Precipitants in general

[bswartzwelder]

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.

 

[JHS]

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

 

[FrugalRefiner]

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

 

[butcher]

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.

 

[bswartzwelder]

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.

 

[FrugalRefiner]

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:

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

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

 

[Marcel]

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.

 

[butcher]

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.

 

[chlaurite]

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.

 

[JHS]

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.

 

[JHS]

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.

 

[tamlove]

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.

 

[jimdoc]

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

 

[tamlove]

thank you jim i shall do just that.

 

[eeTHr]

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.

 

[Lino1406]

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.."

 

[Harold_V]

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

 

[Lino1406]

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

 

[Gratilla]

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.

 

[bswartzwelder]

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