Silver from brazing rods

[TheDoode]

Hi!
As many probably know, brazing rods can contain a lot of silver. Up to 55%
Rest is an almost even mixture of copper and zinc, with low amounts of tin. Or Cd - pre ROHS. I don't know the age of all the stuff, so I often have to assume Cd in solution. Which is a pain!
Sometimes P in the lower Silver content rods.

What is the best way to recover the silver from these?

My most experience is with running "wastefree" hydrometallurgic processes. I am thinking on the following route.

• Dissolving in CuCl2/HCl, or Nitric. I prefer the first as nitric is harder to come by. But silver content may be too high to dissolve in a chloride environment. Up to which %Ag will a piece dissolve in CuCl2/HCl, leaving behind particulate AgCl?
• Drop out the Silver on excess copper when using nitric. Or filter out the AgCl.
• When Silver is gone, add an excess of sulphuric acid and distill off the acid (both for HCl and Nitric routes). Every metal should be in the sulfate form now.
• Electrolyse sulfate solution to recover metals and Sulfuric acid. Copper is very easy, Tin is easy, Zinc is a bit of a pain in the acidic conditions requiring low concentrations and slow electrolysis.

Questions:

• Any completely different approaches?
• How do I deal with metastannic acid on the Nitric route?
• How do I deal with Cd in solution? So far I have just worked on explicitly Cd free material.

 

[Yggdrasil]

Hi!
As many probably know, brazing rods can contain a lot of silver. Up to 55%
Rest is an almost even mixture of copper and zinc, with low amounts of tin. Or Cd - pre ROHS. I don't know the age of all the stuff, so I often have to assume Cd in solution. Which is a pain!
Sometimes P in the lower Silver content rods.

What is the best way to recover the silver from these?

My most experience is with running "wastefree" hydrometallurgic processes. I am thinking on the following route.

• Dissolving in CuCl2/HCl, or Nitric. I prefer the first as nitric is harder to come by. But silver content may be too high to dissolve in a chloride environment. Up to which %Ag will a piece dissolve in CuCl2/HCl, leaving behind particulate AgCl?
• Drop out the Silver on excess copper when using nitric. Or filter out the AgCl.
• When Silver is gone, add an excess of sulphuric acid and distill off the acid (both for HCl and Nitric routes). Every metal should be in the sulfate form now.
• Electrolyse sulfate solution to recover metals and Sulfuric acid. Copper is very easy, Tin is easy, Zinc is a bit of a pain in the acidic conditions requiring low concentrations and slow electrolysis.

Questions:

• Any completely different approaches?
• How do I deal with metastannic acid on the Nitric route?
• How do I deal with Cd in solution? So far I have just worked on explicitly Cd free material.

If it is too high in Silver any Chlorides are out of the question.
It will form AgCl and stop the reaction.

 

[FrugalRefiner]

As many probably know, brazing rods can contain a lot of silver. Up to 55%

They can be up to 55% silver. They can also be as low as 5%.

Dave

 

[canedane]

Hi!
As many probably know, brazing rods can contain a lot of silver. Up to 55%

Hi, what are brazing rods with silver being used for? Where did you find them?
Henrik

 

[Shark]

Often used in heat and air work. I have used them to attach copper to stainless steel. It works but it wasn’t easy.

 

[TheDoode]

If it is too high in Silver any Chlorides are out of the question.
It will form AgCl and stop the reaction.

Sure. But what Silver amount is too high? When parting gold with nitric acid it is 25% gold, hence the in"quart"ation. Any number for silver?
Does the AgCl form an attached layer or can it be shaken off and it continues dissolution of the material underneath?
AgCl in the vessel does not disturb me.

@canedane They are a very versatile method of repairing and joining dissimilar and unweldable metals and even some ceramics (fluxing becomes a pain then). The only reason not to use it, for many, is the price. Although I disagree here, because of the ease of use. I don't think it is hard to use. It is usually the easiest strong method to connect to a lot of dissimilar metals. And that puts the price into perspective.

 

[FrugalRefiner]

Sure. But what Silver amount is too high? When parting gold with nitric acid it is 25% gold, hence the in"quart"ation. Any number for silver?
Does the AgCl form an attached layer or can it be shaken off and it continues dissolution of the material underneath?
AgCl in the vessel does not disturb me.

We inquart gold alloys with a high amount of silver because the silver will form that impenetrable silver chloride crust when the silver content is near or above 10%. And that's in heated AR, which is pretty aggressive.

Running the dissolution in a tumbler can help to dislodge the silver chloride crust.

Dave

 

[4metals]

Typically with karat scrap anything approaching 9% starts to crust over. you can push it with mechanical abrasion but there is a limit to that as well. For example old green gold alloy which had Silver as high as 25% in some cases was a bear to refine in aqua regia no matter how aggressively it was tumbled.

 

[Shark]

It works but it wasn’t easy.

I really should have said it worked really well. It just took more practice than I expected.

I have used brazing for years on metals and even repaired cast iron with a torch for several years. I think this lead me to think it should have been very easy to work with at the time.

 

[eaglekeeper]

I've been holding on to 1 Lbs. of Wolverine Silvaloy 15.... from what I can find they are 15% silver. I'm not sure if they are worthy of the time at today's spot price.... Maybe I'll use them for inquarting in the future.

 

[snoman701]

Typically with karat scrap anything approaching 9% starts to crust over. you can push it with mechanical abrasion but there is a limit to that as well. For example old green gold alloy which had Silver as high as 25% in some cases was a bear to refine in aqua regia no matter how aggressively it was tumbled.

Similar numbers have been shared with electrolytic copper and silver refining. When the insolubles get up above 9% and higher, they are less likely to slake off.

 

[TheDoode]

We inquart gold alloys with a high amount of silver because the silver will form that impenetrable silver chloride crust when the silver content is near or above 10%. And that's in heated AR, which is pretty aggressive.

This is confusing: After inquartation with silver I always dissolved the stuff in Nitric acid. No AgCl crust there. I can even use tap water as it is pretty much chlorine free here.

I did some inquartations with copper and dissolved it in CuCl2/HCl. Which worked fine most of the time and saved a lot of valuable nitric acid. And every now and then a couple of liters was converted to sulphates and went into electrolysis to recover all the reactants. Electricity is almost free compared to acid prices.

Thanks so far.
Any ideas about how to deal with metastannic acid or Cd in solution? Or any other totally different approach?

 

[Yggdrasil]

This is confusing: After inquartation with silver I always dissolved the stuff in Nitric acid. No AgCl crust there. I can even use tap water as it is pretty much chlorine free here.

I did some inquartations with copper and dissolved it in CuCl2/HCl. Which worked fine most of the time and saved a lot of valuable nitric acid. And every now and then a couple of liters was converted to sulphates and went into electrolysis to recover all the reactants. Electricity is almost free compared to acid prices.

Thanks so far.
Any ideas about how to deal with metastannic acid or Cd in solution? Or any other totally different approach?

Silver only creates AgCl if it is dissolved and has Chlorides around it.
So Silver dissolved in Nitric will not create AgCl unless you add Chlorides to it.
Inquarting with Copper is fine but consumes more Nitric.
If dissolved in a Cupric Chloride etch this will not dissolve the Silver.
So if it has Silver in it, this is no good solution.

If I'm not mistaken, Cd will not cement on Copper so cement it on Copper and leave the Cd in solution. Then treat it according to the waste protocol.

Metastannic acid is what it is.
Small amounts can be filtered.
Larger amounts need roasting and dissolving in HCl.

Avoid Tin and Nitric to meet up in the first place with pre treatment in HCl.

Edit for spelling

 

[TheDoode]

Inquarting with Copper is fine but consumes more Nitric.
If dissolved in a Cupric Chloride etch this will not dissolve the Silver.
So if it has Silver in it, this is no good solution.
(...)
Avoid Tin and Nitric to meet up in the first place with pre treatment in HCl.

I meant inquarting gold with copper and then going the CuCl2/HCl route. Off topic here. As I mostly buy 18K Gold (if I rarely buy - 18k is easy to find fake items due to the high density), inquarting with copper and dissolution in CuCl2/HCl worked fine. Some AgCl precipitations happened. I only collected those in a jar so far. I have only been screwed over with 333 or 375 gold as it is much harder to detect fake items there.

Avoiding Tin and Nitric would be a good idea. In case of these brazing rods it doesn't seem to be possible. This is not e-waste where I could dissolve tin first. It is ~2% in the alloy. It won't work on the CuCl2/HCl route due to the high silver content. Nitric acid is my only way left. But I'm open for breaking new ideas to try! This is why I looked here.

Thanks on the Cd advice.

 

[TheDoode]

If I'm not mistaken, Cd will not cement on Copper so cementvit on Copper and leave the Cd in solution. Then treat it according to the waste protocol.

I've done some more research. I does not plate out on copper. Maybe very slowly on iron.
Do we have a tutorial about waste treatment heavy metals of concerning toxicity like Cadmium? I didn't find anything specific in the Library section.

I think I will first make a test tube scale test with tiny amounts of silver, copper and cadmium each. Dissolved in nitric. Cement the silver on copper. Convert to sulfates. Electroplate out copper. Trying to electroplate the cadmium and test for cadmium ions in solution afterwards.

Cadmium is significantly more dangerous to human life and the environment than most elements encountered during gold refining. And I don't want to cause harm. So I'm particularly cautious here.

 

[Yggdrasil]

I've done some more research. I does not plate out on copper. Maybe very slowly on iron.
Do we have a tutorial about waste treatment heavy metals of concerning toxicity like Cadmium? I didn't find anything specific in the Library section.

I think I will first make a test tube scale test with tiny amounts of silver, copper and cadmium each. Dissolved in nitric. Cement the silver on copper. Convert to sulfates. Electroplate out copper. Trying to electroplate the cadmium and test for cadmium ions in solution afterwards.

Cadmium is significantly more dangerous to human life and the environment than most elements encountered during gold refining. And I don't want to cause harm. So I'm particularly cautious here.

Read the thread on waste treatment.

Edit to add:
https://goldrefiningforum.com/threads/dealing-with-waste.10539/post-101993

 

[anarxi]

why did you decide that the alloy contains cadmium?
The silver contacts of electrical releases contain cadmium, so silver does not burn out quickly..
The purpose of your solder is obviously different, for example, soldering carbide tips on drills ...

 

[anarxi]

I just looked at the table with solder brands; these are Soviet and Russian standards, but I don’t think they are much different from the rest of the world.
Of several dozen species, cadmium is present in only 5.

 

[TheDoode]

@Yggdrasil I don't think the waste process described there is any good for Cd. It creates a mixture of iron hydroxides and - in case of Cd contamination - Cd hydroxides. It probably gets most of the Cd out of solution, but I can't throw out the sludge just as if it was iron hydroxide. So... I try the electroplating route. I feel more comfortable with that.

@anarxi
Older braze rods (pre Reach (2011)/Rohs(Date unknown to me) often contained ~2% Cd. It makes the alloy more liquid, lowered the working temperature. Basicly for 2% Cd you could use 10% less Ag. Crude simplification!
After Reach/RoHS Cd quickly vanished and was replaced by more silver, and often tin.
So when I have an unknown Material (and I have collected several kg of that over the years. Ebay, yard sales, workshops closing, etc...) I have to assume it contains Cadmium.

 

[BGDOCK]

I found melting the brazing rods with some copper then casting it in a bar followed by a copper sulfate cell worked well .