# Oops, sodium Hydroxide in AR



## goldenfrog (Jun 14, 2017)

Attention to detail aside, 
I had about 4 grams of Au, I had combined recovered gold from a Melt dish disaster with another drop that seemed a bit dirty to me. (dark dark powder)
anyway.. Dissolved all in AR with a bit too much nitric. 
I intended to use Sulfamic to de-nox but realized too late that I had added a 1/2 spoonful of Sodium Hydroxide instead.  
Hoping for the best I pressed on and added Sulfamic then SMB to drop.
All seemed well except that the powder is at least 1/2 of what I started with. Stannous shows no gold in solution after drop.. is there a chance the NaOH did something new and unexpected? 
I re-refined the filters I had used with fresh AR, but no gold is in that solution either... . 
The only thing I can figure otherwise is that the powder I added may have been REALLY dirty. 
Any words of advice or consolation out there?


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## mls26cwru (Jun 14, 2017)

have you checked to make sure the solution is still acidic?

I have seen gold precipitate out of solution in a dark purple/almost black form before when using NaOH... but if you only dissolved 4 grams of gold, you may have overpowerd the acid with a 'spoonful' of NaOH.


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## anachronism (Jun 14, 2017)

No harm done- re-acidify the solution with HCl and then try your stannous test again to be sure. 

SMB needs an acidic solution to work properly.


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## goldenfrog (Jun 14, 2017)

I will check it out, I have saved all the solutions I used separately (just in case)!
Thanks guys!


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## kurtak (Jun 15, 2017)

Did a precipitate form when you added the NaOH ?

If so did you filter that out before adding your SMB ?

Kurt


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## goldenfrog (Jun 16, 2017)

No precipitate when I added the sodium Hydroxide that I noticed, I filtered the white precipitate from adding a few drops of sulfuric to drop the lead.

but... update.. 

I attempted to re-acidify with some HCL, but there was no change.. heat.. nothing. so last ditch effort was to throw in some copper and see if anything cements.. and WOW there was a lot of black cement!! 
(Not a speedy procedure.. I mean.. not like cementing silver from silver nitrate.. at all) 
so now I cant wait to re-refine the powder with HCL and Bleach. 
really makes me wonder how much is really in my stock pot bucket now, after what seemed to me like many very light drops.
I always test everything with stannous, but I am learning that stannous doesn't always tell the truth.
or at the least, not the Whole Story


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## Topher_osAUrus (Jun 16, 2017)

Stannous is actually very accurate, if done correctly.
4ppm is a pretty spot on result.
One book I have says 1/720000 can be detected with stannous
(Or even less, is stated after that) 
"In special cases 1 part of gold in 100,000,000 parts water can be detected."
..well, I guess it's best to quote the book itself, eh?

*excerpt*


> "The liquid supposed to contain gold is raised to boiling, and poured into a large beaker containing 5 to 10 c.c. of saturated solution of stannous chloride, and the liquids agitated as to effect complete mixture. A yellowish-white precipitate of tin hydrate forms, which settles rapidly, and can readily be separated from the bulk of the liquid by decantation. If the solution originally contained 1 part of gold in 5,000,000 of water (3.5 grs. Per ton), the precipitate is coloured purplish-red or blackish-purple, according to the nature of the solution, and condition of the precipitant. The color can be seen without comparing it to other precipitates. If less gold than this is present it is better to compare the precipitate with one obtained by the use of boiling distilled water, and to increase the quantity of liquid used while adhering to the same amount of stannous chloride.
> In this way the presence of 1 part gold in 100,000,000 parts water (1grain per 6 tons water) can be detected, the amount of liquid in this case being about 3 litres. The gold is concentrated in the precipitate in which a distinct colour is caused by less than 0.05% of the precious metal."



Thats a pretty extreme case though, but, I do believe it (stannous) is very accurate so long as there is no free nitric, and not a lot of base metals in the solution as well. Of course, having a fresh and saturated test solution of stannous is also a good thing to have.
Not sure of the differences between 1ppm gold in water vs 1ppm gold in acid -which I hope someone can elaborate on 
Later in the book, he describes another test for dilute non acidic solutions(arseniate of iron) as well as using copperas to test for gold. (Pg 458, pg26 respectively)

*quoted from "Metallurgy of Gold" 3rd Edition by TK Rose (pg 27)


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## Saeedanwar (Feb 22, 2018)

My problem is I put 16.5 karat gold with extra amount of silver added in gold in aqua regia solution but got stuck as the solution is not dissolving gold and the grains are present at the bottom.what should I do now please help


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## geedigity (Feb 22, 2018)

dissolve in nitric first?


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## g_axelsson (Feb 23, 2018)

Saeedanwar said:


> My problem is I put 16.5 karat gold with extra amount of silver added in gold in aqua regia solution but got stuck as the solution is not dissolving gold and the grains are present at the bottom.what should I do now please help


I'm not trying to be mean, but your problem is that you don't have any experience and knowledge in refining. I recommend you to halt your chemical experiments and download Hoke's book and study before going further. You should also study how to treat your waste so you don't poison someone. The last part is never shown in the youtube videos or in Hoke's book..
http://goldrefiningwiki.com/mediawiki/index.php/Hoke

How to deal with carat gold high in silver is one of the subjects in her book.

Göran


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## rickbb (Feb 23, 2018)

Why were you adding silver with gold in AR?

AR is used to dissolve gold so it can be dropped out separating it from silver and other metals.


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## goldsilverpro (Feb 24, 2018)

Saeedanwar,

I'm with Rick. By your description, it's hard to tell exactly what you did do, but, if Rick's right, what you did will never work. Sounds like you alloyed 22K or 18K down to 16.5K with silver. That is about the worst thing you could have done, because it put the metal percentages in a position where nothing will dissolve them. The alloy you ended up with is now so high in silver that a crust of silver chloride, AgCl, coats the pieces and that prevents the penetration of the aqua regia and stops the dissolving. To dissolve karat gold directly in AR, the silver content is limited to 8% and maybe as much as 9 or 10%, if the karat gold pieces are real thin. 

At those silver limits, the dissolving will slow down and you might have to remove the AgCl crust a time or two to speed things up. There are several ways to do that. You might remove the pieces, rinse them well (especially when using a metal mortar and pestle) and then grind the crust off in a mortar and pestle. A more guaranteed method is to rinse them well and then dissolve the AgCl in a warm solution of either ammonia, sodium thiosulfate (hypo), or sodium or potassium cyanide. The hypo is the safest but the silver is harder to recover from it. The cyanide is quite poisonous and, if all the acid hasn't been rinsed off of the pieces, an extremely poisonous gas (HCN) is released. Most people use dilute ammonia, but the dissolved silver can create an explosive compound if the solution is allowed to sit around for awhile. To prevent this, acidify the solution with HCl, immediately after use. The AgCl will reform and is easily collected. 

One of the pleasures of refining is to learn how to avoid the constant dangers you are exposed to. :!: 

To avoid the silver problem, a method called "inquartation" is used. The gold content is reduced to 25% (=one quarter - thus the name, inquartation) by melting with added silver or copper. The melted alloy is then poured slowly into a container filled with clean cold water large enough so the water is at least 35cm deep. This puts the metal into small thin pieces with a high surface area that are faster to dissolve. All of the base metals and silver are then dissolved with 50/50 nitric acid, diluted with pure water, leaving the gold, which doesn't dissolve, behind as a powder. The gold powder is well-rinsed, dissolved in a minimum amount of aqua regia, and the gold is precipitated as normal. To determine whether to inquart with silver or copper, it takes about 3.4 times as much nitric to dissolve a gram of copper than to dissolve a gram of silver. If you use silver, it is easily recovered as a powder and reused simply by putting copper bars in the silver solution. I have used both, but I feel that using silver simplifies the process somewhat, mainly because there's less acid to deal with.

To finish up what you have started, I would alloy enough silver with your undissolved metal to reduce the gold content to at least 6K (25% gold). Make sure the molten metals are well blended before pouring into water (called "shotting"). Don't go much below 6K because, when dissolving the metals in 50/50 nitric, the gold powder can get so fine that it is a purple colloid and will hardly ever settle. They have found unsettled colloidal gold in Egyptian tombs. Sometimes you can break the colloid by heating the solution.

As Rick said, download and read the Hoke book.


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## Topher_osAUrus (Feb 24, 2018)

this deserved its own thread, no?


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