CC The Development of Science
HEMISTRY IN USE
The Resources of the Ocean
As is apparent to anyone who has swum in the ocean, sea
water is not pure water but contains a large amount of dis-
solved solids. In fact, each cubic kilometer of seawater
contains about 3.6 1010 kilograms of dissolved solids.
Nearly 71% of the earth’s surface is covered with water. The
oceans cover an area of 361 million square kilometers at an
average depth of 3729 meters, and hold approximately 1.
billion cubic kilometers of water. This means that the oceans
contain a total of more than 4.8 1021 kilograms of dissolved
material (or more than 100,000,000,000,000,000,
pounds). Rivers flowing into the oceans and submarine vol-
canoes constantly add to this storehouse of minerals. The
formation of sediment and the biological demands of organ-
isms constantly remove a similar amount.
Sea water is a very complicated solution of many
substances. The main dissolved component of sea water is
sodium chloride, common salt. Besides sodium and chlorine,
the main elements in sea water are magnesium, sulfur,
calcium, potassium, bromine, carbon, nitrogen, and stron-
tium. Together these 10 elements make up more than 99%
of the dissolved materials in the oceans. In addition to sodium
chloride, they combine to form such compounds as magne-
sium chloride, potassium sulfate, and calcium carbonate
(lime). Animals absorb the latter from the sea and build it
into bones and shells.
Many other substances exist in smaller amounts in sea
water. In fact, most of the 92 naturally occurring elements
have been measured or detected in sea water, and the remain-
der will probably be found as more sensitive analytical
techniques become available. There are staggering amounts
of valuable metals in sea water, including approximately 1.3
1011 kilograms of copper, 4.2 1012 kilograms of uranium,
5.3 109 kilograms of gold, 2.6 109 kilograms of silver,
and 6.6 108 kilograms of lead. Other elements of economic
importance include 2.6 1012 kilograms of aluminum, 1.3
1010 kilograms of tin, 26 1011 kilograms of manganese, and
4.0 1010 kilograms of mercury.
One would think that with such a large reservoir of dis-
solved solids, considerabe “chemical mining” of the ocean
would occur. At present, only four elements are commercially
extracted in large quantities. They are sodium and chlorine,
which are produced from the sea by solar evaporation; mag-
nesium; and bromine. In fact, most of the U. S. productionof magnesium is derived from sea water, and the ocean is one
of the principal sources of bromine. Most of the other ele-
ments are so thinly scattered through the ocean that the cost
of their recovery would be much higher than their economic
value. However, it is probable that as resources become more
and more depleted from the continents, and as recovery tech-
niques become more efficient, mining of sea water will
become a much more desirable and feasible prospect.
One promising method of extracting elements from sea
water uses marine organisms. Many marine animals concen-
trate certain elements in their bodies at levels many times
higher than the levels in sea water. Vanadium, for example,
is taken up by the mucus of certain tunicates and can be con-
centrated in these animals to more than 280,000 times its
concentration in sea water. Other marine organisms can con-
centrate copper and zinc by a factor of about 1 million. If
these animals could be cultivated in large quantities without
endangering the ocean ecosystem, they could become a valu-
able source of trace metals.
In addition to dissolved materials, sea water holds a great
store of suspended particulate matter that floats through the
water. Some 15% of the manganese in sea water is present
in particulate form, as are appreciable amounts of lead and
iron. Similarly, most of the gold in sea water is thought to
adhere to the surfaces of clay minerals in suspension. As in
the case of dissolved solids, the economics of filtering these
very fine particles from sea water are not favorable at pre-
sent. However, because many of the particles suspended in
sea water carry an electric charge, ion exchange techniques
and modifications of electrostatic processes may someday
provide important methods for the recovery of trace metals.