Silver chloride to Silver

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Swissgoldrefiner

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Hello,
I would like to change silver chloride to silver metal.
I know that we can add it in caustic soda and then with dextrose obtain the silver powder.
However, i would like to know if there is a way to disolve it in ammonia for example and then make the silver powder precipitate.
My main problem with the caustic soda is:
1. if you add too much of caustic soda it can go to Silver hydroxide and lower yield.
2. Some thimes, if i dont crush the silver chloride well in powder, the caustic soda react only in surface of AgCl and there is some un reacted AgCl.

So i imagine, if i can dissolve it in some reagent and then make the silver precipitate, it can be much more better.

Thank you guys!
 

Geo

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Add sodium carbonate until PH is neutral. Rinse with fresh water to remove excess carbonate. Add fresh water to cover the converted chloride well and have two thirds of your container open for foaming and expansion of the contents. Heat the material to 212°F or to a light slow boil. Start adding formic acid in small doses allowing the reaction to foam up and die down after each dose. If it doesn't react with the first dose, do not add more. Increase the heat until the reaction occurs. Maintain that heat and proceed with dosing and constant stirring. When the conversion reaches a certain point, the glass will "mirror" over on the inside but will clear by the end of the process. The process is complete when there is no reaction with the hot solution when more formic acid is added. Add 5 - 10 ml's per dose. Add slowly while stirring as the reaction tends to foam up.
 

Swissgoldrefiner

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Add sodium carbonate until PH is neutral. Rinse with fresh water to remove excess carbonate. Add fresh water to cover the converted chloride well and have two thirds of your container open for foaming and expansion of the contents. Heat the material to 212°F or to a light slow boil. Start adding formic acid in small doses allowing the reaction to foam up and die down after each dose. If it doesn't react with the first dose, do not add more. Increase the heat until the reaction occurs. Maintain that heat and proceed with dosing and constant stirring. When the conversion reaches a certain point, the glass will "mirror" over on the inside but will clear by the end of the process. The process is complete when there is no reaction with the hot solution when more formic acid is added. Add 5 - 10 ml's per dose. Add slowly while stirring as the reaction tends to foam up.
Dear,
Thank you for your help. The matter is that i may have 50 kilo batch of AgCl to react. I mostly need some industrial way to convert it.
But i will try your way, it looks interessting.
 

Geo

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It can scale up. Just remember to leave the reaction 2/3 open. It can be processed in stainless steel if that will make it easier to acquire a reaction vessel large enough.
 

Geo

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Too, I have found that as long as enough formic acid is added for complete conversion, copper will stay in solution at the end of the process. So, this is a refining process and not a recovery process. The silver should be pure when finished if the process is performed properly.
 

orvi

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Dear,
Thank you for your help. The matter is that i may have 50 kilo batch of AgCl to react. I mostly need some industrial way to convert it.
But i will try your way, it looks interessting.
i would proceed very carefully with those quantities, as you dont want to lose it because of improper method used.
ammonia is dangerous combined with AgCl in that quantity, and you will need a lot of ammonia just to dissolve it, not mentioning reducing agent.
most straightforward method with minimum capital investment is hydroxide/sugar method or to go with formic acid, as geo proposed to you.
i personally like to do things quickly and avoid heating and boiling/refluxing as much as possible (if it could be done quickly and easily).

i stick to lye/sugar with AgCl, but i never run batch larger than one kg. and with my setup for the reaction, I DON´T RECOMMEND TO SCALE THIS UP, IT COULD BE VERY DANGEROUS. better to go for multiple batches like this, reducing the risk of chemical burns and messy runaway reactions. also, i like it only for the easy and cheap setup. for amateur it is impossible to check precisely what is going on, and if the stage of the procedure is completely done, or not. defining the completness of reaction by witnessing a colour change from brown-black to straight black is somewhat "unscientifical". not to mention you are going from solid AgCl to solid Ag2O to solid Ag.

SO, trick is to finely disperse the suspension, wash well from impurities such Cu2+ (if there is washable contamination) with boiling water from kettle few times. precipitate nicely packs down and settle quickly after this treatment. then still hot AgCl cake is drained of majority of water in such manner, that the formed paste is relatively "liquidy", when stirred or swirled.
then add solid sodium hydroxide with stirring, and after each addition stir for like minute and observe, if the sludge is darkening. it must be black coloured sludge, not brown-black and no white spots should be seen. take the stirring rod and push it to the wall - if there are "lumps" of encaged AgCl, you will clearly see the white parts.
you dont want a lot of water in, as it then consumes ridiculous ammounts of hydroxide (silver hydroxide will dehydrate less easily, and thus converting back to AgCl). it should be less than a kilogram and half for kilogram of AgCl. when the pot is moved to the side and milky white-coloured liquid start to separate, too much water was probably at the start, as white colour indicates reforming AgCl in mixture. slightly opalescent is OK.
more of the added lye dont hurt the reaction, only your wallet :)

mixture is now very hot already. dont allow it to cool down, otherwise you will need to heat it up again (more than 90°C is advised). i preffer to do this in ordinary round PP bucket (10-12 L in capacity) inside the catching pan. fill it just to 2-3 L mark (max 25% of capacity), never more, as the violent reaction could splash and spit boiling lye around - certainly nothing you wanna experience flying towards you :)
usually i swirl the whole bucket, stirring rod is less efficient for this i think.
than, measure few hundred grams of ordinary sugar (i go with like 200-300g, but this is maybe huge excess), dump it evenly to the sludge, quickly swirl the whole bucket (sugar distributes evenly and very quickly dissolves to hot mixture) and stand back or promptly move down protective window on the fume hood. usually there is induction period of like few seconds to one minute, when violent boiling will occur. after the reaction die down, i usually add like a tablespoon of sugar more, with thermometer in, just to be sure there is no rise in temperature - and assuring all Ag2O was reduced.

after diluting with water and sequences of decant/wash (wash multiple times, as improperly washed Ag with sugar residue will charr badly on melting, making very hard time for you to get it into the nice ingot), powder is readily melted with a basic borax/Na2CO3. this would assure any possibly entrapped AgCl would transform to Ag2O in contact with base, which in turn decompose spontaneously to silver and oxygen :)

more industrially, direct smelting of AgCl with base is certainly viable in some approach, but i never attempted it personally. vaporizing AgCl is a real issue, not just considering the losses but also safety.
maybe some more skilled members could give an advice :)
wear good quality gloves working with either hot lye or hot soda/formic acid. fume hood is very advised for both reactions, mainly the stench of formic acid is pretty sharp and disgusting :D
stay safe :)
 

snoman701

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Easiest way for that quantity is iron / sulfuric acid in a cement mixer.

You just have to rinse it really well after taking the iron out. That in and of itself is somewhat difficult.
 

snoman701

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Direct smeling of AgCl with carbonate has significant losses. If you aren't set up to capture those losses via your scrubber, I wouldn't do it.
 

Swissgoldrefiner

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Thank you guys and specially thanks for orvi.
I have a master degree in chemistry, However, i have some question/remarque.
You said that you may add 1.5 kilo of NaOH for 1kilo of AgCl. That mean you use 37.5 moles of NaOH to react with 7 moles of AgCl...for me it looks too much.
You mention as well that the only matter is the cost, but you need to keep in mind, you gont get AgO from AgCl. First you get AgOH, which is not stable and convert it self to AgO. If you add too much NaOH, i think you will push the reaction to move back from AgO to AgOH.
Another remarque/question: you mention i dont must let it cool down, why? because the oxydation of the aldehyde with AgO need temperature?
more of the added lye dont hurt the reaction, only your wallet
 

Swissgoldrefiner

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It can scale up. Just remember to leave the reaction 2/3 open. It can be processed in stainless steel if that will make it easier to acquire a reaction vessel large enough.
How many moles of formic acid for each moles of AgCl...or how many ml of 85% formic acid do you use for 1 kilo of AgCl.
 

orvi

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You said that you may add 1.5 kilo of NaOH for 1kilo of AgCl. That mean you use 37.5 moles of NaOH to react with 7 moles of AgCl...for me it looks too much.
You mention as well that the only matter is the cost, but you need to keep in mind, you gont get AgO from AgCl. First you get AgOH, which is not stable and convert it self to AgO. If you add too much NaOH, i think you will push the reaction to move back from AgO to AgOH.
Another remarque/question: you mention i dont must let it cool down, why? because the oxydation of the aldehyde with AgO need temperature?
yes, i meant 1:1 ratio of the hydroxide/AgCl, mishap in the writing. and yes, it is still huge excess. but it worked nicely for me, couple of times i done this. first time, i had too much water in and the conversion was very sluggish and slow, requiring more additions of NaOH.
i just want to be sure that conversion of AgCl to Ag2O is complete, with no big intrusions of unreacted AgCl are trapped in the solid Ag2O matrix. there is a very good thread about exactly the same reaction, but responses are from much more experienced refiners than me, they give also the optimized values for the reactants. and their numbers for NaOH reqired are far lower than mine :)
maybe it could be done progressively by heating and stirring the suspension. i was never concerned about 1 kilo of NaOH, as i dont work on industrial scale.

when silver hydroxide form, it is a matter of temperature and basicity of enviroment in order to get it dehydrated to form Ag2O. similar with copper hydroxide... with baking soda, you will nicely precipitate blue voluminous stuff, but if you use NaOH, Cu(OH)2 will relatively easily decompose to CuO.

and, yes, the mixture should be hot to shorten the induction time, i had more reproducible results when the mixture was hot.

this is very "alchemistic" method, as i stated above. refiner, unless experienced, dont have much opportunity to check, if everything run correctly.
here is the thread from pro´s :)


compared to their findings, i use little water, way more hydroxide and still i was able to smoothly melt the obtained silver without fuming/loosing AgCl in the furnance :) they also point out the importance of good agitation (blender, mixing with a drill) in order to speed up the conversion. maybe i wasnt patient enough, just dumping excessive hydroxide in... but it also worked :)
reducing the AgCl with iron or aluminium is another very interesting procedure, but as lye/sugar worked without any issue for my quantities of material, i never tried these. but sounds very interesting, i would like to hear more about the actual setup :)
 

Geo

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Formic acid also reduces palladium. Silver chloride recovery is the best process that I know to separate silver and palladium. You need to rinse silver chloride well to remove any Pd or it will report in your silver. The formic acid conversion is the fastest process that I know using hydrometallurgy. Direct smelting is the absolute fastest but is a different principle altogether, being pyrometallurgy. It is still a chemical process but performed at very high temps.
 

orvi

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Easiest way for that quantity is iron / sulfuric acid in a cement mixer.

You just have to rinse it really well after taking the iron out. That in and of itself is somewhat difficult.
do you have that mixer coated with some protective layer, or there is no etching from sulfuric acid occuring on the steel case ? i like this idea, for smaller scale, using like small rotating steel drum, but i´m bit concerned about steel.
how do you find the end of reaction ? testing the supernatant by dilution to see some milkiness ( minute remaining dissolved AgCl) ?
with method that Harold disclosed in another thread (AgCl in 10% HCl reduction with aluminium), i could imagine taking sample of solution and dilute it with distilled water to see if some dissolved AgCl is still present. but i am only guessing now :) never experienced this method, and i quite like the approach
 

snoman701

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A plastic coated drum is an awesome thing to have...however, it's not a requirement, just stuff a 5 gallon bucket in a cement mixer. I usually use steel ball bearings as tumbling media, when Lou originally suggested the method he said to use punchings (the leftover material that gets punched out of a hole). I personally think the punchings would work better. Silver chloride has a tendency to clump, and the grinding action of the punchings tumbling is similar to that of a ball mill. It will break up those clumps and ensure intimate contact between the silver chloride and the iron. Once I think it's done (color change), I just take a small sample and smelt it and look for silver chloride in the slag. If you don't rinse it well enough, you will get an annoying black slag that loves to hide values. Don't mistake it with the shimmering glassy slag of silver chloride.
 

orvi

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A plastic coated drum is an awesome thing to have...however, it's not a requirement, just stuff a 5 gallon bucket in a cement mixer. I usually use steel ball bearings as tumbling media, when Lou originally suggested the method he said to use punchings (the leftover material that gets punched out of a hole). I personally think the punchings would work better. Silver chloride has a tendency to clump, and the grinding action of the punchings tumbling is similar to that of a ball mill. It will break up those clumps and ensure intimate contact between the silver chloride and the iron. Once I think it's done (color change), I just take a small sample and smelt it and look for silver chloride in the slag. If you don't rinse it well enough, you will get an annoying black slag that loves to hide values. Don't mistake it with the shimmering glassy slag of silver chloride.
thank you for clarification :) how much sulfuric acid do you add ? some unspecified ammount just to clear the iron surface, or it is somewhat important to measure the acid precisely ?
 

Swissgoldrefiner

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Formic acid also reduces palladium. Silver chloride recovery is the best process that I know to separate silver and palladium. You need to rinse silver chloride well to remove any Pd or it will report in your silver. The formic acid conversion is the fastest process that I know using hydrometallurgy. Direct smelting is the absolute fastest but is a different principle altogether, being pyrometallurgy. It is still a chemical process but performed at very high temps.

Hello,
so today i tryed your way....0 results...lol
Dont know what was wrong, but i add the AgCl in becher and cover it with water. then add sodium carbonate, until basic pH. (here it's different as you suggest, but dont see why it should be nutral, as it will just need more formic acid).
Then heat it and add formic acid...nothing happen. i tested pH and it was acid.
Dont know what was wrong. Where did you find this process? any resource?
I will test with silver nitrate to see if there was some Cl inside the liquide.

I am curious about the mecanism or at least the reaction.
 

Geo

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Hello,
so today i tryed your way....0 results...lol
Dont know what was wrong, but i add the AgCl in becher and cover it with water. then add sodium carbonate, until basic pH. (here it's different as you suggest, but dont see why it should be nutral, as it will just need more formic acid).
Then heat it and add formic acid...nothing happen. i tested pH and it was acid.
Dont know what was wrong. Where did you find this process? any resource?
I will test with silver nitrate to see if there was some Cl inside the liquide.

I am curious about the mecanism or at least the reaction.
The sodium carbonate is the patented reagent for the process But I have used only sodium hydroxide. It has worked perfectly each time. I will do a small conversion and post it to my youtube tomorrow morning and post the link here.
 

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