Processing Sterling Silver without nitric acid

[FrugalRefiner]

Thanks Nick! I have some experiments in mind along these lines. As I get results I'll be posting them here.

Dave

 

[ilikesilver]

hey guys, what if you were to take and melt the low quality silvers with a higher quality silver to get it at the level you need say towards .925 using variations of different qualitys. then couldnt you use that up. a lot of times lower quality silver comes free, were the higher stuff you have to buy or trade for. just a thought tim

 

[maynman1751]

The inital step involes converting the copper nitrate into nitirc acid. This is accomplished with two graphite electrodes, or a graphite positive and a copper mesh negative. The mesh provides more surfaces to extract the copper moss on and tends to allow the moss to adhere better to the negative electrode when the negative needs to be scraped.

When the color of copper that is forming at the negative electrode darkens the positive electrode can be swapped out to the sterling anode. The drawback to using copper for the negative in this inital step that when the power is switched off the plated copper moss will begin redissolving in the electrolyte. also any moss that falls off of the negative will redissolve in the electrolyte. No silver is involved at this stage.

Some copper is still in the electrolyte after this step and will plate out as a red moss.

To recover/remove the copper from the silver nitrate solution could you use two stainless electrodes?

 

[butcher]

You need an anode, which is inert to the nitric acid electrolyte.
Stainless at the anode would be oxidizing into solution at the anode; the graphite is inert, although it may break down a bit from the gas bubbles.

 

[maynman1751]

Thanks Richard! 8)

 

[butcher]

Some types of stainless steel (normally the types with higher chromium content, and non magnetic) will not dissolve into concentrated nitric acid, the stainless steel passivates in the highly oxidizing environment of the concentrated nitric acid.
Type 304 or 316 stainless will passivate in concentrated nitric acid, 304 types would be preferred over 316 for storage of concentrated nitric acid.

Dilute nitric will attack many metals easier than the concentrated nitric acid (stainless steel is no exception here) although it will still not dissolve as easily a many of the other metals will.

When we use electrolysis with a metal as our anode we can force a metal to dissolve into solution (the electrolyte) as ions. The power supply is forcing the electrons to move in the atoms of these metals that may not normally be oxidized in the same solution if it was not used as an electrolyte (or as the anode). Even a metal that would not normally dissolve in this same solution, if this solution was used as just an acid, and not as an electrolyte, or in an electrolytically process.

Besides the power supply forcing electrons to move in the electrolytic process, we also have the anode forming scrubbing bubbles: which can also help to remove an oxidized layer (or passivated layer of salts if it forms.

I am not sure if I explained this very well or not.

 

[the iron dwarf]

I am new here and have a quantity of silver to process sometime in the future.
I have been reading random threads here and am working my way through Hoke's book, then will re read both threads and the book making notes before I consider doing anything.

I have been thinking of dissolving silver in nitric and cementing it out and when needed removing the copper with the process above to make my nitric usable again and reduce the waste I have to deal with.

I have a few of the electrodes from arc air which I think are graphite with a thin copper coating and could probably get some large motor brushes which I also think are graphite, are either of these suitable or should I just buy some graphite rod or block to use for the cell to convert copper nitrate to nitric

 

[butcher]

The copper coated air arc cutting rods are small in diameter, the thin layer of copper will also go into solution as the anode giving you a longer time to remove copper from the copper nitrate solution, I also believe the graphite in them is soft and fairly porous.

Most motor brushes are fairly dense graphite, some motor brushes will also contain a metal depending on the brush type, and some have the graphite around a braided copper lead wire, which if it went into solution would give the electrolyte added copper, for very small lots a large graphite motor brush may work.

All in all I would look into buying large blocks of graphite, it can be cut into sheets for your cell projects, and to make molds out of, you also can find it reasonably priced.

 

[the iron dwarf]

thank you butcher

 

[user 50082]

Good job. I will like to see that video.

 

[spikeyharold]

Hi Guys
Ive been reading through as many posts as I can and Hokes book. Im looking at refining a small amount of sterling silver to create some 999 silver electrodes (for silver plating). Being in the UK getting Nitric is a little difficult, but getting copper nitrate doesnt appear to be too hard. SO.. Reading the initial experiment, would I be correct in surmising , I could use a 40% copper nitrate (shop bought) solution as my starting liquid. A copper cathode (followed by a graphite cathode) and the sterling as the anode. And I would end up with silver (in need of further refining) and a Nitric Acid solution suitable for further processing more silver? Which would be the perfect solution for me or have I missed something?
Thanks
Steve

 

[FrugalRefiner]

You're sort of on the right track. Starting with copper nitrate, you can use electricity to reduce some of the copper, depositing it as metal at the cathode, leaving free nitrate ions (NO₃^-) in solution. But that same electric current will also oxidize the sterling silver you plan to use as the anode. The silver and copper will go into solution. As this happens, you'll start to have both silver and copper depositing at the cathode.

Now if you used a graphite anode and either a copper or graphite cathode, the copper would again be reduced and deposited at the cathode. But since graphite doesn't go into solution, you will start to develop some weak nitric acid. There will probably be a limit that will keep you from pushing all the copper out, so you can achieve a mixture of nitric acid and copper nitrate.

You could then use that solution to dissolve some of your sterling. Then you could cement the silver out by putting in some metallic copper. You would end up with cemented, metallic silver and copper nitrate solution. You could conceivably repeat this process over again and again, but the solution would eventually become contaminated and need to be processed as waste.

The silver cement you produce won't be the 999 you're wanting. To achieve that, you'd want to set up a silver cell. Start with a fresh copper nitrate solution and create some nitric solution as before. Dissolve some of the silver cement into it and you'll have your electrolyte. Melt the rest of the cement and either pour it into an ingot or shot it to use as your anode. You'll find all the details on silver cells here on the forum.

I've often considered running this exact process as an experiment to test the limits of the system, but I just haven't had the time yet. It all works in theory. Since I haven't done it, I can't tell you if you'll run into any problems. Since there is no free H⁺ in the solution, it would have to come from the water. That may or may not cause problems.

It's a lot of work, but it might provide an alternative for those who can't buy nitric.

Dave

 

[resabed01]

Tonight I tried recovering the copper/nitric acid from a waste solution of copper nitrate I had left over from some inquartaion I did a while ago.
I used a copper coated arc rod as Butcher mentioned. If you do it right, you can peel the copper off the rod in a sheet and have both your anode and cathode. I ran the cell for about an hour as a trial and it worked well. Not sure what voltage to run this cell, I ended up using the +5v bus from a old computer power supply. Just from the hour or so I ran the cell I could see several grams of copper removed from the solution and no noticeable erosion of the graphite rod.

Tomorrow I will set it up and let it run all night.

 

[snoman701]

You might look in to carbon arc electrodes. Traditionally these are just copper plated graphite.

Obviously this was posted earlier by Butcher. To make this post worthwhile since I can't delete it....

I have read through the forum in relation to selective refining via voltage variation. It is my understanding that at higher voltages, you have a greater chance of copper deposition, whereas at the lower voltage the nitrate only reacts with the silver atoms.

With that, there was at least one patent which placed a third electrode in the solution, close to the anode, as you can then measure the voltage drop over the solution, as well as the voltage drop right at the transition. This effectively reduces the variation in cell design, but would also allow one to set up a simple PID controller to vary power supply output to match the potential needed to only drop silver. Has anyone on the board played around with such a beast?

 

[Rougemillenial]

All,

I wanted to share the progress of my recent ventures into refining some sterling silver that I had purchased.

The item I experimented on was an old solid sterling silver bowl that I acquired from a lady who had inherited it from her mothers collection. Here's how the bowl looked the day I purchased it last week:


The bowl weighed 25.2 oz (713 g). I cut the bowl into pieces and melted it down into a bar slightly smaller than a US dollar bill and almost 1/4" thick.

I processed the sterling bar using electricity (12V 10A battery charger) and and electrolyte of left over copper nitrate from previous inquartations and cementing reactions(see on my website).

I initially used a copper mesh cathode (negative lead) and when the copper level dropped, I switched to a hard graphite block (2" x 4" x 1/2"). With both cathodes the copper built up as a heavy moss on the cathode and was periodically scraped into a Tupperware dish for further cleaning. As the copper levels dropped silver was co-deposited with the copper onto the cathode. The silver tends to accumulate on the back side of the cathode and the copper on the front.

The solution became more and more saturated with silver nitrate as the experiment went on. Here's is a photo of the partially dissolved anode (left), the cleaned silver powder (center), and a 52.2 gram test melt of the resulting purified silver (bottom left) with a U.S. quarter for size reference(bottom right):


As you can see the purified silver is much finer than the original piece and the anode bar. The surface of the silver button is crabby indicating good purity. The button will now be run through a Thum cell to remove the last traces of impurities.

I plan on posting a video of this process when time permits. As you can see, the bar still has some ways to go before it is completely processed. The bar in the photo has been in the cell for 10 hours. I ran the cell for 2 hours per day for the last five days to get to this point.

More to come...

Steve

I’m quite impressed with this one. Nice work. Would it be possible to take the CuCl2 waste leftover and convert it back to hydrochloric acid by use of sulfuric acid and then electrolyze as Nurdrage did to recycle spent copper chloride PCB etching solution. That way it’s pretty much full circle. All the copper is recovered and separated from the silver.

 

[Rougemillenial]

Hi Guys
Ive been reading through as many posts as I can and Hokes book. Im looking at refining a small amount of sterling silver to create some 999 silver electrodes (for silver plating). Being in the UK getting Nitric is a little difficult, but getting copper nitrate doesnt appear to be too hard. SO.. Reading the initial experiment, would I be correct in surmising , I could use a 40% copper nitrate (shop bought) solution as my starting liquid. A copper cathode (followed by a graphite cathode) and the sterling as the anode. And I would end up with silver (in need of further refining) and a Nitric Acid solution suitable for further processing more silver? Which would be the perfect solution for me or have I missed something?
Thanks
Steve

how did you get Cu nitrate? The only way I could do this is via arc reaction of air to make nitric.

 

[lazersteve]

Copper nitrate is easily produced without nitric acid via basic high school level chemistry. No electricity is required for the production of Copper Nitrate, except maybe to produce some heat to evaporate off the excess water.

Steve

 

[lazersteve]

... The title of this topic is misleading since you do need nitric acid in the whole process. ...

Nothing could be further from the truth. Copper nitrate production doesn't necessarily require nitric acid.

Steve

 

[g_axelsson]

Copper nitrate is easily produced without nitric acid via basic high school level chemistry. No electricity is required for the production of Copper Nitrate, except maybe to produce some heat to evaporate off the excess water.

Steve

How?

Göran

 

[lazersteve]

Take note: You saw this here first as it relates to refining.

Any nitrate plus copper sulfate comes immediately to mind. The nitrate ion can be exchanged almost indefinitely with proper process control. It's only when you start producing BFRC (Big Freakin Red Cloud) that you are losing the power of the nitric acid. There will always be some losses, minimizing these is key to recycling the nitrate.

Nitrates are typically more soluble than sulfates, so simple evaporation followed by cooling leaves the nitrate after pouring/filtering off the cold nitrate solution from the sulfate crystal.

This has the added benefits of virtually no nitric fumes and recyclable in the case of copper sulfate. Copper sulfate is a super useful reagent. It can be converted to sulfuric acid using electricity and evaporation.

Nitrate salts are cheap and ship most anywhere. You can even leach nitrates right out of most any top soil.

I have an entire process related to this "closed loop" production of in situ "nitric". For most hobbyists refining purposes there is no need to isolate the nitric acid at all. Instead all you need is a nitrate source, copper sulfate, muriatic acid, and some electricity occassionally. Of course as with many of the hobby work arounds, an investment of time is required at a few of the stages of these processes.

Proper nitric acid is expensive, hazardous, and not required. It is still a good idea to distill a liter or so of good 68% nitric acid to have on hand. Any of my work around nitric formulations (including this one) can be used as a source for this distillation process to obtain your 68% nitric acid.

Steve