# What role does electrolyte temperature play?



## mikeinkaty (Apr 1, 2013)

Does anyone know if the temperature of the electrolyte has any effect on the quality or amount of silver crystals produced by a cell AND what that effect is? I have never seen any data on that here. I found nothing with a search. Everyone wants to *pump up the volume* but at what price?

Mike


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## mikeinkaty (Apr 3, 2013)

Been googling this question. The only thing I've found so far is that the electrolyte should be in the range of 40C to 70C, or, 104F to 158F. No explaination was given. Mike


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## samuel-a (Apr 3, 2013)

Hot electrolyte = less resistance = higher current density.
Go unplanned, deposition is disturbed.


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## mikeinkaty (Apr 3, 2013)

samuel-a said:


> Hot electrolyte = less resistance = higher current density.
> Go unplanned, deposition is disturbed.



Yeah, but if it gets to hot it can do an undesirable number on an AgNO3 solution. I'm trying to figure out what that undesirable thing is and how hot "to hot" is. The literature is very scant on this subject. I've seen one article that said 40-70C and a couple of others that inferred that it should not get to hot. With H2SO4 electrolysis you apparently want HOT. 

Mike


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## butcher (Apr 4, 2013)

just some thoughts, heated electrolyte the solution moves around better (a plus), the resistance of the cell (I am guessing) here could change (could be good or bad), acids or electrolyte can fume off much easier (bad), nitric or its gases would fume off much easier than sulfuric which has a very high boiling point, here I would guess current would also play a big part too high of a current and you gas off solution easier, higher temperature lower resistance could also result in more gassing as current would increase, I think up to a point the heat could save some on power used which would be more important for the large industrial cells.


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## goldsilverpro (Apr 4, 2013)

mikeinkaty said:


> samuel-a said:
> 
> 
> > Hot electrolyte = less resistance = higher current density.
> ...


According to Butts and Coxe, the typical temp of the silver cell solution (whether Thum or Moebius) is between 80-120F. This is due to the internal resistance of the cell and not from externally heating the solution. 

H2SO4 cells. If you are talking about H2SO4 electrolysis in a concentrated sulfuric stripping cell, the last thing you want to do is run it hot. It starts attacking the base metals. Anything above about 110F and you start having problems. 

For copper refining in a copper sulfate/dilute H2SO4 cell, I think the temp is maintained between 104-122F. Still not HOT. This increases the conductivity and, thus, lowers the power consumption.


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## mikeinkaty (Apr 4, 2013)

Thanks all.

So, if you don't want hot for a silver cell then under normal conditions that would put a damper on how much current you could run. But, by using SS containers one could remove a lot of heat by setting the cell in a water bath thus enabling higher currents and hopefully more silver crystals per unit of time. If you constructed the cell with higher cathode and anode surface areas could you not run higher amperage and still be in the recommended voltage range? 

I want to try pouring an anode 2" x 4" x 1/8". That would be about 5.5 ozt with a surface area of about 17.5 sq inches. With a current density for the anode no more than 0.35 A/cu in, and by using 2 such anode plates, one could run, amperage wise, around 12 amps. That, theoretically, should yield 11 ozt of crystals in about 7 hours.

I was able to run my cell at 9 amps with 2.5 volts and two 5 ozt bars but the solution started getting warm so I backed it off to 4-5 amps. I was exceeding the above anode area rule though at the higher amperage. My SS cathode is now 6" x 13".
Mike

GSP - my bad! I was thinking of dissolving base metals with H2SO4. Adding that sentence was an after thought that had little thought!


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## Lou (Apr 4, 2013)

You tread a fine line with increasing current density. Increased current density does not mean increased cathode purity; side redox reactions are certainly more pronounced, i.e. depletion of nitrate anion by reactions which weren't favored at lower temperature. 

Conductivity increases with temperature as the mobility of ions increases--this means the current density will go up and there will be more ion transport/unit time as statistically more Ag+ --> Ag by contact on the cathode. Increase temperature also means increase in diffusion rates.


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## goldsilverpro (Apr 4, 2013)

mikeinkaty said:


> Thanks all.
> 
> So, if you don't want hot for a silver cell then under normal conditions that would put a damper on how much current you could run. But, by using SS containers one could remove a lot of heat by setting the cell in a water bath thus enabling higher currents and hopefully more silver crystals per unit of time. If you constructed the cell with higher cathode and anode surface areas could you not run higher amperage and still be in the recommended voltage range?
> 
> ...



When considering anode current density, you only use the surface area of the side(s) of the anode that is facing the cathode(s). 

In a Thum cell, that would be the bottom surface of the anode only. 

In a vertical cell with 1 cathode sheet, you would only consider the side of the anode facing the cathode. With 2 cathodes, one on each side of the anode, both sides of the anode would be in play.

If using a SS bowl as a cathode, with the anode placed horizontally, you would only use the bottom area of the anode. If hung vertically, you would probably use both sides of the submerged surface area.


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## mikeinkaty (Apr 4, 2013)

I would be using a SS stock pot with vertical sides, 8" diam x 8" tall with 5 L of solution containing 15 ozt 990 Ag in solution. The bottom would be covered with a 1/8" thick flexible plastic or rubber plate. This would be my 3rd cell. The first one (glass) had 20 sq" cathode and the 2nd (glass) has 68 sq" cathode. In the 2nd cell I've lately been running two 5 ozt anode bars at the same time at 1.5 volts and 4-5 amps. I'm hoping the 3rd cell will let me run 8 to 9 amps at 2.5 volts, or less. I will monitor the temp with a SS probe insulated from the tank.

Mike


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