Reducing Silver Chloride
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Harold is the best bet to answer your question, since that was the method he used. I know that the HCl is needed to provide enough chloride ion to dissolve the required amount of aluminum. I just don't know how much is needed. It could be calculated from the reaction equation.
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Wash your silver chloride well, until the wash water is clear, with no traces of color. You can do that with tap water. Make at least one of the washes with hot water, to dissolve any lead nitrate that might be present. If you make that wash the last, or second to last wash, you'll notice that the silver chloride will settle almost instantly, so you can decant while the solution is still hot. Lead nitrate will self precipitate when the solution cools, defeating the purpose for the hot wash.
I used a thick-walled Pyrex container for the conversion. There's enough heat generated that your chloride can achieve boiling temperature, so don't use glass that won't tolerate heat. Don't do this indoors unless you have a fume hood. There's a considerable amount of gas and vapor liberated in the process.
Place your chloride in the container, and cover it with a 10% solution of HCL and water (tap water is fine). A large diameter container with a shallow layer of chloride is best. You need room to stir. If you have access to scrap sheet aluminum, it works best, for it presents a large surface area to the chloride, and is easily recovered when the operation is complete. Smallish pieces that can be stirred work well, for you have to expose all of the chloride to the aluminum. Avoid tiny pieces that would be difficult to remove when the process is finished.
At first, the chloride will have a tendency to stick to the aluminum, but as it all converts to elemental silver, you'll find that the aluminum will shed it totally. The aluminum goes into solution in this process, so expect it to dissolve as it works. Make certain that the chloride has converted to gray (silver) and there's still some aluminum left. At that point the aluminum will bubble, being dissolved by the HCL, and will be very clean, but there is, otherwise, no action. When you're convinced the chloride has all been converted, remove the rest of the aluminum, checking any place that yields bubbles for small pieces that may be left behind. It's not a bad idea to add a little free HCL after you remove the aluminum, which will insure that the silver is well washed, and will expose any tiny pieces of aluminum that may be left behind. Allow things to sit for a few minutes. If there's any aluminum left behind, you'll see bubbles coming from the location. When you're sure you have all the aluminum, fill the container with tap water and allow it to settle. The solution will appear to be about the same color as the silver, and you'll swear there's silver in suspension, but that is not the case. Allow it to settle for a day, then decant the solution and repeat the wash. The wash will slowly come clear, but it takes a few repetitions. Once the solution is fairly clear, it will filter well, but the dark solution won't go through a filter worth a damn, so don't try filtering until you've washed the silver a few times.
My policy was to place the well washed silver in a Buchner funnel, where the balance of the solution could be removed and the silver compacted well for drying. It's a lot easier to handle the stuff after it's been compacted. I would then dump the Buchner contents into a large evaporating dish to force dry the silver over a low flame. The silver that comes from this conversion is very fine grained and sticky. It melts well once dry, but flux (borax, without soda ash) is a definite asset. The flux should be saved for future re-processing. It could contain traces of unconverted silver chloride, and possibly some prills. Soda ash would convert the chloride traces to elemental silver, but it would also convert traces of base metal oxides should they be present, so I avoided using it. All depends on your objective. If the silver is headed for a silver parting cell, the cleaner the silver, the longer the electrolyte will be viable. How you'll use the silver will determine how to flux. If you use it for inquartation, over and over, use some soda ash in your flux. You'll achieve a 100% recovery (of chlorides) that way.
Hope I've covered it well enough for you to proceed. It will take only one attempt at the process for all of this to make sense.
Harold
I used a thick-walled Pyrex container for the conversion. There's enough heat generated that your chloride can achieve boiling temperature, so don't use glass that won't tolerate heat. Don't do this indoors unless you have a fume hood. There's a considerable amount of gas and vapor liberated in the process.
Place your chloride in the container, and cover it with a 10% solution of HCL and water (tap water is fine). A large diameter container with a shallow layer of chloride is best. You need room to stir. If you have access to scrap sheet aluminum, it works best, for it presents a large surface area to the chloride, and is easily recovered when the operation is complete. Smallish pieces that can be stirred work well, for you have to expose all of the chloride to the aluminum. Avoid tiny pieces that would be difficult to remove when the process is finished.
At first, the chloride will have a tendency to stick to the aluminum, but as it all converts to elemental silver, you'll find that the aluminum will shed it totally. The aluminum goes into solution in this process, so expect it to dissolve as it works. Make certain that the chloride has converted to gray (silver) and there's still some aluminum left. At that point the aluminum will bubble, being dissolved by the HCL, and will be very clean, but there is, otherwise, no action. When you're convinced the chloride has all been converted, remove the rest of the aluminum, checking any place that yields bubbles for small pieces that may be left behind. It's not a bad idea to add a little free HCL after you remove the aluminum, which will insure that the silver is well washed, and will expose any tiny pieces of aluminum that may be left behind. Allow things to sit for a few minutes. If there's any aluminum left behind, you'll see bubbles coming from the location. When you're sure you have all the aluminum, fill the container with tap water and allow it to settle. The solution will appear to be about the same color as the silver, and you'll swear there's silver in suspension, but that is not the case. Allow it to settle for a day, then decant the solution and repeat the wash. The wash will slowly come clear, but it takes a few repetitions. Once the solution is fairly clear, it will filter well, but the dark solution won't go through a filter worth a damn, so don't try filtering until you've washed the silver a few times.
My policy was to place the well washed silver in a Buchner funnel, where the balance of the solution could be removed and the silver compacted well for drying. It's a lot easier to handle the stuff after it's been compacted. I would then dump the Buchner contents into a large evaporating dish to force dry the silver over a low flame. The silver that comes from this conversion is very fine grained and sticky. It melts well once dry, but flux (borax, without soda ash) is a definite asset. The flux should be saved for future re-processing. It could contain traces of unconverted silver chloride, and possibly some prills. Soda ash would convert the chloride traces to elemental silver, but it would also convert traces of base metal oxides should they be present, so I avoided using it. All depends on your objective. If the silver is headed for a silver parting cell, the cleaner the silver, the longer the electrolyte will be viable. How you'll use the silver will determine how to flux. If you use it for inquartation, over and over, use some soda ash in your flux. You'll achieve a 100% recovery (of chlorides) that way.
Hope I've covered it well enough for you to proceed. It will take only one attempt at the process for all of this to make sense.
Harold
Excellent instructions, Harold.
Harold. As always I try to read what you have to say. You explain things very well. For a month or so now, I have been thinking that YOU should write a book.
I was thinking about the sheet of aluminum that you are converting the silver chloride with. How would it work to put it in a dedicated aluminum frypan or aluminum pot, add the HCL & stir untill done? Also, I was thinking about that aluminum seal on the coffee cans would be good to use as a sheet of aluminum.
I,m reading in Hoke about the cell used to purify silver, but so far I see nothing about the electrolyte that they use in it, and am having trouble finding the recipe here.
I was thinking about the sheet of aluminum that you are converting the silver chloride with. How would it work to put it in a dedicated aluminum frypan or aluminum pot, add the HCL & stir untill done? Also, I was thinking about that aluminum seal on the coffee cans would be good to use as a sheet of aluminum.
I,m reading in Hoke about the cell used to purify silver, but so far I see nothing about the electrolyte that they use in it, and am having trouble finding the recipe here.
Phillip,
Check out this patent:
United States Patent 3975244
It should help clear up the process. There are many other patents on Mobious Cell variations.
Steve
Check out this patent:
United States Patent 3975244
It should help clear up the process. There are many other patents on Mobious Cell variations.
Steve
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PhillipJ said:
Chuckle! Well, if I thought I could find a dozen people weak enough in the head to buy a book I'd written, maybe I'd go for it. :lol:
Actually, I don't know that I'd be able. I've never lost sight of the fact that I don't understand why things work as they do--not having an education in chemistry. Mind you, it's not that I can't do a good job of refining----I can, and a damned good one at that, but I am nothing more than a trained monkey, very reliant on the things I learned by studying Hoke, plus a few other sources. When things go south, if it's not something I've experienced, I'm often at a loss to explain the problem. I don't think I'd feel any too good about having information published that was questionable, but I sure don't mind helping others achieve a level of performance that I achieved. That's why you see me here on this forum.
You'd be inviting a bunch of grief if you went the pan route, although I see nothing wrong with using a pan as a source of aluminum. Same goes with any aluminum, right down to aluminum cans if you can eliminate the printing. Just make sure you don't end up with a lot of tiny bits in the silver when it's fully converted.
The problem with using a pan?
Remember me saying that the aluminum gets dissolved in the process? That's exactly why it's not a good idea. The pan, in all likelihood, would have one thin spot and spring a leak when you least expected it to happen. Otherwise I see nothing wrong with the idea, so if you happen to have a few on hand (clean, no Teflon), or can pick them up cheaply at a second hand store, use them accordingly. You could even start out using the pan as you suggested, but make sure you have it sitting in something that will catch the solution and silver when it springs a leak.
The electrolyte is made of silver, dissolved in nitric acid and distilled water. I don't have the information at hand, but there's a book by, I think, Butts & Coxe, that covers silver refining extensively. If I have the name of the authors wrong, I know GSP knows the book of which I speak and he can make corrections to my information.
My cell was used on a batch basis, running an anode that weighed about 200 ounces (troy). By the time I had refined that amount of silver, the copper content of the electrolyte had climbed to the point where it could start co-depositing copper along with the silver. That doesn't happen as long as the percentage of copper is low enough. You can tell when there's a change because the silver crystals tend to grow differently, long and hairy. I'd stop the cell when I approached that threshold and remove the electrolyte entirely, recover the silver within, and make new electrolyte from some of the pure crystal that came from the cell. That was an excellent test of the quality of the silver, for if it had any copper within, it showed in the electrolyte. On rare occasion when that was the case, I'd simply place the silver crystal back in the basket, place a new anode on top of the crystals, and go back to work after replacing the electrolyte. The silver came out beautifully that way, and I was assured of purity.
Running a cell is far more involved than the simple description, but I'm more than happy to give you guidance if you get that far along, including making your electrolyte.
On the subject of electrolyte, I think you'll read that the big boys don't do what I did, likely because their cells are ongoing, never shut down. Instead of replacing their electrolyte, they are constantly replacing a portion of it with new, keeping the copper/silver ratio at a desirable level. I've read that they actually rely on some copper for conductivity, although I'm having one hell of a hard time believing that's true considering there's a huge amount of silver in solution as compared to copper, and it's a far better conductor.
Harold
catfish
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Harold:
You under estimate your technical abilities, vast knowledge base, practical experiences and accomplishments. What you may lack in technical training and formal education, you make up for in having a can do it attitude.
I came from the corporate world and I always would rather have the guy on my team that had a positive attitude and could make things happen. I learned early on in my management career, that there is no substitute for experience and practical knowledge. I used to have several hundred employees that had numerous degrees and very impressive credentials and some of them did not have sense enough to get out of the rain. If it was not for the folks of your caliber, AT& T would have gone broke many years ago. I’ll put my money on folks like you any day.
I again want to thank you for the many hours of posts that you have volunteered for the folks on this forum. Believe it on not, we listen to you and most of us use the very same ideas and techniques you have so graciously shared with us. My hat is off to you.
Also, if you should ever reconsider and do publish a book in lay person terms on refining, I want to be your very first customer.
Thanks,
Tom Smith
You under estimate your technical abilities, vast knowledge base, practical experiences and accomplishments. What you may lack in technical training and formal education, you make up for in having a can do it attitude.
I came from the corporate world and I always would rather have the guy on my team that had a positive attitude and could make things happen. I learned early on in my management career, that there is no substitute for experience and practical knowledge. I used to have several hundred employees that had numerous degrees and very impressive credentials and some of them did not have sense enough to get out of the rain. If it was not for the folks of your caliber, AT& T would have gone broke many years ago. I’ll put my money on folks like you any day.
I again want to thank you for the many hours of posts that you have volunteered for the folks on this forum. Believe it on not, we listen to you and most of us use the very same ideas and techniques you have so graciously shared with us. My hat is off to you.
Also, if you should ever reconsider and do publish a book in lay person terms on refining, I want to be your very first customer.
Thanks,
Tom Smith
aflacglobal
Well-known member
I know exactly what you mean. Give me the street smarts anyday.
Thanks for the info Harold and Steve. Not that I plan to purify any amount of silver, but it is good to know how to do it just in case.
So far today I learned when to clean out the silver cell, or know what to look for when the copper limit is reached. Also that a silver nitrate electrolyte with a ph of 1.5 - 2.5 is used. I am assuming that the cathode can be either 999 silver or stainless steel.
Current density I am not sure of? My plating manual says 1 amp per 16 sq. in. of cathode and air agitation for decorative silver plating.
And Harold. I have allready copy & pasted a small book on your lessons here. Probably others have too. You allready have a good start right here for your book. Think about it.
So far today I learned when to clean out the silver cell, or know what to look for when the copper limit is reached. Also that a silver nitrate electrolyte with a ph of 1.5 - 2.5 is used. I am assuming that the cathode can be either 999 silver or stainless steel.
Current density I am not sure of? My plating manual says 1 amp per 16 sq. in. of cathode and air agitation for decorative silver plating.
And Harold. I have allready copy & pasted a small book on your lessons here. Probably others have too. You allready have a good start right here for your book. Think about it.
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PhillipJ said:
Silver would be a problem in cost and fabrication, and not really necessary. Stainless is very acceptable, although in the process of harvesting the crystals, you must use tools that won't raise burrs, or otherwise scratch the cell surface, and won't precipitate the silver in solution. I built a scraper from green fiberglass board material, about 3/4" thick, which I used to scrape down the crystals when it was time to empty the cell. The scraper had a shank made of stainless steel, with the blade attached with a stainless screw. For me it was no chore, I had a machine shop at my disposal.
To remove the crystals from the cell, I found one of those scoops used for removing litter from a cat's box worked quite well. It held the crystals without losing many of them, and allowed the electrolyte to drain adequately. The crystals were immediately washed with distilled water once removed from the cell, with the wash water making up the following batch of electrolyte. Crystals were placed in a large Buchner, which made washing easy. Once well washed, they were force dried in a large evaporating dish, with a low flame.
There's a template above the cell which was used to cut the fabric for the anode basket. You MUST use a bag, which becomes the collector of values that follow your silver. This is the process where you recover the platinum group of metals that follow silver, along with some gold, surprisingly. The cut fabric was sewed to form a square, which was held in place in the basket by the polypropolylene clips you see in the rather poor picture, below. The basket was made from 3/8" polypropylene as well, held together by stainless screws, and had a gridwork in the bottom that supported the anode. The gridwork was a series of ¼" poly rods with 1/8" sheet strips of poly, spaced with some ½" diameter tubes that fit over the ¼" rods, and between the 1/8" strips. Hope that makes sense.
I ran the cell in that location for about ten years. It's virtually impossible to handle the electrolyte without some splashing, and it stains everything it touches, as you'll see. The cell was fabricated from 304 stainless sheet material 16 gauge, and was TIG welded, then electropolished. You could just as easily use a large stainless container from a steam table, but it would involve some creativity in that you must have a basket that is non-conductive and inert, in which you place your anode. You'd also have to have an anode mold cast so it would be sized according to need.
Voltage and amperage would be determined by the individual cell and its characteristics. Spacing of the anode/cathode come into play, as does anode size, as you alluded. I started out trying to run about 15 amps on my anode, which was, maybe, 9" square (don't recall the dimensions). It ran fine, but deposited fine, long crystals instead of short, compact crystals. They had a tendency to short the anode in only a couple hours. Considering I like to sleep through the night (the cell ran non-stop, and builds a temperature at which it is happy and runs best), I cut back on the voltage, with a corresponding drop of the amperage. I could allow the cell to run unsupervised for a few hours, so I could sleep through most of a night. I benefited by growing larger crystals in the bargain.
Again, each case will be its own. You could even allow the cell to sit idle when you're not there to tend it, but if you have much silver to process, you'd never get finished. I'd run my silver cell two or three times each year, but I ran a few thousand ounces each time I ran it.
Don't confuse silver refining with silver plating-----your objective is not the same. The current density, I think, is higher in parting.
I took the liberty to post a second picture, this one with a series of molds. The large one on the left casts a 100 ounce silver bar, the square one was my anode mold, and the cone mold(s) on the right were used for pouring buttons that came from melting silver, recovered from solution with copper, or from silver converted from chloride. It got a flux cover when melting to absorb any oxides that were present. The cone molds allowed a small surface area on the button from which the flux could be easily removed. Often, once cooled, a tap with a hammer was all it took. The buttons were then re-melted and cast as anodes. Note that the molds are all well blackened. Foundry supplies sell a mold dressing that I highly recommend. It's nothing more than lamp black prepared such that it can be brush applied. Without it, you'll get soldering of silver to the molds.
Chuckle! If I keep posting, it will save you the cost of the book!
I'm highly unlikely to write a book, considering it would be a repeat of Hoke for the most part. I confess, there was a time when I had planned to do so, but realized early on that I was no writer. I've done one hell of a lot of posting since then (early 80's) and have since improved enough to at least make my posts make a small amount of sense. Hope you know that I'm highly flattered, though. It's been real good for my tired ego to have folks respond to my contributions.
Assuming I were to write a book, I could add more on silver, which Hoke tended to disregard, but otherwise I'm not convinced there's anything new I could add. You'll slowly come to understand why I am such a champion of Hoke's book----almost everything I talk about came from applying what was already in print. I've changed a few things, such as including the ammonium hydroxide wash to the cycle of cleaning precipitated gold, but not much more.
I've stressed the fact that Hoke was a master at presenting information in such a manner as to allow people like me to understand her instructions. My only disappointments are that the costs referenced in her book don't come close to today's reality, and she was really big on "tossing on the gasoline" when incinerating. It goes without saying that you should NEVER use gasoline in that manner. There are other means to the same end, that don't present the horrible risks.
Thanks for your support, Phillip.
Harold
Attachments
Harold said:
What type of fabric did you use?
How long do they last?
Great cell design Harold!
Steve
I wrote the post below before I saw Harold's post but I wasn't able to post it yesterday. The traditional Thum cell I'm speaking of looks nothing like Harold's. When I first saw Harold's, I was taken aback, since it looked so strange. On closer examination, I can see what he had in mind. His cell eliminates the need for sliding the basket back and forth in order to remove the crystals. Also. the entire cell is the cathode and will probably last forever. Actually, pretty darn ingenious. At 10 amps, his cell probably produced about 20 to 25 ozs in 24 hours
Most books suggest using unbleached muslin as a filter cloth. I bought mine from Walmart and used a double thickness. It's only problem is that there's sizing in it and it takes an hour or two before the solution penetrates the sizing and there is maximum current flow. The cloth is used once. The muslin cloth also burns well. I never used only gasoline for burning but often used a safer 50/50 blend of gas and diesel.
The 30 gallon cell mentioned below consists of an flat bottomed outer tank about 30" X 60". It was made from 2" X 10" lumber with a 3/4" plywood bottom. It was coated with several coats of polyester boat resin. The last one I made was coated with PVC that was applied with a chopping gun. A sheet of 1/8" 300 series stainless laid flat in the bottom. The stainless had a 90 deg. bend at one end and protruded out of the tank in order to make electrical contact.
The inner basket (also coated) was about 28" X 28". The sides were 1" X 6" lumber. Instead of a solid bottom, there were 19 removable 3/4" OD PVC pipes sealed with pipe caps on each end. A length of 3/8" or 1/2" rebar was put into each pipe for rigidity. Each pipe rested on a support on the sides of the basket. The muslin cloth was laid on the row of pipes and the 21 impure silver bars (about 30-35 oz each - about 600 oz total) were placed on the cloth. The bars were all touching each other. The solution level was adjusted so it touched the bottom of the silver bars. To make contact to the bars, I used a 3#, 60/40 copper/silver bar attached to the power cable. This contact bar was simply placed on the silver bars. A protruding wooden crossmember was attached to 2 ends of the basket. They rode across the top sides of the outer tank and allowed the basket to be slid from one end of the tank to the other.
The drawing in the attachment is a cutaway side view of a standard silver cell.
I once made a 5 gallon cell, using a 7 gallon plastic tray as the outer tank. The stainless was the same as in the 30 gallon tank. The basket was made from one of those plastic carrier boxes, with diamond shaped holes, that are used to carry 4 gallons of milk. I cut off the top 1/3 of the basket and ran 2, 3/8" stainless rods through the holes in the basket. These rode on the top of the tray to support the basket. This little cell made about 75 oz. per day and worked great. It was very cheap and fast to build.
In both these cells, the size of the stainless cathode must sit very flat on the bottom. It must also fit fairly snug and the corners must be slightly rounded to fit without cutting into the tank coating. It must be professionally bent and professionally cut with a large shear.
.
The silver in the cell must be harvested at least every 4 hours. If allowed to run too long without harvesting, the silver piles up under the basket and shorts out with the silver bars. This invariably burns a hole in the filter cloth and allows all the grunge collected by the cloth to co-mingle with the solution. Then, the entire 30 gallons has to be filtered and the tank cleaned and re-setup. One doesn't make this mistake twice. If one has to leave for awhile, the power is shutdown or reduced.
To harvest the silver, the power is shut off and the crystals are pushed to one end of the stainless cathode. The basket is slid to the other end and the crystals are removed. I always used a stainless BBQ spatula, with no holes in it, to remove the crystals. The power is then turned back on. The crystals are filtered and rinsed very well. Then they are melted and cast into 9999 bars.
Yesterday's Post
Steve, I'm quite familiar with the Hunter patent you linked and I remember the interest it created when it was first released. It is not a patent for a silver cell but, it is a patent for removing the build up of copper from the solution, using solvent extraction. However, the cell solution parameters given (1.5 pH, 60 gm/l silver, 30 gm/l) are valid.
There are two basic types of silver cells, the Balbach-Thum (horizontal) cell and the Moebius (vertical) cell. The Moebius cell is usually used for large volume because it takes up less floor space and doesn't need the nearly 24/7 attention that a Thum cell needs, for maximum production. The Thum cell is easier to set up and use. Both are fairly complicated to build. At least, you have to understand what is required. The dimensions are fairly critical. A standard 30 gallon Thum cell will produce about 500 ozs of 9999 silver in a 24 hour period. The books don't come close to telling the entire story. Also, the info in the books is based on mining operations where the composition of the impure bars run the same, day after day. For us, running scrap silver that is different every batch, the situation is much, much more complex. To adequately cover this subject, it would take at least a 30-50 page report, with drawings. There are lots of ins and outs and lots of variables. Each metallic contaminant may require a little different approach.
Just as aqua regia is the final purification step for much of the pure gold that is produced, the silver cell is what finally purifies the silver. With gold, there are other methods available besides aqua regia. To get pure silver, the silver cell is about the only game in town.
I got 5 years of hands-on experience working in a place that had 12 Thum cells and produced about 5000 ozs per day. Two of the cells were, what we called, breakdown cells. We used them to breakdown silver bars that contained lower amounts of silver. Instead of making up the starting solution with pre-mixed copper and silver nitrates, we started it with only a certain amount of nitric acid and water. As the impure bars dissolved electrolytically and silver crystal was produced, the nitric re-dissolved the crystal and formed the silver solution. This stuff isn't covered in any books.
In almost all impure silver, copper is the main contaminant. For example, sterling is 7.5% copper. As the bars dissolve in the cell, the silver plates out as beautiful loose crystals and the copper remains dissolved in the solution. When the copper dissolves, the silver content of the solution decreases. The copper goes up and the silver goes down. At a certain point of either, the crystal purity suffers. The standard way of solving this problem is to remove cell solution and replace it with silver nitrate solution that contains no copper. Thus, the great interest in the Hunter patent mentioned above. This system continuously removes copper from the solution.
Before even thinking about a silver cell, you must have a pot furnace with all the associated equipment, in order to produce bars from the impure silver: furnace; crucibles; tongs; molds; fluxes; safety equipment; exhaust; etc., etc. Also, you have to melt and cast the crystal.
You also need a variable rectifier to power the cell. For a full size 30 gallon cell, you need at least a 250 amp, 4 volt rectifier. You can run cells in series off of the same power supply (PS). A 250A, 12V PS (approx $2500) will run 3, 30 gal. cells. For smaller cells, the PS needs are proportionally less.
Most books suggest using unbleached muslin as a filter cloth. I bought mine from Walmart and used a double thickness. It's only problem is that there's sizing in it and it takes an hour or two before the solution penetrates the sizing and there is maximum current flow. The cloth is used once. The muslin cloth also burns well. I never used only gasoline for burning but often used a safer 50/50 blend of gas and diesel.
The 30 gallon cell mentioned below consists of an flat bottomed outer tank about 30" X 60". It was made from 2" X 10" lumber with a 3/4" plywood bottom. It was coated with several coats of polyester boat resin. The last one I made was coated with PVC that was applied with a chopping gun. A sheet of 1/8" 300 series stainless laid flat in the bottom. The stainless had a 90 deg. bend at one end and protruded out of the tank in order to make electrical contact.
The inner basket (also coated) was about 28" X 28". The sides were 1" X 6" lumber. Instead of a solid bottom, there were 19 removable 3/4" OD PVC pipes sealed with pipe caps on each end. A length of 3/8" or 1/2" rebar was put into each pipe for rigidity. Each pipe rested on a support on the sides of the basket. The muslin cloth was laid on the row of pipes and the 21 impure silver bars (about 30-35 oz each - about 600 oz total) were placed on the cloth. The bars were all touching each other. The solution level was adjusted so it touched the bottom of the silver bars. To make contact to the bars, I used a 3#, 60/40 copper/silver bar attached to the power cable. This contact bar was simply placed on the silver bars. A protruding wooden crossmember was attached to 2 ends of the basket. They rode across the top sides of the outer tank and allowed the basket to be slid from one end of the tank to the other.
The drawing in the attachment is a cutaway side view of a standard silver cell.
I once made a 5 gallon cell, using a 7 gallon plastic tray as the outer tank. The stainless was the same as in the 30 gallon tank. The basket was made from one of those plastic carrier boxes, with diamond shaped holes, that are used to carry 4 gallons of milk. I cut off the top 1/3 of the basket and ran 2, 3/8" stainless rods through the holes in the basket. These rode on the top of the tray to support the basket. This little cell made about 75 oz. per day and worked great. It was very cheap and fast to build.
In both these cells, the size of the stainless cathode must sit very flat on the bottom. It must also fit fairly snug and the corners must be slightly rounded to fit without cutting into the tank coating. It must be professionally bent and professionally cut with a large shear.
.
The silver in the cell must be harvested at least every 4 hours. If allowed to run too long without harvesting, the silver piles up under the basket and shorts out with the silver bars. This invariably burns a hole in the filter cloth and allows all the grunge collected by the cloth to co-mingle with the solution. Then, the entire 30 gallons has to be filtered and the tank cleaned and re-setup. One doesn't make this mistake twice. If one has to leave for awhile, the power is shutdown or reduced.
To harvest the silver, the power is shut off and the crystals are pushed to one end of the stainless cathode. The basket is slid to the other end and the crystals are removed. I always used a stainless BBQ spatula, with no holes in it, to remove the crystals. The power is then turned back on. The crystals are filtered and rinsed very well. Then they are melted and cast into 9999 bars.
Yesterday's Post
Steve, I'm quite familiar with the Hunter patent you linked and I remember the interest it created when it was first released. It is not a patent for a silver cell but, it is a patent for removing the build up of copper from the solution, using solvent extraction. However, the cell solution parameters given (1.5 pH, 60 gm/l silver, 30 gm/l) are valid.
There are two basic types of silver cells, the Balbach-Thum (horizontal) cell and the Moebius (vertical) cell. The Moebius cell is usually used for large volume because it takes up less floor space and doesn't need the nearly 24/7 attention that a Thum cell needs, for maximum production. The Thum cell is easier to set up and use. Both are fairly complicated to build. At least, you have to understand what is required. The dimensions are fairly critical. A standard 30 gallon Thum cell will produce about 500 ozs of 9999 silver in a 24 hour period. The books don't come close to telling the entire story. Also, the info in the books is based on mining operations where the composition of the impure bars run the same, day after day. For us, running scrap silver that is different every batch, the situation is much, much more complex. To adequately cover this subject, it would take at least a 30-50 page report, with drawings. There are lots of ins and outs and lots of variables. Each metallic contaminant may require a little different approach.
Just as aqua regia is the final purification step for much of the pure gold that is produced, the silver cell is what finally purifies the silver. With gold, there are other methods available besides aqua regia. To get pure silver, the silver cell is about the only game in town.
I got 5 years of hands-on experience working in a place that had 12 Thum cells and produced about 5000 ozs per day. Two of the cells were, what we called, breakdown cells. We used them to breakdown silver bars that contained lower amounts of silver. Instead of making up the starting solution with pre-mixed copper and silver nitrates, we started it with only a certain amount of nitric acid and water. As the impure bars dissolved electrolytically and silver crystal was produced, the nitric re-dissolved the crystal and formed the silver solution. This stuff isn't covered in any books.
In almost all impure silver, copper is the main contaminant. For example, sterling is 7.5% copper. As the bars dissolve in the cell, the silver plates out as beautiful loose crystals and the copper remains dissolved in the solution. When the copper dissolves, the silver content of the solution decreases. The copper goes up and the silver goes down. At a certain point of either, the crystal purity suffers. The standard way of solving this problem is to remove cell solution and replace it with silver nitrate solution that contains no copper. Thus, the great interest in the Hunter patent mentioned above. This system continuously removes copper from the solution.
Before even thinking about a silver cell, you must have a pot furnace with all the associated equipment, in order to produce bars from the impure silver: furnace; crucibles; tongs; molds; fluxes; safety equipment; exhaust; etc., etc. Also, you have to melt and cast the crystal.
You also need a variable rectifier to power the cell. For a full size 30 gallon cell, you need at least a 250 amp, 4 volt rectifier. You can run cells in series off of the same power supply (PS). A 250A, 12V PS (approx $2500) will run 3, 30 gal. cells. For smaller cells, the PS needs are proportionally less.
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The fabric was purchased from a company that specialized in filter materials. It was about as thick as canvas that you may see in daily life, but had one side roughed up, so it was fuzzy. I used that side facing in, and got very good results. Seams were all triple sewed to insure they didn't leak solids. The material must permit the passage of the electrolyte, yet retain the smallest of particles that don't go into solution. I was well satisfied with how the fabric worked, and could run several 200 ounce anodes before replacing. It had a tendency to become clogged over time. Because of the exposure to silver nitrate, once dried, they incinerate very well simply by heating in a pan.
Because I processed a fair amount of dental gold, I had a strong showing of the platinum group in my silver. It was often so high that the sludge didn't fall away from the anode, but had to be mechanically removed. I used a porcelain spatula, and simply left the sludge in the basket until it was time to drop in a new anode. I'd remove the remnants of the old anode, scrape it well, then scoop out all the sediment from the bag, using an acid dipper. Drop in the old remnant, with a new anode on top, and start the cell again.
I should have mentioned in my previous post. My cell had a lug welded on the back side for the cathode connection. The anode connection was made via a thick "door knob" cast of silver. It was simply placed on the top surface of the anode, which was never exposed to the electrolyte. That way, should the anode dissolve to the point where the connection was exposed to the electrolyte, nothing was dissolved to add contaminants. I machined the mold that was used to cast the door knob.
When running a cell such as this, the electrolyte should be kept at a depth that just touches the bottom side of the anode, to prevent premature loss of peripheral size. That way you get a more uniform decomposition of the anode, keeping the surface area relatively constant.
My cell design was acceptable, but I'd make a minor change should I ever build another. The vertical sides ended up being a bit of a problem, which I eventually solved by adding a strip of wide electrician's tape. The short distance from the anode to cathode encouraged crystals to grow to the basket, creating a direct short. The tape, coupled with knocking down the crystals on a regular interval, solved the problem. It would be better to avoid it entirely. That involves greater anode/cathode spacing, so it gets complicated because you then limit the size of your anode unless you increase, substantially, the size of the cell.
Harold
Because I processed a fair amount of dental gold, I had a strong showing of the platinum group in my silver. It was often so high that the sludge didn't fall away from the anode, but had to be mechanically removed. I used a porcelain spatula, and simply left the sludge in the basket until it was time to drop in a new anode. I'd remove the remnants of the old anode, scrape it well, then scoop out all the sediment from the bag, using an acid dipper. Drop in the old remnant, with a new anode on top, and start the cell again.
I should have mentioned in my previous post. My cell had a lug welded on the back side for the cathode connection. The anode connection was made via a thick "door knob" cast of silver. It was simply placed on the top surface of the anode, which was never exposed to the electrolyte. That way, should the anode dissolve to the point where the connection was exposed to the electrolyte, nothing was dissolved to add contaminants. I machined the mold that was used to cast the door knob.
When running a cell such as this, the electrolyte should be kept at a depth that just touches the bottom side of the anode, to prevent premature loss of peripheral size. That way you get a more uniform decomposition of the anode, keeping the surface area relatively constant.
My cell design was acceptable, but I'd make a minor change should I ever build another. The vertical sides ended up being a bit of a problem, which I eventually solved by adding a strip of wide electrician's tape. The short distance from the anode to cathode encouraged crystals to grow to the basket, creating a direct short. The tape, coupled with knocking down the crystals on a regular interval, solved the problem. It would be better to avoid it entirely. That involves greater anode/cathode spacing, so it gets complicated because you then limit the size of your anode unless you increase, substantially, the size of the cell.
Harold
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Having seen only one other cell in all my years, I had little idea what others had done. The cell I copied was similar to my design, but was tapered on all sides about equally. Once I operated mine, I understood all too well why that was the case. I mentioned the short distance and shorting by crystal growth. That would have been controlled by wider or tapered sides.
My decision to make the cell as I did was based on the idea that I was not primarily interested in silver, and would likely never run it in large volume. In spite of the restricted volume, I was all too aware that I had a lot of Pt. group metals tied up in my silver, and could recover it easiest in a parting cell, with the benefit of producing pure silver.
I had to balance the amount of silver I had to run against how much I wanted to tie up in electrolyte, which was a part of the reason I kept the sides straight, and included the tapered ends. That is all non-functioning area and need not have depth. While I don't regret the reduced volume of electrolyte, I'd have preferred to not face the shorting issue.
Bottom line is my cell turned out to be very well sized for my operation, which is a serious consideration. I gave considerable thought before deciding on size, and was fortunate to hit something that was functional for my circumstances. If one builds a large cell, running it could border on the impossible unless a large volume of silver is handled on a routine basis. Small cells, run continually, are a far better choice when volumes are small, I'm convinced.
I'd run a +/- 200 ounce anode in two or three days. I don't recall the current density any longer, but the voltage, as you alluded, was very low. I do recall having a target of 15 amps, but the crystal growth was too fast and created rapid shorting, which I mentioned in my previous post. If memory serves, I ran around 9 amps, but I sure wouldn't swear that was true. Could be it was up around 12. Getting old and forgetful really sucks!
The tapered ends are good for reducing the volume of electrolyte, but that's a mixed results kind of thing. Greater volume would have equated to a guarantee that the electrolyte had greater capacity for copper before becoming troublesome. On rare occasion I had to re-run a batch of crystals, which I also mentioned previously.
Aside from the loss of production, it was a trouble-free proposition. The crystals that grew from the virtually pure silver ware small and dense, allowing prolonged running without knocking them down. The trace of copper contained in the crystals was evident as the process ensued, by the electrolyte changing color ever so slowly.
As the crystals were knocked down, I'd push them to the ends, and harvest only when necessary. When things ran as desired, crystal was harvested only when the electrolyte was replaced.
All in all, I'd recommend a cell similar in design, if for no other reason, it was easy to build and maintain.
Harold
Thanks for all your input here guys. You are all talking much bigger than what I would need. For my purpose, I think that I would suspend my anode vertical, in a bag, And plate onto a vertical sheet of stainless, all in an ice cream pail. I see no reason that that wouldn't work.
One thing I don't remember either Harold or GSP mentioning was the use of any agitation.
One thing I don't remember either Harold or GSP mentioning was the use of any agitation.
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No agitation is required. There's a minor amount of convection due to heating of the process, which appears to be adequate. Chris may have a different view, considering he operated cells that were significantly different from that which I used.
There's nothing wrong with the simple design you spoke of. Insure that no copper or iron touches the electrolyte. Titanium, if you can get some, is a wonderful bus system. Stainless will also work, as you already know.
Harold
There's nothing wrong with the simple design you spoke of. Insure that no copper or iron touches the electrolyte. Titanium, if you can get some, is a wonderful bus system. Stainless will also work, as you already know.
Harold
No heat. No agitation. Ideally, the starting solution should be 30 gm/l copper and 60 gm/l silver. You can fudge a little on this but, not much. The purpose of the copper is to make the crystal denser. Without it, the crystal will be fluffy and stringy and will climb all over and soon short out the electrodes.
For the copper, I would dissolve solid, clean (no solder) house wire in 50/50, nitric acid/distilled water. You can dissolve about 120 grams in 1 liter of 50/50 nitric. For the silver, use pure silver coins, US 90% coins, silverware, other types of sterling, etc. You can use US 40% silver coins but, not exclusively. You can also use silver that has been cemented out of nitric with copper, if there's no palladium in it and if it's been very well rinsed. Whatever you use, make sure that the only contaminant is copper. Many other metals will create problems. You can dissolve 420 grams of pure silver in 1 liter of 50/50 nitric.
When calculating the nitric needed for silver alloys, you'll have to take into consideration the amount of copper in the alloy (s), using the figures above. Also, when calculating the copper wire needed, consider the amount of copper in the silver alloys you're using.
After dissolving the metals, it is best to not have any free nitric left in the solution. It doesn't really hurt anything but, until it's used up, the silver crystal produced will be re-dissolved.
After dissolving everything, dilute to final volume with distilled water. Never use tap water in any part of this process. It contains chlorides and the silver chloride produced will create a cloudy solution and contaminate the crystal.
When the cell is operating, for every gram of copper dissolved in the solution, from the impure silver, the total silver content in the cell will decrease 3.4 grams. If the silver in the cell goes below about 15 - 20 gm/l or the copper goes above 100 gm/l, the crystal purity will be affected. Try to keep records and keep track of how much copper is being dissolved. Usually, you know this by the type of materials you are running. When the silver in solution approaches the danger level, you can build up the silver content in 2 ways.
First, you can calculate how much silver you need and add the equivalent amount of nitric acid. This will re-dissolve some of the crystals. This method will obviously cut into your production.
Second, you can remove some solution and replace it with silver solution that contains little or no copper.
When I ran cells, I analyzed the solution silver content with a simple titration method. One of these days, I'll post how to do it. Then, I measured the specific gravity of the solution with a hydrometer. From this info, I calculated the copper content using a graph I had created.
The impure silver you run through the cell should be at least 90% pure. Otherwise, the silver in the cell decreases so fast that you can't keep up with replenishing it. The easiest silver to refine in the cell is silver that has been cemented from a nitric solution and melted into a bar. It runs about 98 - 99% pure and the silver replenishment is not needed nearly as often.
At 100% efficiency, you will produce 4.025 grams of silver crystal per amp-hour. However, no electrolytic system runs at 100% efficiency. Therefore, at 5 amps, you produce about 20.125 grams per hour. It is best to not go over 4 volts. If you're using a battery charger, use the 6V setting. It may or may not work at 6V. The crystal density could be severely affected and the crystals may grow all over the place. Never use 12V. If you're handy, you could rig up an adjustable shunt, with a voltmeter, to drop the excess voltage.
When running vertically, the crystal will fall off of the stainless cathode and pile up on the bottom of the container. The worst thing that can happen is if this pile grows to the point where it makes contact with both electrodes and shorts them out. I would suggest that you use a 5" separation between anode and cathode. Keep the electrodes about 4" off the bottom of the container.
When the crystals build up to a certain point, you'll have to disassemble the entire cell and pour off the solution to collect them. A way around this may be to also bag the stainless cathode. Leave a couple of inches of empty bag below the cathode so there will be enough room to catch the crystals. If you use a bag, you'll probably have to figure a way to hold the bag a little bit away from the cathode surface. If you don't, the crystals may grow through the cloth. I've never used a bag for the cathode but, for some reason, I think this might happen.
Since you're running vertically, you'll need some sort of wire to suspend the electrodes. Stainless is the cheapest choice (gold also works). Just remember that stainless is only about 1/35 as conductive as copper. The wire should be heavy enough to not overheat. You can make S-hooks from the wire.
Vertical is not the best way to do this. I think that, after you read this, you will see that horizontal is best. It should be easy to design a very small horizontal cell. I once made a horizontal one, in a one liter beaker, for my nephew's science fair project. I"ll try to remember how I did it. It's been 20 years.
I love silver cells. They're fun and very easy to run, once you get setup and learn the ropes. Pure gold is about the most beautiful thing on earth. Pure silver crystals come in second.
Good Luck!
For the copper, I would dissolve solid, clean (no solder) house wire in 50/50, nitric acid/distilled water. You can dissolve about 120 grams in 1 liter of 50/50 nitric. For the silver, use pure silver coins, US 90% coins, silverware, other types of sterling, etc. You can use US 40% silver coins but, not exclusively. You can also use silver that has been cemented out of nitric with copper, if there's no palladium in it and if it's been very well rinsed. Whatever you use, make sure that the only contaminant is copper. Many other metals will create problems. You can dissolve 420 grams of pure silver in 1 liter of 50/50 nitric.
When calculating the nitric needed for silver alloys, you'll have to take into consideration the amount of copper in the alloy (s), using the figures above. Also, when calculating the copper wire needed, consider the amount of copper in the silver alloys you're using.
After dissolving the metals, it is best to not have any free nitric left in the solution. It doesn't really hurt anything but, until it's used up, the silver crystal produced will be re-dissolved.
After dissolving everything, dilute to final volume with distilled water. Never use tap water in any part of this process. It contains chlorides and the silver chloride produced will create a cloudy solution and contaminate the crystal.
When the cell is operating, for every gram of copper dissolved in the solution, from the impure silver, the total silver content in the cell will decrease 3.4 grams. If the silver in the cell goes below about 15 - 20 gm/l or the copper goes above 100 gm/l, the crystal purity will be affected. Try to keep records and keep track of how much copper is being dissolved. Usually, you know this by the type of materials you are running. When the silver in solution approaches the danger level, you can build up the silver content in 2 ways.
First, you can calculate how much silver you need and add the equivalent amount of nitric acid. This will re-dissolve some of the crystals. This method will obviously cut into your production.
Second, you can remove some solution and replace it with silver solution that contains little or no copper.
When I ran cells, I analyzed the solution silver content with a simple titration method. One of these days, I'll post how to do it. Then, I measured the specific gravity of the solution with a hydrometer. From this info, I calculated the copper content using a graph I had created.
The impure silver you run through the cell should be at least 90% pure. Otherwise, the silver in the cell decreases so fast that you can't keep up with replenishing it. The easiest silver to refine in the cell is silver that has been cemented from a nitric solution and melted into a bar. It runs about 98 - 99% pure and the silver replenishment is not needed nearly as often.
At 100% efficiency, you will produce 4.025 grams of silver crystal per amp-hour. However, no electrolytic system runs at 100% efficiency. Therefore, at 5 amps, you produce about 20.125 grams per hour. It is best to not go over 4 volts. If you're using a battery charger, use the 6V setting. It may or may not work at 6V. The crystal density could be severely affected and the crystals may grow all over the place. Never use 12V. If you're handy, you could rig up an adjustable shunt, with a voltmeter, to drop the excess voltage.
When running vertically, the crystal will fall off of the stainless cathode and pile up on the bottom of the container. The worst thing that can happen is if this pile grows to the point where it makes contact with both electrodes and shorts them out. I would suggest that you use a 5" separation between anode and cathode. Keep the electrodes about 4" off the bottom of the container.
When the crystals build up to a certain point, you'll have to disassemble the entire cell and pour off the solution to collect them. A way around this may be to also bag the stainless cathode. Leave a couple of inches of empty bag below the cathode so there will be enough room to catch the crystals. If you use a bag, you'll probably have to figure a way to hold the bag a little bit away from the cathode surface. If you don't, the crystals may grow through the cloth. I've never used a bag for the cathode but, for some reason, I think this might happen.
Since you're running vertically, you'll need some sort of wire to suspend the electrodes. Stainless is the cheapest choice (gold also works). Just remember that stainless is only about 1/35 as conductive as copper. The wire should be heavy enough to not overheat. You can make S-hooks from the wire.
Vertical is not the best way to do this. I think that, after you read this, you will see that horizontal is best. It should be easy to design a very small horizontal cell. I once made a horizontal one, in a one liter beaker, for my nephew's science fair project. I"ll try to remember how I did it. It's been 20 years.
I love silver cells. They're fun and very easy to run, once you get setup and learn the ropes. Pure gold is about the most beautiful thing on earth. Pure silver crystals come in second.
Good Luck!
