MadSci Network: Earth Sciences
Query:

Re: Does gold exist in the ocean in an ionized form?

Date: Sun Jan 30 18:41:23 2005
Posted By: John Christie, Faculty, Dept. of Chemistry,
Area of science: Earth Sciences
ID: 1104946058.Es
Message:

Gold is present in the ocean in dissolved form at a level of about 6 parts per trillion. That is a minute concentration, but works out at about 6 kilogram per cubic kilometre. No-one has ever found an economical way of recovering this gold.

The answer to your question appears to be "no". The dominant form of dissolved gold in most seawater is in the covalently bonded Au(OH)(H2O)x.

Here is an abstract from the Harvard/NASA ADS Astronomy/Planetary Abstract Service, it is accessible on the web at http://adsabs.harvard.edu

Gold speciation in natural waters: I. Solubility and hydrolysis
reactions of gold in aqueous solution
Vlassopoulos, Dimitrios & Wood, Scott
Geochimica et Cosmochimica Acta, Vol 54, No. 1, pp. 3-12 (1990)

Solubility measurements of Au in dilute to concentrated aqueous NaOH
solutions at 25C have been carried out. The data were fitted to the
general half reaction  Au ( c ) + 2  H  2  O     AuO  2  H  4- n   1- n
+  nH  +  +  e  -  in order to identify the stoichiometry and stability
of the hydrolyzed species formed. The monohydroxide, AuOH(H 2 O) 0 , is
found to be the most stable species up to pH ~ 12. The equilibrium
constant for the formation of this species (i.e.,  n  = 1) is  logK  1 =
-22.57  0.44. Consideration of competitive complexation of Au by
a number of inorganic ligands which are encountered in natural waters
indicates that AuOH(H 2 O) 0  is the most stable inorganic Au species
over a wide range of Eh, pH, and ligand activities. The only inorganic
ligands which may occur in natural waters at concentrations high enough
to stabilize Au(I) include HS -  under reducing conditions, S 2 O 3  2-
under alkaline oxidizing conditions, Cl -  in very acidic, oxidizing
brines, and possibly CN -  locally, in environments where there is
biogenic and/or anthropogenic production of cyanide. Calculated
equilibrium pe-pH diagrams for Cl -  and  S activities typical of both
fresh and sea water show that AuOH(H 2 O) 0  is probably the dominant
dissolved Au species in these environments, with the exception of anoxic
ocean and lake waters.

Moderator's note:
As an interesting historical aside, extraction of gold from seawater was most famously tried by Fritz Haber. Haber is an interesting character - he was a Nobel laureate in chemistry (for his work on fixing nitrogen from the atmosphere), he is also sometimes referred to as the father of chemical warfare (as the organizer of the first gas attacks in the Great War). In the early 1920's Haber spent a lot of time working on an extraction process to remove gold from seawater, and surveying the oceans for dissolved gold. He hoped that the gold could be used to help pay off Germany's enormous reparations payments from the war. Ultimately, he found that there was nowhere near enough gold in seawater to make extraction economically feasible (by about a factor of 1000).


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