Extracting Gold from Seawater
Can You Believe
It? Sounds hard to believe? Well, it actually is possible.
The total quantity of gold dissolved in seawater is more than ten times the total gold ever mined by man.
Besides gold, almost all naturally occurring elements are dissolved in sea water, to some degree. We have
mined more than 165,000 tons of gold since mining first began about six thousand years ago in the Kolar Gold
Fields in south west India. In comparison the concentration of gold in seawater is, according to scientific
estimates, such that the oceans contain somewhere in the region of nearly a million tons, and that this
quantity is increasing steadily as more gold leaches out from the earth’s mantle. Yes, the ocean is huge, and
a million tons doesn’t seem to be large in contrast, but there are areas where gold in seawater is
Techniques There are several techniques by which this gold could be accumulated,
and there are companies conducting trials.
basically boiling seawater and refining the residue left. This is uneconomic (at current gold and energy prices) as
the energy required to boil off the water is considerable, though it is potentially a product of desalination
plants with added process steps.
Bio Extraction. Now,
there is a potentially economic solution - literally - in areas of ocean floor spreading. In regions of the sea
floor where the earth’s tectonic plates -are diverging (e.g. you may have heard of the Mid-Atlantic Ridge and
continental drift for example), there are fissures in the ocean floor into which sea water penetrates. The seawater
is heated in the hot rocks in these regions and minerals dissolve in the water. This mineral-loaded seawater
emerges through chimney-like structures (the equivalent on land is called a fumarole - such as are found in
Yellowstone National Park), and the minerals are precipitated from the solution, which further builds the chimneys.
Other forms of deposit (such as nodules) are also seen.
Researchers have identified more than} three hundred
previously undocumented species living in this hostile environment, where temperatures can reach over 300 degrees
centigrade and water pressure is as much as three hundred times that at the surface. These new species range from
bacteria to clams, limpets, shrimp and giant tube worms.
Biologists believe that bacteria play a significant role in
the precipitation of the minerals which build the chimneys. Sulphur-oxidizing bacteria of the genera Beggiatoa,
Thiothrix and Thiovulum have been identified and may be involved in this precipitation.
Some observers have suggested that it may be possible to
genetically engineer these or similar bacteria to extract gold and other precious or strategic elements from the
seawater. Bacteria have already been engineered to help in clearing up oil spills.
Economics It will be the economics that ultimately make or break this, of course. Some mining companies have
already developed bacteria to help with the processing of gold ore (the
process step is called bio-oxidation).
World economic problems and even talk of a return to
the gold standard are almost certain to lead to a continuing increase in gold prices
- they have been increasing steadily since
2002) - for at least another ten years -
and this will probably tilt the economic scales of gold extraction and refining towards currently marginal