I'm Ready to Precipitate

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I'm new to the board, so bear with me as I may get long-winded to describe what I have done thus far and ask questions about what I need to do next.

I have been dissolving pins/connectors/electronic parts in nitric acid, filtering then dissolving and filtering a second time. I have been quite successful in separating gold from the parts.

I then have dissolved the resulting gold in AR and filtered again. I have several liter containers of the resulting AR solution. I am now ready to precipate the gold.

I have urea to neutralize the acid. I have read on the forum that I should add only until the solution stops fissing and I reach a pH of 1.0 +/- 0.4. I am going to shoot for 1.0. My first question, and I apologize if it has already been answered somewhere else, is pH paper good enough to check pH in this process or do I need to invest in a pH meter?

I have purchased SMB to drop the gold. Is there an measured quantity I should be aware of? I don't remember reading anything about quantities in this regard. I don't know how much gold I have dissolved in solution, but I do know about the stannous chloride solution to test for gold in the solution.

Any assistance anyone can give me to push my endeavor to completion would be most appreciated.
 
If using pH papers, the standard wide-range papers aren't sensitive enough. I know that pHydrion makes narrow-range papers. One goes from .8-2.0 and another from 0-3. I haven't tried these in this application.
 
I have never used urea personally but the forum has a steady flow of posters that have difficulty with it.

You might want to read up on the triple evaporation of your AR to rid it of nitric instead of using urea. It is simple and effective without adding potential contaminates.
 
I fully agree with oz and recommend it highly.I have never used urea,I have only evaporated.Theres really no guess work in it and it saves money......who isnt all for that?
Johnny
 
Oz and Leavemealone - thanks for the advise.

However, can you be more specific? I have read several entries on the forum about evaporating and then dilluting, but each of the entries is confusing to me. Is it possible to give me a step-by-step recipe for eliminating the nitric acid? I have access to a fume hood, hot plate with or without stirrer and distilled water.

Thank you for any help you can impart.
 
Oz and leavemealone ask right that evaporation is good method but it have more fumes and want more time. I refine my gold with urea it is painless method if you want neutralized acid with urea then must use hot plate(thermostat)not use hot plate without thermostat because over heating can brake the beaker .because in hot AR react with urea very quickly and no pH paper is needed just add urea until no fizzing and no bubbles. stir well and then add urea drop by drop if you see fizzing add urea until no fizzing after five minute stirring add urea drop if you see not fizzing it means AR is neutralized . (make urea solution in water then filter any insoluble urea remain on fiter paper also advantage is if you use too much urea it avoid the urea crystallization if you see urea crystal the cases of too much urea no problem add water and stir well until crystal dissolve )
(the two things can get you success in urea method one is hot plate second is stirrer)
 
Make stannous chloride solution go here

http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=48&t=1692

IF you want step by step gold refining go to books and other information section and download books
 
Triple evaporation is not hard. You simply evaporate your gold bearing AR down to a very thick syrup and add slowly HCl until it no longer fizzes and fumes then repeat. When HCl additions no longer cause a reaction to a syrup consistency (typically 3 times is enough) all nitric should be removed and you now have a chloride only solution ready for precipitation with SMB.

Arumshin,

At no point was I suggesting that urea cannot be used successfully. This is however aggiefanatic’s first precipitation and there is no need to over complicate it with some of the problems others have encountered in its use. My decision to not use urea myself is as simple as I am refining (purifying) gold, why would I wish to add potential contaminate sources by using urea? Just my opinion.

I do agree that triple evaporation causes more fumes but if you are not set up for fume control you should not be dissolving precious metals in AR to begin with considering the fumes given off. I actually seldom need to practice evaporation of AR as I usually prefer to not use nitric for gold and platinum group metals and instead use chlorine gas for most things. Not that chlorine fumes are any safer.
 
I forgot to reply to the issue of dilution you asked about.

Once you have rid your AR of nitric by evaporation diluting it with 3 times its volume of distilled water will help rid it of traces of silver that can carry over. It is also a good idea to add a small amount of sulfuric acid (a few drops per 100ml should do) to precipitate out any lead. Once you have done this filter or decant your solution one last time making sure it is clear of particulates and proceed with your SMB.

Some do not feel that distilled water is necessary with chloride solutions, and I agree. But it is also less inclined to add dissolved metals found in tap water that can be dragged down with your gold when precipitating. The more precautions you follow to not add contaminates, the purer your final results will be. As I live in a humid area I get my distilled water from my dehumidifier for free, but it is cheap enough if you by it from the grocery store.
 
Oz you are right on the money bud.There is one other solution to not having a hood,thats stilling off the nitric.You can keep the nitric and the fumes to a minimum by boiling it in a distilling flask.Also Ive never had a problem with silver,but shouldnt you add sodium to drop it when you drop your lead,that way you can filter it off at the same time?
Just a thought,
Johnny
 
Distillation would work and it is seldom a bad plan to recycle but it is more involved in equipment. Fortunately aggiefanatic mentioned having access to a fume hood.

In the case of AR almost all of your lead and silver will have already formed a chloride from the HCl (I am assuming here that by “sodium” you meant sodium chloride/table salt). While it may be a small amount some of the silver and lead is still soluble in concentrated HCl. Dilution changes this for the silver, and the lead is less soluble in even a small amount of sulfuric acid. They are both filtered off at the same time.

You would have to ask one of the chemists here if you want to know exactly what these solubility levels are.
 
Hey Oz,

Sorry,I missed the fume hood part.
No need on the soluability rates,I rarely deal with those problems anyways.
Johnny
 
Thanks guys. I feel much more confident that I will be successful at dropping the gold out of my AR solution.

After the nitric acid has been removed from the AR solution and the dilution with distilled water has been done, should the resulting solution be heated when adding the SMB or should it be at room temp? I read earlier that it should be heated to maximize the efficiency of the SMB. Also I read that the SMB should also be in solution. What is the amount of SMB to water ration?

Thanks again for your info.
 
Some like solutions lukewarm when using SMB but I have had no difficulty even with solutions that are just above 32F.

The amount of SMB is typically estimated by how much gold is in solution using 1 ½ -2 times the mass in expected gold precipitate. Since you do not know what mass of gold to expect in this case it is hard to estimate, you will have to use stannous to test for your endpoint (always a good idea). Your gold should not have too much in the way of base metals based on your description of recovery, so your solution should go relatively clear in color near the end of your gold precipitation. Always check your stannous with a known gold solution before trusting it. In this case you could set aside a small portion of your current solution as a control for this and future testing of your stannous.
 
I read earlier that it should be heated to maximize the efficiency of the SMB.
Click to expand...

I heat mine to make sure the chlorine has dissipated.However for some reason if you add dry SMB to heated auric chloride it fizzes and bubbles up a lot more.To alleviate that I always put my smb in water first.

The amount of SMB is typically estimated by how much gold is in solution using 1 ½ -2 times the mass in expected gold precipitate
Click to expand...

I think he means the water to SMB ratio,in which case it doesnt take very much water to dissolve the SMB.200ml of water can easily dissolve 5 grams of SMB.Just figure how much you need,use Oz's ratio,then dissolve that in about 100 or 200 ml of water,you'll be fine.
Johnny
 

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