This is how i refine gold

[SAYYED]

Hello every one ,
i have just joined this wonderful forum yesterday , and i really like the the wonderful information published . so decided to share my experience in gold refining as i was working in jewelery factory for many years
any way may be most of you are more experience than me and this information may be well known to you .
this is how i refine gold:
most of the jewelery in Saudi Arabia where i live is 21kt or 18 kt
usually we refine gold scrap in batches of about 4 kg
some 18kt gold scrap pieces with high content of silver will not dissolve in aqua regia these pieces need to be melt and reduce silver content before refining.
- we start by weighing about 4 kg of gold scrap then place it in plastic drum (about 200 liter size)
-we add nitric acid one liter of nitric acid 68% to every kg of gold
-we add hydrochloric acid 4 liter to every kg of gold
- we leave the gold with out disturbing ( no heating nor agitating ) for about 3 hours
- after three hours all the gold scrap will dissolve in aqua regia.
- then we add more water to the dissolved gold solution (not sure but i think that is gold chloride ) we add more water until total solution become about 90 liter .
- after gold dissolve we filter the solution to separate silver chloride through cotton cloth (double cloth small bores ) we don't use vacuum . after filtering we rinse the filter cloth with silver chloride well by water to remove the gold chloride .
- in separate bucket we prepare sodium meta bisulphite solution ,we need one kg sodium meta bisulphite for every one kg gold and mix with water , quantity of water is not critical .
- then we slowly add the sodium meta bisulphite (SMB) solution, before we do that we start agitating the gold chloride with long pvc pipe and keep agitating during adding SMB and keep agitating well for few minutes . gold now will start precipitate.
- then we leave the solution to settle for about two hours.
- then we transfere the solution only to other drum with taking care not disturb the gold precipitate in the bottom. we remove by hand using small bucket to remove most of the solution until only about two inch remains over precipitate , the remaining we pour it carefully directly from the drum .
- after that we transfere the precipitate to plastic washtub and rinse it with water few times and add the rinse water to the refining solution.( we add little SMB solution to the remaining solution to precipitate any gold that may remain in the solution and check after one day ).
now we have pure gold precipitate (about 999) need only to dry then ready to be melt.

regards.

Update : I forgot to mention that we place the drum we use to dissolve in big shallow washtub and after mixing aqua regia with gold we cover the drum with wet cotton cloth then cover the drum with plastic cover
- after dissolving we rinse the cloth cover and wash the body of drum and add the the rinse water to the dissolved gold
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[Lino1406]

Recommended to check for left over HNO3 in the waste

 

[SAYYED]

Recommended to check for left over HNO3 in the waste

in the end of refining process usually we neutraliz waste solution with sodium hydroxide until ph 7 is reached .

 

[butcher]

If I understand this correctly, noticed you do not try and eliminate the silver and base metals prior to aqua regia, I feel you could be locking up some gold in your silver chloride? and what about denoxing the aqua regia or are you just adding urea or using an excess of SMB, which can also precipitate some copper?

welcome to the forum bet you will find some tips here to help in your processes.

 

[SAYYED]

noticed you do not try and eliminate the silver and base metals prior to aqua regia, .

yes i dont eliminate the silver and base metals prior to aqua regia .

I feel you could be locking up some gold in your silver chloride?

after rinsing the silver chloride and filter choth with water , we add the rinse water to the dissolved gold solution i only inspect the silver chloride visulay for unsolved gold

and what about denoxing the aqua regia or are you just adding urea or using an excess of SMB, which can also precipitate some copper?

please elaborate me coz i'm jewller not chimist , you mentioned ( denoxing) i think you mean removing excess HNO3
infact we dont do that , as i mentioned after dissolving and rinsing filter (we add more water until total solution become about 90 liter . )this means we add about three times water to th original quantity dissolved gold solution ,
this may be not the perfect way but it gives satisfiyng result for us .

welcome to the forum bet you will find some tips here to help in your processes.

thanks for your welcome , and i'm sure i will find alot help information .

 

[butcher]

SAYYED, since your gold is such High karat, this make's disolving in aqua regia easier,

and my thinking about removing the base metals prior to aqua regia is wrong. as gold (percentage)would not let you do that, I am used to processing lower karat gold, a totally different process I appologize I did not pay attention to the karat you stated.

and as you stated you have some gold that will not dissolve without remelting (bringing up the gold content).

I am used to adding silver to lower my Karat, then parting with nitric before aqua regia.

if you do not have excess nitric you would not need denoxing.
I always denox (slow evaporation to remove excess nitric acid).


I was thinking any gold undisolved would be in the bottom with your silver?
gold is not always in large pieces.

I do this on a hobby scale, and seem I am blinded by my process?

sorry I should read better before opening my big mouth.

 

[Lino1406]

I had lost 1-2 percent gold (which can be known in advance)
by not denoxing. Vaporizing is not enough, from some reason,
you need to de-nox with addition of HCl.. vaporizing.. HCl.. vaporizing
HCl .. vaporizing to syrup consistency. Then adding water and precipitation

 

[SAYYED]

I had lost 1-2 percent gold (which can be known in advance)
by not denoxing. Vaporizing is not enough, from some reason,
you need to de-nox with addition of HCl.. vaporizing.. HCl.. vaporizing
HCl .. vaporizing to syrup consistency. Then adding water and precipitation

i agree with you that denoxing seems to give better result , any way with my experience (that was few years ago now a days i dont do refining ) in so many batches of refining i never lost more than average 0.3 percent of gold, in most cases less than this percent , i remember in my early days in refining i tried to use urea to kill nitric acid But i noticed strong fizzing reaction and the result in gold lost was not different from average , it will be very helpfull if some one mention denoxing method with out vaporizing
as this method of refining done in plastic drums and with out heating ,
any way i noticed that using only 900 ml nitric acid for every one KG of gold is enough and gives better result .

 

[Harold_V]

Not evaporating is simple, if that be your choice. All that is required is for you to use slightly less nitric than would be required to dissolve all of the gold in question. Make sure you use an abundance of HCl, which does no harm, and assures that you digest gold until the nitric is exhausted. The small amount of gold that remains un-dissolved can be included in the following batch.

Harold

 

[4metals]

The water that he dilutes the solution with (16 liters to start diluted to 90 liters) probably dilutes what little nitric is left to the point that the SMB drops the gold easily.

The price of a filter and paper to make the recovery of the silver chloride easier to collect into batches large enough to process with caustic and sugar. This will probably yield a silver bar with at least a 1% gold content. Heated karat digestions leave 1/4 to 1% in the chlorides so a cold reaction will likely exceed 1%.

If I were to use those quantities of water refining in the US, the cost of treatment would cut seriously into the margins.

 

[Anonymous]

I like to wear a golden jewelery, but when i read this gold refining process at that time i can understand How is typical. lots of materials used for refine the gold. people have to do hard work for refine the gold. Gold refining process take a long time. After finishing refining process lots of waste comes out and they have to deal with this waste at proper place for reuse it.

 

[nickvc]

Butcher in some ways you were right in your thoughts about removiing the silver and base metals first. Been in Birmingham, here in sunny England..lol, I had loads of Asian jewellers as customers at one stage and their methods were the same as ours, they inquarted their scraps and bench sweeps and dissolved in hot nitric to remove all the base metals and silver they could, then they simply melted the resultant gold and tested with the touch stone and reused it. I wouldn't mind betting this is still the process used in many Asian workshops without access to proper refining equipment, acids and precipitants. I reckon that if done carefully you could get 99% Au with this method with the balance been copper and silver which wouldn't cause any problems in the working properties of the gold alloys. The one advantage of this method is that there is no dissolution of the gold so losses are minimized an important point for most workshops.

 

[hfywc]

- then we add more water to the dissolved gold solution (not sure but i think that is gold chloride ) we add more water until total solution become about 90 liter .
-

hi sayyed.

does adding excess water produces silver chloride?

thanks.
alan

 

[qst42know]

Butcher in some ways you were right in your thoughts about removiing the silver and base metals first. Been in Birmingham, here in sunny England..lol, I had loads of Asian jewellers as customers at one stage and their methods were the same as ours, they inquarted their scraps and bench sweeps and dissolved in hot nitric to remove all the base metals and silver they could, then they simply melted the resultant gold and tested with the touch stone and reused it. I wouldn't mind betting this is still the process used in many Asian workshops without access to proper refining equipment, acids and precipitants. I reckon that if done carefully you could get 99% Au with this method with the balance been copper and silver which wouldn't cause any problems in the working properties of the gold alloys. The one advantage of this method is that there is no dissolution of the gold so losses are minimized an important point for most workshops.

I wonder if this short cut isn't the root of the iridium content? A trace added to a trace, and never filtered away. If not added by criminal intent but just accumulated by poor practices.

 

[butcher]

would not inquartered silver also pick up PGM in melt, and would it not follow silver? some removed in parting, some through filtration, some left in aqua regia if not addressed?

or is the silver content not high enough?

 

[qst42know]

I suspect the iridium would follow the gold in an inquart and nitric digest. However I don't know for certain.

:?: :?: :?:

 

[SAYYED]

- then we add more water to the dissolved gold solution (not sure but i think that is gold chloride ) we add more water until total solution become about 90 liter .
-

hi sayyed.

does adding excess water produces silver chloride?

thanks.
alan

Hi alan
purpose of adding more water is to weaken remaining nitric acid , and this doesn't produce silver chloride . silver chloride will be pricpitated after gold scrap dissolved in aqua regia before adding more water

 

[butcher]

Usually some amount of silver chloride will stay soluble in strong acid( even after HCl or NaCl has been used to precipitate the major silver portion), and will precipitate when diluted with water, this I assume is what Alan is refering to.