# Silver Chloride solubility



## MarcoP (Dec 8, 2014)

Hi all, while looking at the solubility table in the wiki I've noticed that solubility of AgCl at 20°C is 0.0001923 gr/100ml but at 50°C is 0.000052 gr/100ml. Less soluble in hot solution.
After denoxing and adding sulfuric acid I always believed that cold and dilution would facilitate lead sulfate and silver chloride precipitation, it may be true for the lead but it seems to be not the case for the silver ... or is the table wrong?

As a side note silver chloride's solubility is very low already so, unless higher purity is desired, I'm not sure if applying heat will benefit the process or not.


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## solar_plasma (Dec 9, 2014)

I think it's an interesting curiosity (if the numbers are correct), but if you want to make highest purity, just follow this link:
"Method for Ultra High Purity Gold" by Lou
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=39&t=3079


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## 4metals (Dec 9, 2014)

Maybe I'm just old but if it comes down to Wiki on the internet or the good old Handbook of Chemistry and Physics, I'll pick the hard copy any day. 

silver chloride solubility in g/100 cc 
0.000089 in cold water
0.0021 in hot water

lead sulfate solubility in g/100 cc
0.00425 in cold water
0.0056 in hot water

Source, Handbook of Chemistry and Physics, 57th edition 1977

I think wiki has a misprint. I remember reading somewhere on the internet that Abe Lincoln once said "You can't believe everything you read on the internet." 

The solubility of lead sulfate is not as greatly affected by cold as silver chloride is.
Cold and dilute always worked on silver chloride for me. And I've refined a few ounces that way.


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## Harold_V (Dec 9, 2014)

In regards to cold and dilute, I can testify that each encourages precipitation of silver chloride. 
When I did my second refining, the solution, prior to the introduction of ice, was heavily concentrated, and always contained free HCl. Upon introduction of ice (three liters of ice introduced to a liter of gold chloride), there was always a slight haze created, which I attributed to traces of silver chloride being precipitated. It was obvious, although just barely visible. 

It is for that reason that I introduced an ammonium hydroxide wash to my wash sequences. 

Harold


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## MarcoP (Dec 9, 2014)

I agree on the fact to not believe everything I read in internet, hard copies and your experience should have been plenty but I was curious about this weird data, glad I've asked.

Cold and dilution will be and I will start adding one ammonium hydroxide wash to powders I will produce as a standard procedure as Harold suggest, maybe just to be sure I'll rinse my gram of double refined, SMD and Oxalic acid, powder. Thank you!

I only have little experience yet but I noticed that an hard boil of AgCl in water will make it settle better, did I correctly interpreted what's happening?


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## Lou (Dec 9, 2014)

AgCl is less soluble in the cold. Most "insoluble" precipitates are less soluble in chilled solutions (this has to do with the activity of a solution). 
AgCl is less soluble in dilute chloride solutions (usually 0.5-1.5 M) due to the common ion effect; higher chloride concentrations will increase the solubility due to the formation of AgCl2- complex (just put a pinch of AgCl in a test tube and add conc. HCl; it'll go yellow and some precipitate will dissolve). 

In practice, one would chill the HAuCl4 in a jacketed glasslined reactor, add a small amount of sulfuric acid, a cationic flocc and then pressure filter into another reactor for SO2 gassing. You can safely cram about six million in gold into an 800 L Pfaulder at today's prices 

MarcoP, when you boil most precipitates (especially AgCl, which is best done in a dilute electrolyte to prevent peptization from occurring), you are "conditioning" the precipitate by causing agglomeration due to increased frequency of collisions. Also, finer precipitates tend to get caught in the matrix of the bulk and drug down. This makes it stick together better and rids the solution of fines. One might notice that AgCl from a concentrated silver solution is much more like cottage cheese than that precipitated from very dilute solutions. Same is seen with high concentration gold solutions, which give a much large grain size gold sponge. 

Needless to say, as most people understand this: always filter your bulk gold first in the filter, then use that sponge to act as a filter bed for your fines that were decanted off into another container. Then remove the liquids and wash in the filter 

Harold,
Given your procedure and technique, in particular, the wash, I am of the opinion your fine gold was probably well in excess of 99,95% pure gold. Some successful inquart work can give you gold of 99,9 purity; getting 4N after aqua regia, lead removal with sulfate, and chilling to remove chloride...that's easily realizable. If you have any left that you're particularly confident in, I'd be happy to give you the actual breakdown of your gold. A half gram is more than sufficient!

I'm starting a UHP gold crystal run so I'll have some spectroscopy to do over the holidays!


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## Harold_V (Dec 10, 2014)

Lou said:


> I'd be happy to give you the actual breakdown of your gold. A half gram is more than sufficient!



Wow! That's an offer I can't refuse. I've always been curious how good the quality was, and, yes, I have some at my disposal. Why don't you contact me via PM (or email) and provide a "mail to" address. 

One of my customers, who trusted no one, told me that he had a question about the purity of my gold, so he had it assayed. The lot in question proved to be 99.97, or so he said. I have no way of knowing if that was true, or if the procedure used was acceptable. Regardless, I'm keenly interested in your discovery, in spite of the fact that I no longer refine. 

Thanks, Lou. 

Harold


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## yar (Dec 10, 2014)

Harold_V said:


> Lou said:
> 
> 
> > I'd be happy to give you the actual breakdown of your gold. A half gram is more than sufficient!
> ...



I do hope you share the results if and when the assay is completed. I and many of us would like to see how our gold stacks up to yours Harold. I am sure you hit .9999 purity consistantley given your knowledge and the set up of your lab. My last two refines assayed at .998 and .9983 and I honestly do not have nearly the equiptment that you had and used.


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## yar (Dec 10, 2014)

Just to clarify my staement above, I am in NO WAY trying to compare how I refine gold compared to how Harold refined his gold. That would be comparing a child in tee-ball baseball to a hall of famer. And I know which one I am in that comparison!!! It would be simply to see how far off I am in my process and learn from that going foward.


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## Lou (Dec 10, 2014)

Yar, no worries. Contrary to some public opinion, Harold is actually hard to tick off 
Harold wasn't even using special equipment (though sulfur dioxide gas certainly does improve quality, in my honest opinion), just beakers, watch glass, hot plate and hood, regular tech grade acids. 


In any event, how was your gold assayed, just by XRF?

I find XRF to be useful for determining 995 gold from 999 gold. That's about the limits of its usefulness to the average operator that doesn't have crazy nice standards.

Harold, see you PM box for the address of where to send it in for assay by difference.

Lou


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## yar (Dec 10, 2014)

Yes it was an xrf machine. I get the printouts as well from the refinery I sell to. I can also have a fire assay done if I decided to do so.


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## Lou (Dec 10, 2014)

Neither of them mean anything above 99,9/1000 parts fine gold or silver.


Lou


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## yar (Dec 10, 2014)

Lou said:


> Neither of them mean anything above 99,9/1000 parts fine gold or silver.
> 
> 
> Lou



I have not studied much on how to determine purity other than what physical characteristics to look for in a refined button which can mean absolutely nothing unless it is my own material. I will keep in mind what you stated as I progress with hopefully refining purer gold. Thank you for the information. 

Now for the obvious question.....if you were in my place where would you start to learn about determining purity of refined metals ?


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## MarcoP (Dec 11, 2014)

solar_plasma, thanks for the link. It was one of my first bookmarks and it was great to reread it again and redo all consecutive searches! This time I was able to understand, think, and search about it.

Lou, thank you. I'm learning about peptization but something is leaving me a little confused. Washing with a dilute HNO3 (5%?) prevents the partial formation of colloids but residual of acid adhered to the surface of AgCl can be only removed by drying.

Since I need to keep AgCl moist at all times, would this acidic residue give me troubles when converting the chloride to metal with lye and sugar?


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## Harold_V (Dec 11, 2014)

yar said:


> Harold_V said:
> 
> 
> > Lou said:
> ...


It would be my hopes that Lou would post on his results. I have nothing to hide---and did the best I could with the knowledge I had at my disposal (Hoke's book, primarily). I coupled that with a burning desire to do the best possible job I could of refining, simply as a matter of pride. 

You can be fairly sure of good quality when your gold melts with a decent pipe, leaves no color in the melting dish, aside from either a purple or pink haze, and has no surface oxide coating, thus requires no pickling to improve the color. You can also conclude that if you have good clean washing and melting procedures, and the barren solution from which your gold came lacks any color, that you have pretty clean gold. Melt with a clean torch--not one covered with dark oxides, which can shed and combine with the molten gold. 

Harold


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## MarcoP (Dec 14, 2014)

Readings never stops, so some questions will always come up.

Reading about AgCl particles size. I do decant the diluted solution early in them morning so the temperature is around 5°C but still pass the solution from a student grade filter. Google tells me that AgCl' particles may have a size between 6nm (0.006um) and 300nm (0.3um). Does anybody know which size are we dealing when using table salt in nitrate or hydrochloric in ammonia?
Or, which filters size are you using?

Soon I'll have some whatman grade 1 and 5 coming in and my inexperienced head is suggesting me that not even the grade 5 would be able to completely remove it.

So if I had to follow Lou' advice:


Lou said:


> Needless to say, as most people understand this: always filter your bulk gold first in the filter, then use that sponge to act as a filter bed for your fines that were decanted off into another container. Then remove the liquids and wash in the filter


 which filter should I use, and would two filters helps?

Maybe I'm over thinking...


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## 4metals (Dec 14, 2014)

Not over thinking but you are paying a lot of attention to something that will not pay off in values recovered. I prefer to go a bit colder if possible and then filter through the finest filter paper you have. The last thing you want to add to the filter are the solids on the bottom. You can then settle and if you see the telltale white precipitate faintly coating the bottom of the vessel. I have found the cold filtration takes care of the majority of the chlorides. 

If you are dropping gold from the next step, an ammonia wash may help as silver chloride dissolves in ammonia. If you did the preparatory steps correctly, this may not be necessary for gold drops but it won't hurt either. 

The waste solutions I prefer to hold in a flow through waste tank which will allow for good settling and also allow values to accumulate on the bottom where they can be collected and processed when it is worth your time. When silver chloride holding solution is accumulating at .000089 grams per 100 CC or 0.0033 grams per gallon it will take a long time to be worth your refining energy.


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## Lou (Dec 15, 2014)

I spoke of filtering the fine and/or floating gold through the gold sponge, something which does pay off rapidly if one doesn't take the time to ensure the best reduction conditions.

In any event, the barren gold filtrate should always be accumulated in a settling vessel just in case.


Lou


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## MarcoP (Dec 15, 2014)

Thanks for the help!

@4metals, my intention is to clear the solution from silver chloride, as you say it doesn't pay off recovering it in so tiny quantity and if done properly it wont interfere much with the purity of the recovered metal.

@Lou, there it was a glitch in my thoughts. I don't have to worry much since AgCl will go through the filter and ammonia wash would, as 4metals point out, will get rid of it. Thanks for the settling advice.

Thank you again.


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