# Self scraping silver cells



## 4metals (Jan 30, 2010)

I'm working with a refiner in Michigan who wanted to run silver cells. I got him up and running with 6, 45 gallon Moebius cells and we're making fine silver to beat the band. Now he wants to change the rules. Originally it was fine to run 3 shifts and shut down on Sunday but now he wants to only staff it for 1 shift. The crystals grow too fast to go un-scraped for that long without shorting out. At 200 amps per cell we're making 18 kilo's of fine silver from each cell per day and 5 cells are always running and 1 waiting to run. Every cell has to be broken down after 5 days running due to the copper buildup. 

My thought was a slow ( 1 rpm) rotating stainless cylinder with a permanently mounted scraper which will dislodge the silver into a funnel below the cathode to collect what falls. A funnel will allow the fine crystals to collect at one central point where I figure we could build an archemedes screw to constantly empty the funnel over the side of the bath. 

We seem to have quite a collection of mechanical minds on this forum, has anyone done this? I'm fishing for opinions here.


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## qst42know (Jan 30, 2010)

Here is a patent for a similar device.

http://www.freepatentsonline.com/5100528.html

This seems much like the operation of this coolant sump oil skimmer.

http://www.coolantconsultants.com/Zebra%20GS4H300.jpg


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## 4metals (Jan 30, 2010)

These cells seem to have a respectable percentage of the silver crystal fall off and lay on the bottom, which also requires cleaning it out. I figured knocking the silver down into a funnel and then pulling it out with the screw would solve both issues at once. 

I think the cell in the patent is a monster, very big piece. Round cathode rotating above and below the solution, possible. Thanks


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## golddie (Jan 30, 2010)

I have never operated a silver cell.
However I did read a lot about it here in this forum and I was wondering why cant you use Junkman jim silver cell instead of a mobeius cell


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## 4metals (Jan 30, 2010)

It's a little different, he's producing 17,000 ounces of silver a week.


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## Palladium (Jan 31, 2010)

See if anything in this PDF gives you any help with ideas.

http://www.intec.com.au/uploaded_files/document_uploads/Cobre_2003_Intec_Ltd_Paper.pdf


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## goldsilverpro (Jan 31, 2010)

Many times, I've slept with Thum silver cells that had to be tended to every 4 hours. 

There are quite a few patents for continuous operation of silver cells. Don't have the numbers in front of me. Check the ones by Adalbert Prior. If I remember right, 1 or 2 of his involved continuous operation


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## 4metals (Jan 31, 2010)

GSP

And I've spent many a night babysitting a roaring incinerator, if it's your own refinery, it's what you do. This guy needed to produce 15000 ounces a week of fine silver and now that he sees the relatively slim margins, he wants to produce the same and pay for less. Looks like a serious investment in engineering some self emptying cells is in order.

The PDF from palladium has similarities to what I'm thinking but it again is for a huge cell. I'm thinking of a unit that will fit into a cell the size of a 55 gallon drum. a rotating cylindrical cathode and an octagonal buss configuration to surround the cathode with anodes. We've been fortunate that titanium anode baskets (1 per cell) have eliminated the melting of the anode stubs which saves in both accounting work and melt time. 

I need to find a good stainless welder to weld up some 316 stainless prototypes.


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## Anonymous (Feb 1, 2010)

4metals try RFQWORK.COM a website dedicated to small job shops, anything from machining, welding to water jet. You may get lucky and find someone close to you, eliminating shipping costs.

Post an add someone will reply with a quote.

Best Regards
G


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## Frankk12 (Feb 1, 2010)

As an example lets take Junkman jims cell.
For this project make the hight longer 
2 or 3 times longer or more
Where the bottom of the cell is make it so that it is like a tray and that it can slip in and out threw a narrow massage
The narrow hole has to be very tight and when it is full of silver it is pulled back and the silver will fall to the bottom 
This can be done with a stepper motor and it will cost about 200 dollars
I wonder if I can get a patent on this idea


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## Irons (Feb 1, 2010)

What about an expanded metal Cathode that would allow the Silver crystals to fall into a sump?


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## goldsilverpro (Feb 1, 2010)

I know you're concerned with modifying a Moebius cell, so what I'm saying is worthless to you.

With a standard 30 gallon Thum cell, however, I've always though that all one would need is a horizontal rod (rigid plastic), about an inch above the cathode, moving back and forth, between the basket and the cathode, the length of the cell. That should be fairly easy to set up. The plating industry sells the same type mechanism to move the parts back and forth - called cathode rod agitators. These are shown on page 736 of this large book download. I just wrote a blurb on this book, here:
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=54&t=6481&p=57415#p57415

The spacing between anode(s) and cathode is about 4.5". The crystal tends to pile up on the cathode sheet, right underneath the center of the anode basket, and, in about 4 hours, the peak of the pile will almost be high enough to reach and short out to the anode. The rod would tend to level this pile out so that, maybe, one could go about 12 hours (instead of 4), or more, between pushings. Instead of starting with the basket at one end, I would put it in the middle. In a Thum cell, there's no need to have automatic collection of the crystal, since it only takes about 10 minutes to do it manually.


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## 4metals (Feb 1, 2010)

GSP,

First off I don't think anything you've ever said to me is worthless. Knocking off the crystals with a cathode rocker is a good simple fix, a Bodine motor from a plating barrel and a few gears will make a nice drive motor for a continuous wiper of the existing plate cathodes. I'm not so sure that an expanded metal cathode would cause all of the crystal to sheet off without some help as Irons suggested, possible but I haven't experienced it. 

A relatively narrow conveyor like in Palladium's post would fit the bill to bring the dislodged crystals up and out of the cell.


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## goldsilverpro (Feb 1, 2010)

4metals,

I just re-read your 1st post. You're getting 92% cathode efficiency, which is excellent.

I guess my only questions are (1) how much space do you have below the bottoms of the anodes/cathodes and (2) how much space between the anodes and cathodes?

I don't think you could get much simpler than removing the crystal with a screw, from a funnel shaped catcher. Also, it wouldn't take up much space. The rocker type mechanism could surely be used to dislodge the crystals or to at least continually clear the crystal in the space between anode and cathode. I did just find an old reference which used wooden scrapers to continuously knock the crystal off - scroll down about 1/2 page.
http://books.google.com/books?id=1YJPAAAAMAAJ&pg=PA267&dq=moebius+silver+cell+scraper&lr=&as_brr=1&cd=23#v=onepage&q=moebius%20silver%20cell%20scraper&f=false


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## 4metals (Feb 1, 2010)

The tanks presently have about 6" beneath the cathode and the distance between the anodes and the cathode is 5" on each side. The anode bags are large enough so they allow all 5 anodes per side to fit in the same rectangular bag, they are held open and firm with a pvc frame. Because of the anode bag frame the anode bag to cathode is 4". Along the bottom of the bags is where the crystal growth comes sneaking into the bag if we wait too long to scrape. 

If we can come up with a screw design we'll probably use round tanks around 55 gallon size. The extra volume will give us more time before the copper levels grow to 8 oz/gal. That's the point where we take it out of service and cement the silver to start over. 

Gotta love those old reference books!


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## qst42know (Feb 1, 2010)

From the link to the book you posted GSP, could this be the answer Peter was looking for on growing the large silver crystals? Clipped from page 269.


http://books.google.com/books?id=1YJPAAAAMAAJ&pg=PA269&img=1&zoom=3&hl=en&sig=ACfU3U0zze7OuSWQi8fZbW5vWG86htolKA&ci=42%2C441%2C832%2C466&edge=0


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## goldsilverpro (Feb 1, 2010)

4metals,

How much copper do you start out with in the solution?

Since you are redesigning the tank, I guess the present dimensions are moot. I was just trying to think of ways to fit all this stuff into the existing tank. With only 6" of space at the bottom, I doubt if that's enough slope to collect the crystal at a single point in the funnel. Maybe, some nozzles all around to push the crystal to the center might work. Instead of something funnel shaped with the low spot at the center, maybe the collection tray should totally slope to one end, with the sides at the low point sloped to bring the crystal to the center, side-wise.

I have a small aquarium with gravel on the bottom. Once a week, I use a siphon to clean the crap from the gravel. The siphon is a plastic tube about 1.5" dia x 7" long, with a length of 3/8" tubing attached to it. Just from the small amount of vacuum produced by this, the large tube totally fills up with the gravel. What I'm wondering is: With air or vacuum, could you somehow suck (or, push) the crystal (and some solution) up in a tube, into a container with a screen on the bottom of it, and then drain the solution back into the tank and hold the crystal in the container? If you could do that, I think it might be simpler than a screw. It might be bad if a hose broke loose, however.

Just thinking.

Chris


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## 4metals (Feb 2, 2010)

GSP

I really appreciate your insight, you are right the bottom clearance isn't enough too do much down there. I have them make up the cells at 1/2 oz/gal as copper. Any less and the start up collecting is too difficult as the silver is too adherent to the cathode. 

Since I'm basically starting a new in Michigan, I also could switch to Thums. A slightly sloped "v" shaped cathode with a valley for a long screw to crank the crystal up and out. The tanks are shallow anyway so lift isn't high to get it out. Then I could sweep the crystal towards the screw with a cathode rocker motor setup on each side. Since we're having little or no anode end remelts by using titanium baskets, I wonder if the benefits of Thum vs Moebius really will be substantial. I can foresee benefits of both approaches. 

I really love this kind of work!


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## peter i (Feb 2, 2010)

qst42know said:


> From the link to the book you posted GSP, could this be the answer Peter was looking for on growing the large silver crystals? Clipped from page 269.
> 
> 
> http://books.google.com/books?id=1YJPAAAAMAAJ&pg=PA269&img=1&zoom=3&hl=en&sig=ACfU3U0zze7OuSWQi8fZbW5vWG86htolKA&ci=42%2C441%2C832%2C466&edge=0



It might be, but due to some quirk in the Danish copyright laws, I'm only allowed to see this:


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## goldsilverpro (Feb 2, 2010)

4metals,

In thinking about using the Thum cell, I have some questions. What is the average silver purity of the material being processed? What is the initial silver concentration makeup of the solution you're now using? 

I wonder if there is any sort of small inert pump that would lift the crystal (and some solution, of course) out? Along the lines of a very small trash pump or a very small dredge? I visualize the crystal slurry being pumped into a reservoir at the top and the solution draining back into the tank from an overflow pipe.

In considering a screw, do you think it could bind due to the hard crystal?

Most probably, this idea is too complicated. What if the tank were elevated and the bottom were sloped toward the center. No tray. Underneath the bottom center would be a double valve arrangement with a length of, say, 4" plastic pipe between the valves. The opening and closing of the valves would be programmed to cycle electrically (the complicated part). To start, both valves would be closed. The top valve would then open and the crystal would dump into the pipe. A vibrator could be mounted to the bottom of the tank to make all the crystal go into the pipe. The top valve would close. The capacity of the pipe would have to be large enough to make sure all the crystal went into it. Otherwise, some would catch in the valve and prevent it from completely closing (that could be a big problem). The bottom valve would then open and dump the silver into a container. A little distilled water would enter the pipe to flush all the crystal out. The bottom valve would close and the cycle would repeat.

A simpler version would be to use a smaller shorter pipe (say, 1" dia.) and have no valves. The crystals and solution would constantly dump into a reservoir, aided by the vibrator (or, two). The reservoir would have an overflow into another tank and the solution would be pumped from there back into the cell.

Just thinking out loud.

Chris


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## butcher (Feb 3, 2010)

heres a dumb suggestion, a deep well at one end, or both ends, motorized push scraper, on timer or sensor triggered, to push crystal buildup into well.


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## 4metals (Feb 6, 2010)

I've decided on a 2 stage approach. As this project requires a reconfiguration of the cells to have a self scraping cylindrical cathode, I figure the first thing to do is to get that process working. The silver can be collected in a polypropylene container placed beneath the cathode and emptied periodically. My biggest concern is the electrical contact on the rotating cathode, it will spin slowly but the guy we will probably have build it has concerns about the heat buildup at the contact point as we are running at 200 amps. 

The next phase would be to replace the collection container with a funnel shaped concentrator and a worm drive to continuously pump it up. But that's after the rotating scraper re-design.

By making the cells deep enough the container can accumulate over a longer period and allow this to work 24 hours a day but be staffed for only 8. 

While awaiting the prototype rotating cell to be made we've installed timers to shut the cells down after a second shift when the cells are last scraped, and start them up 5 hours before the first shift arrives so the first thing they do is harvest the overnight accumulations. So with a timer we were able to only lose about 15% of production capacity while saving 33% of the labor.


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## Anonymous (Feb 6, 2010)

4metals said:


> , it will spin slowly but the guy we will probably have build it has concerns about the heat buildup at the contact point as we are running at 200 amps.
> 
> .



Heat should not be too great, as 200 amp * .5v = 100 watts * 3.4ish btu/hr = 340 btu/hr this should be fairly easy to heat sink away.

Jim


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## qst42know (Feb 6, 2010)

Will we be able to see some photos of what you've come up with when it's finished? 

Please! :mrgreen:


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## 4metals (Feb 6, 2010)

I don't know if that will be possible as I'm being paid to develop this for a refiner, it is his property and his to do with as he pleases. An unfortunate side effect of consulting, covered somewhere in the small print.


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## goldsilverpro (Feb 6, 2010)

4metals,

200A requires a conductor (if copper) of about 0.2 sq in cross sectional area - 1000A/sq.in, to prevent heating.

You should definitely look into those electrolytic units used for plating silver from photo fixer. They're like ready made for what I visualize you need. All of your engineering problems have already been worked out for you. Every one I've ever seen uses rotating cathodes in order to constantly renew the cathode film. The silver thiosulfate complex ion is negative and is repelled by the cathode. A rotating cathode solves the problem. I can't remember the RPM but they don't turn very fast - I'm guessing 10-12 RPM, more or less. 

These SS cathodes are usually about 6"-8" dia. x 8"-12", or more, long in the larger units, although I have seen a lot of different sized cathodes. Some have 3 or more cathode units in one tank and, if I remember right, all 3 ran off the same gear mechanism. The silver can get 1/4" thick and the cathodes get quite heavy (28# on an 8x12 cathode drum). The silver is brittle and is removed in chunks with a hammer. For these reasons, everything is pretty heavy duty. The cathodes run vertically. They've been using these units for a long time and all the bugs have been designed out of them. They are workhorse machines. With x-rays going digital, I would think there would be a lot of used units available. Most every hospital of any size, has (or, had) one, most probably stored somewhere in a warehouse.


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## aflacglobal (Feb 6, 2010)

Link Link !


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## qst42know (Feb 6, 2010)

4metals said:


> I don't know if that will be possible as I'm being paid to develop this for a refiner, it is his property and his to do with as he pleases. An unfortunate side effect of consulting, covered somewhere in the small print.



Sorry I asked. I hadn't considered that.


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## Anonymous (Feb 6, 2010)

goldsilverpro said:


> 4metals,
> 
> 200A requires a conductor (if copper) of about 0.2 sq in cross sectional area - 1000A/sq.in, to prevent heating.
> 
> .



Hi Chris,
Conductor sizing is by amperage, I just did not think with the actual amount of power being applied and with the amount of heat that would sink into the electrolyte, that 340 or so btu/hr would cause heat at the junction, exspecially if a carbon graphite contact was used. I was also addressing the contact point, 3/0 copper would handle 200 amp or if you were using taps you can size even smaller. The main concern on conductor sizing is voltage drop, which causes 2 problems power wasted as heat and the resultant conductor heating causing problems with the insulation.

But all in all my point was the 340 btu/hr.

Jim


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## dick b (Feb 6, 2010)

You might be able to use a rotating ground connector for a welder as your connection point. I believe that they can carry 60v at about 200A.

http://www.thermadyne.com/IM_Uploads/DocLib_947_50_64-2103.pdf

dickb


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## 4metals (Feb 6, 2010)

Dick

Thanks, looks like a nice way to connect.


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## dick b (Feb 7, 2010)

Your welcome.

I've been following this thread and think that a rotating cathode is the way to go. 
If it is fitted with 2 scrapers the wipe each side into a small v shaped sloped tray that uses a small wash stream to carry the silver over the side if the tank and into a settling tank. Then the fluid can be recirculated back to the trays. 
That seems like a lot simpler machine to build than a mechanical scraper to clean the bottom of the tank.
Then the problem becomes, how do you change annodes with the axle running down the top of the tank?

dickb


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## 4metals (Feb 7, 2010)

Dick

My thoughts were to use a cylindrical cathode so all of the falling crystal will collect in a circular area. Then a funnel will concentrate the fallen silver to the center of the funnel where a worm drive screw angled at 45 to 60 degrees along the side of the funnel (depending on the design limits, depth and diameter) to lift the crystal over the side of the cell. 

If I understand your idea correctly you will let fluid flow carry the crystal out a hole below solution level and use a pump to return the solution to the cell. Sort of like bailing a boat in reverse. Whenever I design things I always think of worst case scenarios because they can and will happen sooner or later. A hole beneath the operating level of the solution needs to be closed if the power goes off or if the pump clogs. In my day I've come in to many floods caused by those once in a while snafu's. 

I'm not totally sold on my own ideas yet, there have been some excellent suggestions as to the rotating cathode contacts. I'm quite sure one of those electrical contact devices will make it into the final design. As far as the screw goes, I'm banking on the silver crystal sliding up in front of the screw, but realistically some may get burnished on to the cylinder eventually. One fix for that is to remove the lift unit from the cell when the cell goes down for solution change-out and soak it in 50% nitric to clean up the stainless pipe and recover the silver. I can use a slow speed high torque motor which has a slip gear if the resistance is too high so it will stop spinning and not burn out the motor. 

Thanks again for the input.


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## qst42know (Feb 7, 2010)

How abrasive are silver crystals?

Would a PVC lift tube be sufficient?

Something like this.

http://www.brockmfg.com/uploads/pdf/BR_1946_0108BrockFlex_AugerEM.pdf

I don't know if the screw is available in stainless.


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## dick b (Feb 7, 2010)

A picture is worth 10,000 words. To simplify imagine a disk brake with brake pads rubbing both sides. 
A SS barrel cut in half top to bottom as the tank. 2 bearings mounted in the center with an axle running down the center above the top of the tank. On the axle 3 round disks about 1/2" thick and of a dia that will not touch the outside if the tank. Disks spaced in fron the tank ends and at the center of the shaft. Then 2 - 1/2 disks as annodes spaced half way between the cathodes with both the cathodes and annodes insulated from each other.
The Cathode disks rotate at 1 rpm with about 33% of the lower surface wetted in the tank and rotating clockwise. Annodes and fixed. They enter the fluid at about 3:30 and exit at about 8:30 on a clock face.
At about 3:00 a U shapped trough with 2 spring scrappers wipe both sides the disk and the crystals slide down into the trough. It is made from angle iron (X6) with the v facing up and the wipers on the top edge of the edge closest to the disk.
The ends near the axle are capped and have a fitting to plumb the wash tank fluid into the trough (X6). The flow carries the crystals over the top edge of the cell and into a manifold from all three cathodes which carries the crystals to a settling tank seperate from the cell. After the fluid settles the crystals in this tank, a small pump returns the wash fluid back the the scraper troughs. Repeat.
All of this mechanism would have to lift off the cell for cleaning and replacing annodes.
Does this help paint a picture in your mind of what I am trying to express?
Dickb


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## 4metals (Feb 7, 2010)

Dick

That's not unlike the pictures posted early on in this thread. My concern is scraping from the top leaves the crystals that fall down from the cathode lying on the bottom. Of the 5 cells this guy has running it never fails that at any given time one of them is dropping crystal to the bottom between scrapings. Now with continuous scraping this may not be an issue and in some cells it is never an issue now, but it does happen often enough and if it continues to happen, crystals on the bottom will remain unharvested, or at least not harvested easily.


Quest

Those screw augers are very neat. The hollow center will allow excessive amounts of crystal to fall back through and may prevent the crushing I am concerned about. So screws like that could be PVC or polypropylene. Plus a plastic screw and funnel has an advantage over stainless in that if it does inadvertently touch a buss bar it won't be conductive.


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## qst42know (Feb 7, 2010)

I used to work on a machining center that used a coiled auger. Even if you forgot to turn it on right away and it got completely buried it caught up very quickly.


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## dick b (Feb 7, 2010)

To clarify, the top of the scrapers are resting against the disk in the horizontal position and as the disk turns, the crystals are lifted off the surface of the disk and slide down the outside surface of the scraper and into the v-trough. Just as a shovel is pushed along the sidewalk and the dirt goes into the bowl of the shovel. Most of the scrapings should end up in the trough and not in the cell tank. vIv The 2 v's are the troughs and the I is the cathode.
dickb


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## 4metals (Nov 9, 2010)

Just to update this thread, the Archemedes screw idea looked promising but the crystals chewed up the screw, it worked out that if the screw was tight to the wall of the cylinder evacuating the cell it pumped solution out which had to be returned to the cell. Increasing the clearance between the screw and the cylinder wall (by replacing the auger with one of a slightly smaller OD) allowed drainage but also allowed crystals to wedge under the screw and chew up the equipment. Plus the screws are expensive. 

While this development process was going on I had a 4 foot long Thum cell running. The anode basket was about 18" long and was slid from one end to the other after 4 hours so the cell only had to be scraped once a day for an 8 hour shift. This got me thinking and what we ended up with is a cell that is 12 feet long. The anode basket travels over the cells length at the rate of 6 inches an hour. At the end of 24 hours the cathode, which covered the entire bottom of the cell looks like silver astro turf. Before the crystals grow long enough to be a problem the anode basket is further down the tank so the rapid growth area moves as well. Bottom line, full power production with one scraping every 24 hours. 

First thing every morning the cell is scraped and the anode basket is restocked with bars and slid back to the starting point for another 24 hours of continuous production. 

Not exactly self scraping but the main purpose was to allow continuous (24 hour) operation without 3 shifts of labor. 

I still have some analytical work to do, I'm not sure the cell will produce the same purity silver as the copper levels grow because of the configuration there are some low current density areas which may behave erratically as copper concentration grows. After 1 week of continuous operation (and only 5 scrapings) the silver was still looking very nice with no detectable copper (via AA). 

What I like is this is a simple approach to the problem and so far.....so good.


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## HAuCl4 (Nov 10, 2010)

In the spirit of simplicity: If you put a PVC tube with 2 valves at the bottom of your collecting funnel, you do not need any archimedes screw or other complex contraptions. Leave top valve open, silver fills the tube between valves (make this tube wide enough and long enough that the required volume of silver fits in easily during the time that there's nobody to attend the cells). Then when people arrive, close top valve, open bottom valve, silver falls out. Close bottom valve, open top valve, and replenish liquid. Very simple. I can draw a diagram later.

Use normal scrapers like those depicted in old books and a collecting funnel steep enough that the cystals slide into the PVC tube. A little extra volume of electrolite is the only downside to this. 8)

You can even have 1 person on call to come and collect the crystals if you put sensors and an alarm on the collecting tube. :shock: 

If one times it all well and have the matching anode sizes, I guess one could get away with just 1 shift or less. Come once a day to cast anodes, replace them in the cells and pull, wash and melt the silver crystals. Maybe even have sensors and alarms for "emergencies" or automatic shutdowns to send you an instant message. As simple or as complicated as one wants really.

Never done it, but have seen the ideas above implemented in other or related industrial setups. Even live video surveillance over the internet can be cheaply implemented nowadays.


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## HAuCl4 (Nov 10, 2010)

The titanium basket idea looks very, very good. It elliminates remeltings and simplifies things. 8)

I guess one could feed shot metal to this titanium basket too?.


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## 4metals (Nov 10, 2010)

I considered the funnel idea, there are 2 issues that have to be addressed. First the falling silver needles do not pack tightly without some help. That would mean the storage portion would have to be pretty big to accommodate approximately 20 kilos of needles between emptying. 

Second the top valve would tend to clog up with silver needles that seem to get into the smallest grooves and wear at the seat. A leaky top valve could ruin your day and in the position where it needs to be relative to the cell changing out that valve would require breaking down the cell.

The Thum cell with a moving anode basket,to me, represents a simple modification to a proven technology. The self scraping required all sorts of re-engineering and was costly. Bottom line is running 24 hours at full production needing only 1 scraping a day was the real goal, I just didn't see it that way in the beginning.


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## HAuCl4 (Nov 10, 2010)

On a second reading, your Thum cell with sliding basket is simpler. 

Perhaps it takes more space, but that's all. No valves, no scrapers, little to breakdown and go wrong. If the fineness is there, which it seems to be, there's little else to improve upon. Maybe an automatic electrolyte cleaner/replenisher?. This could be something like: Every 24 hours replace 5% of the electrolyte with clean electrolyte. Or every week replace X%.


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## 4metals (Nov 12, 2010)

I've been tinkering with removing electrolyte with a dosing pump and running it into a constantly aerated cementation tank to drop out the silver and the electrolyte that passes out of the tank goes to waste treatment. The size of the cementation tank assures enough retention time to recover all of the values. 

The electrolyte is replenished with clean 6 ounce per gallon silver nitrate solution using a simple level float on a sealed reservoir. 

By adjusting the flow rate of the dosing pump I can effectively keep the copper level from building too high.


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## HAuCl4 (Nov 12, 2010)

Interesting. When I had my lab and small refinery, I had a small cell just to make silver for the assays. When the electrolyte color reached a certain blue tint (100% eyeballed), I replaced 25% of the electrolyte with nitric acid. Never had any problems, but I can't say that I assayed the silver accurately either. The gold assays were always near perfection.


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## 4metals (Nov 12, 2010)

The working cells have to be titrated (I prefer daily in a production cell) to determine the silver content. When the dosing pump flow rate is balanced well, the cell can maintain an optimum silver level in solution which isn't driven down by copper in solution. If the copper is not climbing and the silver is falling (determined by analysis) it's time for some more nitric acid.


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## HAuCl4 (Nov 12, 2010)

Looking back, I now think it was a miracle that I got away with so many technical shortcuts.


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## amesametrita (Oct 22, 2012)

4metals said:


> We've been fortunate that titanium anode baskets (1 per cell) have eliminated the melting of the anode stubs which saves in both accounting work and melt time.



Dear 4metals,

Could you provide more info about titanium baskets?
Mesh?
How to feed high amperage?
Electrical conductivity is only 3% of copper...

Best regards!


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## NobleMetalWorks (Oct 22, 2012)

I am actually working out a way to auto scrape a Moebius cell.

I have two actuators, what I was thinking about doing was setting them up on timers, one connected to the cathode, and one that would move a tray underneath it once it was lifted out of the cell. So the cathode actuator would, when triggered, pull the cathode up and stop. Then the second actuator would slide a drawer under the cathode. Then the timer would trigger the cathode actuator to rise further, through a mounted scrapper. Then the entire process would work in reverse to put the cathode back into the cell.

I have a power supply that I can program for certain functions, but nothing as complex as what I am trying to do. At a certain point the electrical current needs to be reversed so the actuator moves in the other direction. I need something capable of that.

Any suggestions?

Scott


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## etack (Oct 22, 2012)

A simple way would to use two timing devices one wired up the other wired for down.

Eric


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## 4metals (Oct 23, 2012)

> Could you provide more info about titanium baskets?
> Mesh?
> How to feed high amperage?



You are correct that the conductivity of titanium is pretty bad but I have found that hanging one in a properly run cell allows the anode stumps to dissolve. I do not change the anode area amps per square foot number to accommodate the stubs, and I only add one per cell. The anode basket is bagged and handled as any other basket. 

You can get them here http://www.anodebaskets.net/index.html

____________________________________________________-

As far as designing a cell to auto scrape by lifting the cathode out and scraping it into a tray there is more to that than you think. The main contaminant in silver from a cell is usually copper. If you remove the crystals from the cell dry and do not rinse them well, the blue solution contaminated with copper will dry on the crystals and lower your purity. So you not only have to lift, place the pan, and replace the cathode, you also have to rinse the crystals and dry them. 

Most automated Moebius cells scrape constantly and let the silver crystals collect in a hopper while remaining in the electrolyte but not connected to the electrical circuit. Once a day the silver crystals are emptied by opening a valve and allowing them to drop into a chamber, then the top valve is closed and the bottom drain valve drops the silver crystals and some electrolyte into a filter. The electrolyte is pumped back into the system and the silver is rinsed well and either dried or melted.


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## NobleMetalWorks (Oct 23, 2012)

I never even thought about keeping it in solution, but that makes sense...

So if I used one actuator to periodically move the cathode left to right/back and forth against a scrapper that is mounted inside the tank so that it dropped into a basket under the cathode, would that be another solution? Sounds more KISS to me in any case.

I have these electronic actuators that I would like to incorporate into my design if at all possible.

Scott


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## glondor (Oct 23, 2012)

Just a question....Could you use an air driven vibrator motor to "shake em down" .

The reason I ask, When I was an excavation contractor, many dump trucks had a small air driven motor mounted to the top front of the dump box. when they dumped, once at the top of the box lift they would give the motor a shot of air and everything stuck in the box would come tumbling out. They would shake like heck for a few seconds.

Figured it might shake the silver crystal flat in the cell if it was set to run a few seconds every hour or so. Just a thought. Might need something a little smaller tho... these will shake a tri axle truck.

http://www.chicagovibrator.com/IndustrialVibratorTypes/TruckVibrators/tabid/272/Default.aspx

http://www.grainger.com/Grainger/BUYERS-PRODUCTS-Dump-Body-Vibrator-6ZAL6

What do you think?


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## 4metals (Oct 23, 2012)

The easiest way to scrape the cells is to use what electroplaters call a cathode rocker to pass a rigid "scraper" back and forth constantly knocking the crystal down into a sloped hopper and then drain them off in something like this;


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## Lou (Oct 23, 2012)

I have been told that the large producers extract the silver with a conveyer and have rinse water run down it and over the crystals in countercurrent fashion and then spin dry with a hydroextractor.

We use a similar set up to the job 4metals posted.

Depending on the feed quality, we do not empty silver at all. If it is a high purity material, we just knock it off the cathode in sheets crush, grind, rinse, and then it goes as AgNO3.


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## goldsilverpro (Oct 23, 2012)

One inexpensive, slow-moving, reciprocating cathode rod agitator, commonly used in plating tanks, could easily be rigged to clear the crystal between multiple sets of electrodes in a Moebius cell.


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## etack (Oct 23, 2012)

You could use a rotating basket with some breaker bars of the side to break the crystals.

the connection would be the hard part but I think this might work http://www.mercotac.com/index.html. They make a SS version.


Eric


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## Smack (Oct 24, 2012)

What about vibration to clean the cathode? Maybe ultrasonic vibration could do the trick. Just trying to help with ideas.


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## goldsilverpro (Oct 24, 2012)

etack said:


> You could use a rotating basket with some breaker bars of the side to break the crystals.
> 
> the connection would be the hard part but I think this might work http://www.mercotac.com/index.html. They make a SS version.
> 
> ...


Pretty neat slip rings. I can see several applications for those.


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## IgorGreece (Jan 4, 2013)

http://www.google.com/patents/US6503385


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## mikeinkaty (Jan 6, 2013)

What would happen if you switched the polarity momentarily? Would it blow the silver off the cathode?


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