# sodium hydroxide



## arthur kierski (Jan 2, 2009)

not wanting to be rude, i learned that gold does not form oxide,so it cannot be dissolved by excess naoh---i do not want to get in discussion over this --- but it is tyring that everytime i try to explain a way that i procedd i find a kind of opposition from the same members


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## goldsilverpro (Jan 2, 2009)

No opposition. I was just quoting from a book, "Inorganic Reaction Chemistry" Vol 2, Part A, Burns, Townshend, Carter, 1981, page 183.



> "Sodium hydroxide solution, added to a not too dilute gold [gold (III) chloride or chloroauric acid] solution, precipitates brown hydrated gold (III) oxide, AuO3.aq, so-called auric acid. The precipitate dissolves in an excess of sodium hydroxide solution to form aurate ions, either [Au(OH)4]- or [AuO2]-. The precipitate is also readily soluble in concentrated nitric, hydrochloric, and sulphuric acids. Dilution of a nitric acid solution causes the hydrated oxide to precipitate. Dilution and addition of hydrogen peroxide forms gold metal. If the reaction is done in a test tube, a gold mirror is formed, which can readily be seen on washing out the test tube."


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## Platdigger (Jan 2, 2009)

Gold in nitric..........how bout that


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## arthur kierski (Jan 2, 2009)

this does not invalidate what i wrote---adding naoh to an ar solution at ph 7+ precipitate gold ,pd from the solution as hydroxides----i am sure for au,pd and rh---have doubts about pt which also does not form oxides-----the opposition that i say is that if you change the context(excess naoh,ph let say 9,10,11,--),of course what i wrote seems wrong---- the same happened in a thread which a professor who refined gold by shreding the alloy to less then0,1mm and obtained from it gold with ar without using urea or boiling but diluting the ar 10times also got opposition ---it seems tha only your methods are correct--the others are just playing in this forum


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## butcher (Jan 2, 2009)

problem I see is so many metals will precipitate as hydroxides and if gone to far many will also dissolve in them, this might work if you only had one or two metals in solution but with a soup of metals, a soup will probably precipitate, and alot of the values may not. ????


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## Anonymous (Jan 2, 2009)

Arthur
Thanks, I am going to get some naoh and give it a shot. I think you understood that I just want to get the metals - don't really care what they are out of solution so I can store in small containers not gallon juggs and have them come out quickly.

Jim


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## goldsilverpro (Jan 2, 2009)

Arthur,



> ---it seems tha only your methods are correct--the others are just playing in this forum



That's BS and you know it. Your skin is mighty thin, my friend. We're here to root out everything. I've been successful in this business because I always start with the negatives of a particular process. I always say, "What's wrong with it?"

I think you have a very intriquing process. I think it will work. You're right, the quote that I posted doesn't conflict with your process. If you look carefully, they blend in a complicated way. 

However, I think your analysis of what's happening is not right. If you look in the CRC Handbook, you won't find a listing for gold hydroxide. That means that it doesn't exist. What difference does it make, though, whether it's an oxide or an hydroxide? It's a precipitate that you haven't dissolved because, at a pH of 7, you haven't added excess NaOH. Nothing you've mentioned forms a hydroxide. They all form oxides, including Pt. Look it up. I'll probably have to eat crow when Lou makes his appearance.

Have you tried this with pure weighed gold (plus the other metals) and recovered exactly what you put in?



> ,of course what i wrote seems wrong---- the same happened in a thread which a professor who refined gold by shreding the alloy to less then0,1mm and obtained from it gold with ar without using urea or boiling but diluting the ar 10times also got opposition



You didn't say he shredded it to .1mm. You said he used powder, Big difference in my mind. You said YOU shredded it to .1mm. My only complaint was the 20% silver. Did you have 20% silver? How does the average guy shred his gold alloy to .1mm?

For the last 20 years of refining maybe 100,000 oz of gold, I have rarely (maybe 1 time out of 100) had to use urea, boiling down, or any other method to get rid of the nitric. My trick is to never use more nitric, in the AR, than I need. I have detailed this process many times on this forum and haven't received 1 response.


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## Platdigger (Jan 3, 2009)

Chris, I think everyone here, would agree that your method of only using as much nitric as needed is best......at least when using AR. And of course as long as you don't mess up and use too much. 

Not all of us are doing karat jewlery. And it sometimes is hard to tell just how much is needed.

As for wether or not gold hydroxide exists, I am not sure, altho this company seems to think so...... http://www.kd-chem.com/pe6-8.htm

Randy


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## goldsilverpro (Jan 3, 2009)

> Not all of us are doing carrot jewlery. And it sometimes is hard to tell just how much is needed.


If you have an excess of hot HCl, you add nitric in small increments until no more reaction is observed. It tells you how much is needed. I used this technique on all gold, not just karat gold. 



> As for weather or not gold hydroxide exists, I am not sure, altho this company seems to think so.....


You're right. There's lots of listings for gold hydroxide on the internet. I was about to cut into the crow when I found this in my 9th edition of "The Condensed Chemical Dictionary."



> *gold hydroxide* Properties: Brown powder. Sensitive to light. Keep in amber bottle! Probably a hydrated gold oxide (Au2O3), and loses water easily.



I know that it doesn't make a damned bit of difference whether it's gold hydroxide or gold oxide. When this book was written, 30 years ago, they didn't seem to know what it was.


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## lazersteve (Jan 3, 2009)

Goldsilverpro said:


> My trick is to never use more nitric, in the AR, than I need. I have detailed this process many times on this forum and haven't received 1 response.



Chris,

For the record, I have referenced your controlled use of nitric in several of my post. Additionally, I have improvised and posted a modified poor man's AR process incorporating your methods. I can honestly say that since you have posted the process, I have rarely needed to remove any free nitric via boiling or addition of urea with my solutions. This 'controlled addition' of nitric works even with PGMs. I also have used Harold's method of adding a nugget of gold in the solution to react any remaining nitric.

Arthur,

From the numerous references I have seen in texts, the precious metals (Au, Ag, Pt, Pd, and Rh ) exist in several forms of hydroxides and oxides. Older texts refer to them very heavily. As an example Platinum forms platinous and platnic oxides as well as hydroxides. 

I'm at a loss as to how this debate over the formation of oxides and hydroxides got started. I assume there is another thread that this is in reference to. In any case, I feel the results that one achieves in their experiments is heavily dependent on the reaction conditions. Without knowing the reaction conditions it' very difficult for anyone to determine exactly what the products may or may not be.

I'm sure no one wants to take away from your input to the board, more likely they want to be sure all comments and suggestions are taken in context by our readers.

Steve


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## Platdigger (Jan 3, 2009)

Steve, there is another thread, by the same name.
Randy


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## Lou (Jan 3, 2009)

Au(OH)3 does exist but it is in a very heavily contaminated state--it is a mixed hydroxide/oxide, and this is the same for most of the platinum metal group and other transition metals. In this case, whether or not you get a high proportion of the oxide versus the hydroxide or vice versa, is dependent upon the thermodynamic stability of the product. In silver's case, Ag2O is more stable than AgOH.

When you have an HAuCl4 solution and you add base, you get Au(OH)3*xH2O _and_ Au2O3.

Very, very gentle heating of Au(OH)3 will yield Au2O3, which under further heating, will yield gold.

Now as you can imagine, gold (III) hydroxide is unstable. It would prefer to be the oxide, and it would be happiest to be elemental gold. This is why it is light and temperature sensitive. This photosensitivity of Au(OH)3 is known to anyone who's ever looked into doing alternative photography.

Lou


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## goldsilverpro (Jan 3, 2009)

Very good explanation, Lou. The more I read, the more I knew it had to be something like that.


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## Harold_V (Jan 4, 2009)

lazersteve said:


> I can honestly say that since you have posted the process, I have rarely needed to remove any free nitric via boiling or addition of urea with my solutions. This 'controlled addition' of nitric works even with PGMs. I also have used Harold's method of adding a nugget of gold in the solution to react any remaining nitric.


The only problem I have with the idea of using just enough, not too much nitric acid, is that many of these guys work with cold solutions. Even heated, it is difficult to tell when you have consumed all of the nitric. Reactions slow down to a crawl so it's not clear. It is for that reason I started using the added gold button. 

Because I preferred my solutions to be concentrated, to minimize the size of the vessels required, I evaporated my solutions whether they required it or not, so it was no inconvenience to add a gold button and allow the solution to work slowly. If there was free nitric, it was removed. If not, the solution was concentrated enough to permit the addition of water so the excessive level of HCl didn't complicate filtration by destroying the filter. That worked for me, and worked flawlessly for years. 

Had I not been concerned about evaporation for concentration, I would have been far more concerned about the amount of nitric involved---but it was a non-issue in my case. It's not that the information isn't good--it's just that it doesn't fit all requirements, and is subject to error, proven time and again by my processing method. Needless to say, I would have dedicated more time and attention to my solutions had I not desired to evaporate. For me, that was essential. Puzzling out the exact ratio of nitric simply wasn't important. I already had an excellent idea how much would be required, so a small amount of my added gold would get dissolved in evaporation. Besides, that way I was insured that I had removed all of the values from materials that left behind a great deal of waste matter. Jeweler's bench filings are notorious for such contamination. 

Different strokes for different folks. I truly believe that application will dictate what works best. 

I never encountered any process where the use of a blender was a good idea (this comment is not related to this thread). *How I wish that was not constantly presented to readers---*readers that may not understand the _stupidtiy _involved. The bearings in a blender are a copper alloy, and are exposed to the contents of the blender. What possible reason can anyone have for exposing nitric solutions to such a scenario? There are so many other ways to accomplish the same end without putting an individual at risk that I have a mind to delete the post involved. It appears that nothing has been learned by negative comments in the past. 

Harold


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## Senh (Wednesday at 5:35 PM)

Hello I took crushed ore and dissolved I AR and let evaporate. I added ammonia but realized I need to precipitate out first by ph. Any ideas what to do with this ? Trying to precipitate gold. I also have a pint of mercury to use if needed. I need help!!


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## eaglekeeper (Wednesday at 11:32 PM)

Senh,

Did you do an assay on your ore before you used acids?

I have no experience with ore's.... but using ammonia on this material is a bad idea. Ammonia and certain dissolved metals can produce unstable compounds...do not let them dry out or crystalize out. I would make sure the material/solution stays in a low PH.

I see absolutely no use for Mercury in this process.. Dissolved Mercury sound pretty toxic to me.


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## wlearly (Yesterday at 8:06 AM)

AR and Mercury? wow! I wouldn’t play with that mix. That’s the reason nitric is difficult to obtain here unless your making the little poppers you throw on the ground in July or are a reloader making your own primers for some reason I would keep those two very far apart


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## orvi (Yesterday at 8:31 AM)

Senh said:


> Hello I took crushed ore and dissolved I AR and let evaporate. I added ammonia but realized I need to precipitate out first by ph. Any ideas what to do with this ? Trying to precipitate gold. I also have a pint of mercury to use if needed. I need help!!


Please post to the right section of the forum.
Second, do not randomly put chemicals together, and unless you do not know what is inside, never, NEVER put acids on rocks. They can contain arsenic or mercury sulfides, and by pouring acids over, you create very very TOXIC gasses and liquids.

For gold precipitation, you want acidic pH, not basic. 

Do you know that ore indeed contained gold ?


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