# most efficent removal ?



## pwa (Jan 25, 2012)

HI to all, Sorry for the length of the post,it will take some explaining new.I am looking for the best way to remove silver that has been plated onto a variety of size and shape steel parts.These parts have been removed from radial aircraft engines from the 40's when silver was widely used for many reasons.The parts heavily plated, say .010 thick I sweat the silver off with a torch but on the items having only .001 or .002 thickness the surface tension wont allow this.So the problem is most of the items have a small amount plated surface but there is alot of bare metal surrunding it.My goal is not to get it to a pure state but just get it off.I send my material to a refinery that and a hallmark for resale.I can get nitric and tried it out.The nitric attack the steel but it also dissolved the silver.I know next to nothing about this, so this is where Ive started.Thanks in advance for any input.


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## henos (Jan 25, 2012)

Hi ... My English is not the best ...
It seems to me that the method would be not bad with the mixture in a ratio of 95 / 5 H2SO4 + HNO3, both concentrated, process at 80 * C
Of course, a very dangerous method

Yours


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## butcher (Jan 25, 2012)

Dilution of the acid can be extreemly dangerous if done wrong, you could end up blinded or burned alive.


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## pwa (Jan 25, 2012)

I wasnt thinking of a process that has an extreme danger warning.I have some knowledge of electroplating and access to the materials involved in operating a lead tank,indium tank,and tin tank.I just thought at 30.00 an ounce there should be a way to get at this silver before it ends up in the steel scrap bin.I quess an option would be to remove it with burs and grinders in a cabinet then process it from there.It would be alot easier to strip chemicaly some how.


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## kdaddy (Jan 25, 2012)

How about bead blasting in a cabinet, beads and all into Nitric, filter, cement with copper?


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## pwa (Jan 25, 2012)

The blasting cabinet is a great idea should I go with grinding it off,but silver is almost unaffected by glass bead.That is actually how I prep beargings along with pumice to lead plate them.


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## qst42know (Jan 25, 2012)

I think GSP mentioned steel shot a long while ago.


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## pwa (Jan 25, 2012)

I dont want to appear negative but shot peening the silver after plating is an adhesion test.It will on dimple and kinda of slide around with shot unless there is an adhesion problem then it will blow it off.I like the idea of nitric and cement with copper but I dont know how to get around all the steel sorrounding the silver using up my acid.If that makes any sense?


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## butcher (Jan 26, 2012)

what type of steel, could it be stainless, or a steel resistant to nitric?

GSP (gold silver pro), he would be someone who should be able to give answers to this question.


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## Geo (Jan 26, 2012)

stainless steel over 300 series is resistant to attack from nitric acid but because of the nickel content it is attacked by sulfuric at almost any concentration.


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## pwa (Jan 26, 2012)

I dont think I explained that very well.These are engine parts of a high carbon steel, some are quite hard and quite bid.If I use a 1/2 gallon of nitric to sumbmerge the part and only a small portion of the material has silver on it wont the acid be used up by the high percentage of steel.Is so this would not make it very economic.I do have smaller pieces that are completely plated and I think the nitric cemented with coppper will work well.Thanks for all the input thus far.(the steel will be scrapped after stripping)


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## goldsilverpro (Jan 26, 2012)

Since the steel used is attacked by the nitric, I don't see you having much luck in using it. I would think that any dissolved silver would tend to cement back onto the steel. Also, I think this process would "fight" you constantly and would be very hard to control.

I once spent some time trying to use nitric to dissolve the thick silver layer from carbon steel aircraft bearings. I used a 4 liter beaker so I could see what was happening. I started with full strength nitric and it did strip silver without attacking the steel, but it was way too slow. I sped it up with water additions (1% at a time) and/or heat. At some point, if too much water or heat was added, a strange "flash" appeared on the entire surface, and the steel immediately started dissolving, evidenced by the sudden total coverage of gas bubbles on its surface. The dissolving generated heat, which made it dissolve faster and hotter. In less than a minute, the solution foamed over, in a *runaway* fashion. I found the windows to be small - about 35C and/or just a few % of water were the upper limits. Not a workable system. 

To use nitric, I did consider applying a small negative current to the parts (make the parts the cathode) from a power supply - just enough to suppress, inhibit, or neutralize the oxidizing effect on the steel from the nitric. I would probably have used a Ti, or carbon anode - gold would also work and, maybe, some form of stainless. Hopefully, the silver would still dissolve - I think it would. I once saw a guy use this method for something quite similar, with great success, and I was impressed. There may be many uses of this method in our work. I've thought of several over the years.

I've processed many types of PM bearing aircraft scrap in large quantity and the only 2 forms of silver I've seen on these are silver brazes (alloys) and silver bearing surfaces (pure silver, I think, with an overlay). I have never seen silver plating on these parts.

If the silver is in the form of a braze (Ag/Cu or Ag/Cu/Pd), I would first try stripping the silver, anodically, at about 4-6 volts, in a 40 g/l sodium cyanide solution containing enough sodium hydroxide to maintain the pH at 12. The silver, etc., should deposit easily on a preferably passivated stainless sheet cathode taped with plater's tape on the edges. The solution can be reused.

Sounds like you have bearings? On these, there is an overlay of tin or lead, etc., on the silver. These overlays won't strip in cyanide. There are some sodium hydroxide strippers that will remove just the overlay metals first, thus exposing the silver for subsequent cyanide stripping. The bearings we had ran about an ounce per pair of bearing halves. We also had several drums of aircraft wrist pins with a large silver area.

For the bearings, we finally ended up simply chucking a pair of bearing halves in a lathe and cutting the silver off. Much easier than using chemicals in this case. Worked great. I think we just flux melted the turnings and ran the bars through the silver cells. Any iron cut off with the lathe ended up in the slag but, for various reasons, we tried to cut the silver off as close as possible.

I once stripped the silver from 50,000 pounds of silver brazed, magnetic, 410 SS using 50/50 nitric acid, with no attack on the stainless.


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## pwa (Jan 26, 2012)

Thank you for the post GSP, The brgs. I have are plated with lead which I reprocess after every use.2 parts Glacial acetic acid and 1 part hydrogen peroxide is used to strip lead and anything it maybe alloyed with tin,antimony,and indium the ones I know of.These are the gravy for me.The silver is so thick I use my oxy/act torch to melt it off,its like using a squeggy.The pins you mentioned could these have been link pins and not wrist pins.Those are great to I just chuck them up and cut off the silver.It sounds to me that going after the material thinly plated and surounded by steel will not be so easy.What about using a blasting cabinet and removing the silver with carbide burs,roloc discs,cartride rolls ect. and then nitric cemented with coppper.That sounds like a plan? The only other thing I could think of using the nitric would be to mask all the steel off with bees wax or some other form of platers masking.


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## pwa (Jan 26, 2012)

oh yea the silver has been assyed at 98.6 upon receipt report to me by essential metals corp(sunshine mine) here in idaho up in wallace.Over the past 10 yrs they have processed about 1400 oz for me.They may be kinda of pricey I think but thier always a pleasure to deal with.They will take silver to cover all thier fees and services even shipping if one wants and return the balance in bar sizes of your choice.They used to have extruded bars that look like works of art,now they are all hand poured.


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## butcher (Jan 27, 2012)

I have been wondering if we could not come up with some type of etching paste, from chemical salts, these could be smeared on the silver surface to maybe corrode or dissolve or soften the silver, or maybe even if silver scratched into, to expose the base metals in places maybe the salts could undercut the silver by oxidizing the base metal layer underneath. Maybe this salt could be heated to make reaction. Or a two part paste, or solution, one part corrosion or converting silver (oxide, chloride, or??) part two takes silver in solution, or is another salt that will dissolve silver or pull it off easily into polishing compound and buffer wheels or something.

Silver article could even be packed into chemical salts for long period of time for reaction to occur.

Maybe two solutions one attacks silver making chloride passivated layer, other solution dissolves this layer, part is moved back and forth in these till stripped.

I know silly idea the wheel is round; I do come up with silly ideas now and then?

Well since I am expressing this silly Idea, they etch silver with pastes or solutions, why could we not etch them off without removing a boatload of base metals, maybe iodine based etch,

Any way this is something that I have thought about but have not looked into.

Ok I need to go fix the flat on my truck now.


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## Oz (Jan 27, 2012)

Actually Butcher I think that is a dang fine idea. If you digest silver with a paste instead of a solution who cares if it cements back onto the base metal, it should easily brush off.


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## butcher (Jan 27, 2012)

We need to come up with some safe pastes, I would think speed of reaction would not be as important as most silver plate sit on the shelf a long time anyway.

Or maybe a paste smeared on and heated with torch to fuse the silver into the salt and then washed of into a solution.

Another thought, solder is sometimes removed from circuit boards using a copper braid wick, this wick is between soldering Iron and part with solder pin and pad on circuit board, the heat of the solder iron pulls the majority of the solder toward the hot solder Iron, the hot wick soaks up this solder, a thin film of solder is not removed but the major portion is.

Could we use a chemical salt (maybe with metal powder, or metal salt) and heat to wick up silver?


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## Geo (Jan 27, 2012)

Butcher,

that's a hell of an idea. think about a paste that you wipe on and let dry, then brush off or wash off in some solution that brings the silver off with it.that would be very marketable. just remember all us little guys when you make your first million. :lol:


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## pwa (Jan 27, 2012)

Ok its easy to see you guys are very smart about this subject.When you guys talk about salts and paste it just makes me think about my wifes gravy(hell that might even work).Keep thiniking but its gonna have to be pretty simple for me to accomplish it.I am gonna get some acid and will be needing a old post to walk me through cementing with copper.One question I already have is when doing calculations you start with how much silver you have.I dont really know and do I factor in the wieght of the base metal the silver is plated onth yea my smilies are turn on but all I get is text when i use them,what am I doing wrong.Thanks again for all the feedback


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## butcher (Jan 28, 2012)

pwa,

When we dissolve a metal in an acid we make a salt of that metal.
Silver dissolved in nitric acid will give silver nitrate salts.

Sodium is a metal it is very high in the reactivity series of metals, in fact it is so reactive it will not be found in nature as a metal, it can be extracted from its salts, but it is so reactive that it reacts so violently with water (or moisture in the air) that it explodes, they would have to store it in mineral oils if separated. With water sodium would form sodium hydroxide NaOH (caustic soda), (lye), and hydrogen gas.

Hydrochloric acid HCl (a dangerous acid) and sodium hydroxide NaOH (a dangerous base or caustic)
If added together in proper proportions, would form a (neutral pH 7) table salt NaCl and water. (in a fairly violent reaction).

HCL + NaOH --> NaCl + H2O

Hydrogen H joins with hydroxide OH to form water, the sodium Na and chloride join to form table salt.

Goggle reactivity series of metals; read about this subject it will help you understand better what is happening with the cementing of silver with copper, it is also very useful in what we do,

Also studying some chemistry can also help you understand how these metals and acids react.

But Hokes book should be a top priority to read, She teaches in a very understandable manor how these reactions react (acids and metals), not so much on the chemistry side but so that you gain a working knowledge of how and why we use the methods we do. And she teaches how to test for these metals in solution when we cannot see them.

If your talking about calculating the amount of nitric acid needed to dissolve your metals, you would need to know much base metal and silver you are dissolving in the nitric, then base metals would need to be figured as it takes about 3.4 times more nitric to dissolve base metal than it does to dissolve silver.

1.22ml 70% HNO3 + 1.22ml H2O will dissolve about a gram of silver.
4.2ml 70% HNO3 + 4.2 ml H2O will dissolve about a gram of copper or other base metals.
1oz of copper will cement about 3.4oz silver from AgNO3 solution.


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## richardbal (Jan 28, 2012)

Hello 
need your help???
i have a CUSO4 electrolyte 1 Liter put into the solution one silver plated spoon coneted to the(plus + wire) and a inox sheet conected to(minus - wire ).i run the electrolyse with 5V/10A.
questions??? on the inox is a white gas bubels?? what is that?
2-on the inox is a dark braun color sludge??? what is that?

after 20 minuts the silver is going up from the spoon in many pieces isnt disolved in the solution.the spoon is now red is look like copper.
i filter the silver washit in water many time diluet some hno3 in des water and put the silver inside ,and heated but no way to dissolve the silver.
what is the solution
can i melt the silver direct
what is the problem why the silver didnt dissolve in hno3????
thanks for any help
richard


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## pwa (Jan 28, 2012)

Thanks butcher I"ll look for book


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## pwa (Jan 28, 2012)

Ok, da! I can download a copy from site


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## butcher (Jan 28, 2012)

richardbal,

It makes the forum confusing when you post the same question in several places, do not double post, your post will get read in one place, and if someone can help they will.

I tried to help on your other post.


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## pwa (Jan 29, 2012)

yea,his post is listed by mine,I quess he didnt open right listing when posting.Being new myself it had me going for a while i.e.(what the #$!^ does this post mean)


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