Is there an alternative to sulfuric acid for lead precipitation

[Cozza]

Hi all,
This may be a silly question so please bare with me.
Is there an alternative to using sulfuric acid to precipitate lead after gold digestion in AR?
I am new on the forum and still do not have a good handle on the search function as yet- I have tried many searches that all bring up the words i am searching for, but they are not in association with each other.
I ask this as here in the 'land down under' ( Australia ) sulfuric acid is looking nearly impossible to get hold of in any practical quantity. You either have to pay $70 odd for a 100ml bottle from a lab supply company, or a 20 liter tank from an industrial supplier @ several hundred $. I cant even seem to get it as car battery electrolyte! Surprisingly nitric was not too hard to find @ $45 for a 5litre container of 68%.
Anyways, I would appreciate any guidance ( even suggestions on appropriate search terms!) On the matter, and thank you all for your time and wisdom.

 

[cuchugold]

Many drain cleaners are made of sulfuric acid.

I believe you could also use sodium bisulphate (not bisulphite) to precipitate lead in solution.

Automobile battery acid is also diluted sulphuric acid. It must be the most common acid commercially available in one form or another. Many leather factories use it too. They may sell you a few gallons very cheap.

 

[FrugalRefiner]

If you can find sulfamic acid, it serves a double purpose. It will eliminate any excess nitric acid in the AR, and in the process it is converted to sulfuric acid which will precipitate any lead. Sulfamic acid is often available in hardware stores as a tile and grout cleaner.

Dave

 

[anachronism]

Cozza

You might also want to determine whether you have lead or not in your base material.

 

[Cozza]

Wow, great info fellows. I think sulfuric is highly restricted here due to some acid attacks here some years ago. Sulfamic I can get at the local hardware shop. I was actually wondering if that would work.
I am still in the learning stage so have yet to refine any gold as yet. I want to ensure I learn as much as possible before I even attempt to. I will start reading up on sulfamic.
Thank you all for your time and wisdom.

 

[goldsilverpro]

The sulfate (SO4) is what's important, not the acid. The lead precipitates as the sulfate. When I am out of sulfuric, I sometimes use dissolved Epsom Salts, magnesium sulfate, which is 81% SO4. Also, battery acid is usually about 35% Sulfuric Acid.

 

[anachronism]

The sulfate (SO4) is what's important, not the acid. The lead precipitates as the sulfate. When I am out of sulfuric, I sometimes use dissolved Epsom Salts, magnesium sulfate, which is 81% SO4. Also, battery acid is usually about 35% Sulfuric Acid.

And a lot more user friendly too!

 

[rickbb]

The sulfate (SO4) is what's important, not the acid. The lead precipitates as the sulfate. When I am out of sulfuric, I sometimes use dissolved Epsom Salts, magnesium sulfate, which is 81% SO4. Also, battery acid is usually about 35% Sulfuric Acid.

And a lot more user friendly too!

And if you ever need 98% sulfuric, you can just heat up battery acid until the water vaporizes off.

 

[Lino1406]

The circumstances leading to lead contamination in the gold are parallel with silver contamination. That is why after boiling the precipitated gold with HCl you wash it with ammoniac.

 

[anachronism]

The circumstances leading to lead contamination in the gold are parallel with silver contamination. That is why after boiling the precipitated gold with HCl you wash it with ammoniac.

Sorry to disagree but there's no need for Ammonia when doing e-waste. It's an inefficient way to take out a small amount silver from powder anyway.

 

[IdahoMole]

Will sulfamic acid drop the lead from AR if there is NO excess nitric in the solution or is the nitric necessary to convert the sulfamic to sulfuric?

Jon, what method do you prefer to remove trace amounts silver from powders?

 

[butcher]

Nitrous acid and sulfamic acid reacts to evolve nitrogen gas:

HNO2 + H3NSO3 → H2SO4 + N2 + H2O

while with nitric acid, evolves nitrous oxide gas:

HNO3 + H3NSO3 → H2SO4 + N2O + H2O

Either reaction gives a byproduct of sulfuric acid which will precipitate the lead as insoluble PbSO4 lead sulfate.

Sulfamic acid and Hydrochloric acid gives chlorosulfuric acid HSO3Cl also called chlorosulfonic acid and ammonia gas.

H3NSO3 + HCl --> ClHSO3 + NH3

Hydrochloric acid and sulfuric give a similar reaction:

HCl + H2SO4 --> ClHSO3 + H2O

 

[anachronism]

Will sulfamic acid drop the lead from AR if there is NO excess nitric in the solution or is the nitric necessary to convert the sulfamic to sulfuric?

Jon, what method do you prefer to remove trace amounts silver from powders?

My first choice is having a system where you perform recovery of gold then refining of gold. In the recovery stage, the solution is filtered till crystal clear, dropped with Ferrous Sulphate, and the powder washed in 50/50 HCl and water.

You can HCL wash Silver out of your powder. Wash, pour off, wash in water. Check for white residue in the water stage, then repeat the "acid then water" process until the wash water is completely clear. There's no need for Ammonia, it's just an additional stage that complicates things.

You can clean most gold to over 99% like this.

Hope that helps- any queries just ask away.

Jon

 

[IdahoMole]

Thank you for the replies.

Butcher, you are speaking far above my knowledge of chemistry but if I understand, the answer to my question is yes?

Jon, after the recovery process any silver present would be in the chloride form correct? I didn't think AgCl was soluble in HCl. What am I miss understanding?

 

[FrugalRefiner]

I didn't think AgCl was soluble in HCl. What am I miss understanding?

In general, silver chloride has a very low solubility. But in a solution very high in chloride, its solubility does increase to the point where it can carry through to the precipitation step. GSP found that diluting a highly concentrated AR / chloride solution by three times prior to filtering would precipitate the AgCl so it could be filtered out prior to dropping the gold.

Dave

 

[IdahoMole]

I am familiar with chilling, diluting, and filtering the pregnant AR to remove AgCl prior to dropping the gold, however I wasn't aware that a HCl/water wash would rid the gold powders of residual silver. Now that you mention it I can see how a chloride rich wash would be enough to take trace amount of silver into solution.
I took notice of Jon's statement because I normally do an ammonia wash and I hate it. It stinks, must be re-acidified, and I keep it as a separate waste product. It is a general pain and I will skip it for the time being.

 

[FrugalRefiner]

Lou provided his washing procedure that does not use ammonia in Gold has been refined and melted, now has orange hue.

Dave

 

[IdahoMole]

Thanks Dave. It has been awhile since I have read Lou's method and was able to learn a few new things now that I have a more experienced perspective than before.

 

[FrugalRefiner]

It's much like reading Hoke. The more I understand, the more I learn each time I re-read things here on the forum, especially Lou's posts. The first time through, much of it was just over my head. Now I like to think I understand at least half of it. :lol:

Dave

 

[anachronism]

Lou provided his washing procedure that does not use ammonia in Gold has been refined and melted, now has orange hue.

Dave

Lou's method is certainly good, though it's not what I use. He uses cold HCl and a Buchner. I use Hot 50/50 HCL and water. Simmer until the gold cleans and clumps and then decant. The first rinse will have some gold in it unless you've been re-refining almost pure gold, so test it and drop it and add back to the powder. Most first HCL washes even with Harold's method will contain gold so do account for that. This is the action of your base metals dissolving gold with the HCl. Then boil in water, pour off and repeat until your liquid is clear. Sometimes a second HCl/water 50/50 is required but you'll get the hang of it with more experience.

It's all a learning curve- one that never seems to end. 8) 8)

Jon