Seawater electrolysis...

[Externet]

Hi.  Somewhere I read that electrolysis deposits collected on electrodes depend from the elements available in suspension and the voltage used.   How was that ?  Can someone explain or direct to a link to learn ?

Does it mean that a 0.1Volt potential can deposit/separate perhaps one or a few elements;  0.5 V yields some additional more; 1V gets even more ?  Where to find a table that relates voltage used for electrolysis and elements deposited ?

[Sensei]

What you are searching for is "electroplating"

https://en.wikipedia.org/wiki/Electroplating

2 hours ago, Externet said:

Where to find a table that relates voltage used for electrolysis and elements deposited ?

Google for "electroplating table"

Quote

 

Seawater electrolysis...

 

Seawater contains very few metal ions. See content of seawater <= 1.3% by mass.

It's not fixed. Different oceans, and different seas, have different concentrations of salts.

Process of analyze of seawater, should begin from boiling water to evaporate excess of water.

 

[John Cuthber]

3 hours ago, Externet said:

Hi.  Somewhere I read that electrolysis deposits collected on electrodes depend from the elements available in suspension and the voltage used.   How was that ?  Can someone explain or direct to a link to learn ?

Does it mean that a 0.1Volt potential can deposit/separate perhaps one or a few elements;  0.5 V yields some additional more; 1V gets even more ?  Where to find a table that relates voltage used for electrolysis and elements deposited ?

well... sort of.

The voltage needed to get something out of solution also depends on the concentration- the more of it there is, the easier it is to extract.

There's another factor, there are hydrogen ions in sea water (not many but...) and so, if you get the voltage  high enough (well, low enough- they plate out on the negative electrode) you start to "plate" hydrogen gas onto the electrode. Similarly, for elements that need to be oxidised to convert them to the element (chlorine is an obvious one in this context) you have a competition with production of oxygen.

And hydrogen production happens before most metals come out of solution.

About the only useful things you could get would be chlorine, bromine and (maybe) iodine.

If you have metal salts at reasonably high concentrations in water it is possible to extract them in the way you suggest.

The voltage needed is related to the electrode potential.
https://en.wikipedia.org/wiki/Electrode_potential
And there are tables of them

https://en.wikipedia.org/wiki/Standard_electrode_potential_(data_page)

 

[Externet]

 

57 minutes ago, John Cuthber said:

If you have metal salts at reasonably high concentrations in water it is possible to extract them in the way you suggest.

Thank you.

Let's see if I got something from it.... Electrolysis of seawater at say 2.5 Volts will deposit a mixture of all items under 2.51 V electrode potential onto the electrodes.  If the seawater has depleted of those by a long enough process;  electrodes replaced with new ones, and the process started again at 3.0 V;  The group between 2.5V and 3.0V will be deposited onto the clean new electrodes ? 

[John Cuthber]

Not quite, for a start  you won't be able to get the electrode potential to (e.g.) 2.5 volts because all the energy will go into making hydrogen.
Also the voltage depends on the concentration

https://en.wikipedia.org/wiki/Nernst_equation

so there's isn't a specific voltage for a given element, there's a specific voltage/ concentration curve (and that's temperature dependent too).

You can sometimes get it to work in simple mixtures- you could separate copper from iron.

It's also important to recognise that there are two voltages in a cell- one at each electrode. The solution isn't at the same potential as either of them.

 

 

Edited October 14, 2018 by John Cuthber

[Greenfield]

Once additional process is underpotential deposition (UPD). This occurs when the substance being plated onto the electrode, initially (the first mono-layer) deposits at a lower potential (less energy required) than the expected equilibrium potential (redox potential). This is due to more favorable interactions with the  "foreign" surface, over the elements own surface. For example, Cu will deposit on a Pt electrode before it would deposit on an electrode made of itself (Cu). 

 

 

[tinkerer]

"Seawater contains very few metal ions.    "This leads me to wonder: The two commonly considered water "hardness" elements are Calcium and Magnesium. Both are thought of as metals. Both are present in virtually all water present naturally upon this planet. Both contribute to the factor arbitrarily called "water hardness".  Therefore, the statement regarding Seawater containing very few meta lions, seems misdirected, at best. 

However, what is your point, Grandma? Obviously seawater is highly ionized, but so what?