Best Ball Mill Media for Plated Silver Removal

[Fever]

Hi Guys!

It's been a while since I've participated on the forum, but I have been gleaning knowledge in the shadows as a lurker! I have a question for those who may have input regarding the best abrasive media option for grinding Silver plated metals in my ball grinder. This is my plan: (1) Cut my Silver plated scrap into workable sizes that will fit in my 35Gal cylinder. (2) Add the best abrasive media in the best sizes (I figure a variety of small-medium to get in all the nooks and crannies). (3) Grind the materials until all of the plated Silver is abraded as a powder, and collect. (4) Use the Nitric technique to dissolve the silver/Copper values, and precipitate the Silver using Copper. (5) Recover the dissolved Copper from solution and fire into buttons (need advice here too). (6) Collect the Silver crystals, rinse thoroughly, and fire into buttons. (7) Re-activate the Nitric solution for continued use, or dispose of accordingly.

I am thinking that non-metallic media would work best, as there would be no metal contamination outside of the abraded target metals in the cylinder. I am leaning toward Zirconium-based abrasives, as they are extremely durable.

Anyone have some advice in this category? I know the recoveries from Plated materials is low, but I have access to a variety of cheap plated scrap.

Thanks very much in advance for any help you can give!

-Fever

 

[rusty]

Zirconium good choice, rather than spend time cutting your scrap into little pieces why not buy or make a sandblasting cabinet and remove the silver plate. When blasting your media will cut faster by angling the nozzle to the work.

Direct hits are much slower to remove rust and paint so I would expect the same results removing silver.

 

[Fever]

Thanks for the input Rusty. I thought about sandblast, but since I already have the ball mill, and plenty of time, I thought I'd go that route. I also think the powders will be easier to collect by just dumping out my cylinder, which is tapered, into a vessel for later use. I would think the sandblast method would encourage lots of particle dispersion all about the machine, and may prove difficult to remove entirely. But, both methods should produce similar results.

I agree on the Zirconium. It's not cheap, but I believe the initial costs will be offset by the abrasive's longevity.

Thanks,

Fever

 

[nickvc]

This sounds very similar to the barrelling process used to finish jewellery mechanically.
The idea is to use different forms of media in the barrels to remove casting marks and blemishes down to a very high finish when a quick polish will finish the process. The process works well but the metallics are in very small particles and are usually recovered from settlement tanks along with big volumes of the media that's broken down during use. You might avoid that problem using zirconium but will I'm sure have some of the media grind down into your silver copper powders. If I remember correctly ceramic cones and coconut shell were some of the media used. Don't know if this helps but a quick google search might give you some further ideas on media and times taken. A point to remember is that though you have plenty of time your power isn't free to run your mill so do your maths before running for weeks and see if it really is worth it.

 

[Fever]

Thanks for your advice nikvc,

As far as the time it will take to break down the Silver plating, I do not foresee this taking very long at all. Most Silver plate is quite sparse in thickness. But you are right, the process will consume electricity- a deduction I am willing to suffer through to obtain my powders =)

 

[Barren Realms 007]

This sounds very similar to the barrelling process used to finish jewellery mechanically.
The idea is to use different forms of media in the barrels to remove casting marks and blemishes down to a very high finish when a quick polish will finish the process. The process works well but the metallics are in very small particles and are usually recovered from settlement tanks along with big volumes of the media that's broken down during use. You might avoid that problem using zirconium but will I'm sure have some of the media grind down into your silver copper powders. If I remember correctly ceramic cones and coconut shell were some of the media used. Don't know if this helps but a quick google search might give you some further ideas on media and times taken. A point to remember is that though you have plenty of time your power isn't free to run your mill so do your maths before running for weeks and see if it really is worth it.

Corn cob's for shure and I think pecan shells have also been used.

 

[4metals]

When I dealt with jewelers wastes a common material was walnut shells, they did a great job of polishing and obviously removed metal because they were payable as sweeps after they were incinerated. Extracting the values from the sweeps chemically will be an issue. Probably not profitable with silver at $30.

I agree with Rusty, sand blast, possibly with glass beads, and separate the media from the values with acid.

 

[Fever]

All valid and acknowledged points, thanks guys.

Moving forward with my original formula. Here's a snapshot of the Zirconium Oxide media I will be using. I'm going to use the small 2mm spheres, which should gently grind the coatings without smashing the living hell out of the base metals.

 

[goldsilverpro]

I tried this once with silicon carbide abrasive and all it did was get the parts dirty. I do think that, with the right media, it could work.

 

[Ian_B]

I've been using green plastic triangles with silica for cleaning and polishing sterling silver after casting in a rotary tumbler
here is the exact media from the same site purchased from
http://www.contenti.com/products/tumbling/180-623.html

the tumbler is here http://www.contenti.com/products/tumbling/180-525.html

with the media about 1/2 filling drum, about 1/4 full of water maybe 1 tbsp of dish soap and about 400grams of sterling and it polishes it up quite nice after a couple hours

take the drum off let it settle over night and it leaves a nice cake of silver powder/media dust at the bottom

I know it would be different with the plated items but just explaining my experiences with a tumbler with liquid not sure if that would be better then just media on its own allowing the silver plate layer become dust and get all over the place might be easier to collect the silver if it is in water because it would collect wherever the lowest spot is

good luck and keep us posted

 

[goldsilverpro]

You also must consider the separation of the removed silver from the media, which could be a problem. I would probably first try a media that is inert to nitric acid. That way, the Ag/Cu could be leached from the media. Your zirconium oxide might fit the bill.

 

[Fever]

Thanks for the info guys!

GSP- What size/shape were the Silicon abrasives you used? How long did you tumble them to get the "dirty" result? I assume by that term you mean that the plating was not removed?

Ian- Yes, water always encourages the heavies to settle at the lowest points. Yet I think the way I am proposing this procedure (dry, no grit, just Zirconium Oxide balls and the Silver plated materials), it should result in an easily collectible dry powder comprised of Silver and small amounts of whatever base metals were beaten away from the original material. This mixture will dissolve readily in Nitric, after which the values can be precipitated.

I will keep everyone posted!

-Fever

 

[Fever]

GSP- Yes, my thoughts exactly. Zirconium Oxide is incredibly strong stuff, totally non-porous, and should not break down in the least under these circumstances. That is precisely why I chose this particular abrasive. If it all goes according to plan, the powdered remains will be almost exclusively metal.

 

[goldsilverpro]

GSP- What size/shape were the Silicon abrasives you used? How long did you tumble them to get the "dirty" result? I assume by that term you mean that the plating was not removed?

I don't remember the grit size. I ran it several hours. The SiC was probably powder and thus too small. Silicon carbide is black and it coated the parts. That's what I meant by "dirty". I did it on gold plated pins and the gold was not removed.

Were it me, I would try to find a media that was sharp, irregular (to get in all the cracks and crevices), hard, heavy, and impervious to nitric. Size would be important. Also, I would guess that the media/parts ratio would be quite high. I would think a vibratory finisher would work better than a tumbler.

 

[Barren Realms 007]

When I dealt with jewelers wastes a common material was walnut shells, they did a great job of polishing and obviously removed metal because they were payable as sweeps after they were incinerated. Extracting the values from the sweeps chemically will be an issue. Probably not profitable with silver at $30.

I agree with Rusty, sand blast, possibly with glass beads, and separate the media from the values with acid.

That's what it was walnut shells, not pecan shells.

 

[qst42know]

Silicon carbide is hard and sharp but is friable. It readily fractures exposing fresh sharp edges. It's tendency to to embed in soft metals makes it useful for cutting the hardest metals with brass or copper tools.

Ceramic deburring media comes in a variety of shapes that should prove useful.

http://www.kramerindustriesonline.com/tumbling-media/ceramic-media.htm

Finding the right grade is going to be the key. A polish grade will be to slow while an aggressive cut grade sheds worn abrasive that may embed in soft metals.

 

[AuMINIMayhem]

I tried this once with silicon carbide abrasive and all it did was get the parts dirty. I do think that, with the right media, it could work.

admittedly... I did the same in a vibratory deburring machine. what a mess! :roll:

 

[Irons]

Here's some zirconia medium for sale on fleabay:

http://cgi.ebay.com/Zirconia-M-Grinding-Media-1-2-lot-5-/400187393813?pt=LH_DefaultDomain_0&hash=item5d2d070715

he has man lots listed

 

[Fever]

UPDATE

I have been having great success in abrading and reclaiming the Silver plating in the ball mill! I re-tooled my process slightly, primarily in the type and size of grinding media I used. I decided against the Zirconium Oxide for the simple reason that round or quasi-spherical objects would not penetrate all of the nooks and small spaces in the target materials. I switched to an Aluminum Oxide media called Duramedia XC, in a small cylindrical shape with 30 degree angled ends. This has proven to be very efficient at removing the plating. I tumble the objects for about 4 hours to insure all of the plating is removed, then I empty the ball mill into a classifier screen placed over my gold prospecting pan.




I then spray the individual object down with water to remove the silver sludge, and it collects in the pan.



After rinsing all of the items and the media itself, I add the washed media and a fresh batch of plated items, and start the process again. I let the collected Silver sludge/water solution settle for 24 hours, then I pour off the contents into a jar for drying. This sludge/water is likely primarily Silver, but it will undoubtedly also contain smaller amounts of various base metals and bits of media as well. Neither should pose a problem when digesting the dried powders in Nitric, and any ceramic media particles left in the mix will be filtered out appropriately. I posted a few pics below, the last being the ongoing collected result of continued batches.



- Fever

 

[lazersteve]

What do the stripped items look like after they have been processed?

Steve