Creamy-coffee colored suspension appears when washing silver metal powder

[Geber]

If someone could tell me what in God's name this is and how to fix it that would be greatly appreciated.

This was my first jewelry sweeps refine. I burned them with a torch until they wouldn't smoke. I dissolved them in hot dilute nitric acid. I filtered the solution in a Buchner funnel with a medium filter paper and set any solids aside. The solution looked very clean and blue. I added HCl and got some nice AgCl. This I washed many times with hot distilled water until it failed an ammonia test. Then I converted to Ag2O with lye. The Ag2O had an unusually light brown color that I had never seen before. It usually looks almost black when I do it. Even still, it was homogeneous looking and extra lye did not make it darker. Then I added some glycerin with water to reduce it. I stirred it and it never got very hot. The beaker became mirrored and then the mirroring went away and it looked like all the metal was completely reduced, some 150 g.

I resolved to wash it until the water had a neutral pH because I wanted to see if getting rid of the NaOH would make a noticeably purer silver`. It was somewhere like 13-14 and took many many washes with distilled water, heated to steaming temperature. Every two washes, I tested the pH with strips. As it got to 8, and then seven, the COFFEE color appeared. Adding distilled water, which was clear, caused the coffee color when it hit the silver. All the previous washes did not do this, but once the coffee appeared, every wash after that caused it to reappear. It is now sitting in the coffee-colored liquid (hopefully it will be ok tomorrow).

A few caveats: I distill my water with a Vevor water distiller. I use water that is filtered, but has some oxides suspended in it, but it comes out clear. I'm pretty sure the same batch of water was seen causing the coffee color and being clear on the silver. Before the color appeared, the silver behaved very well in terms of sinking down, like gold in a gold pan, and was easy to decant. When the coffee color appeared, it seemed to want to float on top more. I think it is a suspension or colloid, not a solution because it is opaque. Finally I would add that this color, or something similar, but more green, appeared when I first added the glycerin water. Is it silver? Should I try to wash it all off? Will I lose silver? Please help.

Thank you

 

[4metals]

First off Ag₂O is always black or very dark brown. The mud you showed I assume was the result of filtering out the solids after you treated the Silver Chloride with lye. Bottom left image. It actually looks more like what the Silver metal looks like after reduction. Are you sure the lye you used had no additives? I am a bit spoiled having always used bulk reagents for processing and the Silver Chlorides always came out black and uniform. So the first question was the lys just sodium hydroxide or were there additives?

Second did you reduce the oxides with glycerine? I am not familiar with that process as I always used sugar or corn syrup. If you did mean glycerine what was the process you followed?

 

[Geber]

First off Ag₂O is always black or very dark brown.

I should have taken a picture of the silver oxide. It had to be silver oxide... It's what I got when I added the lye to the AgCl.

The mud you showed I assume was the result of filtering out the solids after you treated the Silver Chloride with lye.

All three of those pictures with the mud - that's silver metal after reduction. It looked totally normal until the pH got to around neutral. Then the creamy coffee color appeared.

I didn't filter anything after treating the AgCl with lye. I left in the beaker and reduced it.

Are you sure the lye you used had no additives?

Yes. It says 99+%.

Second did you reduce the oxides with glycerine? I am not familiar with that process as I always used sugar or corn syrup. If you did mean glycerine what was the process you followed?

Yes I reduced the oxides with glycerin. It's the same as sugar/corn syrup. I added a mixture of glycerin and water to the silver oxide and stirred it in.

 

[4metals]

I started using the caustic corn syrup method in the 1970's when Silver was $4 an ounce so more a nuisance than it was worth. So I used corn syrup because it was, and still is, cheaper than glycerin.

You said the original material was jewelers sweeps. Were there any brushes and buffs in there before you burned them? Brushes often have lead hubs and can generate sweeps loaded with lead. Lead is soluble in nitric acid and will drop out of solution with Hydrochloric Acid along with Silver. Is it possible that a percentage of your white chlorides were partially lead chloride. Lead chloride is soluble in hot water and Silver Chloride is not (or much much less soluble than lead chloride). Did you boil the chlorides to assure no lead chloride was in the mix?

I may be grasping at straws here but lead may be a part of the problem.

 

[nickvc]

Knowing how many throw all sorts in the sweeps is it possible there was some tin in the mix ?

 

[Geber]

I started using the caustic corn syrup method in the 1970's when Silver was $4 an ounce so more a nuisance than it was worth. So I used corn syrup because it was, and still is, cheaper than glycerin.

You said the original material was jewelers sweeps. Were there any brushes and buffs in there before you burned them? Brushes often have lead hubs and can generate sweeps loaded with lead. Lead is soluble in nitric acid and will drop out of solution with Hydrochloric Acid along with Silver. Is it possible that a percentage of your white chlorides were partially lead chloride. Lead chloride is soluble in hot water and Silver Chloride is not (or much much less soluble than lead chloride). Did you boil the chlorides to assure no lead chloride was in the mix?

I may be grasping at straws here but lead may be a part of the problem.

I had a gallon of glycerin from another project so I have been using that. Like I said I washed the chloride with near boiling hot water many times. Brushes like the things with bristles? I did not see any brushes. What are buffs, like buffing wheels? Didn't see any of those or pieces of them. I'll ask the jeweler.

The thing is everything seemed normal until the pH got to 7-8 by me washing the alkali/glycerin off the reduced metal. Right then the coffee color appeared. I really want to know if it is silver so I don't wash it away.

Knowing how many throw all sorts in the sweeps is it possible there was some tin in the mix ?

I guess it is possible, but they would be dissolved in the nitric acid and not precipitate with the silver (and lead) chloride.

 

[Yggdrasil]

I had a gallon of glycerin from another project so I have been using that. Like I said I washed the chloride with near boiling hot water many times. Brushes like the things with bristles? I did not see any brushes. What are buffs, like buffing wheels? Didn't see any of those or pieces of them. I'll ask the jeweler.

The thing is everything seemed normal until the pH got to 7-8 by me washing the alkali/glycerin off the reduced metal. Right then the coffee color appeared. I really want to know if it is silver so I don't wash it away.



I guess it is possible, but they would be dissolved in the nitric acid and not precipitate with the silver (and lead) chloride.

No Tin do not dissolve in Nitric, it creates the dreaded Metastannic acid.
But it would as such not follow the Silver Nitrate into the Silver Chloride.

Any reason you did not cement the Silver on Copper?
It is a much cleaner process with much less waste.

 

[Geber]

No Tin do not dissolve in Nitric, it creates the dreaded Metastannic acid.
But it would as such not follow the Silver Nitrate into the Silver Chloride.

Any reason you did not cement the Silver on Copper?
It is a much cleaner process with much less waste.

Wow never knew that. I don't think he works with tin but I have to ask him.

I did not cement on copper because I wanted 999 silver and don't have a silver cell yet.

 

[Geber]

The jeweler does not think there could be any lead or tin.

Grok has some interesting suggestions:
1. Silver not completely reduced. There may have been Ag2O hiding in the silver that has formed a suspension.
2. Colloidal silver. The water is being colored by extremely fine silver particles.

I'm concerned because it looked how it's supposed to look all the way down to pH 7-8. If this was caused by pH change, it would have to mean that I didn't reduce all the silver oxide, right? Has anyone ever seen this before?

In the case of colloidal silver, should I just wash it until it stops giving the coffee color? Should I just add a little base and see if it stops and then dry the silver? Do you guys bother to wash all the base out, or just wash out the reducing agent?

 

[4metals]

Brushes like the things with bristles? I did not see any brushes. What are buffs, like buffing wheels?

Yes brushes are polishing bristles that go on a wheel, buffs are similar but fabric and the rouge is put on them to polish. The wheels have a wooden core. Large jewelry manufacturers keep them separate but smaller shops often throw them in with their bag house rouge, some even burn them first.

 

[Geber]

Yes brushes are polishing bristles that go on a wheel, buffs are similar but fabric and the rouge is put on them to polish. The wheels have a wooden core. Large jewelry manufacturers keep them separate but smaller shops often throw them in with their bag house rouge, some even burn them first.

I did not see any. Maybe there were small pieces. Everything was filtered through a medium filter paper before crashing out the AgCl. Do you think the color could be caused by these contaminants after filtration?

Also do you bother to wash your silver metal powder after lye/sugar until it is no longer basic? Or do you just wash off the sugar?

 

[4metals]

This is the spreadsheet I made years ago for converting chlorides using corn syrup and caustic. I never rinsed between the caustic addition and the corn syrup. I felt the heat from the caustic sped the reaction along. however the blue liquid you have with the chlorides on the bottom is not what I would start the process with. The chlorides need to be rinsed until the rinses flow clear because the caustic will drop any copper or base metals as hydroxides to mix with your clean chlorides.

 

[Geber]

This is the spreadsheet I made years ago for converting chlorides using corn syrup and caustic. I never rinsed between the caustic addition and the corn syrup. I felt the heat from the caustic sped the reaction along. however the blue liquid you have with the chlorides on the bottom is not what I would start the process with. The chlorides need to be rinsed until the rinses flow clear because the caustic will drop any copper or base metals as hydroxides to mix with your clean chlorides.

I'm asking if you rinsed after you added the syrup more than just removing the syrup. Did you remove the rest of the caustic?

 

[4metals]

I'm asking if you rinsed after you added the syrup more than just removing the syrup. Did you remove the rest of the caustic?

After the chlorides were converted to metallic Silver I rinsed until the water ran clear. The Silver metal is well behaved so I decanted the liquid added more liquid and agitated well, decanted again, and continued until the water ran clear. I never checked the pH. Then the Silver and remaining liquid was poured on to a büchner funnel and the remaining water was sucked out until it was dry enough to melt.