refine 9999 pure gold

[Anonymous]

it is possible to refine 9999 pure gold in a small shop. most of my refined golds come out only 999 plus if i am lucky. what am i doing wrong?

 

[Harold_V]

Yes, it is possible. You'd be best served to confer with Lou on this one.

While my gold turned out exceptionally well, I'd be lying to you if I suggested it came out 4n's.

I used tech grade acids, but did my final wash with reagent HCl. Used tap water, which will serve quite well unless it is contaminated with metallic traces.

Does your gold melt without oxides? Can you describe your procedure? Could be you could improve in some area and make the difference.

For the record, I refined all my gold a second time to achieve high purity. Once through, unless you are using a proprietary system, it's unlikely you'd achieve outstanding quality.

Harold

 

[Anonymous]

Thanks Harold, I first dissolved the scrape golds in aqua regia (1:3) , I don't think it is tech grade acid. Then filter out the solution just one time. Add urea until the solution stop boiling. After that I precipitate with sodium bisulfate or sodium bi something, sorry but can't remember the name off the top of my head, but it will precipitate to a coffee like powder. After that I washed it with HCL 3 times and 1 or 2 time with ammonia. Then melt the gold but the gold bar doesn't come out clean on the surface.

 

[Harold_V]

I didn't read anything about inquartation, which, alone, could improve your quality. If you're happy processing the way you are, no big deal, but you're going to have to process the gold a second time if you'd like it to improve. By not inquarting, you're precipitating the values from very dirty solutions----decreasing your chance of high quality gold. A lot of the base metals in solution get dragged down when you precipitate. Eliminate the base metals, there's nothing to drag down.

The only gold I processed directly with AR was filings from the jeweler's bench, and they always yielded dirty gold, even after a prolonged boil in dilute nitric before dissolution of the values. Everything else got inquarted.

Once you've washed the gold, simply re-dissolve it and re-precipitate. Second time it will come down from a much cleaner solution, leaving behind the vast majority of the contaminants. Hoke discusses re-processing, so turn there for more information.

I used SO2 from a cylinder to precipitate, so nothing got added to my solutions that changed their appearance. The contamination eliminated in the second refining was obvious by the color of the solution. Generally a light blue color, indicating copper, and, perhaps, a trace of nickel.

By now, most everyone has seen this picture to the point where they're tired of it-----but if you've missed it---this is what my gold looked like after a second refining. It has been converted to shot, but not pickled. No visible oxides formed on the shot in the process.

Harold

 

[Anonymous]

Thanks Harold! I'll will try to refine the gold twice. If you have anything to help me improve my technique please let me know. My main goal is 4/9 but anything less is no good. Thanks again

 

[Harold_V]

I would suggest you learn to evaporate. Adding anything to your solution that isn't necessary, when trying to achieve 9999, is asking for problems. You also must scrub your vessels until they are perfectly clean, and melt with virtually sterile appliances. Contamination can come from many sources, even after the gold has been refined.

Your goal of 4n gold is rather lofty for chemical refining. I would think that you'd have to use reagent grade acids, and distilled water. I was hoping Lou chimed in with advice. GSP claims to have developed a proprietary process for achieving that degree of fineness, with one precipitation. He may be willing to provide his comments, perhaps leading you to his process.

I was more than pleased with the quality I achieved with the gold I produced, using tech grade acids and tap water. You should be able to achieve similar results, but if you must have 4 n's, you're not likely to achieve the goal by doing so. I never claimed to.

Your other option is to run your recovered gold in a parting cell.

Harold

 

[Bernie Foley]

Hi all,
Could it be incineration that is the missing step! That might be the one thing that would change the whole picture and start looking toward the magic 9999"s. Good luck! It is very hard to be shure that everything is clean. Don't forget to clean the tip on the torch! Also be shure your flame is set properly!.........Bernie

 

[Lou]

There is a method here that reliably gives 6N, 99,9999 gold, or better depending on technique. Look for it in techniques.


Lou

 

[goldsilverpro]

hasoviboy,

How do you know your gold is 999+ pure?

 

[Anonymous]

I got it fire assay in downtown LA. If I wash my gold with atleast 3 time with HCL, I get 9991 or sometime less. What is incineration step?

 

[OMG]

I have a question about purity as well.
When talking about precipitating gold from solution, people talk about base metal drag down. From what I can infer, this means that a small amount of base metals are also precipitated along with the gold. Does anyone know what actually is happening to make this occur?
IE. If you still have free acid in solution, how can base metals survive without getting redissolved? -- or -- how can they precipitate in the first place when there is acid there available to dissolve them?

 

[Harold_V]

I'm not convinced the drag down is the result of solids being dragged down. When you wash gold that has come from dirty solutions, even with repeated washings, the wash solution changes color. It's an indicator, at least to me, that traces of base metals, whether they be in solution or not, are being removed.

When gold that is not washed clean is melted, perhaps not all of the metals are included, but some are. You can see evidence of that by melting the gold a second time, with a clean dish----and clean flux. The flux will become discolored, and the gold will have oxides on the surface.

You can also see evidence of dragdown by re-processing well washed gold. Even if your last wash solution is clear, when the gold is re-dissolved and re-precipitated, the remaining solution will almost always show signs of base metals, in my case, generally traces of copper. Consistently, when I processed from dirty solutions, the gold quality suffered. So much so that I used gold from processing filings as my added gold when evaporating, insuring that it got processed a third time.

Please consider that I used bottled SO2 gas for my precipitation----I didn't introduce any other reagents, so the appearance of the now barren solution was a perfect indicator of garbage removed from the re-processed gold.

Drag down is a fact, although I may not fully understand the mechanics of how it works. I do know that I spent years double refining the gold I dispensed in order to assure its quality. I never managed to consistently precipitate gold of acceptable quality with one precipitation.

Not sure this helps----

Harold

 

[Lou]

Drag down is something the analytical chemist fights on a frequent basis! Basically, when you go to precipitate your metal from a dirty solution, you end up adsorbing some of the solution onto the surface of the gold precipitate. Also, what can happen is some of the solution being entrained in the actual precipitate.

This is all a fairly interesting, and somewhat complex physical phenomenon that has much to do with the surface area, the concentration, the concentration gradients (dictated by how quickly and with what stirring you add your precipitating reagent), and the temperature.

Without getting into the math and the real chemistry (if anyone really wants it in a nutshell, PM me). So the basic idea here is to make it agglomerate (stick together) quickly. The ''bigger'' the gold precipitate is, the less impurities will be in it because of the relationship between surface area and volume.

A precipitation from a hot solution, by the slow addition with vigorous stirring, of your reducing agent will generally yield a superior precipitate. The washing procedure Harold talks of is well known--basically disrupts the adsorption layer of ions onto the surface of the gold.

It is entirely possible to get 4N gold on a consistent basis. I know for a fact that a dirty (copper/nickel/Pd) solution will give 4N gold if proper procedures and techniques are used. SX and a good wash will ensure this.


Lou

 

[Noxx]

I'm interested in the math behind this. I know for sure that slower precipitation will decrease mechanical drag down. (I learned it in Analytical Chemistry II).

So slow precipitation with a stir bar in should yield purer gold ?

Thanks

 

[Lou]

Very good Noxx, that's the idea.

 

[Anonymous]

Guys I'm lost, It look like I need a Ph.d to understand what is going on here. How about basic cook book reciept for 4N? Now I know why I didn't do good in chemisty class. I just like lab, all I needed to do is to follow the handout procedures. I guess I need to read more and ask more question.

 

[Harold_V]

If you're lost, the best advice I can offer you is to read Hoke. I learned refining from that book----and have studied no others aside from information on dealing with silver, and processing gold bearing ores. The point being there's enough information in the book to get you on the path to refining gold that meets industry standards.

While 4 n's sounds impressive, the industry accepts 9995 readily. It's more than pure enough for all but the most demanding of needs. Jewelers are more than happy with that quality, and they present the best possible market for the small refiner, assuming you can get recognized as producing quality goods.

There is no magic bullet. Achieving good quality demands you become familiar with good and accepted practice, and practice excellent hygiene in your operation.

Harold