Investigating
the transport of engineered nanoparticles through
representative soils is an important issue in assessing their mobility
and fate in the environment. In this study, successive injections
of gold nanoparticles (AuNPs) were performed in a quartz sand column
with an eluent composed of 10–2 M NaCl at a pH of
7.5. After this series of injections, remobilization of the AuNPs
was examined by raising the eluent pH to 10. 197Au and
the conservative ionic tracer 79Br were monitored simultaneously
by online inductively coupled plasma mass spectrometry (ICP-MS), and
the particulate nature of gold eluting from the column was confirmed
by setting the ICP-MS in the “single particle” mode.
The extent of AuNP attachment was greater than predicted by DLVO theory
considering quartz as the sole collector, decreased with the number
of injections and with particle size. In contrast with the repulsive
interaction energy between the particles and the quartz surface, kaolinite,
a secondary mineral of the sand, provided favorable conditions for
particle attachment. The superimposed signals of 197Au
and 27Al in the column effluent after pH increase suggest
that gold nanoparticles were essentially remobilized as heteroaggregates
with the kaolinite colloids they were attached to when favorable conditions
for clay detachment from the sand grains were encountered.
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