Chloroauric acid dissolved in cement - Please help

[Blunt Machete]

Hi everyone, I would appreciate any help on our current problem.

We recently had a pipe come loose from the gold cell and unfortunately all the chloroauric acid in the bath spilled over the floor. Some was recovered immediately, but the rest had dissolved into the cement brick floor. Roughly 3cm of floor was scraped (XRF scanner helped determine the area envelop of which to dig) and was put into a large drum for storage. Around 1 kg of gold was lost (hopefully all of which was dug) and heterogeneously distributed within all the pieces of cement. Even if we recover 200 grams, I would consider that a win.

Proposed solution: I would like to put in large amounts of conc HCl to dissolve all the cement and have chloroauric acid in solution. The solution can now be filtered. From there, UREA can be added to knock off any nitric and then SMBS can be added to precipitate out gold sponge. The rest of the process is trivial.

However, dissolving cement is tedious and it seems like it is impossible to dissolve anywhere close to all of it. My question - Is there any way to dissolve all the cement and is the proposed solution thereafter a viable strategy?

 

[Yggdrasil]

Hi everyone, I would appreciate any help on our current problem.

We recently had a pipe come loose from the gold cell and unfortunately all the chloroauric acid in the bath spilled over the floor. Some was recovered immediately, but the rest had dissolved into the cement brick floor. Roughly 3cm of floor was scraped (XRF scanner helped determine the area envelop of which to dig) and was put into a large drum for storage. Around 1 kg of gold was lost (hopefully all of which was dug) and heterogeneously distributed within all the pieces of cement. Even if we recover 200 grams, I would consider that a win.

Proposed solution: I would like to put in large amounts of conc HCl to dissolve all the cement and have chloroauric acid in solution. The solution can now be filtered. From there, UREA can be added to knock off any nitric and then SMBS can be added to precipitate out gold sponge. The rest of the process is trivial.

However, dissolving cement is tedious and it seems like it is impossible to dissolve anywhere close to all of it. My question - Is there any way to dissolve all the cement and is the proposed solution thereafter a viable strategy?

Cement will dissolve in HCl, and the Gold Chloride will follow that, but it will mean a substantial amount of liquids produced.
It will probably need to be somehow re concentrated and then dropped by SMB or other as normal after proper filtering.
The issue may be that some Gold may have cemented out, inside the cement.

We had a similar situation pop up a couple of years back, but I don't recall the solution or how it went.
Try searching Gold and Cement in the search function and see if you can find something.

 

[Blunt Machete]

Cement will dissolve in HCl, and the Gold Chloride will follow that, but it will mean a substantial amount of liquids produced.
It will probably need to be somehow re concentrated and then dropped by SMB or other as normal after proper filtering.
The issue may be that some Gold may have cemented out, inside the cement.

We had a similar situation pop up a couple of years back, but I don't recall the solution or how it went.
Try searching Gold and Cement in the search function and see if you can find something.

Hi PoA,

What do you mean by "re concentrated"? I am making the assumption that you mean mostly gold chloride is present in solution. But, if HCl makes up most of the solution (from adding it to the bricks) with the remainder only being gold chloride then I would presume SMB would still drop all the gold.

Kind regards,
LA

 

[Yggdrasil]

Hi PoA,

What do you mean by "re concentrated"? I am making the assumption that you mean mostly gold chloride is present in solution. But, if HCl makes up most of the solution (from adding it to the bricks) with the remainder only being gold chloride then I would presume SMB would still drop all the gold.

Kind regards,
LA

I did not realize it was bricks.
That may or may not complicate things.
If the surface of the bricks are dense enough to not have soaked up the Gold Chloride, it may simplify things.
If not the "offending" bricks need HCl washing as well.
Then it should be enough to dissolve the cement that has been saturated with the Gold solution.
Filter out the undissolved sand and stuff.
It still may represent a massive amount of HCl needed to do that, that is why I talked a bout concentrating it, so you will have less solution to treat.
And yes as long as the solution is acidic the SMB will work, since concrete is a base, testing is necessary.

But of course after filtering it properly.
Anyway, first you secure the material in buckets, pails or whatever needed, then do some small tests to see what gives the best result.

And of course search this forum for cement floors and Gold and such to see what you find.

 

[orvi]

Hi everyone, I would appreciate any help on our current problem.

We recently had a pipe come loose from the gold cell and unfortunately all the chloroauric acid in the bath spilled over the floor. Some was recovered immediately, but the rest had dissolved into the cement brick floor. Roughly 3cm of floor was scraped (XRF scanner helped determine the area envelop of which to dig) and was put into a large drum for storage. Around 1 kg of gold was lost (hopefully all of which was dug) and heterogeneously distributed within all the pieces of cement. Even if we recover 200 grams, I would consider that a win.

Proposed solution: I would like to put in large amounts of conc HCl to dissolve all the cement and have chloroauric acid in solution. The solution can now be filtered. From there, UREA can be added to knock off any nitric and then SMBS can be added to precipitate out gold sponge. The rest of the process is trivial.

However, dissolving cement is tedious and it seems like it is impossible to dissolve anywhere close to all of it. My question - Is there any way to dissolve all the cement and is the proposed solution thereafter a viable strategy?

My lord... Hopefully you dug it all. But Au in solution is distinctively colored. It is impossible to get it all if something is spilled/soaked - but the colour of the cement will tell you how far to dig Clever idea with XRF tho. Use Geochem mode for better LOD for gold.
If it isn´t your existential immediate situation, take time for thinking how to go with it. Don´t rush unless you really need to.
For leaching, you will need to break cement to small pieces in order to speed up the maceration.

It would take a very very good ammount of HCL to liquify it, it will foam and fair ammount of insoluble residue will be left, which could be hard to filter.
If there was a rebar in the concrete, pay attention to that as gold could precipitated onto rebar. This will not go to the solution wth only HCL.
It would be huge volume of liquid I assume, but not too heavily contamined with another metals, so disposal should be relatively easy. If gold would be too diluted, I would not reduce the volume of solution, but rather concentrate the gold from leachate by means of copper cementation (make sure liquid is acidic). This will reduce all gold to the powder form, which will be conveniently settled and decanted, and you will be left with small residue of gold powder, which you are familiar to work with already.
Thing is that concrete is basic. Some gold could have beed knocked from chloride to form some sort of hydroxide or oxide. I don´t know how these behave in general (eg if they can be re-chlorinated back to chloroauric acid).

Another option will be to add low-melting flux and try to directly smelt the concrete. Not very nice idea, but if one has access to bigger tilting furnance capable of going say past 1300°C, then it could be done I think - and if done, it would be done quicker than leaching. Important will be basic fluxing, as AuCl3 is volatile and can be lost if mixture is not basic enough. All in all, also CaCl2 or NaCl could cause some loss of volatile Au chlorides... Just an idea. I like to deal with inorganic matrixes by smelting - it is more convenient, and quicker.

Do small tests, recover the gold by wet route from some sample, then smelt washed and dried sandy residue with collector and cupell it away to find out how much gold was left in solids.

 

[snoman701]

What is the actual quantity of cement or bricks removed?

 

[snoman701]

Suggest sealing your concrete with epoxy.

But don't worry, I made a boneheaded mistake today as well.

 

[Shark]

But don't worry, I made a boneheaded mistake today as well.

Feels good to know I’m not the only one to screw up today.

 

[eaglekeeper]

I have no experience with pyrometallurgy, but would that be possible with the right flux mix and a collector metal?

 

[snoman701]

It should be. The gold likely reduced to metallic very very quickly. All of the components of concrete or bricks are essentially components of flux.

 

[Martijn]

I remember a story exactly like this one here on the forum. Can't find it anymore. It will also have good ideas to consider.
@ Orvi: I love your posts and the priceless, clearly written and to the point information you share with us, great to have you here!

 

[Yggdrasil]

I remember a story exactly like this one here on the forum. Can't find it anymore. It will also have good ideas to consider.
@ Orvi: I love your posts and the priceless, clearly written and to the point information you share with us, great to have you here!

Yes there was a similar story, but I thinks that was plain concrete, here it is a mix of bricks and cement.
There might still be lessons to learn if the story could be found.

I think it might be this one:
https://goldrefiningforum.com/threads/dissolved-gold-spilled-on-groung.6732/post-60056

 

[Yggdrasil]

Yes there was a similar story, but I thinks that was plain concrete, here it is a mix of bricks and cement.
There might still be lessons to learn if the story could be found.

I think it might be this one:
https://goldrefiningforum.com/threads/dissolved-gold-spilled-on-groung.6732/post-60056

I was wrong I think this one is the correct one
https://goldrefiningforum.com/threa...recover-aucl-after-spillage.30241/post-316748

 

[Blunt Machete]

Hi everyone.

Thank you for your inputs. I really appreciate all the advice. I will do some testing and hopefully make progress.

@orvi - We are still debating if we should get access to a capable furnace as our one does not operate at those high temperatures. But definitely as a last resort it might happen.
@Yggdrasil - Your advice on the conc HCl and brick management is noted and thank you for referring me to that forum.

I have one more question (I hope it is not a silly one ). Instead of filtering so much insoluble material( as it will clog up the filter and take a while to completely filter out) would a viable method be to wait for the solids to settle and suck up as much liquid as possible from the top of the beaker until the liquid level reaches the solids.

Kind regards,
LA

 

[Yggdrasil]

Hi everyone.

Thank you for your inputs. I really appreciate all the advice. I will do some testing and hopefully make progress.

@orvi - We are still debating if we should get access to a capable furnace as our one does not operate at those high temperatures. But definitely as a last resort it might happen.
@Yggdrasil - Your advice on the conc HCl and brick management is noted and thank you for referring me to that forum.

I have one more question (I hope it is not a silly one ). Instead of filtering so much insoluble material( as it will clog up the filter and take a while to completely filter out) would a viable method be to wait for the solids to settle and suck up as much liquid as possible from the top of the beaker until the liquid level reaches the solids.

Kind regards,
LA

Of course settling and siphoning is an option, but it needs several rounds of washing to get as much Gold Chloride as possible out.
If you have the option to smelting that may be an easier way.