Non-Chemical Precipitation for newbs

[jarlowski1]

There should be a video section where members can upload material (I don't know if the forum has space for that or not). 1 video I certainly would like posted is the use of nitric acid and how to avoid using too much nitric in the first place. I believe that too many (especially newbies) people get impatient with the speed of a reaction and then just "throw" more nitric into the beaker just to speed up the reaction when that is not always the best thing to do.

 

[butcher]

For many purposes, I do not understand why every new member thinks they have to use a sled-hammer like aqua regia (or using nitric) when most of the gold (even base metals for that matter) will go into a solution with a tack-hammer approach such as HCl and sodium hypochlorite (bleach).

When working with most of this the gold or other metals or alloys are finely divided ( placer gold, electronic scrap...) are fairly easily dissolved with their high surface area and the cupric chloride Copper II Chloride leach miss named the acid peroxide process) works well to dissolve copper and most base metals from much of the sources of electronic scrap to recover the gold, and the finely divided gold can easily be put into solution with HCl and chlorine gas making things much simpler...

 

[Jmk88]

“What make you thing the copper contamination was because the button "was from old dirty papers"

Because I filtered copper chloride through some of them.

I do not precipitate using hydroxide. I simply raise the ph. I would never start to cement before I had tried what I have described.

It created far more work than needed - its a last resort for me. I’m looking for the best outcome I can every time. I have never had any of the issues that have been identified in this post.

I have thoroughly tested materials and reactions with various things and am very much aware of the oxides formed upon excess base. I’ve never had this.

Diluting hydroxide at 30g per 146 grams of water allows me to manipulate ph and keep solution volume down. It doesn’t get used to precipitate or enough to.

 

[Jmk88]

I have no adversity to using bleach either, which I do. That just wasn’t really the purpose of the post to begin with.

I find bleach more than effective however, when you have a lot of material it is not efficient and you can significantly increase volumes and need to evaporate.

My first three refines were using bleach on recovered gold filled material which was fine.

 

[butcher]

jarlowski1,

Many of our members have made some very good videos, they normally upload it in a post they made concerning the subject, several of these members have made many videos that will show the techniques they use in the lab (Streetips is one member that comes to mind you may enjoy his videos) but there are many.

Try this experiment in a small beaker (50ml) on a coffee cup warmer, or hot plate in a corning dish...
Add 1 gram of gold (powder, flakes, shot...).
Add 4ml HCl (little more would do no harm),(noting that one teaspoon of a solution is around 5ml).

Now we can expect to use up to 1ml of nitric to put the gold into solution,(noting about 20 drops of nitric is around 1ml) this in most cases would give us an excess of nitric acid which in some cases we may need to get the shot or larger pieces of gold into solution with a high loss of the nitric as gases evolving from solution.

Add HNO3 by few drops giving time for the reaction to slow.

Adding heat to warm the solution will help to drive off the water (water from the acids used and any produced in a chemical reaction), this will also help to consume the nitric used, increasing its ability to dissolve the gold, as it concentrates the solution.

{Here you can do some experimenting, try a stannous test (where you know you have some gold in solution), and after you add a few drops of nitric, Now with free nitric (the test would be negative as the gold cannot be reduced in the test). Now heat the solution a while letting the nitric getting consumed dissolving gold, with some gold still left undissolved after concentrating the solution take another reading with stannous chloride, with the free nitric consumed the test should show positive...}

Now remembering we only had a gram of gold in about a spoonful of aqua regia.

We can continue to periodically add drops along with using heat, until almost all of the gold is in solution.

We want to stop using nitric when we have a little gold left undissolved, with the heat we can normally finish consuming the gold and the free nitric...
At this point you may already have a concentrated gold chloride solution (almost red), if not concentrating the spoonful of liquid will most likely finish consuming the gold with just the heat of evaporation.

Using heat and a gold button to de-NOx a solution was Harold's trick, Here we are using the last portion of our undissolved gold to de-NOx the solution before we finish dissolving it...

With gold in solution and minimal nitric usage, add a few drops of HCl to the warmed concentrated solution, paying close attention to any red fumes of NOx, let it sit to evaporate the water from the few drops of acid you just added, and then try another few drops of HCl watching for the red cloud, after that water evaporates and the solution re -concentrates, after the third evaporation and HCl cycle, and no more indication of NOx evolution, you can take another stannous chloride test, (if free nitric the test may show negative for gold, or may show positive Purple of Cassius and then disappear to a negative for gold), (if the free nitric is consumed and the gold chloride solution is de-NOxed the test will show positive as the gold can now be reduced from solution using your choice of reducing agent...

Try a few different expieriments to gain a better understanding (and you can always scale up), but doing things in small experiments can teach you much, and not make such a big mess......
Do small experiments as Hoke taught in her book to get acquainted...
Do a few more experiments of your own, you can take some of the gold chloride solutions as a reagent to verify the effectiveness of your SnCl2.

Add some excess nitric to a sample of the gold chloride, do some other experiments with urea, sulfamic acid, different reducing agents...

In a spot plate test dish try testing the solutions with different reagents, for example, the Stannous chloride (will not de-NOx the solution your testing for gold) while in another spot of the dish copperas will de-Nox the solution as it tests for gold.
Using FeSO4 is helpful to precipitate where NOx gases or some free nitric is an issue, although SMB can overcome some NOx in the solution if the excess of reagent is used, it is not helpful where free nitric is involved...

You are only limited by your imagination and your test-tubes...

 

[anachronism]

Butcher do you still really think it takes 1 ml of Nitric to put a gramme of gold powder into solution?

I'm using your analogy above not a dirty dissolve.

 

[FrugalRefiner]

Now we can expect to use up to 1ml of nitric to put the gold into solution,(noting about 20 drops of nitric is around 1ml) this in most cases would give us an excess of nitric acid which in some cases we may need to get the shot or larger pieces of gold into solution with a high loss of the nitric as gases evolving from solution.

Butcher do you still really think it takes 1 ml of Nitric to put a gramme of gold powder into solution?

Do you actually read his posts, or are you just so anxious to discredit what he writes that you have to say something?

Dave

 

[anachronism]

I'm not anxious to discredit anything Dave.

My point is that the old adage of 1 ml of Nitric to dissolve 1g of gold has been disproved therefore why even use it?

 

[butcher]

Jon,
I find it takes as much nitric as it takes, every circumstance is different.


In general terms, or speaking in general then, yes it takes approximately 4 fl oz. (118,29ml) HCl: 1fl oz (29.57ml) HNO3 to dissolve an ounce of gold just as C.M. HoKe so eloquently proved.


Although just like gas whether you drive a big truck or a small economic car, the gas may take you further in one, then the other. One batch of gold is not necessarily the same as all others...

Much depends on the conditions but generally speaking this will get the job done and the gold dissolved, even under some of the more extreme cases (gold and PGM's...), will this be an excess of nitric? Yes for most circumstances, Can we and should we use much less HNO3 than this calculated amount? Yes, we should, and we can as we have discussed thousands and thousands of times.

So can I dissolve a gram of gold using less than 1ml of HNO3? Yes in most cases with much less nitric usage, but depending on many factors such as the physical size of the gold, the alloying of other metals with the gold (silver, PGM's...), temperatures, pressures, concentrations, for speed of reactions hours versus weeks or months, ability to contain the volatile gases in solution which are what is doing the work chemically, the chloride salts contents... The mileage will vary widely of how much nitric acid is actually needed or how much would be an excess...

It does not take large volumes of acids to put gold into solution, and there is no set amount of acid for a set amount of gold unless you controlled all other factors, and you only worked in a very tight window of conditions...

How much is a mute argument? it takes what it takes.
How much to expect is useful not only in our discussions but also in understanding and in our practical work...

 

[Jmk88]

I think for me personally evaporation is a difficult one. Especially for someone starting. As I’ve got more used to things I can tell by the colour change when I need to remover the heat and add hcl.

However again, similar to cementing, I don’t see the value in this when what I initially explained can get you the desired outcome.

I’ve not had contaminating salts in with my gold and have filtered and melted straight after flushing with two litres of boiling water.

My intention was to share something I use and find fairly simple that does indeed precipitate pure gold. That’s why I posted the pic as you can see even after the first refine it’s not bad at all.

Certainly pure enough to refine again straight into AR.

 

[jarlowski1]

Thanks Butcher for you time writing your post. I have been refining gold for the past 6 years (thanks to you and many others here). I have made mistakes before, but nothing that could be fixed with patience (set things aside and study). I don't make too make mistakes nowadays. What I meant as I seem to always fail to articulate what I am thinking is; we have a dedicated section where we can post videos on the basics. I feel that many people are impatient and their quick thinking is "Ok well I will just add more nitric" (or sodium hypochlorite if dissolving using that method) when all they would have to do is gently warm the solution and watch for the reaction. I feel a video with commentary might be able to show the newbies what they are supposed to be looking for. I do enjoy Sreetips videos as well as Owltechs (keep up the good work). Hope this clears up what I meant

 

[Jmk88]

I suspect Butcher the reason why they use nitric is they read Hoke and as advised follow. That’s why they use nitric over bleach.

However as someone who is experienced will know, recovery is where you do 80% of your work which a newbie rarely understands before losing gold, and coming to guys like you to clean up the mess. Like I have. Trying to use AR if it’s overly contaminated is not something a beginner wants to be dealing with in my opinion.

They then go to dissolve the gold and have all sorts of problems as they have more base metals in than they should and therefor need more acids to do the job. I had a friend who ended up with 3 litres of crap from 3G of 18k gold. It was unbelievable.

They then end up with excess nitric and precipitation won’t work. When I tried to pass on advice to my friend that I had received he wouldn’t listen and proceeded with evaporation. It was a sight to behold. 3 litres. He was doing it for weeks. Then he cemented and ended up with .4 grams after 3 months. It was painful.

 

[Jmk88]

Streetips is like the new age Hoke....

Or the Beethoven of refining.... such finesse, and grace.

He makes it look like making toast.

 

[butcher]

Jmk88,
You can get gold in the method you are describing, and you could get it to high quality.

Although adding urea, and hydroxide, large volumes acids and solutions, and ... It is just not what you should be working towards, or pointing our new members towards...
it is just basically trying to fix some other problem and getting into another...

Forget using Urea, it will not do what you think it will...
Forget adding caustic soda to your gold solutions...

Let's learn how not to create the problems if possible, and learn how to recognize a problem if it does rear its head, and have an understanding of how to troubleshoot and correct it,

 

[anachronism]

Richard

In the context of your last post to me - we're not a million miles apart to be honest. We both agree it's down to the specific set of circumstances with the dissolving at hand.

Where we disagree is that if you had 100g of gold powder to dissolve then simply assuming that it would take 100ml of Nitric and working according to that would be incorrect and leave a lot of excess.

That given I accept that putting the Nitric in in smaller stages would alleviate this to a large degree but people tend to blindly follow prescribed recipes no matter how many time we tell them otherwise.

 

[fishaholic5]

I've used Sodium Hydroxide to adjust pH for dropping Gold from Ore Leaches where it was hard to get a clean precipitation.
This is a pic from one of those precipitations during rinsing of the Gold.

It may not be necessary in the refining stages but it gave me a better precipitation and larger particle size when I was having trouble precipitating from some very dirty solutions.

Cheers Wal

 

[Jmk88]

Looks nice! That’s exactly the result I get; instant precipitation the second the sulphite touches the surface and then the solution is clear within 30 minutes.

The gold comes out like a beige brown and you just know you’ve hit the nail on the head.

Thanks for the post. I can only talk from experience and I have nothing but good results.

 

[fishaholic5]

My solutions from this ore are never clear after precipitation, mostly red or brownish from Cobalt and other metals still in solution. This was after rinsing several times with water.
I still use the same process with new ore samples for rough wet assay results where I have mixed metals and excess acid in a HCl/ Hypochlorite leach to save time.
The remaining solution gets cemented for PGM's using Copper

Cheers Wal

 

[Jmk88]

Nice.

I can’t see why there seems to be so much adversity to it!

 

[fishaholic5]

There are some very skilled refiners here whose focus is helping and educating people with the best, most effective and safest methods for recovery and refining.

As a refining process using Sodium Hydroxide to adjust pH for precipitation is not necessary or best practise but it works in your process and there is a place for it in mine.

They are just discussing things and putting forward better methods to help you and others.

Cheers Wal