Just a quick question about removing HCL from gold

[Sharding757]

Upon reading the forums and learning,I read alot about after precipitating your gold to boil it in HCL, Wash it with water, wash it with ammonia and wash it with water x3 and incinerate prior to melting. (forgive me if I got the order wrong, I searched and search for harold's article "AGGGHH!!!" couldnt find it prior to writing this "getting your gold pure and shiny" had it last night didnt bookmark it!!!). I also believe have read in the article that if you do not remove the HCL by incineration you will vaporize your gold leaving just a small bit to melt(like instead of 10g, 1g). This question popped into my head randomly and i figured I'd just ask. Since backing soda neutralizes HCL, would a wash in Baking soda/water do the same as incineration? Again just a question that popped into my head upon looking over at the baking soda i have in case something got spilled. Im not trying to shortcut anything just one of those questions one thinks about.

 

[etack]

baking soda will make everything a mess.

Just rinse till its gone. You can test if there is any HCl left by holding an open bottle of ammonia next to the container, if it "smokes" there is still HCL left if it does not its gone.

Eric

 

[g_axelsson]

You don't need to be afraid for evaporating some of your gold with left over HCl when melting. HCl is a gas dissolved in water and when heated it just evaporates away. Heating to remove HCl is the most effective way of removing HCl, it's called incineration and is used whenever we go from hydrochloric acid to nitric or the other way around and don't want to dissolve any gold by mistake.

The risk of evaporate gold is when we have chloride salts together with gold and heating it up. I don't know the exact mechanism behind the process but I have found references which stated that half of the gold was lost in the gases when roasting gold ore with sodium chloride.

Göran

 

[artart47]

Hi !
If I correct? If you have a solution with disolved gold (gold chloride salt), it can evaporate. Not metallic gold.
artart47

 

[butcher]

The answers above are very good I will try to add to them.

When the gold is pure or fairly pure, there are no base metals to make chloride salts, and during the washing process of the fairly pure gold powders, and if there are a tiny bit of these base metal chlorides, these are water soluble, so as we wash our pure gold these are washed away during the washing process, with the water washes that follow in the process, and the HCl acid is also water soluble and is washed away., as well as the HCl fumes vapor off at a fairly low temperature at the beginning of the heating process, if they have not already evaporated during the drying process.
so basically in following the proper washing procedures in getting your refined gold pure and shining, you will not have to worry about vaporizing your gold in the melting process.

And as stated above it is when we have metal Chloride salts, that when heated with the gold to high temperatures, is where we can result in loss of gold as fumes.


Chlorine gas can dissolve gold at high temperatures of around 800 degrees C, this gold can be carried away as fumes.

Metal chloride salts, like sodium chloride NaCl. or many other metal chloride salts like copper chloride can decompose with heat to give off chlorine gas, depending on the metal chloride involved, these salts can decompose at different temperatures, releasing the chlorine gas as the chloride ions are oxidized to chlorine gas in the heated chemical reaction, some metal salts like sodium chloride have a very high melting point, NaCl has a melting point of about 800 deg C,and a boiling point of around 1400 deg C, so with gold and the chlorides from the salt oxidizing to chlorine gas at these temperatures we will lose some of the gold as it is dissolved by the chlorine gas, if the gold is fine powders the loss would be much higher than for thicker chunks of gold, the fine gold is more volatile at this temperature, when heated to this temperature with chlorine gas, with NaCl we cannot heat it at a lower temperature to oxidize the chloride anion to chlorine, and form a sodium metal oxide.

Chlorine will also attack gold at a somewhat lower heat but not as fast, as with much of the chemistry heat can speed up a chemical reaction...

NaCl salt (or some of the other chloride salts) are not only a problem with gold but also a very big problem with silver...

With some metal chloride salts they can be heated at a lower temperature, to oxidize the chloride anion with heat and drive off chlorine chlorine gas at a temperature that will not attack gold so rapidly, before raising the temperature to a roasting or incinerating heat. forming metal oxides as the chloride anion is driven off in the heat and the oxygen and heat oxidize the metal cations.
But much of this depends on the metal chloride salt involved, and the temperature and conditions of the process involved.

Even gold chloride salts if heated to 800 degrees C can vapor off gold as fumes.
But if heated at a much lower temperature ( about 300 deg. C ) and held there, the chlorides can be oxidized to chlorine gas with little to no of loss gold, (gold chloride decomposes at around 254 deg. C ), and then after the chlorine is vaporized off, we can safely raise the heat to melt the reduced gold to metal, at a higher temperature without the chlorine involved.



I hope I explained this well

 

[kurtak]

to boil it in HCL, Wash it with water, wash it with ammonia .

You only need to do the ammonia wash if your original source of gold had silver involved such as karat gold or gold fill or if silver was used as a collector metal in a smelting process or gold being recovered from anode slimes - the ammonia wash is to get rid of the "trace" silver chloride (be SURE to acidify the ammonia wash right after decanting to avoid making explosive compounds)

Washing procedure after dropping gold & decanting off the AR

(1) Hot (light boil) water wash 3 or 4 times 10 minutes each wash (test 3rd wash with litmus paper if acidic wash one more time)

(2) Hot (light boil) HCL wash 3 or 4 times 10 minutes each wash (when HCL does not change color its done)

(3) Hot water wash again till litmus test shows no acid

(4)Hot ammonia wash (ONLY if silver was in the mix - so skip this wash if no silver)

(5) Hot water wash again 3 - 4 times (skip this wash if ammonia wash was not needed

(6) dry & melt (bring up to melt temp slowly so heat drives of trace chems before reaching melt temp)

Kurt

Edit; to add ammonia wash

 

[justme2]

Thanks for reposting this valuable info.

 

[Palladium]

http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=49&t=325

 

[Sharding757]

Thanks to everyone that posted...It was just a hairbrained question that I thought of and to my surprise I got alot more useful information from everyone's replies. Thank you all again!

 

[bswartzwelder]

I don't think it is necessary to incinerate the pure, cleaned gold prior to melting. That is used for the recovery processing such as incinerating used filter papers. If I am wrong, I am certain someone will correct my mistakes. Show us a picture of your gold when you are finished.

 

[Anonymous]

to boil it in HCL, Wash it with water, wash it with ammonia .

You only need to do the ammonia wash if your original source of gold had silver involved such as karat gold or gold fill or if silver was used as a collector metal in a smelting process or gold being recovered from anode slimes - the ammonia wash is to get rid of the "trace" silver chloride (be SURE to acidify the ammonia wash right after decanting to avoid making explosive compounds)

Washing procedure after dropping gold & decanting off the AR

(1) Hot (light boil) water wash 3 or 4 times 10 minutes each wash (test 3rd wash with litmus paper if acidic wash one more time)

(2) Hot (light boil) HCL wash 3 or 4 times 10 minutes each wash (when HCL does not change color its done)

(3) Hot water wash again till litmus test shows no acid

(4)Hot ammonia wash (ONLY if silver was in the mix - so skip this wash if no silver)

(5) Hot water wash again 3 - 4 times (skip this wash if ammonia wash was not needed

(6) dry & melt (bring up to melt temp slowly so heat drives of trace chems before reaching melt temp)

Kurt

Edit; to add ammonia wash

Kurtak do you mind another opinion on this?

We tend to get a better result by initially washing the gold in water first, with a hard boil for just a couple of minutes. THEN hard boiling in straight HCl at which point the colour change in the HCl and the gold powder is very marked and very quick.Again a few minutes suffices - possibly 5 tops.

Then we wash again in water, followed by another HCl wash (if required) and then a final water wash (or two.)

Alternating seems to give a better result although I'm sure that everybody has their individual preferences. Certainly we've never had to do 3 or 4 water washes to remove the acid. The silver/ammonia is a separate issue so I'm not going there in this post.