Brown Powder after converting AgCL with sugar?

[Punterr]

Dear all,

Help please....

I had some Silver Chloride which i had attempted to convert back to silver metal with lye (NaOH) and sugar.

The lye was added to the AgCl (very little water) and the solution turned black as expected (forming silver oxide) , however when adding the sugar to convert to silver metal the solution and resulting deposit changed to a brown colour not a grey silver colour as expected.

Please can anyone have an answer or a suggestion to what it may be and or what may have happened?

Many thanks in advance.

 

[orvi]

Does the solution heat when you added sugar ? Thing is, it doesn´t look like silver to me. Maybe heavily contamined AgCl. If you have silver oxide - without AgCl (passed "smear test"), conversion to Ag metal is very quick when hot (past 80-90°C), and silver cement is grey. Everytime. Depending on what reducer you use (glycerin, sugar, syrup etc), the color of the solution can be ranging from yellowish, to reddish brown to just dark. But ppt will be white.

I suspect contamination with another metal. I dont feel that copper will cause this, but I don´t know for sure.
How did you obtained silver chloride ?

 

[Punterr]

Silver metal was from smelting. Silver was used as the collector, then parted with nitric.. and converted to AgCl with salt solution. Was initially white, buy had a purple hue to it.. maybe it was trapped gold?

 

[orvi]

I wonder if lead isn´t mixed with your batch. If it is from smelting - and we don´t know what was smelted...
It could just happen that your silver was reduced to nice bigger particles, which could be white-ish colour, compared to regular grey coloured particles.

I would take a small sample of that suspension, filter it and try to smelt it as is, and then with sodium carbonate as flux. Be careful as toxic fumes could evolve in these experiments, if you have silver, lead or worse cadmium present.

If you see glassy slag arising from direct smelting of the precipitate, you have unconverted silver chloride mixed with probably silver. If you had mixed lead chloride with silver chloride (lead chloride has not the best solubility in cold water, and if you do not wash multiple times with hot water, it stay in) - so you produce mixture of lead oxide/hydroxide and silver metal, you will see melting the oxide into dark slag (as during cupellation) and some silver remaining.

Smelting with sodium carbonate could help you to convert AgCl to Ag back again during the smelting.

 

[Punterr]

OK many thanks Orvi,

Good info, as far as i know there is no lead in the mix..anyway i will check it out.

Best regards

 

[Yggdrasil]

I think lead is at best in small amounts. I was there during smelting and dissolving.
It was dissolved in Nitric and completely clear until salt was added. The salt should not change solubility of Lead Nitrate that much.
What about the Iron Sulphuric method?

 

[Shark]

Lye and sugar for clean silver chloride. Iron and sulfuric will work better on silver chloride that less clean.

 

[Punterr]

Ok, 'less clean'.. i got it..😁
I have a small iron Wok and some 30% H2SO4 (maybe dilute a little?). I will try that on the next small batch, which should be in a few days time.

Many thanks

 

[orvi]

Fe/H2SO4 takes time to complete. I don´t recommend wrecking the iron pan for this. Better may be to use some old pieces of iron punchings, or screws/pieces of iron rebar etc. and get them tumbled with AgCl. It must agitate otherwise practically nothing will happen.

 

[Shark]

10% sulfuric. And as mentioned, it needs aggressive agitation. Or tumble them with something like this.

 

[4metals]

Lye and sugar for clean silver chloride. Iron and sulfuric will work better on silver chloride that less clean.

Iron and sulfuric is a good process for dirty silver chlorides from an aqua regia process. It is a good way to reduce chlorides to determine how much gold is in them by parting and weighing the gold. If you have a good analytical balance laying around. (some of us old chemical nerds actually do!) Then you can decide if you want to process it immediately by dissolving all of the Silver to get the gold and dropping the Silver Chloride to convert with Lye and sugar, or run it in a silver cell if the gold is lower in concentration.

 

[geedigity]

Have you rinsed the brown converted material? The color of the silver appears to have a gray tinge to it. Many times when I run the conversion of AgCl to Ag, if I use a lot maple flavored pancake syrup, the Ag has a brownish tinge. However, even if I use the clear Karo syrup, the mixture still will have a brownish tinge to it. What type of sugar did you use?

Also, per Palladium, when rinsing the silver, add a bit of HCl. This will help the silver settle quickly.

 

[Palladium]

What was the source of salt? I had this happen one time to me. I use commercial pool salt in my system. It's not as clean as table salt. I used to add it as a solid and stir it in. After i had the problem i started dissolving and letting it settle first before adding. You would not believe the sediment left over. Try dissolving some of your salt in water and let it settle. That should give you a clue.

 

[Lightspeed]

maybe take a small sample of your converted product, from the pics your silver may be ok but in need of a really good rinse as is normal with the AGcl process, give your sample many rinses to get rid of your caustic and brown ick. If your powder comes out greenish grey in colour i would say you are ok, if not then all of the above advice applies.

@Palladium is dead on with his statement of the salt used, table salt or table rock salt if need be even go to the trouble of filtering this solution if its dirty, i personally never just dump a solid salt into the solution i am reclaiming from, if i use salt i always add as saturated solution only. I only do chlorides from my stock pot nowadays as i HATE dealing with AGCL, (but i know what metals are in my stock pot also as i know the feedstock used, you may have a different monster in this case) due to this i can just use a small amount of good quality HCL for conversion to chloride in the stock solution, even clean your AGCl with an acid rinse before you go to the oxide conversion step to clean it up a bit and ensure your AGcl is thoroughly rinsed (hot water rinses) before converting to oxide. whatever i retrieve from chlorides is always melted into shot then re digested into nitric before cementing out again. Many threads on the topic.

https://goldrefiningforum.com/threads/rinsing-silver-chloride.29824/

 

[Punterr]

Thanks to all for the additional info (Orvi, Shark, 4metals, greedigity, palladium, Lightspeed, Yggdrasil)


I will take all this into account for the next batch, however, for this small test batch (the brown stuff), further to my last, i put in a small amount of Nitric for a while and then for fun i added some HCL (now AR) and the colour changed to a grey/purple. I tested with stannous and there was a small indication but not much.

I will wash it and put it in a crucible and melt it with some soda ash and start again. 😁

Anyway many thanks for the help

 

[orvi]

Powder look very heavy. That is a good sign. Also compacted like silver or silver chloride would look like. Just that colour isn´t spot on. But if you are having some stannous indication, there could be some PGMs or even gold, so be cautious with throwing away washes from AgCl, since PGM chlorides are soluble.

 

[GuyGuyGuythe1st]

Sorry I am late to the party. @Punterr it is contaminants from other metals. You get it from not washing the AgCI enough. Especially if it is drop from dirty solutions. When you convert it with sodium hydroxide. The hydroxide will oxides other base metals present in the AgCI. The best way to deal with this situation is to 1.) once converted with hydroxide. Dissolve the Ag Oxide back in nitric/distilled. 2.) cement out on a piece of sheet copper. 3.) Rinse and repeat your first process.

Also speculation, is you are not adding enough hydroxide/sugar during the conversion process. Suggestion use a stir plate when adding the chemicals in to assure its in direct contact with the particles.

PresidentGold

 

[Punterr]

Many thansk 3Gthe1st..

I will take it into consideration for the next batch..

All the best..

 

[Swissgoldrefiner]

It happen to me too. Few times...
I found out that thr main reason is that the befor adding the sugar, the solution is not enought hot.
The brown powder, even after wash, smell sugar/caramel.
The strange thing is that when you try to add water and heat it, it release some Cu ( solution goes blue). If you try after that to add sugar...there is no change.

 

[SteveevetS]

Dear all,

Help please....

I had some Silver Chloride which i had attempted to convert back to silver metal with lye (NaOH) and sugar.

The lye was added to the AgCl (very little water) and the solution turned black as expected (forming silver oxide) , however when adding the sugar to convert to silver metal the solution and resulting deposit changed to a brown colour not a grey silver colour as expected.

Please can anyone have an answer or a suggestion to what it may be and or what may have happened?

Many thanks in advance.

found this interesting
https://woelen.homescience.net/science/chem/solutions/ag.html