Designing a DIY silver cell

[snoman701]

I am more interested in a cell like this for purposes of breakdown. I get a lot of low grade silver material. The breakdown cell is an effective way of getting it to a much more pure state without the release of as much NOx

 

[4metals]

I used a piece of stainless steel expanded metal as the cathode. The "scrape" in this case need not actually scrape it, just knock off the needles. They then fall to the bottom of the tank. In my case, I wasn't even scraping, just tap tap with a hard metal object.

That sounds like something worthy of consideration. The expanded metal for sure has enough openings to allow the majority of the needles slip through. A good hard mechanical tap every few minutes may clear the screen effectively and it can fall to a sloped ledge to concentrate the scraped needles along the front of cell to be collected with a scoop. There is surely a maximum size that can be cleared with the tapping but finding it may be a matter of trial and error.

 

[netgeek3]

Selling the silver, at volume, isn't a huge problem for us as I have two industrial buyers who are quite interested in buying more than we can provide right now. For us, a good bit of the concern is with the power, but really, once converting to DC, the need for 300A or so is very small compared to typical AC loads for our pulverizers and such. We are working to get our copper line up right now and it is a bit of a power hog, so that certainly has me thinking about the load for this setup. We currently have an 1800A service, but I can expand up to a total of 6MW without having to put together an investment plan for the utility. Cost effectiveness and labor requirements are my number one concern. I love the idea of running 24h/day with just two guys.

 

[markscomp]

It's minimal cost for silver. Copper the cost of electricity starts to add up.

It's a lot of current, but a low voltage, so the actual power utilization is small.

go thru numbers based on your amperage in theory and or all costs (theoretical costs include some labor , time to work deals a little, cost of product, electrolites, equpt costs versus returns ) with elect bills and returns - that would help - all would understand that once equipt is in place that the initial cost becomes a repair / replacement cost situation or just maintenance costing

 

[snoman701]

That sounds like something worthy of consideration. The expanded metal for sure has enough openings to allow the majority of the needles slip through. A good hard mechanical tap every few minutes may clear the screen effectively and it can fall to a sloped ledge to concentrate the scraped needles along the front of cell to be collected with a scoop. There is surely a maximum size that can be cleared with the tapping but finding it may be a matter of trial and error.

Once you know that the crystal can go somewhere, a mechanical scraper like the one you posted will work as well. You don't have to strip it clean, you just have to get it clean enough to make it 12 hours until there's a human to look at it again.

 

[Shark]

That sounds like something worthy of consideration. The expanded metal for sure has enough openings to allow the majority of the needles slip through. A good hard mechanical tap every few minutes may clear the screen effectively and it can fall to a sloped ledge to concentrate the scraped needles along the front of cell to be collected with a scoop. There is surely a maximum size that can be cleared with the tapping but finding it may be a matter of trial and error.

It does sound interesting. The cathode scraper could work, a small single hammer type hammer mill could be triggered at intervals to work pretty easy as well. A motor with a plastic pulley and a bar of heavier plastic on a timer to rotate every so often and tap the edge of the cathode. Maybe a way to slow the motor down. Lots of ways could be used to scrape the cathode to some extent.

 

[4metals]

You don't have to strip it clean, you just have to get it clean enough to make it 12 hours until there's a human to look at it again.

Once the crystals are scraped from a cathode in a thum cell you have about 4 hours before they grow enough to short out the circuit. But if they fall through a cathode of expanded metal they can be collected in a deeper tank. Some cells can run 3 days without scooping out the crystals that have been dislodged from the cathode.

 

[snoman701]

Once the crystals are scraped from a cathode in a thum cell you have about 4 hours before they grow enough to short out the circuit. But if they fall through a cathode of expanded metal they can be collected in a deeper tank. Some cells can run 3 days without scooping out the crystals that have been dislodged from the cathode.

Right, so if you have a breaker bar that runs on even a 15 minute cycle you should be fine. A timer, solenoid valve and pneumatic cylinder would do this just fine. It wouldn't hurt to do the motor like you posted, but I'd imagine a stainless pneumatic cylinder off ebay has nearly an infinite lifespan running once every 15 minutes. Most refineries will have compressed air to run their filter press.

 

[Lou]

I always pushed the crystal to one end of the Thum cell, then scooped it. They are nice for the butts out of the Moebius.

For Thum cells I have seen the anode box pulled up and down UHMWPE rails on the Thum cell using two winches that slowly pull it back and forth until a contactor is touched on the anode box and the rail opposite the bus bar on the other end. The effect is a continuous uniform crystal carpet. Those cells are “pushed” every 12 hours into a “goal box” where the crystal is dumped out of it 40-50 lbs at a time. The goal box had a sliding piece of stainless that could effectively dam it such that you could dump the crystal without much loss of electrolyte. The amount of fine crystal is sufficient that a stainless scraper is used and it is pushed not scraped.

 

[snoman701]

I always pushed the crystal to one end of the Thum cell, then scooped it. They are nice for the butts out of the Moebius.

For Thum cells I have seen the anode box pulled up and down UHMWPE rails on the Thum cell using two winches that slowly pull it back and forth until a contactor is touched on the anode box and the rail opposite the bus bar on the other end. The effect is a continuous uniform crystal carpet. Those cells are “pushed” every 12 hours into a “goal box” where the crystal is dumped out of it 40-50 lbs at a time. The goal box had a sliding piece of stainless that could effectively dam it such that you could dump the crystal without much loss of electrolyte. The amount of fine crystal is sufficient that a stainless scraper is used and it is pushed not scraped.

Wonder why they dam it as opposed to pushing it into a backet and draining upon lifting.

 

[Shark]

Crystal size most likely would be very small.

 

[4metals]

This is just a crude design concept put to paper because if the expanded metal cathode can be made to work, it can be made into a system that eliminates the 4 hour scrapings and simplifies the sucking out of anode slimes in a moebius cell.

The expanded mesh needs to sit on a lip and will likely have to be framed in PVC to give it rigidity. Also the gauge and the spacing in the expanded metal needs to be experimented with to determine the best cathode to space ratio to maximize silver needle drops when thumped. When the silver drops it hits the angled sheet and slides down into the collection trough. This can be assisted with a pump blowing electrolyte from the upper right of the slope towards the bottom.

The silver needles can be scooped out daily or after a weekend because they are not (hopefully) accumulating on the expanded metal cathode.

This design uses an off the shelf PVC tank and the sectioned off space needs to have sheet PVC welded in to make it watertight. The only other welding would be the support ledge for the expanded metal cathode to sit on.

The mechanism for thumping the cathode to break off the siver and allow it to fall through would likely sit on the right end and mechanically lift a weighted rod to rise a few inches and drop onto the cathode, only to be lifted again and drop again continuously. We need to discuss this mechanism more.

Finally, the typical anode basket, which is not detailed here other than a box, could stand some improvement. When insolubles are generated in the anode basket of a Moebius cell, they fall to the bottom where they can be vacuumed out. (easier said than done) On a thum cell there is no place to fall and the mud tends to accumulate and in extreme cases cover the anodes in mud. I am thinking of making a basket to contain the anode bag. In that basket will sit the anode basket which has the anodes spaced 3/4" above the bottom on the support rods. This space will allow the anode slimes to fall. And they will collect in the anode bag below. Routine anode additions will stir up any slimes sitting on the existing anodes and it will settle into the bag as well. Time and experience will determine an effective length of time between anode bag changes and it will vary with the feedstock. But changing the bad is simple, lift out the anode basket, lift and drain the anode bag by allowing the solution to filter through the bag back into the tank, roll up the anode bag (did I mention with long rubber gloves!) and incinerate it to process the slimes.

This design can serve as a basic starting point, let the discussion begin.

 

[Shark]

Yamamoto cathode rocker or similar item. I won’t be home until late tonight or sometime tomorrow and and cannot figure out how to copy links from this phone yet.

 

[4metals]

Those just push and retract. As per Snowman I think the expanded metal needs a firm hit. I envision lifting a weighted rod and dropping it. I have an idea for a mechanism that may work but my mechanical sketching skills are truly lacking.

 

[Shark]

They make one that operates both ways. It is tunable to do a smooth up and down or a smooth up with a sudden drop. They also have a speed setting from 0 to 25 times per minutes. I just cannot get the link to work from my phone, pretty sure it’s operator error.

 

[Shark]

My sketching would be better if my two year old nephew drew it.

 

[Shark]

Sorry for being gone so long. Here is a video that show both the impact type rocker and a smooth type.

Rocker video

 

[Shark]

Not sure if these would handle the weight but would be easy to adapt to to the impact type rocker.

https://flexcoat.com/shop/rod-building-equipment/motors/gear-motor
Edit for spelling.

 

[Shark]

Motor and gear box for a windshield wiper.

 

[4metals]

I think an impactor can be easily made from a slow spinning (1rpm) disc about 6” in diameter with a slit running between a pair of 1/2” holes on opposite sides of the edge connected by a 3/8” slot spanning the diameter. The slow rotating disc has a heavy metal rod with a PVC pipe covering it and a rod sticking out close to the end about 1”. When the disc is spinning the shaft will rise up because the 1/2” hole won’t let it slide freely but is loose enough not to grab it. When it is vertical the weighted pipe will fall the length of the slot and hit the cathode. With the right length it will repeat lifting and dropping continuously.

The rod sticking through the slot needs to have a washer and a locknut so it doesn’t fall out of the slot or hole but loose enough to drop freely. On the back of the disc a piece of metal shaped like a door handle installed across the slot will allow the nut and washer to slide under freely and centered on the back of the handle is a connection to the drive motor. I use drive motors similar to what Shark posted for a hydroponics drive wheel and have learned, after many failures, to get the model with metal drive gears.