# Silver Nitrate - is there a downside to lye/sugar method?



## Dawnsdad (Jul 22, 2019)

First I want to say that I bought LaserSteve's CD a few years back and I highly recommend it.

My situation: I am currently doing a test run, treating 10lb of floor sweeps from an industrial grinding area in nitric acid. Normally I would have thrown this stuff away after picking out visible pieces of braze. But I got the idea that the rest of it might have enough silver to be worthwhile going after. I have about 250lb of it and may be able to get more. I have already gotten positive test showing the presence of silver. So, now I am ready to drop the silver out of solution. The amount of this solution is going to be too great to lend itself to sitting at a table and working with a beaker. It's more like working in a 5 gal. bucket and stirring with a drill and paint paddle. Other than the obvious waste of lye and sugar and the need for extra rinsing, are there any other complications that would occur if I get too much lye and/or sugar in the solution?


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## kernels (Jul 22, 2019)

Hey Dawnsdad, I assume you mean after precipitating the Silver as Silver Chloride. Have you got a plan for how to separate that much Silver Chloride from the rest of the solution ? 

You could certainly cement out the Silver, but you would then also cement out everything else less reactive in the solution.

I would definitely go the Hydroxide / Syrup path and it sounds like you have a good plan going with the paint mixer in the bucket. This system obviously relies on a lot of mixing, just keep an eye on the temperature as you go.

Use corn syrup for the final conversion, I believe regular sugar can also work, but not as well as corn syrup from what I've heard.

If you haven't done it before, start on a small batch until you get the feel for it.


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## Dawnsdad (Jul 22, 2019)

I started by weighing up 10lb and washing it thoroughly in a little cement mixer to get rid of as much water soluable crap as possible. Then I started the acid dissolution, stirring with the paint mixer 2 or 3 times a day. I used a more dilute acid solution at first because grinding dust has so much surface area and the reaction to the acid can get out of hand very quickly. After a couple of days, I added more acid. 

I don't really plan to remove the AgCl from the bucket. After it settles to the bottom, I'll pour off most of the solution, add water, stir and let it sit until everything settles to the bottom again. Then repeat until I'm satisfied that the AgCl is clean. Then start with the lye. I have done it this way before with higher quality source material. But I am always concerned that I might not get every bit of silver. I don't mind using a little too much lye, but I'm always worried that too much might have some unintended consequences. Same with the sugar. A few extra rinses is no problem, but I don't want to cause chemical reactions that would harm my end result. Hence, my question.

I'm not going for super pure silver. I'll probably dry it in an oven, melt and pour into water to make shot. The refiners I have used in the past have always melted what I brought them and done their own pin assays anyway. So why bother trying to make nice bars? As long as it comes out 95% or better, they charge me the same refining fee.


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## snoman701 (Jul 22, 2019)

I'm not following your process.

So lets start at the beginning.

You have a material with silver in it, what else is present? Is there cadmium in the braze? 

You are dissolving this material in nitric acid? You know those fumes are nasty right?...and if there is cadmium, you are poisoning yourself with not only NOx but also cadmium? 

You are then filtering I hope? Or at least decanting?

Then you are precipitating the silver as a chloride? 

Then filtering the chloride?

So you now have a wet silver chloride, washed until the washing liquid is colorless. If you have this in any appreciable quantity, the best thing to use is your cement mixer. Get yourself some punch slugs from anyone with an ironworker. Now put those in the plastic lined cement mixer, add your silver chloride and some dilute sulfuric acid. Tumble it until a sample melts without showing signs of silver chloride. The slugs provide iron which reduces the silver, but when tumbled, they also grind the silver chloride clumps. 

Wash your silver well. Flux with borax and soda ash, slags should be creamy colored. If they are black and hard, you didn't wash it well enough.


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## Dawnsdad (Jul 22, 2019)

You have a material with silver in it, what else is present? Is there cadmium in the braze?

The source braze is 50% silver, 30% copper, 20% zinc. There is absolutely no chance of any cadmium. Because it comes from a grinding area, there is likely a very small amount of steel. And there is a considerable amount of chips from ceramic grinding wheels.

You are dissolving this material in nitric acid? You know those fumes are nasty right?...and if there is cadmium, you are poisoning yourself with not only NOx but also cadmium?

Yes, I am dissolving in nitric and I'm well aware of the dangers if NOx and precautions are taken.

You are then filtering I hope? Or at least decanting?

Filtering prior to treating with brine.

Then you are precipitating the silver as a chloride?

yes

Then filtering the chloride?

no. I plan to wash it in the bucket until the water is clear. Then treat with lye and sugar. Your idea of using my cement mixer and punch slugs is not an option I would consider at this time, but thanks anyway.

OH Crap!! Cleaning up, gathering stuff I will need to continue this project and moving stuff around to make room in my workshop, I came across a 5 gal bucket with about an inch of silver chloride in the bottom.I think I should start another thread to deal with this issue separately.


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## galenrog (Jul 22, 2019)

Perhaps it is the stroke talking, but I am confused. Why are you converting silver nitrate to silver chloride? Seems to me that when I have silver nitrate solution, I just cement with copper and have silver pure enough for sale or further refining through a cell.

As I said, perhaps it is the stroke talking.

Time for more coffee.


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## kernels (Jul 22, 2019)

Agreed, based on the composition of the sweeps, cementing on Copper is definitely an option.


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## Shark (Jul 23, 2019)

If it is silver nitrate, I agree with the others, cement it with copper. If it is silver chloride, I would use the iron and sulfuric method. It is not near as messy and seems easier to wash afterwards for me.


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## anachronism (Jul 23, 2019)

Shark said:


> If it is silver nitrate, I agree with the others, cement it with copper. If it is silver chloride, I would use the iron and sulfuric method. It is not near as messy and seems easier to wash afterwards for me.



IMHO correct on all counts. The silver Chloride Lye thing is messy and horrid. Sulphuric and iron all the way if you MUST make Silver Chloride in the first place.


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## Lou (Jul 23, 2019)

I don't see anything wrong with the silver chloride process.

Some modifications I'd make if I were doing it, presuming silver is the principal component in the sweeps:

1.) Burn the sweeps
2.) wash the sweeps in DI water, as you're doing
3.) Dissolve sweeps by adding them cautiously to nitric acid solution (I always add material to be dissolved to an excess of the dissolution mix, to ensure it dissolves more readily)
4.) After no visible reaction, briefly heat to completion, cool, decant, then filter. If not an option, decant, then decant rinse, and do NOT combine the second, third, fourth rinses (use those for next batch of dissolution, etc.) to keep waste down
5.) settle and finish decant the pregnant solution
6.) titrate to see how much silver is present, then add in 99% of required muriatic acid with stirring
7.) decant and wash silver chloride, keeping the decants for the next digestion
8.)silver chloride in cement mixer with sulfuric and iron per instructions on forum
9.) rinse, wash, then wash with borax-carbonate-nitre solution (BCN) solution
10.) melt 

This way you can regenerate your nitric. A lot of time burnt floor sweepings with iron will not react in reasonably strong (25%<) nitric if they're well burned to Fe2O3.


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## Dawnsdad (Jul 23, 2019)

For me it was a toss-up between cementing on copper and going the AgCl route. The deciding factor was the cost of copper vs. the cost of NaOH and the amount of time it would take. I still have about 35lb. NaOH, so I decided to go that route. But copper is not out of the question. When I was processing over 100lb. of braze a month, there was always some of the braze that the refiners wouldn't accept because it contained Fe. So I dissolved it in nitric acid. Since it was 30% copper, I got the idea to recover the copper. I have a few pounds of copper that I precipitated out of solution with scrap iron. I have been thinking about crushing it into powder form and sprinkling the powder into the new silver nitrate solution. I wouldn't want to cement all the silver out of solution because any excess copper would contaminate the silver. But I could do a partial drop with it and finish the process with scrap copper. What do you think?


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## anachronism (Jul 23, 2019)

Sure- if you can be completely sure that you use up ALL that copper then there's no reason at all why that would not work. 

That given you would need to do a lot of stirring and your copper would have to be fine otherwise you would foul your silver.


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## Dawnsdad (Jul 23, 2019)

Sure- if you can be completely sure that you use up ALL that copper then there's no reason at all why that would not work.

That's the reason to only partially cement with the copper powder. If I get silver on a fresh piece of copper, then I would assume that all the powder had been dissolved. Even if there is a little copper in the silver, the refiner I use charges 5% on anything over 95%. So I have a little wiggle room.


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## nickvc (Jul 23, 2019)

Simple thought if you could wash the material clean could you melt some of it into bars, if you can simply add those bars to your solution as you will get the bars refined for free and the copper present will cement the silver in solution.


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## snoman701 (Jul 23, 2019)

A pound of copper cements 3+ pounds of silver. That's 0.004% at a cost of $3/lb for your copper.

I'm cheap and I'm stubborn. I've been wearing shoes with holes in them for two months because I want them to make it another two months just so I can know I got a year out of them.

And I make plenty of silver chloride.

But I do it for a solid reason.

I make silver chloride using HCl to rejuvinate the nitric so I can use it at least once more.

I make silver chloride because it makes easier to wash silver.

I make silver chloride to rid a solution of silver while keeping other elements in solution. 

Choose your battles wisely. There are very valid reasons to make silver chloride.


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## kurtak (Jul 25, 2019)

Dawnsdad


I have sent you a PM

Kurt


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## peter i (Aug 1, 2019)

Lou said:


> I don't see anything wrong with the silver chloride process.
> 
> Some modifications I'd make if I were doing it, presuming silver is the principal component in the sweeps:
> ...
> ...



So many years, and new things still pop up.
Is there more somewhere on the forum about BCN?


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## FrugalRefiner (Aug 1, 2019)

I think Lou first mentioned it in Silver Chloride Conversion With Lye and Sugar - VIDEO.

Dave


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## Lou (Aug 1, 2019)

I don't know if it's something I came up with or not, but I never saw it at any refinery I went to and the concept is sound and it does work. I just remember that one day 6 or 7 years ago, when I was rinsing a load of cement silver I got into a discussion with my coworker about the best ways to get rid of lead, bismuth, tin, copper and such in silver intermediate products. We talked reverbs (too lossy of Ag), blown converters (too expensive and also lossy), and melt fluxing. I used to literally watch nitre decompose upon hitting the melt and I could tell by the slag produced how much metal was being trapped in the glass. The idea struck like a bolt of lightening and I probably should have patented but it's public now!

Anyway, when I rinse a filter cake of higher surface area material, like cement silver or even gold sponge and use a solution containing dissolved fluxes, particularly nitre, it produces a purer product. The concentration of the flux solution can be increased for dirtier, crappier stuff and decreased for finer material where the operator doesn't want a bunch of flux on the melt. I personally hate an excess of flux as it is an increased opportunity to have metal hold up and I'm of the "less crap I do to it all, the better it ends up" school of thought. 

Think of it this way, when nitre goes on top molten silver, it quickly decomposes into nitrite, oxygen, NOx, then sodium oxide and more oxygen. Its oxidizing effect is limited and local and even in inductively stirred melts, it doesn't effectively polish out copper and iron. The same is true with nitre and Pd/Pt in gold. Normally nitre isn't very effective at toughening the gold in this manner because it can't distribute throughout the melt. 

Now consider when it's mixed through the cement silver from AgCl/Fe/H2SO4 reduction process by washing the filter cake with a mixture containing sodium carbonate, sodium nitrate, and borax. _It's flux in situ_.

My experience/thoughts on it are 

1.) no way to ever rinse out ALL of the iron and other soluble species in the cement. Maybe most but never all (can tell by the color of the borax slag
2.) using the flux rinse precipitates base metal carbonates/hydroxides but doesn't blind the filter because the cement silver acts as a filter aid. 
3.) the flux ingredients distribute all over the filter cake and dry onto the individual metal particles. As the material is briquetted and put into a crucible and heated, the nitre first does its work by melting (I think it melts at like 450C), wetting and oxidizing any impurities to oxides and keeping them there. I also believe it can oxidize/mediate the conversion of AgCl into Ag2O (which goes to metal) and Cl2 (which goes to stack). 
4.) any unconverted AgCl reacts with the carbonate like the classic Kundu process. The stuff still isn't quite molten but now all the silver is metallic.
5.) any unused carbonate thins the borax and keeps the viscosity of the slag-flux low so that clean silver can coalesce and pool
6.) all the slag ends up on top, all the silver on the bottom.

In this fashion, I was able to obtain commercially pure silver from cement silver fairly consistently. 

I do worry about HCl laden damp AgCl with Au in it or any soluble gold chloride salt. Adding nitre to it basically makes aqua regia if HCl is present and I suppose but don't know if that'll cause Au accountability issues. I think the best thing there is to cement the silver with iron and not even attempt to go straight from AgCl to silver in this method. 


A shout out to solar_plasma for testing it and showing photos of the result.


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## peter i (Aug 1, 2019)

Nice! 
Thanks for the walk-through.

It makes very good sense.


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