The effect of the addition of an organic monolayer to the surface of a clay
mineral on the speciation of metal ions intercalated into the clay
interlayer is probed by X-ray absorption spectroscopy. The presence of the
monolayer changes the surface of the clay from hydrophilic to hydrophobic.
It inhibits the interlayer ions from exchanging freely into environmental
water and reduces the leach rate of cations out of the clay by approximately
a factor of 20. Significant changes are observed when these coated samples
are treated under hydrothermal and thermal conditions. Reductions of
uranium(VI), in the form of uranyl, and copper(II) ions occur. In addition,
the uranium aggregates, forming small particles that appear similar to
UO2. Comparable conglomeration occurs with lead cations and
with the reduced copper species.