Precipitation: SMB vs NaOH

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Stowmaster

Well-known member
Joined
Dec 10, 2011
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48
100 grams of computer pins were dissolved in 65% nitric acid. Filtered. Washed. The precipitate was dissolved in a mixture of nitric acid and NaOCl. Filtered. The solution was divided into two equal parts, one part added to SMB, the other - an excess of NaOH. Where was the SMB sediment fell dark brown, with NaOH - purple. Why the difference?
 

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the purple is a colloid. you should read Hoke's book on the correct process for precipitating gold. the colloid is still gold, but is much more difficult to work with in that state.sodium hydroxide would not be my first choice as a precipitant.

besides, adding NaOH to hcl creates NaOH + hcl = NaCl + H2O or salt water.
 
You had some tin from solder in solution, and from the looks of both these powders other base metals present, I would say your solution was fairly contaminated with tin and copper, which can form colloids in solution a major cause for loss of gold in the recovery process.

Tin in your solution and using SMB and keeping the solution acidic most of the tin remained in solution, but also the colloids of gold (reduced in solution by the tin) this gold in solution (as colloids) would not precipitate with the SMB, in the powder you did get to precipitate I suspect is not all of the gold that was in that solution this came from, so you may have some gold still in the solution this precipitant cam from.

NaOH you reduced the tin, chlorides, gold and other metals in solution,
The purple probably came from the reduction of gold with the tin chloride in solution very similar to the stannous chloride test we use to detect gold in solution.

Both of the powders you have in your picture are contaminated with other metals, the black powder from the precipitation using SMB would have been a light brown if your solution was not contaminated with base metals, also the reduction of gold with NaOH would have been brown, you could get several different colors of powders by dropping the metals from solution using caustic soda, the colors would be the results of the metals the solution contained, as NaOH can reduce them all, and it also can form oxides and hydroxides of these metals.
 
In the process I did not use hydrochloric acid. Hydrochloric acid is prohibited in our country as a precursor. Nitric acid dissolves everything except the gold plating, tin transforms into an insoluble Sn (OH) 4. Instead of aqua regia, I used a mixture of HNO3 + NaClO. Gold is dissolved in this mixture, Sn (OH) 4 remains in the sediment. The solution became yellow.
In the case of SMB solution remained yellow, precipitate was brown, but then became almost black.
In the case of the NaOH solution became colorless, and precipitated other hydroxides, which were separated by 10% HNO3. Purple powder does not dissolve in HNO3 or in NaOH.
 
I still believe you had tin in solution with the gold also mixed with chlorides is what is giving you this purple color, the nitric acid and the bleach would have generated chlorine gas in solution , which would dissolve the gold to form gold chlorides with the tin in the nitric acid, giving that purple color.

If you cannot get HCl, it can be made from sulfuric and NaCl rock salt, distill and bubble the gas into water to get the hydrochloric acid.
 
Not sure how research already done, but search for phosphor bronze. it is possible to have intruduced a considerable amount of tin to your soup if this was the alloy your pins were made of. nitric+heat+tin=metastannic acid BAD!
If you already checked the composition of your feedstock before beginning, never mind this good reminder.
 
I dried and weighed precipitate with metabisulfite, it should weigh 0.3 grams (assuming 6 g / kg), but weighs slightly more than 1 gram. So there is an impurity, probably tin. Thank you! I will look for decision treatment. Here is the photo of another experiment with sodium hydroxide, the precipitate after 24 hours. You can compare with this: http://en.wikipedia.org/wiki/Colloidal_gold
 

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The meta-tin acid - it is bad. It is similar in chemical properties on the sand or glass. But it is not dissolved (or nearly is not dissolved) in a mixture of nitric acid + chlorox. This effect I want to use.
 
The blue solution looks like copper to me, (not to say that there is no gold in solution), also colors can be deceiving, they can be indicators but you really cannot just count on them as the only indicator, testing solutions give more accurate indications as to what is actually have dissolved in solution.

I suppose the powder in the bottom of the vessel is the purple powder, if so this may be a mixture of the tin and gold (my assuming), how does the solution filter before and after? this can be an indicator of tin (it does not filter well at all.

It seems to me that it would be hard to dissolve gold very well in a solution of nitric acid and NaClO (bleach), but I do see how it may work somewhat, Have you heard of the SSN leach saturated salt and nitric is what I think the initials stand for.
 
Stowmaster - if HCl is prohibited in your country try search for concrete cleaners in building stores or suppliers. Most of them will contain 10% strong HCl some even up to 20% that is how I am getting HCl as it is not for sale here too.
 
Stowmaster said:
In the process I did not use hydrochloric acid. Hydrochloric acid is prohibited in our country as a precursor. Nitric acid dissolves everything except the gold plating, tin transforms into an insoluble Sn (OH) 4. Instead of aqua regia, I used a mixture of HNO3 + NaClO. Gold is dissolved in this mixture, Sn (OH) 4 remains in the sediment. The solution became yellow.
In the case of SMB solution remained yellow, precipitate was brown, but then became almost black.
In the case of the NaOH solution became colorless, and precipitated other hydroxides, which were separated by 10% HNO3. Purple powder does not dissolve in HNO3 or in NaOH.
Click to expand...

?????

Where do you live???

What doesn't make sence to me is you have all that chemistry knowlege and you don't know how to make your own HCL???

Somethings not right!!!
 
That is perfectly OK. Not every baker is milling his own flour. Sometimes there is no point to spent time making your own tools if you can get them cheap enough.
His point was probably that if one do have problem to obtain HCl then producing it in home may be deemed illegal too.
 
I still can't imagine how HCL would be illegal but you can get nitric (I don't have to say what can be done with nitric!)??? That said, Stowmaster, if your still around and want to know how to make HCL just ask me. Unless that would get me into trouble, in that case you can find recipes on youtube. It's very simple!
 
you can distill hcl from pyrolizing any PVC plastic and running the off gas through water. Deano let that cat out of the bag awhile back.
 
Two moles of NaCl salt, one mole of H2SO4 sulfuric acid, will give two moles of HCl hydrochloric acid, and one mole sodium sulfate salts.

2NaCl + H2SO4 --> 2HCl + Na2SO4

The HCl hydrogen chloride gas is distilled with and bubbled into chilled water to form hydrochloric acid.

Water will be involved in the boiling flask, this water will begin distill off before HCl (if in excess), or until the HCl in the boiling flask azeotrope’s at about 20% HCl, so consider this when you decide how much water to use in your reaction, the chilled water in your receiver used to bubble the HCl gas into, When deciding how much water also consider the HCl azeotrope and shoot for 20% acid add only the amount of water to get 20% acid when done, considering water in the receiver and also the water as steam as water vapors with the acid, this can also be condensed acid from water as steam condensing with the HCl gas from boiling flask before reaching getting to receiver with the uncondensed gases.
Consider how much water in the reaction is needed to give you about 20% HCl.

Rock salt and battery acid could be used to make HCl acid.
 
Thank you all for your answers.

I live in Ukraine. According to our laws, hydrochloric acid 15% and above, and sulfuric acid 45% and above are precursors.
http://search.ligazakon.ua/l_doc2.nsf/link1/KP000770.html (ukrainian lang.)
To purchase them need a special permit. Nitric acid is not prohibited, and may be purchased at the price from 1,5 USD to 4 USD per 1 liter, depends on the amount.

10% hydrochloric acid is available in the form of toilet duck or Cillit. The use of this tool for the dissolution of tin, is not economically viable. In addition, there are impurities in the form of R-SO3H and other impurities.

I did an analysis of errors in this experiment.
My target was to get the gold, but not hydrochloric acid, and I believe that this is possible without hydrochloric acid. A mixture of nitric acid and Clorox form nitrosyl chloride ClNO, which perfectly dissolves gold. However, I did not realize what happened instead of gold chloride - sodium hloraurat NaAuCl4. For the precipitation of gold from NaAuCl4 need not SMB, but other methods. This part of the experiment, I found failed.
Purple powder of NaOH I was processed for re-leaching with J2-KJ, got about 0.1 grams of gold powder. Melting is not done because it was a small amount.

Currently, I spend my experience of dissolving gold plating without dissolution of base metals. Use a mixture of Na2S2O3 and H2O2. Gold plating slowly dissolves at about 1 micro-inches per day. At the moment, I think, this method is the best (and safest) for removing flash gold platting.
 
2NaCl + 2HNO3 --> HCl + NaCl + NaNO3+ HNO3
SSN leach very similar to poor-mans aqua regia, here HCl is formed from acid and salt.

Something I would look into more if I could not get HCl, or did not want to distill HCl from sulfuric acid and salt.

I am not positive this is the correct formula, or equation balanced, (SSN) for saturated salt and nitric leach, but it does give us some clues for dissolving our gold without HCL

This would need more reseach to come up with the best formula.
 
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=33&t=16744&p=170994#p170994

More discussion on making aqua regia
Without using HCl or HNO3.
Using rock salt, nitrate fertilizer, and battery acid.
 

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