13
exchanged with those of the mineral surface.
is not possible,
If anion exchange
a trace element cation may be adsorbed to the
mineral surface by formation of bonds between its coordinated
anions and a cationic constituent of the mineral surface.
this case,
In
the selectivity of certain minerals for trace ele-
ments is governed by the relative polarizability of the ionic
species involved.
In general,
the separation and distribution
of trace elements in minerals are dependent upon adsorption
and bond-energy relations between the trace elements and the
major components of the host minerals.
3.13
Krauskopf
Impoverishment of trace elements in the sea.
(1956)
studied the factors controlling the concentra-
tion of thirteen metallic trace elements
Ni,
Co,
Hg,
Ag,
Cr,
Mo,
W and V)
(Zn, Cu,
in sea water,
Pb,
Bi, Cd,
and concluded
that sea water is grossly undersaturated with respect to these
metals - that precipitation of compounds containing these ele-
ments with ions normally present in aerated sea water,
under extreme conditons of pH and temperature,
for the observed concentrations.
even
could not account
He concluded that adsorption
is a possible mechanism for removal of all these elements from
solution except Vv,
W,
Ni,
Co and Cr.
The observed concentra-
tions of these may be accounted for if Cr can be assumed to be