Refining gold from karat scrap step by step beginner

[nickvc]

Your metal lends itself nicely to the teachings of Hoke and would be an excellent way to learn virtually all the processes. The inquartation with silver would act as a collector of your PGMs and would be recovered with the silver in the cementation stage after dissolution in nitric, this material is a good candidate for the silver cell as the slimes left would be your PGMs and any gold that sneaked through. The gold would be fairly simple to refine after the nitric through Aqua Regia this is in Hoke and is pretty easy to follow if you have the equipment, the chemicals and your stannous.
Separating and refining your PGMs is a little more difficult but is also in Hoke and discussed in detail on the forum, this is all very possible if you want to spend the time studying and reading.

 

[kadriver]

Nick:

Thank you for your comments. For now, I am just going to save all the silver cell slimes until I have enough to make a go of it.

I did process a small batch of silver cell slimes a while back, got a .2 gram piece of gold from it! I precipitated the PGMs and have the black powder in clean water.

I began to learn PGM refining, but as one person said, "refining gold & silver is like a cookie recipe compared to refining platinum group metals".

I have lots of material and about 4 gallons of pregnant PGM solutions all safely tuck away at my shop.

After more study, I will proceed with the PGM refining.

kadriver

 

[mich2012]

Awesome Thread! Much learned and appreciated!

 

[mikeinkaty]

Hi all -

I'm new to this forum and have a question. When inquarting silver into the gold scrap I noticed that as the gold % goes up that more and more silver is needed. With 40 grams of 20 carat scrap you would need around 100 grams of silver. Is there an upper limit to the beginning gold purity where the inquarting of Silver becomes impractical?

Oh, and another question - after the nitric acid, why is aqua regia neccessary? Is it to get out the last bits of contaminents?

By the way, the tutorial here is outstanding. The best I have seen so far on the web.
Sincerely
Mike
Katy TX

 

[AndyWilliams]

Hi all -

I'm new to this forum and have a question. When inquarting silver into the gold scrap I noticed that as the gold % goes up that more and more silver is needed. With 40 grams of 20 carat scrap you would need around 100 grams of silver. Is there an upper limit to the beginning gold purity where the inquarting of Silver becomes impractical?

Oh, and another question - after the nitric acid, why is aqua regia neccessary? Is it to get out the last bits of contaminents?

By the way, the tutorial here is outstanding. The best I have seen so far on the web.
Sincerely
Mike
Katy TX

Hi Mike,

You are going to need to read Hoke first, it is always the first, and best, suggestion. Inquarting would not be the best method for your scrap. By my calcualtions, you would need to add about 94 grams of material. Hoke covers the proper method to refine your already rich scrap.

 

[mikeinkaty]

Hi all -

I'm new to this forum and have a question. When inquarting silver into the gold scrap I noticed that as the gold % goes up that more and more silver is needed. With 40 grams of 20 carat scrap you would need around 100 grams of silver. Is there an upper limit to the beginning gold purity where the inquarting of Silver becomes impractical?

Oh, and another question - after the nitric acid, why is aqua regia neccessary? Is it to get out the last bits of contaminents?

By the way, the tutorial here is outstanding. The best I have seen so far on the web.
Sincerely
Mike
Katy TX

Hi Mike,

You are going to need to read Hoke first, it is always the first, and best, suggestion. Inquarting would not be the best method for your scrap. By my calcualtions, you would need to add about 94 grams of material. Hoke covers the proper method to refine your already rich scrap.

Andy, I have no karat gold yet. I will be getting some next year in the 10K-14K range with maybe some at 18K. I also now see why the Aqua Regia is recommended. I have downloaded that PDF file and am about 1/4 through it now.
Mike

 

[AndyWilliams]

Hi all -

I'm new to this forum and have a question. When inquarting silver into the gold scrap I noticed that as the gold % goes up that more and more silver is needed. With 40 grams of 20 carat scrap you would need around 100 grams of silver. Is there an upper limit to the beginning gold purity where the inquarting of Silver becomes impractical?

Oh, and another question - after the nitric acid, why is aqua regia neccessary? Is it to get out the last bits of contaminents?

By the way, the tutorial here is outstanding. The best I have seen so far on the web.
Sincerely
Mike
Katy TX

Hi Mike,

You are going to need to read Hoke first, it is always the first, and best, suggestion. Inquarting would not be the best method for your scrap. By my calcualtions, you would need to add about 94 grams of material. Hoke covers the proper method to refine your already rich scrap.

Andy, I have no karat gold yet. I will be getting some next year in the 10K-14K range with maybe some at 18K. I also now see why the Aqua Regia is recommended. I have downloaded that PDF file and am about 1/4 through it now.
Mike

Glad to hear that Mike, take care!

Andy

 

[kadriver]

Hi Mike,

You are going to need to read Hoke first, it is always the first, and best, suggestion. Inquarting would not be the best method for your scrap. By my calcualtions, you would need to add about 94 grams of material. Hoke covers the proper method to refine your already rich scrap.

Hokes book is fantastic, and I would recommend reading it to anyone interested in refining precious metals. But it skips all over the place and is sometimes difficult to follow.

I refined my first batch of karat scrap before I even knew the book existed (other than being told repeatedly to read it by many forum members).

There is little to no information concerning refining silver or how to set up an electrolytic silver cell in the book either.

Lazersteve's DVD entitled "Silver Refining A to Z" blows Hoke out of the water when it comes to silver refining.

Also, there are very important things that were not given in Hoke that I have learned here on he forum that are absolutely essential:

1) incinerate your material before dissolving in aqua regia - especially black gold powder from sulfuric acid stripping cell and GOLD FILLED SCRAP.

2) and, do not premix the acids when making aqua regia - instead, add just hydrochloric acid to the gold first, then meter in small amounts of nitric (adding just drops at a time toward the end). This prevents having to expell large amounts of nitric acid through evaporation (from goldsilverpro).

I did not begin to read "Refining Precious Metals Waste" by C.M. Hoke intently until I began to experiment with platinum group metals.

But I would still recommend it simply because it is the only game in town, so its got to be played!

kadriver

 

[kadriver]

Hi all -

I'm new to this forum and have a question. When inquarting silver into the gold scrap I noticed that as the gold % goes up that more and more silver is needed. With 40 grams of 20 carat scrap you would need around 100 grams of silver. Is there an upper limit to the beginning gold purity where the inquarting of Silver becomes impractical?

Oh, and another question - after the nitric acid, why is aqua regia neccessary? Is it to get out the last bits of contaminents?

By the way, the tutorial here is outstanding. The best I have seen so far on the web.
Sincerely
Mike
Katy TX

Inquartation is the best way to rid your 20 karat gold scrap of base metal impurities. With 20k gold (I have seen 21k and 22k, but I have never seen 20k gold - not to argue that is does not exist because it may), there are other metals mixed with the pure gold to get it to down to 20k from 24k.

Plus, you don't have to use silver, you could use clean copper wire from the hardware store instead - gram for gram.

Since we can't be quite sure of what metals were added to the pure gold to get it to 20k, then the best thing to do is to inquart the 20k gold with scrap 925 or sterling silver (or clean copper wire).

40g of 20k gold would be 40g x (20/24) = 33.33g of pure gold

To get it to 6k, we would need 3 x 33.33g = 99.99g of silver.

First, since there is some non-gold metal in the 40 grams of 20k, then we must subtract that amount from the 99.99g of silver needed:

40g of 20k - 33.33g pure gold = 6.67g of non-gold already in the 40g of 20k gold

So, we would subtract 6.67g from 99.99g to get a final figure of 93.32g, therefore we will need 93.32g of silver added to the 40g of 20k gold to get the gold down to 6k.

I always take this final figure and add 10% and use that amount of 925/sterling silver to alloy with the gold: 93.32 X 1.1 = 102.65g

I would add 102.65 grams of silver (or clean copper wire) to the 40g of 20k gold.

Inquarting even 22k gold will get rid of the unknown base metals and after several treatments with dilute nitric acid will give some nice gold nearly 3 nines fine.

Here is an example of gold that was inquarted only, no aqua regia was used:

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=61&t=15067

If the gold is going to be sold to a refiner (as was the case with the above example) then there was no need to expend the extra time and chemicals to refine the gold any further. Getting it to over 3 nines fine would have taken a little extra time and more chemicals.

To get the gold to 4 nines, it would have taken even more time and chemicals.

So to answer your question "is aqua regia necessary?" it depends on what you are going to do with the gold once you refine it.

Refining is an art and a science combined. From time to time I take the extra time and chemicals required to refine a batch to as high a purity as I can so I can stay proficient. That way, when the time comes and I need to do it, I can - like a practice.

I just recently started using oxalic acid to precipitate the gold from karat scrap batches - my last batch assayed at 4 nines fine by the refiner I sold it to.

Of course, at the end of the day that beautiful bar (as pure as a Canadian Maple Leaf) was just tossed in with all the other gold scrap for the day by the refiner to be re-refined all over again - like dejavu all over again!

But I gained the knowledge and confidence that when it becomes necessary, I can produce very high purity if I need to.

kadriver

 

[kadriver]

Hello:

Unfortunately, I will be unable to complete the rest of this tutorial.

However, the rest of the information on how to continue will be made avaialbe on DVD soon.

I believe that there is already a DVD availble entitled "Testing and Refining Karat Gold" produced by lazersteve available from his website at http://www.goldrecovery.us

kadriver

 

[africangoldking]

hi,

am relately new to this forum. i will like an honest opinion about my business plan in relation to scrap gold business. due to economic situation in africa and availability of gold i always think it will be a good idea. moreover, most old computers, mobile phones and other electronic eqquipment somehow makes their way to africa, so i strongly belief its worth giving it a try. i must admit that am a novice to gold business

1, i want your opinion concerning the concept of setting up a scrap gold buying business in one of african populous nation which has no competion in this field.
2, how much do i need to set up the business which include buying of gold and a budget refinery?
3, how do i go about the advertisement to reach a country of of about 120,000000?
4, how can i find a consistant buyer oversee to enable my purchasing power?

your sincere opinion will be much appriaciated.

 

[rustyle]

Best use for heat is electric skillet. When boil over it will not damage the heat ellement and no loss of boil over solution.

But don't buy cheap one. GE skillet is what I use. Cheap brand, the none stick coating is not as good as good brand. So cheap brand will withstand hot solution for short time.

The next step in the process:

Dissolve the base metals (including the silver) out of the inquarted gold with nitric acid.

I use dilute nitric acid. Dilute means 50 percent concentrated (68%-70% Technical or ACS grade) nitric acid, and 50 percent DISTILLED water. DO NOT use tap water or you will get chlorides in your solutions.

The nitric acid will dissolve the silver & other base metals, but it will not dissolve the gold. The gold will be left in the bottom of the container (see photo below).

First, dry and weigh the inquarted gold. record the weight.

In our sample we started with 47 grams of 14k and 32 grams of 10k karat scrap gold. To this we needed to add 84.356 grams of silver to get the gold down to 6k alloy. I chose to add 90 grams of silver - adding too much silver is better than not adding enough.

So now I have 47g of 14k plus 32g of 10k plus 90g of silver. The total weight should be 169 grams of 6k gold.

Of this 169 grams, 128.161 grams will be base metal:
169g inquarted gold minus 40.839g pure gold = 128.161g base metal.

I will need to dissolve 128.161 grams of base metal & silver from my sample.

I use this number to calculate the amount of acid needed - 1.44 ml of 68% to 70% nitric acid per gram of base metal in my sample.

I got this number off the forum. There may be some who disagree with this figure and I am open to correction, but this is the number I use.

128.161g base metal multiplied by 1.44 ml concentrated (68% to 70% Technical grade or ACS grade) nitric acid = 184.55 ml nitric acid.

I will need 185 ml (rounded up from 184.55 ml) nitric acid for this first reaction.

I will be diluting the acid with DISTILLED WATER. Do not use tap water or you will get silver chloride in your reaction vessel.

I will use a 50/50 mix of acid and water:
185 ml DISTILLED WATER and 185 ml Concentrated nitric acid.

DO NOT LEAVE THE REACTION VESSEL DURING THE REACTION - KEEP AN EYE AND EAR ON IT AT ALL TIMES WHILE THE ACID AND HEAT ARE AT WORK.

Do the reaction OUTSIDE as thick poisonous fumes are produced - they can make you sick. Don't even think about doing this inside a closed room or in your house. IT MUST BE DONE OUTSIDE away from people and pets.

I set up my reaction container outside consisting of a black plastic tub to catch any spillage (Lowes), an electric hot plate (ebay) a corningware casserole dish to catch overflow (thrift store) and the reaction vessel, in this case a heavy pyrex coffee pot. (see the photo)

I place the inquarted gold into the heavy pyrex coffee pot with lid.

I then measure and add 185 ml DISTILLED WATER to the 6k gold. I use a graduated cylinder.

I place the lid on the coffee pot with the 6k gold & distilled water inside. I then set the coffee pot on a corningware casserole dish. The corningware dish distributes the heat and will catch any liquid in case i have a boil over - they do happen as you can see by the condition of my hot plate.

Then I place the dish with the coffee pot onto an electric hotplate set inside a large plastic tub (Lowes Cement Mix Tub - $25.00). I DO NOT ADD HEAT AT THIS POINT.

I carefully measure out 185 ml concentrated nitric acid with a graduated cylinder and pour it into a 250 ml beaker, then cover the beaker with a watch glass and set it inside the black plastic tub.

I add the acid to the coffee pot a little at a time and put the lid back on. Adding it all at once could cause a boil over. I add about 50 ml at a time and wait a few minutes until the reaction calms down between additions.

As the acid is added and the reaction starts, there will be thick red or brown fumes - do not breath these fumes as they are very harmful.

Keep adding the acid a little at a time until it is all in the reaction vessel (coffee pot). Keep the lid on the coffee pot and add gentle heat at first. Adding heat too quick or too intensely can cause a boil over.

Harold from the forum advises: do not crush the inquarted gold chucks in the bottom of the vessel while the acid is dissolving the base metals. I take his advice and leave the chucks of gold alone and let the acid do all the work.

Crushing the gold while the base metals dissolve in the acid will cause tiny particles of colloidal gold to be released - causing possible loss of some of the gold. So I just leave it alone and let the acid do the work.

I keep adding heat until I have it turned up all the way - gradually.

This first reaction takes about an hour to complete, sometimes more or less depending on the amount of material in the vessel.

I can tell when the reaction is over when no more red fumes are being produced inside the vessel with the lid on - the atmosphere inside the coffee pot will be clear (or just slightly tinted brown).

The liquid in the coffee pot will probably be blue. This is silver nitrate solution along with copper nitrate and other metals that have dissolved in the acid. You want to save this solution so that you can recover the silver from it later on. The silver will be from the silver you used to inquart the gold - the silver is now dissolved into the acid.

In the bottom of the coffee pot will be the gold. You can see it. Nitric acid will not dissolve the gold. It is left, untouched by the acid in the botton of the container - but nearly all of the base metals including the silver I added, have been dissolved (see photo below).

Once the reaction is complete, I remove from the heat and allow it to cool. During the cooling period you may observe some crystal formation inside the vessel. These are silver nitrate crystals and this is normal.

Once the solution is cool, I usually add some DISTILLED WATER to dissolve the silver nitrate crystals if any are present.

Then I filter the solution in a filter flask using a vacuum filter rig (see photo)

The purpose of filtering at this point is to remove solids from the silver nitrate sloution. I pour the liquid into a medium filter paper.

I do not pour the gold into the filter. I leave the gold in the bottom of the coffee pot and rinse it with DISTILLED WATER right in the bottom of the coffee pot.

I then pour the rinse water into the filter paper, but I make sure none of the gold gets into the filter, it stays in the bottom of the container. I rinse it with about 200 or 300 ml Distilled water.

Leave the filter rig set up to filter the rinse water used to transfer the gold to a smaller vessel in this next process.

I save the silver nitrate solution in the filter flask because i want to recover the silver that is dissolved in the solution - don't throw it away as it contains silver.

Most of the base metals are now dissolved in the acid and all that is left in the bottom of the container is nearly pure gold.

Next, I transfer the gold from the coffee pot to a smaller beaker. I use a 1000 ml tall form beaker. I use a squirt bottle to carefully wash all the gold from the coffee pot to the 1000 ml tall form beaker.

I then pour off the rinse water into the same filter i used earlier to filter the silver nitrate.

Now I measure about 100 to 150 ml concentrated nitric acid and add it to the beaker with the gold that I just transferd. Edit for additional information; I have been advised by one of the moderators that adding concentrated nitric acid produces no benefit, and could do harm from popping steam bubbles spitting hot acid and gold out of your reaction vessel! It is best to add an equal amount of distilled water WITH the acid in this step. By using diluted acid, you can actually boil the liquid with no problems - I often repeat this step several times until my dilute acid is almost colorless and no more fumes are produced. Save the used acid as it can be used for digesting silver in a later process.

DO NOT set the beaker directly on the heating element. Put a corningware casserole dish on the hot plate, then set the beaker inside the corningware dish. This will evenly distribute the heat and catch any liquid in case you have a boil over.

Start with low heat - make sure and do it outside. There will be more red fumes. Cover the beaker with a watch glass or glass saucer. Don't leave it unattended.

The concentrated acid will dissolve some left over silver and base metals the first reaction missed. Do not crush the chunks of gold as stated earlier - let the acid do all the work. Edit for additional information; make sure to use DILUTED acid - a mixture of 50% concentrated nitric acid and 50% distilled water by volume - using concentrated nitric acid here could be dangerous as the acid may erupt from the reaction vessel spitting hot acid and gold on you!

Adding too much heat to this mixture can cause steam bubbles to form little explosions that will spit hot acid and gold out of your container - so make sure and put a watch glass on the beaker and add the heat slowly. Edit for additional information; This problem can be avoided by using DILUTED nitric acid (50/50 nitric acid and distilled water by volume). Use extreme caution when heating acids under any circumstances.

Slowly add more heat until no more fumes are produced and the atmosphere inside the beaker is clear. DO NOT GO OVER HALF way on the hot plate setting or it will spit hot acid and gold all over the place. Edit for additional information; As stated earlier, this problem can be avoided by using DILUTE acid in this step. The dilute acid can actually be boiled with no problems. I often leave the gold on the heat boiling in the dilute acid for an hour or longer.

Do not leave the beaker unattended - as soon as you leave, the little eruptions will start and you will come back to a mess of acid and gold all over the place (see attached photo of one of my mishaps below). Edit for additional information; This mishap illustrates perfectly why concentrated nitric acid should not be used. I have never had this happen since I started using dilute (50/50 nitric acid/distilled water) for this step.


If you begin to hear little pops and eruptions inside the beaker, then immediately remove the container from the heat and turn the hot plate setting down to a lower temperature.

Once the heat is lowered and the eruptions have ceased, return the beaker to the heat and continue the reaction until there are no more fumes inside the covered beaker.

After all fumes have ceased (about 15 minutes to 1/2 hour, but sometimes longer) remove from the heat and allow it to cool.

Once the mixture has cooled, I pour off the acid into a container with a lid (I use a 500 ml flask with a ground glass stopper I got off ebay).

I save this acid for dissolving silver later on in another process. The acid is still good and probably contains a little silver.

I rinse the now almost 99% pure gold in plenty of distilled water. I do not save the rinse water, but you can as it may contain a small amount of silver.

The gold is now ready to be dissolved in Aquq Regia.

That is all I have time for right now.

I am sharing this as my experience in refining gold. I hope I have not made any mistakes - but if I have then please let me know.

I have refined about 20 or 25 troy ounce of pure gold since I have started back in Sep of 2010. I am still new to refining.

Thanks for looking, any input as to correctness would be greatly appreciated.

kadriver

 

[saadat68]

Hi
In GOLD REFINING FORUM HANDBOOK we have:

Hoke states 4 fluid ounces HCl + 1 fluid ounce HNO3 dissolves 1 troy ounce
gold. This is equivalent to 31 mL HCl + 8 mL HNO3 per gram of gold.

1 fluid ounce = 29.57 ml
1 fluid ounce = 31.1 gram

So we have 118.2 ml HCl + 29.57 ml HNO3 for dissolving 1 troy ounce
gold.

This is equivalent to 3.8 mL HCl + 0.95 mL HNO3 per gram of gold.

Right? What is the problem?

 

[anachronism]

A bit lost about your post Saadat. What was it about?

 

[saadat68]

I am talking about how much aqua regia we need to dissolves one gram gold
In hoke book we have:
4 fluid ounces HCl + 1 fluid ounce HNO3 dissolves 1 troy ounce gold

In handbook we have:
For dissolving 1 gram gold we need 31 mL HCl + 8 mL HNO3

That is not true
We need 3.8 mL HCl + 0.95 mL HNO3 per gram of gold. Right?

 

[anachronism]

Are you talking about pure gold in a re-refine or are you talking about gold with other base metals during recovery?

I'd like to know what strength of Nitric is being referred to because I dissolved 284g of pure gold two weeks ago using less than 200ml of Nitric, so I don't believe those figures anyway. I haven't for years.

 

[FrugalRefiner]

saadat, in this case the handbook is wrong. There are a few other mistakes in it, like the ratio of HCl and H₂O₂ in AP. It was a collection of posts made in the early days of the forum, and there were a few errors.

How much nitric you really need depends a lot on your technique. If you dump it in all at once in an open beaker, you'll lose a lot to the copious NO_x fumes. If you add it in small increments, use a cover glass or reflux condenser, and keep it from getting too hot, you'll need less because you'll lose less.

Dave

 

[saadat68]

Thank you Dave and anachronism
----------------------------------------------------

Hi
If we drop gold with SMB from aqua regia solution we must test remaining solution with stannous chloride to make sure there is no any gold in solution.
Can we test solution with ferrous sulfate test ? (SMB will not trouble?)

Thanks

 

[FrugalRefiner]

Stannous is more sensitive.

Dave

 

[4metals]

Stannous, as Dave said is more sensitive and....... once the gold is gone it effectively indicates the presence of other PGM's that may be remaining in solution.