped gradually from the surfaces of GO in 0.01-1.0 M NaHCO3 solutions although the stripping kinetic process was very slow. Accompanied with OD detachment from GO, 5.47%-23.45% adsorbed Pb(II) on spent GO (i.e. GO-Pb(II)) was released in the form of an OD-Pb(II) complex under 0.01-1.0 M NaHCO3 conditions. OD-Pb(II) could disperse steadily in water even at pH > 7.0. The deposition and detachment of the OD in the quartz sand media were markedly affected by the ion strength of the solution, and the greater mobility of OD than GO improved the transport of OD-Pb(II) through a saturated sand column. Our results provide valuable information about the characteristics and mechanism of transport of adsorbed heavy metals on GO nanomaterials in the aqueous environment and the possible environmental risks when spent GO-based heavy mental adsorbents are discharged into natural groundwater systems.