Designing a DIY silver cell

[markscomp]

Commercial systems run at 25-50 amps per square foot - was posted

sorry it may be worse than i thought (3.59 may be a typo ) 3.5 per is what was posted also

 

[markscomp]

Shark - you get the jist run with it

 

[Shark]

Looking back at the various tanks most of those I found could be questionable as to how much space would be usable for storage of the crystals in the bottom while building up more silver growth.

Do most prefer to save in crystal form or do they melt the silver soon as possible?

Another question is would the people buying such quantities prefer bars or crystal?

Am I over thinking that seemingly smaller space?

 

[Lou]

I think we should do a really awesome silver cell thread. We should then do a wohlwill cell so we can trash talk them because they're terrible wastes of money.

Shark,
The crystal was bulky and mine was fine like sand because I never wanted (in production, anyway) big dendrites of silver crystal, so it was easier to melt it.

I think unless you're growing huge crystals that have a really cool look to them (HT patch used to grow these), people want bars.

 

[4metals]

Lou,
Weren't you using grain as anode material? I think it was you,but maybe not, my gray matter is dropping off at an exponential rate these days.

 

[netgeek3]

Guys, this is of intense interest to me, as our volume has exploded, and this addresses one of our outstanding issues. We cannot keep up with the amount of silver we're extracting, and it's something we really want to leverage as the economy prepares to take a dump. The ability to process 1200ozt per day would help us tremendously, versus the scaled up and multiplied bowl system we've been using. I know there are commercial systems out there, but not spending many $$$ is very attractive to me. Also, I have a lot of DC rectifiers available to me at no cost, so leveraging that is something we are trying to do with each plating line that we set up.

 

[Shark]

Thinking out loud here…..

What would be the minimum angle for the fine crystal to move down to the exit point under its own power? If the angle is steep enough this could help eliminate one point of manual labor. This leads back to the original round tank as well. I would need to figure out how much cathode in square inch’s or feet would be needed to produce the amount of silver we need to produce. This would help me picture the volume plus needed holding space.

 

[4metals]

The Moebius cells made to sit on the floor don't have such a steep slope, maybe 15-20º. The movement of the scraped silver crystal is enhanced by a circulating pump which pumps solution from a bar across the back of the slope downward towards the collection trough. It is quite effective because there is never much Silver needle accumulating on the slope.

 

[Shark]

Check my math..

We need to produce 1200 ounces in a 4 day work week. This would be 300 ounces in a 24 hour day. Or 12.5 ounces per hour. The way I have always done things I would be shooting for 13 ounces per hour to allow for days that didn’t go as planned. So, if I figured right, 13 ounces an hour starts to sound more reasonable. Now figure the cathode area needed next.

 

[4metals]

You will never get the 300 ounces in a day without running high (>99%) Silver to start. That is because of the copper in the cell, I always figure on 90% so I would bump up the 300 to 333 to get the 300 produced. And the consistency is a function of free nitric acid content and how your nitric is added as well as a list of other scenarios affecting production.

All of these systems that give a convenient 3000 oz per week estimate or larger based on the number of cells, are living in a "perfect world" bubble. I've never lived in one of those! Too many things can vary like the copper content in the anodes, the electrical connectivity of the buss bars, the nitric acid content, the silver nitrate content, and the list can go on. So the estimates are just that. If you buy or design a system because you need 3000 ounces in X time, be prepared to be disappointed.

 

[Shark]

So, I am only allowing for 12 additional ounce per day and 33 would be more realistic in the real world. That is the experience that I don’t have. Thanks.

 

[Shark]

A goal of 1350 ounces in a 4 day week, or 96 hours.
Equals 14 TOz per hour.
5 square foot of cathode at 25 amps per square foot equals a total of 125 amps.
125 amps per hour at 3.5 grams an hour makes 14 ounces an hour.
Or, at 50 amps per square foot would require 2.5 square foot of working cathode space. Producing the same 14 ounces per hour. I think I am starting to see the general idea behind the cathode to amp per ounce but my head may fall off anytime now..

 

[Shark]

Guys, this is of intense interest to me

Your input would be appreciated. The more people involved the better we can make this for the most people. With out the help from others it takes forever to learn this stuff.

And I will stop using TOz in place of ozt.

 

[Shark]

Why is the rectangular shape consider better than the round shape?

 

[4metals]

It’s all about the surface area of the cathode

This can be a little misleading so let me clarify it a bit.

The cathode plates are just a site for the silver needles to grow. They are also the largest surface area hanging in the cell which is why I said the tank size has to be able to house the cathode. But as far as current density is concerned, the amperage per square foot is calculated based on the area of the anodes. This poses a bit of a conundrum as the anodes are constantly getting smaller. I always try to have some worn down anodes mixed with some full sized anodes to preserve the "approximate" area. Cast anodes molds made by silver cell manufacturers are tapered so they are fatter at the top and thinner at the bottom so they maintain a more consistent surface area as they erode A general rule is cells run at 25-50 ASF. Most prefer to aim for the 25 ASF figure knowing as the anodes shrink the ASF will increase but it will remain well below the upper limit.

 

[4metals]

Why is the rectangular shape consider better than the round shape?

Silver cells are usually square or rectangular because you can fit more volume per unit of floor space in a square tank than a round tank. Plus the relationship between the anodes and the cathodes are always parallel to each other so it allows for better use of space.

Of course all of this flies out the window when you run a silver cell from a 2 liter stainless bowl but I'm talking about large scale producers.

 

[Shark]

Cast anodes molds made by silver cell manufacturers are tapered so they are fatter at the top and thinner at the bottom so they maintain a more consistent surface area as they erode A general rule is cells run at 25-50 ASF. Most prefer to aim for the 25 ASF figure knowing as the anodes shrink the ASF will increase but it will remain well below the upper limit.

Would these be the same basic shape as the copper cell anodes, using the basket so they could progressively drop down as the lower end is consumed? I am thinking this would keep the amps needed within the usable range when done right?

 

[4metals]

No, the anodes are placed into the cell and immersed just shy of where the anode hook grips the anode so the same quantity of anode is submerged every time. It is thicker at the top as the tops dissolve faster than the bottom. This is a mold for casting anodes, from the photo you can see the shape.

The silver is poured into the mold and the reducing flame from one of the torches helps the keep the anodes free of oxygen. You can see the taper.

One of the down sides to Moebius cells is that about 20% of the silver needs to be recast into new anodes because they remain out of solution to hold the anode in position. By contrast a Thum cell completely consumes the anodes eliminating that step. But the two cell types have other trade offs which maybe we should discuss first to decide which type of cell we want to design.

 

[FrugalRefiner]

One of the down sides to Moebius cells is that about 20% of the silver needs to be recast into new anodes because they remain out of solution to hold the anode in position. By contrast a Thum cell completely consumes the anodes eliminating that step. But the two cell types have other trade offs which maybe we should discuss first to decide which type of cell we want to design.

I'd be interested in your views on that. Here are some considerations to start (I think).

As you've said, a Thum cell eliminates having to remelt and recast the anode stubs.

A Moebius cell can usually output slightly higher purity.

A Moebius cell requires less attention to knocking down needles that can short out the cell.

A Thum cell requires a "candlestick", or some similar device to make electrical contact where Moebius anodes hang from a buss bar.

What else would you add?

Dave

 

[Shark]

But the two cell types have other trade offs which maybe we should discuss first to decide which type of cell we want to design.

Will it have a factor in choosing the cell shape, round or rectangle? Or would the discussion of which type cell help determine that?

Myself, I am good with which ever you think best. This is new territory for me.