Precipitants in general

[goldsilverpro]

I might add that when you are re-refining a batch of gold, many of the books advise using a different precipitant for the 2nd refining. They also suggest melting and shotting the powder from the 1st refining before re-dissolving in AR. For maximum effectiveness, I can see the logic of both.

 

[FrugalRefiner]

I might add that when you are re-refining a batch of gold, many of the books advise using a different precipitant for the 2nd refining. They also suggest melting and shotting the powder from the 1st refining before re-dissolving in AR. For maximum effectiveness, I can see the logic of both.

GSP,

I've read the advice of using a different precipitant for the second refine many times and that has always made sense. Each has strengths and weaknesses. Using different precipitants minimizes the weaknesses.

But this is the first time I have seen the recomendation to melt and cornflake before the second digestion. In most cases on this forum, readers are advised to go right to the second refine since their gold is a powder and will be digested readily. So I had to think about it. It would help to oxidize base metals so they wouldn't be carried through the second refine, right?

Thanks in advance,
Dave

 

[goldsilverpro]

I might add that when you are re-refining a batch of gold, many of the books advise using a different precipitant for the 2nd refining. They also suggest melting and shotting the powder from the 1st refining before re-dissolving in AR. For maximum effectiveness, I can see the logic of both.

GSP,

I've read the advice of using a different precipitant for the second refine many times and that has always made sense. Each has strengths and weaknesses. Using different precipitants minimizes the weaknesses.

But this is the first time I have seen the recomendation to melt and cornflake before the second digestion. In most cases on this forum, readers are advised to go right to the second refine since their gold is a powder and will be digested readily. So I had to think about it. It would help to oxidize base metals so they wouldn't be carried through the second refine, right?

Thanks in advance,
Dave

That seems to be the reasoning. Makes sense.

 

[sakosakarian]

hey guyz
i have gold plating water and i finish my work and i wanna get back gold how can i precipitate it from solution and it contain 24-k gold

 

[butcher]

sakosakarian,

I do not have enough experience in that area of recovery to give you advice, but I can help you in this, you need to be more clear in your question, giving more details of what you have, the plating solution could be cyanide, or some other plating solution which uses acids, giving more detail in your question will help those who can answer your question, giving them more to go on, to give you an the answer, or to help you find an answer.

Also you have asked similar questions several times at different places on the forum, this will not help you get an answer, it only waste forum space, ask the question once, give all of the details you can, people who can help will find your question and help.

 

[Harold_V]

But this is the first time I have seen the recomendation to melt and cornflake before the second digestion. In most cases on this forum, readers are advised to go right to the second refine since their gold is a powder and will be digested readily. So I had to think about it. It would help to oxidize base metals so they wouldn't be carried through the second refine, right?

While I normally didn't follow that routine, I had a reoccurring experience when refining waste from the jeweler's bench. Not being a chemist, I was never able to isolate the problem material, but I discovered that the melting process was instrumental in its removal.

Here's the scenario, and it occurred only with specific jewelers, but was routine for their wastes.

After precipitating and washing, some substance that doggedly followed the gold would rinse from the resulting gold powder. I had determined it was not soluble in HCl, but would rinse out with plain water, given enough rinses. It was clearly visible and manifested itself as a coffee colored rinse solution. When the powder was melted, it wasn't uncommon for miniscule droplets of gold to fly from the powder as it was heated, which I attributed to the unknown contaminant.

It was this gold that was used by me in evaporation. I'd melt all of it to buttons, then it would be consumed in the evaporation process. In essence, it actually got refined a third time. I never found the unknown substance in my second refined gold, so the process I chose to use appeared to be effective.

So then, yes, melting can provide a benefit. However, the quality of my second refining was always superb, so I did no melting beyond that which I described. I also used SO2 for all precipitations. The only thing I did that was out of the ordinary in my second refining was to use a #5 Whatman for filtration, and to use reagent quality HCl for the final wash. I routiney rinsed with tap water, but our water was quite clean, albeit chlorinated.

Harold

 

[NobleMetalWorks]

For me, it is not as easy to butyl diglyme as the other precipitants. It's as simple as that.

BDG doesn't precipitate anything, it falls under solvent extraction, you still need to reduce the Au with Oxalic Acid. The benefit is that you can extract gold out of dirty solutions, or solutions with excess HNO3, not that you should have excess HNO3 if you are properly digesting your material. BDG is easy to clean before reducing Au with Oxalic acid. I can easily obtain 99.99 purity and if I take special care when washing the BDG with HCl, 99.999 purity.

But Solvent Extraction is not precipitation!

There is also ion exchange resins, scavenger materials, etc. But still, not precipitants.

If you are just selling your refined material to a refinery, there really is no need to produce purity beyond standard.

Scott

 

[solar_plasma]

Not really important, but

https://archive.org/stream/atextbookinorga01hollgoog#page/n388/mode/2up

Page 369, lines 6 and 7:

Ferrous sulphate, oxalic acid and acetylene water serve well for this purpose. Hydrogen peroxide precipitates gold quickly in alkaline solution.

Just being curious, what is meant by acetylene water? Is it acetaldehyde, which can be made from acetylene and water using a catalyst?

Would hydrogen peroxide be still a valid choice today for precipitating gold from alkaline solutions as for example thiosulfate leaches?

 

[butcher]

I would suspect that precipitating gold with acetylene would be very dangerous, I suspect you would have an unstable explosive on your hands.

To form an oxide of gold I would think the solution would need to be far to the base side of the pH scale.

I would think the hydrogen peroxide would try to oxidize the thiosulfate Na2SO3 to sodium sulfate Na2SO4

Na2SO3 + H2O2 --> Na2SO4 + H2O

I cannot say how well a caustic like sodium hydroxide and strong peroxide would work to precipitate gold from a thiosulfate solution, although with all of the trouble with getting the gold back out of this type of leach I suspect it would not work that well, but who knows.

The thiosulfate leach for gold ore is such a complex mix normally with many metals and reactions, I am unsure of all of the reactions with the other metals and compounds in solution, if you tried a reduction with caustic and peroxide, but I would think if gold could be recovered with NaOH and H2O2 any gold would have a slew of other metal hydroxides or compounds you would have to deal with, that is if it would even work at all.

H2O2 is very unstable and can be catalyzed to oxygen and water by several metals.

I think the reason the NaOH and strong H2O2, works with a Auric chloride solution is because it precipitates an oxide of gold, possibly Au2O which is insoluble in water.

 

[pu_239]

While I can't adress all the possible reducing agents, I'll give you a few comments about the three you mentioned.

Copperas (ferrous sulfate), SMB, and oxalic acid are all relatively inexpensive and readily available.

Copperas
Pros:
It is easy to use, working fine at room temperature.
According to GSP, copperas will provide better separation when you have gold and PGMs in the same solution.
Cons:
Copperas pollutes your PM solution, resulting in drag down of iron which is difficult to wash out.

SMB
Pros:
Easy to use at room temperature, wet or dry.
Causes less contamination during use with powder being easier to wash.
Cons:
Can precipitate PGMs as well as base metals if overused.

Oxalic Acid
Pros:
Produces the highest quality gold precipitate.
Cons:
More difficult to use as solutions must be heated.

I'm sure others can add more pros and cons than this brief list, but it's a start.

Dave

Dave can you elaborate a bit on the oxalic acid. Are you referring to contamination of the gold powder by the oxidizing agent for example if we use SMB contaminating the gold with Sulfur oxides?

 

[solar_plasma]

Pu_239, different precipitants will cause different drag down or co-precipitates. SMB is more likely to co-precipitate copper, while oxalic acid might co-precipitate PGMs. Ferrous sulfate is said to be serving well to precipitate from dirty solutions. Depending on the source of the gold, you might want to use a different precipitant for the second refining. On the other hand, Harold taught in some threads, that SO2 alone will do the trick, if you use the proper methods in all steps, especially the washes and the incinerations. Reading all his posts about the matter is absolutely mandatory, in my eyes.

 

[FrugalRefiner]

Dave can you elaborate a bit on the oxalic acid. Are you referring to contamination of the gold powder by the oxidizing agent for example if we use SMB contaminating the gold with Sulfur oxides?

These are reducing agents, not oxidizing agents. The gold is oxidized (it loses an electron and becomes a cation) when it is dissolved into solution. To precipitate it as a metallic solid, we need to reduce it (add an electron).

As solar_plasma said, most of the contamination comes from species that are coprecipitated and/or dragged down, although copperas does add iron to the mix.

Dave

 

[Lou]

and actually, oxalic acid is less likely to drag down PGMs. It is more likely to bring down copper oxalate.

Sulfites shouldn't precipitate copper unless used in gross excess in copper rich solutions, where the copper(II) is reduced to copper(I).

Lou

 

[MarcoP]

As I can see working with Chloric solutions does precipitate cleaner metals. What if I carefully evaporate down, to a concentrate, a nitrate solution containing palladium and then starting the routine of adding hydrochloric and evaporation to denox? Is this a feasible method to go from nitrate to chloride?

 

[solar_plasma]

and actually, oxalic acid is less likely to drag down PGMs. It is more likely to bring down copper oxalate.

Sulfites shouldn't precipitate copper unless used in gross excess in copper rich solutions, where the copper(II) is reduced to copper(I).

Lou

Thank you for correction, I have to find the posts I misunderstood.

http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=38&t=5662#p48665

In this post 4metals mentions at least, that oxalic

may bring down traces of palladium but they can be removed by a nitric boil

 

[Lou]

I have not experienced that. In my experience, oxalic acid is a good way to remove the last dozens of ppm Pd from Au during its reduction.

On the other hand, palladium may be precipitated (depending mostly upon pH) from a variety of solutions with the excessive use of sulfite. It is more likely to occur with sulfite as sodium sulfite is a weak base (being the salt of sulfurous acid and sodium hydroxide) which modulates the pH of the solution through 1.) abstracting a proton from the acid HCl to generate SO2 in situ, 2.) simple neutralization.

Freechemist (RIP) mentions the complex palladium salts, which are much less soluble than their halogenated brethren and need no exotic reducing agents. The disadvantage is that those sulfite salts should only be prepared from highly pure palladium.

Lou

 

[jeweler1]

I work part time for a jeweler who like all jewelers nowadays buys and sells scrap gold to the refiners (me sometimes).
Yesterday he started selling to another “refiner” I had never herd of but his prices were good .I got to talk with him and it seems he has a fairly large operation out west. What fascinated me was that he said to obtain the purest gold he precipitates with Nitrogen gases? I was wondering if this was true? I have never heard of Nitrogen gas being used as a participating agent?

 

[MarcoP]

I work part time for a jeweler who like all jewelers nowadays buys and sells scrap gold to the refiners (me sometimes).
Yesterday he started selling to another “refiner” I had never herd of but his prices were good .I got to talk with him and it seems he has a fairly large operation out west. What fascinated me was that he said to obtain the purest gold he precipitates with Nitrogen gases? I was wondering if this was true? I have never heard of Nitrogen gas being used as a participating agent?

May be sulfur dioxide (SO2)?

 

[jeweler1]

I did a series of searches on Goggle and came up empty also I think he was “pulling my chain” “full of BS” or he was just making up something to look smart. Anyway thanks for trying. So much for the credibility of his “refining business” I should have been suspicious when he said he didn’t like the smell of the acid? That’s what a hood and scrubbers are for. Happy holiday to all

 

[MarcoP]

One more of my "what if" I burn some sulfur in a small chamber and pump the fumes into the chloroauric acid, that's SO2 right?