# Precipitants in general



## bswartzwelder (Jul 5, 2013)

I have read the forum for several years now and have learned quite a bit. I have learned that every type of gold to be processed has it's own particular way(s) of being processed. There are probably 2 or 3 ways for every type of "scrap" out there, but usually one stands out as being superior. Using AP for circuit board foils and fingers stands out (at least for getting rid of base metals). And an electrolytic cell jumps out as almost everyone's favorite for gold plated items.

When it comes to precipitating gold from your solutions, SMB seems to sit at or very near the top of everyones list. Hoke appeared to like Copperas (Ferrous Sulfate). Perhaps she was not aware of SMB, I don't know. If you want to obtain the highest quality, brightest gold, it has to be refined to a high degree of purity. Therefore, you should dissolve it once with your choice of solutions. Clean as per Harold V's method, then dissolve in true (not poormans) AR. At this point, I've been led to believe the best precipitant would be Oxalic Acid. Has anyone ever made a list of all the various precipitants and their pros versus cons? I, for one would really like to see what I've been missing, and I'm sure it could benefit others as well.


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## JHS (Jul 5, 2013)

That would be great to see,but i think you are asking someone to write a book.
I wouuld buy it if someone did.
perhaps this is an oppertunity, 
john


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## FrugalRefiner (Jul 5, 2013)

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


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## butcher (Jul 6, 2013)

I may repeat some of the above info, or just say it in a different way.

Copperas (ferrous sulfate) (FeSO4), easy to make works good if PGM in solution, will precipitate gold and not platinum, (SO2 or SMB can carry down PGM), I have not heard of trouble with Iron being dragged down as stated above, I believe the iron should stay in solution, (I would like to learn more about how the iron would be dragged down).

Sodium metabisulfite (SMB) can also precipitate copper and PGM.

sulfur dioxide (SO2) gas, good to use when tin oxide is in solution will not precipitate tin (oxalic acid can carry down tin and copper), it is OK also for second refining, SO2 can carry down PGM.

Oxalic acid (H2C2O4), not good for first refining, oxalic acid will carry down tin oxide and copper (SO2 gas will not), but is very good for second refining and can produce high quality gold in the second refining.

Refining twice using a different precipitant than was used in the first refining will greatly improve the quality of gold.
From above we see copperas would make a good choice for the first refine if PGM was in solution, and SO2 the second refine.
Or SO2 the first refine and oxalic acid the second refine.
Basically using a different precipitant the second refine so that what the first precipitant allowed to follow our gold, the second refine and using a different precipitant, the different precipitant would not let it follow our gold through the second refine.
Hokes discusses these topics, to learn more about it read Hoke's book.


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## bswartzwelder (Jul 6, 2013)

You see? YOU SEE? I totally forgot SO2. Probably because as a gas, it's not readily available unless you eat a lot of beans or chili and capture the resulting effluent. I am sure other people use other precipitants for other reasons. It would be good to hear from them as well. Frugal Refiner and Butcher, thank you for your inputs. I have known for a while about the three I mentioned from reading the forum. I also knew of Sulfur Dioxide, but had a typical brain fart when making my original post. Enough of them might produce some SO2?

We also use two "different" solutions when dissolving our gold, but for different reasons. Poorman's AR works very well for the first refining, but it is, well AR. I have had really limited success with the Acid Chlorox method. When mixing chemicals, I like to use my el cheapo electric stirrer and every time I added Chlorox to the mix, it fizzed up and then seemed to do nothing else. I think it might have benefitted from being chilled. The final refining should always be true AR. I fully understand the reasons for the different solutions 1. to to be more "selective" when we precipitate our gold, and 2. Be as financially responsible as possible. I will most likely never be the recovery expert or refiner of many of the members, but every time it is made easier or more understandable for me, it is also easier and more understandable for someone else. By the way, I'm doing yard work this weekend and most of my Urea will hopefully help promote grass growth. Now, that's a hoot.


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## FrugalRefiner (Jul 6, 2013)

butcher said:


> Copperas (ferrous sulfate) (FeSO4), easy to make works good if PGM in solution, will precipitate gold and not platinum, (SO2 or SMB can carry down PGM), I have not heard of trouble with Iron being dragged down as stated above, I believe the iron should stay in solution, (I would like to learn more about how the iron would be dragged down).


butcher, I read about the problem with iron in a couple of posts from GSP. Here's a link to one of them: General Chat | What can YOU buy for $5000, in which he says:


GSP said:


> With today's purity requirement of 99.99%, it's virtually impossible to get that purity with FeSO4 - the iron is the problem.


Also, in Gallery | MY VERY FIRST GOLD BUTTON 90 GRAMS he says


GSP said:


> You'll have a better chance of not re-precipitating Pt in your gold if you use Ferrous Sulfate for your 2nd drop. However, the FeSO4 requires excellent rinsing - see Hoke for the best procedures for using FeSO4.


Dave


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## Marcel (Jul 6, 2013)

Steve posted a table long time ago. i cant find it right now, but there were several precipitants for gold, palladium and platinum. Some that are never described here and some were missing that are beeing used now.


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## butcher (Jul 6, 2013)

FrugalRefiner,
I really appreciate you spending the time to find those post by GSP and the iron problem, I am still wondering if the iron contamination he is speaking of is coming from oxidized ferrous sulfate, and not the nice green crystals, this would make more sense to me as any iron oxide or hydroxides would also be insoluble with the gold and depending on the state of the iron oxide or hydroxide could be hard to impossible to wash out,although a second refining with a different precipitant should leave them behind.

I am still wondering if the bright green fresh copperas could possibly leave iron with the gold, I could see how the oxidized junk they sell from the garden centers that they call ferrous sulfate would, that stuff is not ferrous sulfate any more it is getting fairly close to being rust, I could not find any that was not oxidized to the point of being useless, I do not see how fresh bright green copperas crystals would be reduced to iron in the precipitation process, or how it would precipitate iron with gold.
But then again if I knew everything I wouldn't be here trying to learn something new every day.

bswartzwelder, 
There are several other reagents used to precipitate gold not mentioned here.


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## chlaurite (Jul 6, 2013)

bswartzwelder said:


> You see? YOU SEE? I totally forgot SO2. Probably because as a gas, it's not readily available unless you eat a lot of beans or chili and capture the resulting effluent.



No you didn't. You can think of SMB as "SO2 in granular form". Much, _much_ easier to work with than actual SO2 gas.


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## JHS (Jul 6, 2013)

I think,but i am most likely wrong,i usually am but,i was thinking that i was reading a post by Harold that he used SO2 gas,and it was more effective than smb,and he got a much better recovery from it.


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## JHS (Jul 7, 2013)

I was reading a post by GSP about using hydrazine sulfate to drop gold involving stainless steel.
he said you do not have to put the nitric in a nuteral state.


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## tamlove (Jul 8, 2013)

Hi. does anyone know if i can use ferrous sulphate tablets for iron deficiency to precipitate my gold? can i just crush it fine and add it as powder or dissolve it in some water and then add it. or do i have to get the green crystal form of it. it is hard to get smb where i live.


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## jimdoc (Jul 8, 2013)

tamlove said:


> Hi. does anyone know if i can use ferrous sulphate tablets for iron deficiency to precipitate my gold? can i just crush it fine and add it as powder or dissolve it in some water and then add it. or do i have to get the green crystal form of it. it is hard to get smb where i live.



Search the forum for how to make ferrous sulphate. It is easy to make.

Jim


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## tamlove (Jul 8, 2013)

thank you jim i shall do just that.


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## eeTHr (Jul 8, 2013)

lazersteve posted a chart showing precipitants and their pros and cons.

http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=6026&p=87562#p87562

There are also some links in that post, which give further explanations.


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## Lino1406 (Jul 8, 2013)

Ascorbic acid (vitamin C) also is a gold precipitator 
When you get used to one (learn to work with it optimally),
you may think it is the best
Lino1406, author "30 recovery procedures.."


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## Harold_V (Jul 9, 2013)

JHS said:


> I think,but i am most likely wrong,i usually am but,i was thinking that i was reading a post by Harold that he used SO2 gas,and it was more effective than smb,and he got a much better recovery from it.


Not a better recovery. Gold will precipitate fully by many precipitants, which can be verified by testing with stannous chloride. 
The real advantage of SO2 gas is it's convenience. It adds nothing harmful to the solution, nor does it add to the volume of solution. It is also inexpensive to use. The negative is that it is difficult to obtain. SMB, for all practical purposes, is the same process. 

Harold


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## Lino1406 (Jul 10, 2013)

I think it is of concern that CuCl is not precipitated (together with gold)
by copperas and it also does not have the irritating smell


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## Gratilla (Jul 10, 2013)

Why does nobody (except me <g>) mention Solvent Extraction (SX) for cases such as this???

After your first precipitation (or even before, particularly if you're dealing with concentrates), dissolve (your precipitate, after silver extraction or before) in your favourite acid-side leach (eg AR, AP, Acid Hypochlorite, SSN), SX with Butyl Diglyme (or similar) and drop with Oxalic Acid. Even I can get four 9s gold. Some claim to be able to get five 9s.


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## bswartzwelder (Jul 11, 2013)

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


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## goldsilverpro (Jul 11, 2013)

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.


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## FrugalRefiner (Jul 11, 2013)

goldsilverpro said:


> 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


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## goldsilverpro (Jul 12, 2013)

FrugalRefiner said:


> goldsilverpro said:
> 
> 
> > 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.
> ...


That seems to be the reasoning. Makes sense.


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## sakosakarian (Aug 10, 2013)

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


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## butcher (Aug 10, 2013)

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.


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## Harold_V (Aug 11, 2013)

FrugalRefiner said:


> 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


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## NobleMetalWorks (Aug 11, 2013)

bswartzwelder said:


> 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


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## solar_plasma (Dec 13, 2014)

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?


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## butcher (Dec 13, 2014)

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.


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## pu_239 (Dec 13, 2014)

FrugalRefiner said:


> 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.
> 
> ...




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?


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## solar_plasma (Dec 13, 2014)

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.


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## FrugalRefiner (Dec 13, 2014)

pu_239 said:


> 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


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## Lou (Dec 15, 2014)

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


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## MarcoP (Dec 15, 2014)

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?


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## solar_plasma (Dec 15, 2014)

Lou said:


> 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


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## Lou (Dec 15, 2014)

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


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## jeweler1 (Dec 17, 2014)

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?


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## MarcoP (Dec 17, 2014)

jeweler1 said:


> 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)?


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## jeweler1 (Dec 18, 2014)

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


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## MarcoP (Dec 19, 2014)

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?


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## Lou (Dec 19, 2014)

Yes.

Then you have to deal with molten sulfur. A sulfur burner is easy enough to make, pretty blue flame. For small operators, best to stick with sulfites unless you can justify the purchase of a cylinder of SO2, a cabinet, and a dedicated exhaust for "just in case" something goes wrong. Also, there are certain reporting requirements (under CERCLA/Right-to-Know) for the installation of even a 150# cylinder here in the US. If you insist on making SO2 g, then you can do it as per kadriver.


Lou


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## Richard NL (Dec 20, 2014)

jeweler1 said:


> he precipitates with Nitrogen gases


If he did not eliminate the excess nitric, he precipitates with (oxidized) Nitrogen gases NOx.
LOL

Best regard,
Richard.


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## MarcoP (Dec 20, 2014)

Lou said:


> Then you have to deal with molten sulfur.


I'm doing my homeworks on this but all I could gather is that molten sulfur is simply elemental sulfur heated to 240°F (115°C) and it seems to still produce S02(g). I could not found any resource with a complete equation of the cumbustion process, not even a line about the left over of the combustion.
Could you pass me a link where I could study on it or gether some hints?



Lou said:


> If you insist on making SO2 g, then you can do it as per kadriver.


Really interesting but expensive, I wanted to avoid using SMB as it is expensive in my area and hardly available. Sulfur here is really cheap and easily available.

Thanks.


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## Richard NL (Dec 20, 2014)

A equation of the combustion process of sulfur: http://www.tigurl.org/images/tiged/docs/activities/431.pdf
You can study this google search or similar ones:
http://tinyurl.com/o9p6mjt
http://tinyurl.com/pxvms6m
http://tinyurl.com/lo5x9nk

Or wait for Lou.

Good luck with your homework

Best regard,
Richard.


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## MarcoP (Dec 20, 2014)

Thanks Richard, I actually came to read the same PDF you posted and that's why I'm still perplexed as it seems that all sulfur combust to the dioxide and no solid remains thus I don't quite understand Lou's comment about dealing with molten sulfur which I initially believed to be the remaining solid. Bad luck my dad never wanted me to help him he used to burn sulfur.

The other three links seems to take me on a "Discussion" search, will try to open them when back home.


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## Shark (Dec 20, 2014)

Lou made a pretty good point. If you dig deep enough you will find information on kadrivers method scattered around the internet. Some pretty good information on generating your own sulfur gas, and how to do it. I have been slowly working my way into trying it. Still need just a bit more information yet.


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## butcher (Dec 20, 2014)

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=48&t=17070&hilit=sulfur+dioxide

Kadriver made a great video of his chemistry setup to generate the SO2 gas, I am not sure how to point you to the video.

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=48&t=17070&hilit=sulfur+dioxide


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## MarcoP (Dec 21, 2014)

Thanks gentlemen, I've read the topic and watched the video of this nitty closed system as soon Lou mentioned it but I think I can produce SO2 gas by burning sulfur in a closed system and still in a fume hood but as Lou pointed out I might end up with molten sulfur to deal with, which should still be sulfur but in a liquid form and that will solidify on cooling to a really hard solid sulfur.
Not sure how much is correct in infos gathered from internet.

I'm only asking for any type of details about the mentioned residue.
Will letting the combustion continue to it's end eliminate most of the residue? (as it is always done in some of it's multiple uses - never tried on first hand and not going to try until I know what I'm dealing with)

Being aware of it will let me study on the disposal, complications or other possible uses of this still unknown to me by-product. Then and only then i'll be able to decide to go into overusing SMB route to obtain SO2 gas, or none at all.

Basically if someone can overuse smb, in fact there are no complications on doing it, should be doing it Kadriver's way, still in a closed system.
I can always keep going between copperas and smb depending on the feed stock, and i'll keep using oxalic acid for the second drop, still some issues but i'm getting the hand of it.

What i just learned about elemental sulfur, on a complete combustion with pure oxygen:
S(s) + heat + O2(g) --> SO2(g) [dioxide]
2S(s) + heat + 3O2(g) --> 2SO3(g) [trioxide]

But if i take easy on the oxygen, slowing down the combustion, I should mostly get the dioxide.

But none of those equations reports any particular material left to deal with, that's where I'm stumbling.

This will off course be done in future inside a fume hood as I'm aware of the enormous dangers of the reaction of the trioxide with water. Breathe it and it will use the water in your lungs!

Normal air oxygen supply will be enough to reduce the trioxide. Limiting the source of oxygen to further slow down the combustion will keep it to the minimum, if any will be produced, and in any case it will end up in the chloroauric acid to form sulfuric acid.

If you read till here and you are a moderator feel free to split this part of the discussion to resume another thread or create a new one. Originally about a precipitant but not anymore.

P.S.: I even fall at sleep writing this, hope you don't when you read it :lol:


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## solar_plasma (Dec 21, 2014)

Burning pure sulfur there is not much left over, if anything at all. In a more or less closed reaction chamber you might observe sublimated sulfur condensing at the colder glass areas. Very hard to remove. If this vapor is condensing on the surface of water you get some chewing gum-like form of elemental sulfur there, which is going back to a hard form after some days. 

You don't need pure oxygen, just air flow.

If you want to heat in a closed vessel like a quartz tube or a borosilicate test tube you should make sure those sublimates will not reach the precipitation vessel.

Instead of burning sulfur you could also burn (roast) metal sulfides (with "D"!).

You could use the generated SO2 to make sulfurous acid or sodium sulfite by scrubbing through water or NaOH.


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## Shark (Dec 21, 2014)

Richard NL said:


> A equation of the combustion process of sulfur: http://www.tigurl.org/images/tiged/docs/activities/431.pdf
> You can study this google search or similar ones:
> http://tinyurl.com/o9p6mjt
> http://tinyurl.com/pxvms6m
> ...



Thanks for the document link, it has gotten me closer to the information I have been looking for.

Edited for spelling


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## solar_plasma (Dec 21, 2014)

In the first link there is a typo:



> , where it forms calcium sulfate hydrate



but CaSO3 is sulfite, not sulfate.


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## Shark (Dec 21, 2014)

solar_plasma said:


> In the first link there is a typo:
> 
> 
> 
> ...



Thanks, I will add that change to the document I have.


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## MarcoP (Dec 22, 2014)

Thank you solar_plasma, I guess using SMB or scrap copper with sulfuric acid will eliminate the hard-to-remove condense issues.
If so, I'll avoid the sulfur and try to get some glassware when it's time.


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## Richard NL (Dec 25, 2014)

Some more Literature about burning elemental sulfur/sulphur to get SO2.
Because it is nice if you have another tool at your disposal.
Mainly the first part of this book, the second part is also fun to read (producing small bubbles of gas in liquids by submerged orifices).
I hope that this book still tells the truth (because i like it)!
https://www.scribd.com/doc/250829045/The-Ferric-Sulphate-sulphuric-Acid-Process

Second book: https://www.scribd.com/doc/250853307/Recovery-of-Manganese-From-Low-Grade-Resources

Third book: https://www.scribd.com/doc/250840257/SO2air?secret_password=yDoDZwHBBnMjdsJXw9Q6

Best regard,
Richard.


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## MarcoP (Dec 25, 2014)

Richard, I'm at the first one, thank you!

Reading more and more about it but I just realized that if using sulfur dioxide, independently how it's produced, in a concentrated gold chloride solution might produce less sulfuric acid. Will search on this to make sure if it.


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## kadriver (Mar 9, 2015)

butcher said:


> Copperas (ferrous sulfate) (FeSO4), easy to make works good if PGM in solution, will precipitate gold and not platinum, (SO2 or SMB can carry down PGM), I have not heard of trouble with Iron being dragged down as stated above, I believe the iron should stay in solution, (I would like to learn more about how the iron would be dragged down).
> 
> Refining twice using a different precipitant than was used in the first refining will greatly improve the quality of gold.
> From above we see copperas would make a good choice for the first refine if PGM was in solution, and SO2 the second refining.



Butcher, I have recently started using ferrous sulfate for the first refining, and SMB for the second refining.

The gold powder from the second refining comes out looking real good, that nice light colored tan look, and the gold always tests three nines via XRF.

I did notice that the barren solution (tested with stannous chloride) from the second (SMB) refining was tinted yellow so I did a third refining using SMB and the barren solution was then colorless. But before this third refining I put a few drops of the yellow barren solution in a spot plate and added a crystal of ammonium thiocyanate.

Sure enough it turned red indicating the presence of iron. If the pure gold powder was not properly washed free of this yellow solution then wouldn't this cause a slight bit of iron contamination in the gold? Of course it would not be "drag-down" of the iron, but if ANY of the yellow tinted iron solution remained in the gold powder, due to poor washing, and the gold powder melted, then the iron would report in the gold, correct?

The reason I bring this up is because I turned in some gold once, precipitated with ferrous sulfate, and the tech said that the gold had some iron in it.

Also, I use copperas from the hardware store. I dissolve a couple of pounds in a little hot water to make a concentrated solution, and filter. THERE ARE BITS OF IRON IN THE COPPERAS that filter out as well as other solids. If one was to try and add the dry copperas, right out of the bag, then these bits of iron would contaminate the gold powder for sure.

I then pour the filtered concentrated ferrous sulfate solution into a large PYREX dish and let it evaporate to a hard green solid.

I keep the solid in a covered dish until I need it. To use, I put some of the green solids in a beaker, add distilled water and a little hydrochloric acid, then heat it on a stirrer until it dissolves.

Thank you,
kadriver


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## kadriver (Mar 9, 2015)

butcher said:


> Kadriver made a great video of his chemistry setup to generate the SO2 gas, I am not sure how to point you to the video.



The video is here on the forum somewhere. Doing a search for "precipitating gold with sulfur dioxide" on YouTube will pull it up also.

I used sodium metabisulfite and dripped sulfuric acid on it in a gas generated setup in the video. It worked quite nicely, but using SMB is much easier.

kadriver


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## g_axelsson (Mar 9, 2015)

kadriver said:


> If the pure gold powder was not properly washed free of this yellow solution then wouldn't this cause a slight bit of iron contamination in the gold? Of course it would not be "drag-down" of the iron, but if ANY of the yellow tinted iron solution remained in the gold powder, due to poor washing, and the gold powder melted, then the iron would report in the gold, correct?


I thought that was the definition of drag down.

Mechanical inclusion of contamination when precipitating a product. 

Göran


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