Reduce sulfurous odor from waste products to be reused?

[Edwin Price]

Edwin, as to your original issue with the sometimes extreme issue of sulfur dioxide gas when using SMB, all the replies are correct, as far as they go, including the rather facetious attempt at humor from Goldshark.

4metals gave the best answer, however. Of the two, ferrous sulfate would be my choice. Easy to make. Easy to get. Easy to use.

His other option, ascorbic acid, is both easy to get and easy to use. Not so easy to make, however.

In time, you will likely have on hand SMB, ferrous sulfate, and ascorbic acid. Each has its place. Each has advantages above the others in different situations. These you will learn as your expertise progresses.

The cleanest drop from a clean solution is done with sulfur dioxide gas. Something you will read on the forum from time to time. It is, however, an option that most here have not used for several reasons I will not dive into here.

Enjoy.

Time for more coffee.

Yes sir. I purchased ferrous sulfate last week. Thank you.

Careful now, for all parties involved, keep this civil!!

How much do you have, 2-3 liters?
If it still smells of SO₂ you have had to have used a massive overload of SMB.
If you have a lid on it, not much will evaporate neither water nor SO₂.
How about keeping it in your fume hood?

yes

Careful now, for all parties involved, keep this civil!!

How much do you have, 2-3 liters?
If it still smells of SO₂ you have had to have used a massive overload of SMB.
If you have a lid on it, not much will evaporate neither water nor SO₂.
How about keeping it in your fume hood?

Yessir. I used way too much SMB, Nitric, water, etc. I have about 2-3 gallons of waste that's largely water. I completely uncovered the bucket to improve evaporation. I do not have a fume hood. I would never do gold refining work indoors, or even in my garage which is mainly used to house two muscle cars. I work in an outdoor, covered facility and use a huge fan to blow away noxious gases. I live in a golf course community about 100 yards from Lake Norman. I have a deck, fenced backyard and plenty enough land such that my chemistry activities don't impact my neighbors. If I cannot eventually retrieve any gold from this waste mess I created, that's fine. I'll evaporate or boil off the liquid and incinerate the remains. I haven't put anything into the sewer system. I have plenty of e-waste source material and access to more. And, I'll be much more judicious and conservative with chemicals (especially HNO3) when I start my second campaign. ty

 

[Golddigger76]

Yes sir. I purchased ferrous sulfate last week. Thank you.

yes

Yessir. I used way too much SMB, Nitric, water, etc. I have about 2-3 gallons of waste that's largely water. I completely uncovered the bucket to improve evaporation. I do not have a fume hood. I would never do gold refining work indoors, or even in my garage which is mainly used to house two muscle cars. I work in an outdoor, covered facility and use a huge fan to blow away noxious gases. I live in a golf course community about 100 yards from Lake Norman. I have a deck, fenced backyard and plenty enough land such that my chemistry activities don't impact my neighbors. If I cannot eventually retrieve any gold from this waste mess I created, that's fine. I'll evaporate or boil off the liquid and incinerate the remains. I haven't put anything into the sewer system. I have plenty of e-waste source material and access to more. And, I'll be much more judicious and conservative with chemicals (especially HNO3) when I start my second campaign. ty

Edwin,
If your 2 to 3 gallons of waste is still putting out SO² any gold that was in it is settled on the bottom of your container and yes I have done the same thing as far as over using smb.

If you can decant the AR waste solution all the way to the material that has settled on the bottom you can easily recover whatever amount of gold that is missing.

So you need to decant down close to the bottom and then filter out the solids.

Once you have the solids filtered then you can transfer it into a beaker and wash it several times with hot (almost boiling) water.

Since you over used smb you are probably going to have very fine gold, it might even look black and take several hours to settle.

Once you get it washed very well and decant most of the wash water out you can add some hydrochloric acid and then start adding either bleach or nitric a few drops at a time until it's dissolved.
Maybe try precipitating the gold with ferrous sulfate this time.

I doubt that you will have any gold in solution after over using smb but most certainly need to test it with stannous chloride before you start trying to recover the gold just in case there is still gold in solution.

The recovery of your gold in the waste solution is very simple.
If you still have gold when you test with stannous you will do best by cementing it out with thick copper bar, then start the process I'm describing above after it's all cemented and stannous test is negative.

One more thing that I didn't address above is that you might have some silver along with whatever gold has settled out so also test the solids for silver.
If it has silver it will be silver chloride and you can filter it out.

 

[Edwin Price]

Edwin,
If your 2 to 3 gallons of waste is still putting out SO² any gold that was in it is settled on the bottom of your container and yes I have done the same thing as far as over using smb.

If you can decant the AR waste solution all the way to the material that has settled on the bottom you can easily recover whatever amount of gold that is missing.

So you need to decant down close to the bottom and then filter out the solids.

Once you have the solids filtered then you can transfer it into a beaker and wash it several times with hot (almost boiling) water.

Since you over used smb you are probably going to have very fine gold, it might even look black and take several hours to settle.

Once you get it washed very well and decant most of the wash water out you can add some hydrochloric acid and then start adding either bleach or nitric a few drops at a time until it's dissolved.
Maybe try precipitating the gold with ferrous sulfate this time.

I doubt that you will have any gold in solution after over using smb but most certainly need to test it with stannous chloride before you start trying to recover the gold just in case there is still gold in solution.

The recovery of your gold in the waste solution is very simple.
If you still have gold when you test with stannous you will do best by cementing it out with thick copper bar, then start the process I'm describing above after it's all cemented and stannous test is negative.

One more thing that I didn't address above is that you might have some silver along with whatever gold has settled out so also test the solids for silver.
If it has silver it will be silver chloride and you can filter it out.

Wow! That is excellent, hopeful detail instruction on the process. I really appreciate you and the others that have offered actionable advice based on experience and previous success. Exactly what I need. Thank you good sir. Regards,
edp

 

[Martijn]

Wow! That is excellent, hopeful detail instruction on the process. I really appreciate you and the others that have offered actionable advice based on experience and previous success. Exactly what I need. Thank you good sir. Regards,
edp

I don't think a strong sulfurous smelling solution will contain any gold.
It goes away after letting it vent for a while, an air bubbles helps speeding it up.

Did you test this solution with stannous?

And it can dissolve gold in HCl if i'm correct, so filter out any solids before you do.

Edwin,
If your 2 to 3 gallons of waste is still putting out SO² any gold that was in it is settled on the bottom of your container and yes I have done the same thing as far as over using smb.

If you can decant the AR waste solution all the way to the material that has settled on the bottom you can easily recover whatever amount of gold that is missing.

So you need to decant down close to the bottom and then filter out the solids.

Once you have the solids filtered then you can transfer it into a beaker and wash it several times with hot (almost boiling) water.

Since you over used smb you are probably going to have very fine gold, it might even look black and take several hours to settle.

Once you get it washed very well and decant most of the wash water out you can add some hydrochloric acid and then start adding either bleach or nitric a few drops at a time until it's dissolved.
Maybe try precipitating the gold with ferrous sulfate this time.

I doubt that you will have any gold in solution after over using smb but most certainly need to test it with stannous chloride before you start trying to recover the gold just in case there is still gold in solution.

The recovery of your gold in the waste solution is very simple.
If you still have gold when you test with stannous you will do best by cementing it out with thick copper bar, then start the process I'm describing above after it's all cemented and stannous test is negative.

One more thing that I didn't address above is that you might have some silver along with whatever gold has settled out so also test the solids for silver.
If it has silver it will be silver chloride and you can filter it out.

We tend to say the same thing in many different ways...
As I said earlier that I doubt there will be any gold in such a solution, I also doubt there will be any silver in a HCl solution...
It should have been filtered out long before going to the cementing step. any AgCl is along with the precipitated gold after SMB.
But he said he is still getting a weak purple stannous test result. Indicating an excess of nitric?
I would not bother with the sulfurous smell and just let it vent to the air, cement out your values and proceed with waste treatment.

 

[Argentum Auricle]

Hello, All,

This is a subject to which I've given a fair amount of thought. As I am a small scale precious metals refiner... a hobbyist really... I don't have a lot of space to store waste - especially waste that emits noxious fumes.

I've decided to treat liquid wastes containing volatiles immediately after refining, opting to forego the usual stockpot method. Instead, after precipitation with SO2 gas, I follow this treatment pathway:

1.) Waste gold refining solution containing base metals, trace PMs, free HCl, and dissolved SO2 gas
a. Add zinc metal until everything
drops from solution.
b. 2HCl + Zn -> ZnCl2 + H2
SO2 + 3H2 -> H2S + 2H2O

This secondary reaction produces some hydrogen sulfide gas, and needs to be done outside or in a fume hood - which you should already be doing, as the original liquid contained dissolved sulfur dioxide gas.

2.) Decant and filter Zn-precipitated solids from waste solution. Solution should be clear and barren (no PMs). Keep solids for later processing, when you have enough of them to make it cost effective to recover PMs.

Note: Up to 5% of your original PM material could be trapped in the un-treated PM waste solution - which may be undetectable by stannous test - and will now be in your Zn precipitates. Do not discard.

3.) Filtered waste solution is treated with household lye (NaOH). Depending on your location, this can be bought rather cheaply from most home and/or hardware stores. This step converts any dissolved hydrogen sulfide gas in solution to sodium sulfide - a solid at pH 7.0.
a. ZnCl2 + 2NaOH -> Zn(OH)2 + 2NaCl
b. H2S + 2NaOH -> Na2S + 2H2O

Keep in mind that zinc hydroxide is amphoteric and will dissolve in strong acids and strong bases. To fully-drop all (99%-ish) Zn(OH)2 from solution, pH must be between 7-8.

Decant and filter the solids (slurry) from the remaining waste solution. This solution is now safe to dispose - Neutralize the pH of the liquid, and pour down the drain.

4.) I like to decompose the collected zinc hydrozide slurry into zinc oxide, which is much better for the environment to dispose than the hydroxide form. To do this, gently heat the hydroxide at 130 degrees C until dry and powdery (a couple hours).
a. Zn(OH)2 + heat -> ZnO + H20. Of
course, this will also contain
trace crystalized NaCl and Na2S.

The waste stream from this recycling process is (for each two moles of waste HCl solution and one mole of Zn metal used):

- One mole of ZnO(s)
- Two moles of NaCl(s)
- Three moles of H2(g)
- Five moles of H2O(l)
- Trace amount of H2S(g)
- Trace amount of Na2S(s)
- Zinc precipitates; solids

For what it's worth.


-Mike T.
Silver Spur Refining

 

[Edwin Price]

Hello, All,

This is a subject to which I've given a fair amount of thought. As I am a small scale precious metals refiner... a hobbyist really... I don't have a lot of space to store waste - especially waste that emits noxious fumes.

I've decided to treat liquid wastes containing volatiles immediately after refining, opting to forego the usual stockpot method. Instead, after precipitation with SO2 gas, I follow this treatment pathway:

1.) Waste gold refining solution containing base metals, trace PMs, free HCl, and dissolved SO2 gas
a. Add zinc metal until everything
drops from solution.
b. 2HCl + Zn -> ZnCl2 + H2
SO2 + 3H2 -> H2S + 2H2O

This secondary reaction produces some hydrogen sulfide gas, and needs to be done outside or in a fume hood - which you should already be doing, as the original liquid contained dissolved sulfur dioxide gas.

2.) Decant and filter Zn-precipitated solids from waste solution. Solution should be clear and barren (no PMs). Keep solids for later processing, when you have enough of them to make it cost effective to recover PMs.

Note: Up to 5% of your original PM material could be trapped in the un-treated PM waste solution - which may be undetectable by stannous test - and will now be in your Zn precipitates. Do not discard.

3.) Filtered waste solution is treated with household lye (NaOH). Depending on your location, this can be bought rather cheaply from most home and/or hardware stores. This step converts any dissolved hydrogen sulfide gas in solution to sodium sulfide - a solid at pH 7.0.
a. ZnCl2 + 2NaOH -> Zn(OH)2 + 2NaCl
b. H2S + 2NaOH -> Na2S + 2H2O

Keep in mind that zinc hydroxide is amphoteric and will dissolve in strong acids and strong bases. To fully-drop all (99%-ish) Zn(OH) from solution, pH must be between 7-8.

Decant and filter the solids (slurry) from the remaining waste solution. This solution is now safe to dispose - Neutralize the pH of the liquid, and dispose down the drain.

4.) I like to decompose the collected zinc hydrozide slurry into zinc oxide, which is much better for the environment to dispose than the hydroxide form. To do this, gently heat the hydroxide at 130 degrees C until dry and powdery (a couple hours).
a. Zn(OH)2 + heat -> ZnO + H20. Of
course, this will also contain
trace crystalized NaCl and Na2S.

The waste stream from this recycling process is (for each two moles of waste HCl solution and one mole of Zn metal used):

- One mole of ZnO(s)
- Two moles of NaCl(s)
- Three moles of H2(g)
- Five moles of H2O(l)
- Trace amount of H2S(g)
- Trace amount of Na2S(s)
- Zinc precipitates; solids

For what it's worth.


-Mike T.
Silver Spur Refining

Excellent info! Much appreciated, good sir.

 

[Argentum Auricle]

Excellent info! Much appreciated, good sir.

You're welcome.

 

[Martijn]

Trying to get the facts straight:

Note: Up to 5% of your original PM material could be trapped in the un-treated PM waste solution

Isn't that a bit high? 5%?

which may be undetectable by stannous test

Care to explain a bit more? I thought traces can be detected with Stannous Chloride, and 5% (of your total PM content) would be a dark spot imo.

 

[Argentum Auricle]

Trying to get the facts straight:

Isn't that a bit high? 5%?

Care to explain a bit more? I thought traces can be detected with Stannous Chloride, and 5% (of your total PM content) would be a dark spot imo.

Hello, Martijn,

Thank-you for your question. It would be my pleasure to clarify.

This is really a catch-all statement - including, and up to a worse case scenario (5%). Considering all the variables to any given refining operation:

- What is source material - clean, dirty, highly contaminated?
- Multiple PMs in source material or just one?
- Type and concentration of contaminants in source material
- Methods of dissolution
- Methods of PM separation (if necessary)
- Methods of reduction
- Concentration of PMs in solution upon reduction (i.e. - 1g/L? 100g/L)
- Residual oxidants left in PM solution (Like a slight excess of HNO3, left un-neutralized)
- Another item to consider is stannous freshness. New stannous is very sensitive to trace PMs. However, when it starts to degrade, it will not be as sensitive and trace PMs might go undetected, below certain concentrations.

In practice and for example... if I do a refining well, I can refine an ounce of gold in 750mL of solution (final volume, after filtering and rinsing), and recover nearly all of the Au, leaving only a very small amount in the waste solution. Last time I quantified recovery from waste solution for a good refining, it was ~0.07g from ~22g of source material (parted Au from carat gold scrap). Final volume of solution, after filtering and washing; before reduction ~800mL. This recovery represents 0.3% of the gold from the source material.

On the otherhand, I've done micro-experiments when the process didn't go as well as planned, and I ended up with very dilute gold bearing solutions. For instance, I had to recover 9 grams of pure gold from a melting/casting accident, where Au became partially alloyed with a steel mold. Not to bore you with all the details, but using SMB, I was only able to drop about 8.75g of gold from the first-round refining solution. Final volume of gold bearing solution was ~ 1L. After treating the liquid waste as I outlined above, and after refining the collected, solid, zinc precipitates, and was able to recover the remaining ~0.25+g of Au. This represents ~2.7% of the weight of the source material.

I collect and save my Zn precipates from all PM refining batches until the bucket I keep them in is full. This usually gets me anywhere from 0.3g - 1.0g in recovered gold... again, depending on the make-up of source materials and refining methods, etcetera, etcetera.

I think this should explain my claim a little better. I hope this helps.


Regards,
Mike T.

 

[anachronism]

I find that the best way to reduce sulphurous odour from waste solutions is to not use SMB.
Ever.
Horrid, nasty stuff and really rubbish compared to other precipitants. I do get why people use it of course but there are far better methods.

 

[Argentum Auricle]

I find that the best way to reduce sulphurous odour from waste solutions is to not use SMB.
Ever.
Horrid, nasty stuff and really rubbish compared to other precipitants. I do get why people use it of course but there are far better methods.

Agreed. I think ease of acquisition, ease of use, and efficacy are the among the driving factors as why so many refiners use SMB. In the U.S. we can get 100% SMB from stores like Lowes, Home Depot, Ace, TruValue, Walmart... and can also be bought rather cheaply online from sites like Amazon, eBay, Duda Energy, etcetera. Most refiners don't even prepare a clean solution of concentrated SMB, but rather just dump the raw powder directly into gold bearing solutions.

Admittedly, I primarily use SMB to precipitate gold, but I use it in a gas generator to produce SO2 gas, and never add it directly to the gold-bearing solution.

Its just so cheap and easy to use!

 

[Yggdrasil]

I find that the best way to reduce sulphurous odour from waste solutions is to not use SMB.
Ever.
Horrid, nasty stuff and really rubbish compared to other precipitants. I do get why people use it of course but there are far better methods.

I don't mind the smell

 

[Shark]

I don’t mind the smell but my wife is allergic. It is bad enough she can smell it on my cloths at times. This lead me to asking about other precipitants a few years ago. A few of them I still haven’t got to try yet.

 

[anachronism]

I don't mind the smell

You're weird Ygg

 

[nickvc]

I have never used smb, I used ferrous or ascorbic acid neither of which gives off that disgusting aroma.

 

[Yggdrasil]

You're weird Ygg

I know

 

[Darkthirty]

You're weird Ygg

Smells like $$$!

 

[patnor1011]

I cant stand that choking smell. Ferrous is much better for me.