Can I just go ahead and melt it?

[Dawnsdad]

I have used LaserSteve's method of NaOH + sugar to convert AgCl. But I am going to be processing a lot of material soon and would like to simplify things if possible.

I am using an induction melter. In the past, I have just melted AgCl with soda ash. That seemed to work fine but I'd prefer to go ahead and get the Cl out with NaOH before I melt. If I am not mistaken, the result is silver oxide. Is there a practical reason to not just wash, dry and melt at that point rather than adding sugar? Wouldn't the melting release the O2 and leave more or less pure Ag? I'm not concerned about getting the highest possible purity because I have to take it to a refiner anyway and they will melt and assay.

 

[goldsilverpro]

If you can convert 100% of the silver chloride to silver oxide with the NaOH (hard to do without power mixing for a couple of hours), there will be no problems with direct melting. The oxygen comes off at a fairly low temperature and you can then pour all of the silver into bars when it is molten. If less than 100% is converted, there will be a silver chloride layer on top of the silver bar. Any slag will form a 3rd layer on top of the silver chloride. Once you get silver chloride into that solid form by melting it, it is a big chore to refine it.

You could test the silver oxide for unconverted silver chloride first by putting a pinch in a small beaker and rinsing it many times with distilled water until the pH of the rinse tests between about 6 to 8 - hot distilled water rinses will speed this up somewhat. Then add a few ml of 50/50 nitric cut with distilled water to dissolve all the silver oxide. If silver chloride is present, you will see a white precipitate. If that happens, add a little more NaOH and stir it longer. Retest.

The NaOH requirement is probably the same as what's needed with the NaOH/Karo method. If so, that would be 22g per troy oz of silver. That's about 10% over what is really needed, but I often add a little extra of certain chemicals (except nitric) in my processes. Usually it's better to add a little extra and make sure, than have to redo it or suffer a loss.

Never let the silver chloride dry out! It will tend to crystallize and that will impede, or even make impossible, 100% conversion. The drier and/or older the silver chloride, the harder it is to convert. The mixer used should have a chopping action for best results. A search will bring up discussions of members using blenders for this, but strong NaOH can play havoc on some types of rubber seals.

If you don't have a power mixer, I would suggest using a plunger stirrer when converting. A drum-size one is essentially a 3/4" plastic pipe with a 6" plastic disc mounted on one end. A bucket-size one can be an actual plunger from the hardware store. The motion with a stir rod stirs the liquid around in circles. The up and down motion of the plunger stirrer lifts the silver chloride and totally mixes it with the liquid. With a drum, 2 or 3 of us would stir for about an hour, taking turns. Here again, don't let the AgCl dry out. Keep it moving and keep it wet. Don't let it sit around.

 

[MarcoP]

As GSP notes a couple of times, a good stirring is essential otherwise this process leads to losses. I've done two small scale experiments, the first went decently, the second one was a disaster since the rubber seal started leaking badly due insufficient wash after the first use.

Processing silver chloride with lye and sugar is sensible and needs two steps to get to metal.

I believe that if you really want to simplify and fasten the whole procedure use 5% sulfuric and iron nails with a plastic tumbler, no silver chloride will survive. Search for the exact procedure in Lou's posts. After much reading it came up to be the perfect method for my circumstances. One step, simple, easy, fast and produce pure metal.

Marco

 

[goldsilverpro]

I believe that if you really want to simplify and fasten the whole procedure use 5% sulfuric and iron nails with a plastic tumbler, no silver chloride will survive. Search for the exact procedure in Lou's posts. After much reading it came up to be the perfect method for my circumstances. One step, simple, easy, fast and produce pure metal.

I agree.

 

[Dawnsdad]

Thanks for the replies. I do batches that amount to about 50oz each time in 5 gal. buckets, stirred with a paint mixer drill attachment. I'm pretty sure that I get all the AgCl converted.

 

[kurtak]

Thanks for the replies. I do batches that amount to about 50oz each time in 5 gal. buckets, stirred with a paint mixer drill attachment. I'm pretty sure that I get all the AgCl converted.

If you are running that much silver at a time why are you not cementing the silver back out of solution with copper & then running it in a silver cell :?:

Kurt

 

[Dawnsdad]

Thanks for the replies. I do batches that amount to about 50oz each time in 5 gal. buckets, stirred with a paint mixer drill attachment. I'm pretty sure that I get all the AgCl converted.

If you are running that much silver at a time why are you not cementing the silver back out of solution with copper & then running it in a silver cell :?:

Kurt

lol, because there's not enough hours in the day. I recycle waste for a major manufacturing company. The big stuff, I just clean up and take to a refiner and let them do the hard work. That stuff amounts to over 1,000 t.oz a month. If I refined it, they are going to melt it anyway. I'd get melt loss that would cost me as much as I would gain from bringing them purer silver. The way I do it now, they melt it and assay, and pay me for the total silver content. The material I am processing here is stuff that I have yet to find anyone who gives me a reasonable return. It's a very fine powder that comes from grinding parts. I sent samples to several major refiners and the best assays I got came to close to 1 oz/lb. But my experience has been that most refiners don't even want to mess with it. The ones who do seem to start with a reasonable return at first but the oz/lb begins to gradually drop. I know processing this material is a lot of trouble, but that's what they are supposed to be in business for. The declining results leave me with the feeling that either they don't care to do the best job they can or they are simply stealing. I really don't care which is true, I just care about the results. So I am left with processing it myself. This powder is so fine that it floats on water. I have to wash it several times using a surfactant. Each wash takes about half a day just for the particles to settle out. When I finally am done with the wash, I start adding nitric. This reqires a lot of care because there is so much surface area that the reaction with the acid can be almost explosive if the acid is too concentrated. I tried cementing with copper but that takes too long. Dumping brine in the solution is pretty much instant precipitation. I can dry it and melt with soda ash but I don't like to deal with the chlorine gas. I get about 300-400lb of this stuff a month, so copper isn't very practical for me.

 

[goldsilverpro]

I would sure want to know the silver content before processing. For about $200-$300, you could set up to analyze the silver in solution, before adding the NaOH, using the Volhard titration method - very fast (~10 minutes) and quite accurate. Are you sure you're using enough NaOH? If you don't use enough, you will likely lose silver in the melt.

What do you think the Ag % should be? Why? What are the other metals? What type parts are manufactured that generate these grindings?

 

[Dawnsdad]

I would sure want to know the silver content before processing. For about $200-$300, you could set up to analyze the silver in solution, before adding the NaOH, using the Volhard titration method - very fast (~10 minutes) and quite accurate. Are you sure you're using enough NaOH? If you don't use enough, you will likely lose silver in the melt.

What do you think the Ag % should be? Why? What are the other metals? What type parts are manufactured that generate these grindings?

I have to be careful what I say because my customer and I have a mutually binding non-disclosure agreement. The other metals are copper and zinc....probably a little ferrous metals as well, but only traces. I try to be sure that I use a little more NaOH than is needed and I mix for quite a while. As for the powder, I can ouly go by the previous assays for the Ag %. This powder is so fine that you can pour it from a glass like water. You can't just melt it, even with different kinds of flux. All you get is a sticky mess. The first refiner I found that would process it got about .75 oz/lb in the first batch they did for me. But the return declined steadily with each progressive batch I sent them. The last I sent them only yielded .32 oz/lb. They always had excuses why. Sorry but I don't buy it. This powder is very consistent. Same source material, same workers,etc. It gets sucked into a ventilation system and deposited in a drum.The only variable is the return from the refiner and the decline in results was consistently lower and lower. I found another refiner capable of processing this stuff and they got .73 oz/lb on the first 1,000lb I sent them. But the second 1,000 only got .62. Funny how that seems to work. I can understand a slight variation but, like I said, this dust is very consistent. .11 is a pretty big variation. On a much smaller sample, it would be believable. But 1,000lb is a big enough sample to cover variations in the source material. .11 difference batch to batch is about 110oz. That's a lot of money.

 

[kurtak]

The other metals are copper and zinc....probably a little ferrous metals as well, but only traces.

You can't just melt it, even with different kinds of flux. All you get is a sticky mess.

I sent samples to several major refiners and the best assays I got came to close to 1 oz/lb.

First off I am not sure why you are having a problem doing a smelt on this material - it may be because you are not using enough flux & or your flux combination is not such the it runs fluid enough to provide good circulation in the crucible when molten & thereby allowing for good collection &/or settling when poured to a cone mold

That said - I don't think I would go with trying to smelt this material to start anyway

However - I think I would still go with a cementing process because you already have the base metals to do so --- its just that they are in the form of a powder rather then a solid mass (like a buss bar)

Considering you have a constant large volume supply of this material I would set it up as a sort of "counter current" leaching/recovery process using the powders them selves to cement the silver from the first batch - then the second batch - then the third - & so on

You said you get 300 - 400 lbs/month & that you do your batches in 50 ozt Ag per batch with recovery of 1 ozt Ag per lb material so that's 50 lbs material per batch

The principle of "counter current" leaching (then recovery) is to increase yield with better chem utilization &/or less chem & therefore less waste &/or chem cost

How it works - You start with your first batch (50 lbs) - dissolve all your metal (copper/zinc/silver) --- then "before" you start your next batch - you use some of your powder (which contains copper & zinc) to cement the silver from batch one - so you get the silver back from batch one "plus" the silver in the powders used to cement the silver from batch one

So - what you have done here is you have used some of your powders to recover the silver from batch one (thereby reducing the amount of powder you have to process) AND you have also increased the yield of batch one

Now - repeat that process with each batch till you come to the end of your 300 - 400 lbs of your material & you will find that your last batch is going to be smaller in size (which means less chem over all) because you have used your powders (for the copper & zinc in them) to cement you Ag from each previous batch

Setting it all up - with the volume of material you are getting on a constant bases - I would go buy a floor model variable speed drill press with a chuck that will chuck a 1/2 inch drill bit - then have a stir rod/paddle made with a 1/2 inch SS rod & SS sheet welded on one end for paddles & a snap ring barrel (like in the pic - which is a 25 or 30 gallon drum) drill a 5/8 inch hole in the center of the lid for the stir rod to fit through & then drill another hole over to the side of the lid to set a funnel into for adding your powders to the reaction vessel (drum)

Fill the drum 1/4 - 1/3 with your 50/50 nitric/D-water - put the lid on - turn the drill press on to start stirring - put the funnel on & start adding your powders

If your material is in fact relatively consistent (as you say) you should be able to determine how much powder to ad (per volume of acid/water starting in the drum) to attain the initial complete dissolved & pregnant solution (as well as reaction time to complete it) & then how much more powder to ad for cementing - with a 90% plus silver cement as your end result --- by first doing a few 1 lb batches to come up with large batch calculations

I would also plumb the reaction vessel (drum) to vacuum the Nox through a scrubber with H2O2 in the first scrub chamber to recover nitric which can then be used for dissolving following batches --- thereby reducing the amount of "new" chem (nitric) needed for each following batch

At least as you have explained the material & the fact that you have an on going continued supply of it - this sort (or some sort) of "counter current" leaching/recovery is what I would explore - as it will reduce chem use/needed - reduce waste & increase yield per chem used

& you will not need to mess with first washing the material with a surfactant - the acid & the stirring should take care of the metals as they are added to the reaction vessel --- I use ultra fine copper (- 300 mesh) sometimes to cement values from my stock pots - between the reaction with the acid & the stirring it poses no problem even though the copper powder wants to float if just added to solution or solution added to it - without stirring

Kurt

 

[Lou]

Geez, what Kurt said.

Yeah, iterative concentration is the key. Sometimes one doesn't have the option if the material is in low grade but high in volume.

When we used to do much, much more silver, all the low grade 50% or less stuff got melted with copper cement or buss bar to alloy it down, and was then used to cement out silver, the net result being a higher grade 95% silver mud that could be further smelted to up it to a high grade anode feed.

I would say that you can probably smelt the stuff, I'd look at a sample if you want. It might just not be the right flux composition--there could be some finicky stuff in there. An example of a devilish material that's almost impossible to melt into silver without pretreatment is silver paste (an emulsion of silver powder in mineral oil, various celluosic polymers and other thickening agents). The silver paste needs spread into pans and incinerated before being milled with borax/carbonate and sent to the furnace.

Regarding your material, and not having all the details, probably what is happening is improper treatment in the beginning at the refiner. If it's only 31.1 g Ag/lb, the balance of the material is probably what is holding up values in the slag and giving such a bad recovery. I'm just presuming they're melting it, as that's what pretty much everyone likes to do for various reasons.

So like, what is this, an atomized powder that floats on water due to surface tension? Might also be that they added some sort of grease or perhaps anti caking agent. More you can tell us about generating process, the better we can be to help. You can contact me privately by PM if you wanna discuss further; send over a mutual NC/NDA if you like, or I have a generic one.

Lou

 

[Geo]

Take a sample that is a nice round number and record the weight as low as you can and incinerate the sample or just roast it really well and then re-weigh it. That will give a good ratio of organic material in the mix. Proceed to mill the sample and smelt with your flux but add a thinner like fluorspar and see if it helps. Two quick fixes so even if it's either, problem solved.