[pnacze199204]

Recently I've read that there is a lot of dissolved gold in seawater, but it is very difficult to extract it. I would like to know where the gold comes from in oceans and seas, since it is well known that this element is insoluble in water? Thank you!

[jeffmoonchop]

If you have unlimited water you'll be able to extract dissolved gold. Seawater isnt exactly pure so the other components may solubilize it more than pure water would. I don't know the extraction process but I'm guessing if you use enough water you'll get some out.

[Borek]

it is well known that this element is insoluble in water?

Broadly speaking there are no things that are insoluble, to some extent everything dissolves in everything. Just for some combinations of substances and solvents the saturated solutions have concentrations so low we can - for all practical purposes - ignore them.

Even pure water as a solvent is surprisingly aggressive and capable of attacking almost everything (which is one of the reasons why it is so difficult to produce and store). Sea water additionally contains plenty of ions, which will act as complexing agents. Chlorides are quite good ligands, they will further increase solubility of many metals, gold included.

Gold is sea water typically listed in 3 (or 4) ppt range (3×10^-12 kg/L, or 3×10^-9 kg/m³). That's way too low for any economically viable method of reclaiming it, still, with the volume of oceans estimated at over 10¹⁸ m³ mass of dissolved gold can be estimated as more than 30 millions metric tons.

Estimates say we have so far mined a bit below 200 thousand tonnes of gold.

[pnacze199204]

So does that mean that every time we put something into the water it dissolves? For example, a diamond that has very strong covalent bonds and that we throw into the water, "dissolves slowly" every time in some way?  Or the point is that this process is very very slow, such as the transformation of a diamond into graphite, and that's why we say something is "insoluble in water"? I don't understand this.

[jeffmoonchop]

Solubility isnt the rate at which something dissolves. In a set volume of water a maximum amount of substance will dissolve. So for sugar you can dissolve a lot per litre of water. For diamond you may not dissolve any of it in a litre, but in a trillion litres you may dissolve 1 atom. Or you may not.