Self scraping silver cells

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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?.
 
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.
 
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%.
 
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.
 
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.
 
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.
 
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.
Click to expand...

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!
 
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
 
Could you provide more info about titanium baskets?
Mesh?
How to feed high amperage?
Click to expand...

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.
 
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
 
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?
 
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;

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


Eric
Click to expand...
Pretty neat slip rings. I can see several applications for those.
 

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