Just Precipitated Gold, Now What?

So I have a couple years experience with gold recovery and chemistry, but not refining gold. I recovered foils off of fingers I have saved for 8 months. I felt I had sufficient foils to refine, so I did. I dissolved them in AR but measured the AR before dissolving, rather than adding Nitric until it just dissolves the gold. I remembered excess free nitric is not good for precipitating. So, while waiting for my Sodium Metabisulfite, I heated the gold in acid on a hot plate to dry it. I used low temps and stopped when it looked thick. While cooling, it dried. I re-dissolved it with distilled water.

After It was re-hydrated, I received my Sodium Metabisulfite and dropped the gold. It turned lighter in color immediately but took nearly 15 minutes for the gold to precipitate. I expect about 0.5 grams of gold, so I added (an excess) 2-2.5 grams of SMB for the precipitation.

Here's my issue.....

The gold is suspending a lot, so I let it settle for 30 minutes. A lot settled to the bottom, but a portion I don't want to decant is still floating in suspension. Also, on the surface is shiny particles of gold (leftover nitric issues?)

I attempted to decant it to another jar, but it seems impossible to remove the majority of the solution without decanting fine gold in suspension. I cooled it to aid in collection of the particles, let it sit another hour, and just keep fighting myself trying not to decant gold powder.

So, my question is, what should i do? I'm working with a small amount here and I really don't want jars sitting around forever with gold in the bottom I cant get out? I read coffee filters are a no-go. What are my options?

Welcome to the Gold Refiners Forum!

You could try to add a bit HCl to the solution. SMB works a lot better with an acidic environment, the acid releases SO₂ that precipitate gold.

The one time I did like you, evaporated close to dryness and diluting with water the gold precipitated first when I added some acid.

The gold on the surface can be knocked down with a spray bottle.

Göran

You can add heat to release all the excess SO2 that is in solution from the excess of SMB you added.
There will still be floating gold, but a brisk stir with a stir stick will release the trapped gas.

The shiny gold is from a dirty glass, use that vessel next time you process gold and it will be recovered.

As you now know, not overdoing the nitric is best.
With a single evaporation and adding distilled water, you did not expell the nitric.
Use sulfamic acid next time to remove the extra nitric, or less nitric.
Or
To properly denox with evaporation, you need to add a little HCl after its a thick syrup, then evaporate again, add HCl and evaporate again (3x)
Add a little sulfuric acid to remove lead as a sulfate, and help prevent it from crusting.

Your gold powder will need washed. Use Harolds method, or Lous high purity method, both are very similar and work wonders.

Personally, if Im running my own gold, I decant the fines into another glass and let them settle out. Dumping off the barren liquor after a few days of settling, so I have room for the next batch's fines. After a good layer is on bottom, I redissolve them and clean them up. If I do my job well, the fines in that vessel are a very very small percent of the gold in total.

For other peoples gold, I let it settle overnight and siphon off the barren liquid. And wash it up in the same glass it was precipitated in.
After a good rinsing and washing routine, those fine particles that wouldnt settle seem to agglomerate with ease.

Edit for continuity

So a couple ml of HCl should assist in it dropping? I'll give it a try. My solution was filtered and pretty free of contaminants before precipitating. I'll add a couple ml drop by drop and come back with results.

Topher_osAUrus said:

You can add heat to release all the excess SO2 that is in solution from the excess of SMB you added.
There will still be floating gold, but a brisk stir with a stir stick will release the trapped gas.

The shiny gold is from a dirty glass, use that vessel next time you process gold and it will be recovered.

As you now know, not overdoing the nitric is best.
With a single evaporation and adding distilled water, you did not expell the nitric.
Use sulfamic acid next time, or less nitric.

To properly denoxx, you need to add a little HCl after its a thick syrup, then evaporate again, add HCl and evaporate again (3x)
Add a little sulfuric acid to remove lead as a sulfate, and help prevent it from crusting.

Your gold powder will need washed. Use Harolds method, or Lous high purity method, both are very similar and work wonders.

Personally, if Im running my own gold, I decant the fines into another glass and let them settle out. Dumping off the barren liquor after a few days of settling, so I have room for the next batch's fines. After a good layer is on bottom, I redissolve them and clean them up. If I do my job well, the fines in that vessel are a very very small percent of the gold in total.

For other peoples gold, I let it settle overnight and siphon off the barren liquid. And wash it up in the same glass it was precipitated in.
After a good rinsing and washing routine, those fine particles that wouldnt settle seem to agglomerate with ease.

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Wow, thank you. I will burn this info in my head for further use. Is adding a couple ml of Hcl still recommended at this point? I have sulfuric acid. I actually have a lot of chemicals and some knowledge of their propertie.

Yes and no
No, in the case of :
The gold is already precipitated, so the excess nitric has been used up by the gold powder dissolving and reprecipitating until it was reduced and dropped to the bottom.

Yes, in the case of:
The gold powder now needs washed, I usually go with an HCl wash after I have removed the barren liquid
-but-
Have you tested the liquid to make sure it IS barren?
Stannous chloride will be your saving grace while learning this trade. It lets you know when gold is in solution (as well as Pd, Pt, Rh)
Test the solution (a small sample of it) to make sure the SMB added was enough to overcome all of the nitric AND precipitate all the gold. Sometimes its not. It just depends on how heavy handed you were with them both.

Dont fret though, it happens

I was probably a bit heavy handed on the SMB. I feel it has all precipitated but i have no stannous chloride. I was planning on making some but I couldn't think of anything that would contain tin that I have easy access to. The solution looks nearly clear after precipitation, except for a slight hint of copper in solution. I will likely melt this powder into a small nugget and restart the refining process to bring the purity up even more.

Just to be sure ( this never was fully answered), filtering is not a good practice right? I cant just filter what floats or is suspended and air dry the rest that sits in the bottom of the beaker?

PS: adding about 2.5ml of Hcl did make more SO2, but did not appear to drop any more gold.

Adding a bit HCl doesn't hurt so in worst case nothing will happen. In best case something is going to happen.

Göran

Somehow I didn't see your response until after I had written my answer. Well, it seems like your SMB used up all the acid available but the gold dropped thanks to the acid that was still present.

Sometimes boiling can make hard to settle gold clump together and drop faster. A danger with this is that if you have gold on the bottom the glass could be heated too much and when water reaches it the glass can shatter or there might be a small steam explosion, throwing out the content.
If you try boiling the solution, use a large enough container to keep it from boiling over the edge and have a catch vessel below. Stirring while boiling is highly recommended, either with a stir bar or manually with a glass rod.

The advice to boil seems to be against the standard rule to never boil, but gold isn't in solution and most of it is on the bottom already.

Göran

CuO said:

I was probably a bit heavy handed on the SMB. I feel it has all precipitated but i have no stannous chloride. I was planning on making some but I couldn't think of anything that would contain tin that I have easy access to.

.

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g_axelsson said:

The advice to boil seems to be against the standard rule to never boil, but gold isn't in solution and most of it is on the bottom already.

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Another reason it's okay: generally, we are telling people not to say "boil" when they should be saying "evaporate". You don't need to boil to evaporate, but in this case, a good boil is needed to clean up and agglomerate that gold.

The difference between boil and evaporate is a very big difference. A beginner will say something like "I boiled the solution down to" when they should have said "I evaporated the solution down to". It's okay to give advice to boil if boil is what you mean. For instance, to destroy chlorine from using bleach, heat is not enough. Sodium hypochlorite is decomposed at 101°C. So to tell someone they must boil the solution to destroy the chlorine is very accurate.

In a solution, we may have several different acids or salts of acids in solution (anions), along with the metal (cations) in solution.

Water boils around 212 deg F (100 deg.C). but if we add other ions (metals, or nonmetals like acids), we can change the boiling point of that solution.

Adding salts, metal ions anions and acid cations to water will change the boiling point of the solution.

If we add 20 grams of salt to five liters of water, instead of boiling at 100° C, it’ll boil at 100.04° C.

We can easily evaporate off water and the free acids without ever reaching the boiling points of the water or the acids, the reason we do not want to boil our solutions is that the mechanical action which spits out ions from the solution, even our valuable gold ions. We can achieve our purpose just as easily with evaporation that we can do with a boil.
By not bringing our solution to a boil we keep the gold ions in solution, evaporating every thing volatile in solution out just as well as if we had brought our solution to a boil.

In boiling the bubbles of gases pop explosively when they reach the surface these explosions carry acids and ions with the vapors.

With evaporation, the volatile mixtures leave the solution calmly leaving you the ions in solution. Ions like your gold that you are working so hard to get.

During evaporation each component has a different volatility, we can evaporate water from an acid until that acid reaches its azeotropic point (the point the acid will evaporate off with the water.

Water is more volatile than nitric acid, nitric more volatile than HCl, HCl more volatile than sulfuric.
When we evaporate mostly water comes out first, then nitric then HCl than sulfuric. Any nonmetal anions of the acids that can make a salt with the metal cations stay in solution, the acids break down to gases...

By boiling your solution you are just spitting and splashing your gases and acids and gold metal ions all over the lab.

By evaporating you are evolving the gases only.

Geo said:

The difference between boil and evaporate is a very big difference. A beginner will say something like "I boiled the solution down to" when they should have said "I evaporated the solution down to". It's okay to give advice to boil if boil is what you mean. For instance, to destroy chlorine from using bleach, heat is not enough. Sodium hypochlorite is decomposed at 101°C. So to tell someone they must boil the solution to destroy the chlorine is very accurate.

Click to expand...

I don't agree with the need to boil a solution of gold chloride where we used HCl and sodium hypochlorite to dissolve the gold.

We do not need to boil the solution to decompose the hypochlorite as there shouldn't be any left in our solution. Sodium hypochlorite isn't stable at low pH and we are always operating at low pH or metal hydroxides will form. A gentle simmering is all that is needed, we only want to get rid of dissolved chlorine in our solution.
http://www.engineeringtoolbox.com/gases-solubility-water-d_1148.html

Göran

g_axelsson said:

Geo said:

The difference between boil and evaporate is a very big difference. A beginner will say something like "I boiled the solution down to" when they should have said "I evaporated the solution down to". It's okay to give advice to boil if boil is what you mean. For instance, to destroy chlorine from using bleach, heat is not enough. Sodium hypochlorite is decomposed at 101°C. So to tell someone they must boil the solution to destroy the chlorine is very accurate.

Click to expand...

I don't agree with the need to boil a solution of gold chloride where we used HCl and sodium hypochlorite to dissolve the gold.

We do not need to boil the solution to decompose the hypochlorite as there shouldn't be any left in our solution. Sodium hypochlorite isn't stable at low pH and we are always operating at low pH or metal hydroxides will form. A gentle simmering is all that is needed, we only want to get rid of dissolved chlorine in our solution.
http://www.engineeringtoolbox.com/gases-solubility-water-d_1148.html

Göran

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You beat me to it! We aren't trying to destroy anything. We are trying to purge it! Hcl nor bleach alone will not dissolve gold or oxidize it any more than they would copper. It's the cl gas that does the work and the hcl that complexes. The cl gas is created when we add the bleach to the hcl. Once the cl gas is created a certain amount of it can remain in solution according to the temp curve. Only a slight heating of the solution will drive off the oxidizer rendering the solution inert.

Given enough time, the chlorine will evaporate on it's own. In my experience, beginners will never do anything in moderation. I have personally seen a solution remain chlorinated for over a week when I first started. Sodium hypochlorite decomposes at 101°C which is one degree hotter than boiling water. It's a matter of whether you want to wait and let the hypochlorite decompose over time or destroy it fast and get on with the precipitation. Given the fact that a person is using bleach instead of nitric leads me to believe that they are either just beginning or can't source nitric acid. If people are going to use this chemical, they should be taught how to neutralize it or destroy it. To assume that people will use the exact amount needed and not have to destroy the excess may not be helping them with the process.

https://en.wikipedia.org/wiki/Sodium_hypochlorite

I think I see what Ralph and Göran are getting at. It's not the bleach that has to be eliminated from the solution. If at the point of ready to drop the gold you've dissolved, the sodium hypochlorite will have already reacted. Something like this?

NaClO + 2HCl ---> NaCl + Cl₂ + H₂O

So the NaClO is already broken down so no need to destroy it. Just to heat the solution enough to drive off the excess Cl₂.

But, like Geo said, I've used way too much bleach in the beginning also and waited for days for the Cl₂ leave. The reaction seems to be a quick one with the way it tends to foam when the bleach is added. If too much is used could there be some hypochlorite still in the solution for a while that has yet to react?

NaClO + 2HCl > Cl2 + H2O + NaCl

Why do we keep going back to the bleach being the problem? The decomposition of bleach has 0 to do with this discussion! It's the chlorine that's the problem and the oxidizer. Given an excess of hcl their will be no NaClO to decompose. Goran pointed that out above. The only thing we need to do is purge the cl gas and by doing that your not destroying anything. Their is nothing to destroy or decompose in this equation that would interfere with the gold dropping because of excess oxidizer. You are right in the heat aspect, but for the wrong reasons.

You beat me to it Ben.

Palladium said:

You beat me to it Ben.

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Only by a minute! :lol: