More karat gold scrap with pictures

I would be glad to help you. Here are the basics:

I will assume you are refining karat scrap - scrap 14k 10k 18k jewelry items. This process is not for refining gold plated or gold filled items - get Lazer Steve's video for refining gold filled scrap - it is excellent.

Edit to add important information.
The very first step is to test, sort and mechanically clean the metal to remove stones and dirt, then incinerate (not melt) the metal to remove external impurities such as oils and other junk that may adhere.

I begin by sorting everything according to the markings on the metal.

I then carefully test EACH PIECE of metal to be refined. Both the gold and the silver get acid tested - no exceptions. (the silver will be used for inquarting later on).

I have an acid test kit for testing the gold and some gold testing needles (a set of needles that are tipped with a known karat gold - 8k thru 22k) and some silver test solution (called Schwerter Solution) for testing the silver. I got all three of these from Ebay.

I never rely on the stamp, except to do the initial sort. Some pieces are stamped but they are NOT gold.

Or they are stamped with a value that is higher than the actual precious metal content. This applies to silver even more so than gold.

Each piece, no matter how big or small, gets the acid test. Some pieces get tested several times when I get inconclusive results.

Some gold pieces are marked 14k, but test to be 10k with the acid. I throw them in the 10k pile, even though they are marked 14k.

To test the silver pieces, I take a fine file and cut deep into the metal. I then add a drop of Schwerter Solution to the cut.

Schwerter Solution turns red almost immediately when it comes in contact with silver. If it turns green, grey, or black, then re-file it and test it again to make sure.

If it does not turn red after the second test, then it is probably not silver. I set the non-silver items aside, or throw them away.

About two or three percent (estimated) of all the silver jewelry I get that is marked 925, is not silver - the schwerter solution test reveals this.

Once everything is sorted and carefully tested, I remove all stones and other non metal material from the scrap. I use pliers and wire cutters.

I carefully cut open the clasps on necklaces and bracelets and remove the steel springs and throw them away.

Using heavy wire cutters, I cut the rings and spread them out. I then use a tooth brush size wire brush to gently remove the grime that builds up inside the ring where it is hard to get at.

When finished, I have several piles of clean metal, all sorted according to their precious metal content.

This process is tedious and time consuming, but it is time well spent if you want your metal to be clean, and it can be enjoyable.

Next, I carefully incinerate the clean metal with a propane torch, heating each piece to redness.

I hold the big pieces with a long steel tweezer in the flame until it turns red hot. Or you can just put everything in a large melt dish and heat it to redness, all at once.

The purpose of incineration is to burn off impurities from the metals, and prevent them from getting into your reaction vessel.
End of edit

The first step is to inquart the gold - add enough silver to get the gold down to 6k or lower. This assumes that you have some scrap silver jewelry or other scrap sterling silver available for doing this. The silver can be recovered after it is dissolved out of the gold.

The root word of inquart is quart or quarter: (1/4 gold) with (3/4 base metal) = 6k gold.

The reason for doing this is because you will be dissolving the silver and other base metals from the inquarted 6k gold with nitric acid. Nitric acid will NOT dissolve gold. The nitric acid WILL dissolve the silver and other base metals in your karat scrap much more easily and completely if the gold alloy is 6k or lower.

1. weight the gold scrap that you want to refine - record the weights.

2. calculate the amount of silver you will need to add to the gold scrap to get the scrap down to 6k or lower:

Say you have 47 grams of 14k and 32 grams of 10k.

Get out your calculator.

14k gold and 10k gold are both alloys of pure gold, plus some base metal such as copper, nickel, or sometimes silver. 14k has less base metal than 10k gold.

First, determine the amount of pure gold in your sample, you must multiply the weight in grams by the karat purity:

14k:
47 grams multiplied by .585 (14k divided by 24k = .585)
47g X .585 = 27.495 grams
You have 27.495 grams of pure gold in your 47g sample of 14k.

10k:
32 grams multiplied by .417 (10k divided by 24k = .417)
32g X .417 = 13.344 grams
You have 13.344 grams of pure gold in your 32g sample of 10k.

Now add the two products together to get a total amount of pure gold:
27.495 + 13.344 = 40.839 grams
You have 40.839 grams total of 24k gold in both samples of 14k & 10k.

Now, calculate the amount of silver needed to get your samples down to 6k or lower.

First, see how much base metal is already in your 14k & 10k Gold

in your 14k sample you determined that you had 27.495 grams of pure gold. So, take 47 grams and subtract the amount of pure gold:
47g minus 27.495 = 19.505 grams
You have 19.505 of base metal ALREADY IN your 47g of 14k.

do the same for the 10k, it had 13.344 grams of pure gold, so take 32 grams and subtract the amount of pure gold:
32 minus 13.344 = 18.656 grams
You have 18.656 grams of base metal ALREADY IN your 32g of 10k.

now add the two together to get the total amount of base metal in your samples:
19.505 + 18.656 = 38.161 grams
You have 38.161 grams of base ALREADY IN THE SAMPLES.

Now multiply the amount of pure gold you have, 40.839 from above, by 3:

40.839 of 24k X 3 = 122.517 grams
You will need 122.517 grams of base metal to make a 6k alloy.

But you ALREADY HAVE 38.161 grams of base metal in the 14k & 10k samples.

So, you must subtract the amount ALREADY IN your samples from 122.517 grams needed.

122.517 (needed) minus 38.161 (ALREADY IN) = 84.356 grams
You will need to add 84.356 grams of silver to your 14k & 10k samples to get the gold down to 6k alloy.

I always add a little extra to get the alloy a little lower than 6k. In this case, I would probably add 90 or even 100 grams of silver. It is better to add too much silver rather than not enough.

Once you have calculated for inquartation, then you mix all the metal - 47 grams of 14k, 32 grams of 10k, and 90 grams of silver - in a large melting dish and melt all the metal together with a torch. I use an oxy/accet torch I purchased from Harbor Freight for about $279.

Once the metals are molten, I stir the molten metal with a graphite stirring rod (from Ebay). I stir it for at least 60 seconds to ensure thorough mixing/alloying. Then I pour the molten metal into a tall METAL container of cold tap water. Don't use plastic or glass or the hot metal will melt through or break the vessel. I use a tall metal coffee brewer I bought from a thrift shop for $5.

As you pour the molten metal into the METAL container of water it will form bits and pieces of 6k alloy gold as it hits the cold water in the METAL container.

I drain off the tap water and then rinse the 6k alloy metal with distilled water. If you don't rinse with distilled water, then some silver chloride may form when you add the nitric acid to dissolve the base metals. Silver chloride is hard to get out and may end up in your final pure gold bar.

Please cut & paste to see a video I made of inquarting gold on youtube:
http://www.youtube.com/watch?v=WBr4cTJfLtM

This is all I have time for now. I hope I have not made any mistakes. If you find something, then please let me know and I will try to get it right.

I will post more on the forum including this whole process above.
Please feel free to ask any questions - but you must understand that I am still new to refining and still learning - any feedback will be appreciated.

thank you for you interest - kadriver

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 breathe 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 bottom 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 solution. 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 transferred. 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 ounces 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

kadriver said:

I rinse the now almost 99% pure gold in plenty of distilled water. I do not save the rinse water.

Click to expand...

I think you should, just add them to the first nitic leach, the rinse water can still hold some silver.
other than that, your process seems flawless.

I'm unsure if it's just me, but this picture doesn't look right to me.



It looks like you formed oxides on top of your inquarted gold. It happened to me in the past.

If you successfully dissolved silver and base metals, you would end up with a very fine black/brown powder.

Also, your Aqua Regia solution would be yellow/orange, not blue or green.



Did you weigh your gold after the Nitric acid dissolution ?

Noxx said:

I'm unsure if it's just me, but this picture doesn't look right to me.

Click to expand...

This happens to me sometimes but it's all good. Sometimes inquarted shot stays in one piece but is still digested. I bet when kadriver poked at this shot it broke apart into the fine black dust we are all so accustomed to seeing. My guess is that the reaction wasn't violent enough to break it all apart. Could also be that the reaction wasn't 100% completed but very very close.

Noxx said:

If you successfully dissolved silver and base metals, you would end up with a very fine black/brown powder.

Click to expand...

Noxx,
It's far more desirable to end up as he did. When you end up with fine particles, you have issues with settling---often equating to losses. When the material remains intact, you can change solutions with reckless abandon, secure in the knowledge that you aren't losing any gold. Comes in handy when you wish to give the remains a final boil in fresh acid.

Note the deep brown color of his cornflakes after the nitric digest. That's a sign that the remains border on falling apart, so they have been well penetrated by nitric (I'm assuming he has heated the dilute nitric to boiling---which was my routine). The only real negative by processing this way is that you have a little difficulty rinsing out all of the silver and base metals, but that's a small problem compared to inquarting such that the material crumbles. Yes, it tends to carry with it a trace of silver and base metal, but with double refining, that's not much of an issue, either.

I always advise that the material remain intact. In my opinion, he's done an exemplary job.

Harold

Harold_V said:

The only real negative by processing this way is that you have a little difficulty rinsing out all of the silver and base metals, but that's a small problem compared to inquarting such that the material crumbles. Yes, it tends to carry with it a trace of silver and base metal, but with double refining, that's not much of an issue, either.

Click to expand...

Somtimes I get uneven shots, so the bigger ones doesn't get good penetration of the acid so I need to crush them and boil the nitric, so I just crush all of the shots.
When this is done I filter everything using vacuum, then wash with d. water and throw the filter into AR, upon boiling the filter is gone and no apparent losses are experienced.

Not a bad system if you don't mind filtering unnecessarily. As far as the need to crush, if you inquart properly, that doesn't happen, even with heavy cross sections. I successfully dissolved copper from gold wire that was 40% gold by prolonged heating. Set your sights on 25% gold and it's a piece of cake (or is that Bob's your uncle?).

Once I put the inquarted gold in a beaker, it left only after it was dissolved and ready for filtration, and while I hoped to eliminate all base metals entirely, traces that didn't rinse out were perfectly acceptable to me, because all of my gold received proper washing and then a second refining. Traces that may make it through the first refining were eliminated in the second refining. Considering I ran multiple batches simultaneously, not uncommon at all to have eight or more beakers in process at a time. For me, not having filtration to tend was a plus.

The concern I'd have with filtration is that once you've broken the gold down to fine powder, unless you use a very slow paper, some gets through the filter. Also, if you've processed anything that tends to create filtration problems, you can find yourself with a solution that won't filter readily, even with vacuum assist. Processing gold filled materials is a good example.

On occasion I would inquart improperly, and would end up with fine particles of gold. The only thing that slowed me down more than that was encountering tin.

It's obvious, each method has its plusses and minuses----neither of them necessarily right or wrong. I expect each person will pick that one that best fits their needs, and, indeed, both may be used, depending on circumstances.

Harold

Harold_V said:

On occasion I would inquart improperly, and would end up with fine particles of gold. The only thing that slowed me down more than that was encountering tin.

Harold

Click to expand...

Harold, when you mentioned inquarting improperly, exactly what did you mean? Too much silver? Not enough?

Thank you - kadriver

Sorry about not getting the rest of the process on here. I will do it this week.

Also - a bar from a single refining I just finished at 3am - just under 3 troy ounces - a small speck of flux is what the dot is.

Not to speak for Harold, but I think he meant that an un even alloy was produced.
That can produce, for example a prill of 3K alloy and its neighbor being 8K alloy...

I know you are sending it to a refiner so it probably doesn't matter to you, but the bar have a clear oxidation tell tale signs.

samuel-a said:

Not to speak for Harold, but I think he meant that an un even alloy was produced.
That can produce, for example a prill of 3K alloy and its neighbor being 8K alloy...

Click to expand...

While that is a distinct possibility, that was never an issue for me. I stirred my inquarted gold religiously, and made certain that everything was in solution before pouring cornflakes.

My comment about proper inquarting was one whereby you shoot for 25% gold. I do NOT subscribe to the notion that more is better---not more gold, nor more silver. If you have too little silver, you experience uneven dissolution, often with thick sections remaining untreated. If you achieve 25%, or very close, that doesn't happen because the silver is never isolated from the nitric in use.

What I disliked even more than too little silver was too much silver. There are those that like to break up the gold as the silver is removed. That creates one hell of a lot more work, and, if you work without assays, as I did, you tend to cheat the customer. Miniscule particles of gold are carried away from the mass when the nitrates are removed. If you use cementation with copper to recover the silver, the gold reports in the slimes from the silver cell, but the customer has been cheated. I'm proud to say that when I'd process a few thousand ounces of silver, it was unusual for me to recover even a quarter ounce of gold, so my technique was quite good. I expect that the little that was lost was from those occasions where I managed to add too much silver. There were times when the resulting gold was reduced to black powder, something I tried hard to avoid.

Harold

So true Harold!
I've had times when I didn't have enough silver for the inquart & I ended with gold sponges that had silver still inside. When running the sponges thru AR, I ended with the white sediment... And on the other hand, like 2 days ago, wanting to refine some extra silver (for my silver cell anode), I added too much silver, knowing that I could end up with fine gold dust... :roll: Well, I'm glad the gold was mine, so it was just more trouble for me to filter & recover later, (which I already did).

The times I've added the right amount, beautiful results & much less hassles.
Here are the pics of my first try some months ago, after putting into practice what I learned from Harold.

Thanks Harold!

Harold_V said:

Here are the pics of my first try some months ago, after putting into practice what I learned from Harold.

Click to expand...

Nurds porn :mrgreen: fine by me 8)





Only traces of AgCl left after AR digestion if: 1) Nitric leach is allowed to work it way, all the way. 2) Alloying ratio and consistency are done correctly.
just my 2 cents

Here's a shot of the alloy before nitric:



and after nitric:



And the resulting gold bars:



Steve

Sorry - I had forgotten about this until I was reviewing some of my posts.

I revised the previous sections to eliminate the use of concentrated nitric acid while digesting the inquarted gold. It is too dangerous and provides no benefit. Instead, I use dilute (50/50 nitric acid/distilled water). The section was edited and the edited remarks are in red letters.

Also, I used to transfer the gold to a different container. It is probably better to use the same container to do all the reactions.

However, I do use a separate container to precipitate the gold - as per Harold's recommendation, I use a pristine, 2 liter beaker to drop the gold. Using a container that has scratches causes fine gold particles of gold to cling to the scratches. I avoid this by using a beaker free of scratches (pristine).

Here is the process that I use to dissolve the gold recovered from the inquarting process, using aqua regia.

If the inquarting was done properly, and the material was treated properly with the acids until the acid was nearly colorless with no more fumes, then the gold that remains is nearly pure. But there are still some impurities and the next process usually reveals them.

I start by washing the recovered gold (from the inquarting process) with plenty of DISTILLED water, right in the same container used for the inquarting. Make sure and rinse the inside of the container with a squirt bottle as you wash the gold to remove any silver nitrate clinging to the walls.

I add about 200ml or 300ml of distilled water to the recovered gold and give it a good swirl then allow everything to settle.

I carefully pour off the wash water into a separate container and save it. This wash water contains silver. Later on, I precipitate the silver from the wash water using hydrochloric acid - the precipitate is allowed to settle and the resulting silver chloride is added to my silver jar.

After each wash, I pour a small sample of the wash water into a small 10ml beaker or test tube. I add a few drops of hydrochloric acid to this test water and look for a reaction of silver chloride.

If I see a cloud of silver chloride form after adding the hydrochloric acid, then I pour the test water into my wash water container and do another wash of the gold with more distilled water - I used about 200 to 400 ml of distilled water for each wash depending on how much gold I am working with.

I repeat this process, making sure to rinse the inside walls of the container as I go, until I get a clear test - no silver chloride formation in the sample of the wash water after adding hydrochloric acid.

It usually takes 4 or 5 washes until the test comes out clear, but can take as many as 6 or 7 washes.

By thoroughly washing the recovered gold free of visible silver chloride in this manner, there is that much less silver chloride formed when I go to dissolve the gold with aqua regia. A gallon of distilled water cost me $0.87 at Walmart.

Once the gold is washed I calculate the amount of acid needed to dissolve the amount of gold that I have.

In this example, I determined that there was 40.839 grams of pure gold when I performed the calculations for inquarting. I will use this number to determine the amount of acid to use to dissolve the recovered gold.

I will use 41 rounded up from 40.839 grams.

Aqua regia is a mixture of two acids: 1 part nitric acid to 4 parts hydrochloric acid (some folks use 3 parts hydrochloric).

The nitric acid can be technical or ACS grades (68% to 70%)

The hydrochloric acid can be bought at Lowes (31.45%)

Using the number 41 from above, I will measure and add 164 ml of hydrochloric acid to the rinsed/washed gold (165ml of hydrochloric or even 170 would be ok). Do not add any nitric acid yet.

I pour the hydrochloric acid right in on top of the gold. This is where I get to see how effective my washing has been. If I washed properly, then there will be little if any silver chloride form upon addition of the hydrochloric acid.

One time I got in a hurry and forgot to wash the gold after inquarting. I realized it as soon I poured in the hydrochloric acid and watched much silver chloride form around my gold.

Once the hydrochloric acid is in with the gold, I set the container (reaction vessel) in a corningware casserole dish, then I set the dish (with the reaction vessel inside) on my hot plate or burner. Do not add any nitric acid yet.

Add low heat and gently warm the hydrochloric acid and gold mixture. Do not boil this mixture ever - boiling will cause your gold to be carried off into the atmosphere with the vapors emanating from your reaction vessel!

Next I measure out a small amount of nitric acid, in this case about 15 or 20 ml or so - roughly half the number of grams of gold I am working with.

Using a dropper, I add 2 or 3 ml of the nitric acid to the gently warmed container with the hydrochloric acid and gold mixture.

I wait a few minutes to see if the reaction (dissolving) starts. After a few minute I add 2 or 3 ml more nitric acid. The gold will start to bubble as the reaction starts.

The key here is patience. Take your time. Add the nitric acid in small increments.

Calculating the amount of nitric acid to use is somewhat of an enigma to me. The trick is to use just enough nitric acid to dissolve the gold, and no more. Excess nitric acid has to be eliminated before I can precipitate the gold.

Several places on this forum recommend 1ml nitric acid to dissolve 1 gram of gold - but my experience has been different.

Recently, I dissolved nearly 70 grams of gold with just 35 or 40 ml nitric acid. If I would have added 70ml of nitric acid (1ml nitric per gram of gold), then I would have way too much nitric.

Regardless - the most important thing I try to remember is to use just enough nitric acid to dissolve the gold I am working with, and no more.

I must leave now, I will continue this post until it is complete. Read Hoke's book!

kadriver

Thank you for the comments, here goes right where I left off....

One safety note; the fumes produced from this reaction are different from the fumes created while dissolving the inquarted silver and base metals. But they are just as deadly. Make sure and do this reaction outside and away from people, pets, and metal objects (these fumes on metal will cause the metal to corrode almost instantly).

While dissolving the gold in aqua regia, newcomers (and some not so newcomers like myself until recently) add too much nitric acid in an effort to speed things up.

Adding fresh nitric acid will speed the process, but I will probably end up with much residual (excess) nitric acid that has to be removed before I can drop the gold.

By adding small amounts of nitric acid a little at a time I can better control the amount of nitric that I add to the reaction vessel.

When most of the gold has dissolved, there will be some small undissolved pieces emitting tiny bubbles as they continue to dissolve - almost looks like the bubbles in a glass of champaigne.

When you see this, add the nitric acid in even smaller increments - a few drops at a time. Here is where patience really pays off.

As I said earlier - I used only about 35 to 40 ml of concentrated nitric acid to dissolve nearly 70 grams of pure gold.

Once all the gold has been dissolved, remove the container from the heat and allow it to cool for a few minutes.

I place the container with my dissolved gold inside a CLEAN corningware casserole dish or pyrex baking dish. This dish will catch your gold solution should you experience a boil over.

Placing the container inside the dish is a precaution. If you are careful and add chemicals in small amounts and wait for the reactions to stop completely before adding more, then you reduce the chance of a boil over. But they do happen from time to time especially for the beginner - better to have it and not need it, then the other way around.

I usually rinse down the insides of the reaction container with distilled water from a squirt bottle to get all the gold bearing liquid down into the main solution.

Next, I add some concentrated sulfuric acid - about 5 or 10 drops - to precipitate out any lead that may be present.

This is a good idea even if you are certain there is no lead in the solution, it does not hurt a thing (and may be helpful when evaporating later on) plus it helps ensure that no lead will make it into your final pure gold.

The resulting lead sulfate (if any) will precipitate out of the solution and get trapped in the filter during the filtering process.

The sulfuric acid can be purchased at Ace hardware. It is called Rooto drain cleaner, or Liquid Fire drain cleaner.

Rooto is my preference as it is nearly colorless - it comes in a white plastic bottle and is sealed inside a plastic bag.

The Liquid Fire works just as well, but it has orange dye in it. Liquid Fire comes in a red plastic bottle and is also sealed inside a plastic bag.

I believe that both of these products are 98% concentrated sulfuric acid.

Once the sulfuric acid has been added and stirred (or swirled nicely), the next thing I do is decide on what method I will use to remove excess nitric.

I have used two methods and each produces excellent results although each has advantages and disadvantages.

Method number one, and the one I use most frequently is; add some urea.

Urea is a course crystal chemical that is inexpensive and readily available. I buy mine off Ebay.

Urea will consume or "kill' residual or unused nitric acid from the aqua regia that I used to dissolve the gold.

The more excess nitric I have in my dissolved gold solution (called Auric Chloride Solution) the more urea will be required to eliminate the excess nitric acid.

I add the urea in small amounts (1/2 table spoon at a time) and stir with a glass rod to ensure that all the urea has reacted with the excess nitric in the solution. I continue to add urea until I get no more reaction or fizzing.

Adding too much urea at once, or adding more urea before the reaction from the previous addition is complete may cause a boil over. Patience and small incremental additions will greatly reduce the chance of a boil over.

If a boil over does happen, stand back and wait for everything to stop. Go get a cold soda, take a deep breath and thank yourself for putting that baking dish under the container.

Then, carefully rinse any auric chloride solution from the outside of the container and set it aside on a clean surface. I would then pick up the dish that received the boiled over auric chloride and pour it back in with the main solution. It is critical to ensure this dish is clean before hand - you can see why.

If there is much excess nitric acid, there will be a vigorous reaction upon adding a small amount of urea. As the nitric acid is consumed, the reaction will become less and less. I can usually tell when I have killed all the nitric acid in the auric chloride solution when there is no reaction upon addition of more urea.

The advantage of using urea; speed. There are times when I don't have time to wait for evaporation. The disadvantage; I am adding a compound that may introduce contamination to my final gold.

method two; evaporation. I place the unfiltered auric chloride on low heat and gently warm it to evaporate off most of the liquid so that my auric chloride becomes syrupy in consistency, then, I add hydrochloric acid a few ml at a time to rehydrate the syrupy liquid.

As the hydrochloric acid is added, brown fumes will be given off (if there is excess nitric acid). These brown fumes are the excess nitric acid being driven off from the auric chloride solution.

This process is repeated, evaporating down again to a syrup, then adding hydrochloric acid to drive off the excess nitric acid. When no more brown fumes are given off, then the process is complete.

If there are no brown fumes upon addition of hydrochloric acid, then congratulations. The amount of nitric added to dissolve the gold was properly meted in and there is very little if any excess nitric acid to be driven off.

Once all the nitric acid has been driven off, as indicated by no brown fumes being driven off when hydrochloric acid is added, then the solution can be rehydrated with distilled water - about three or four volumes. I usually just note the liquid level before evaporating and rehydrate to that level with distilled water after the evaporation process in complete.

The advantages of evaporation; it does seem to produce a cleaner final product and removes the nitric acid more completely than urea (in my opinion). The disadvantage; it takes much longer to do. To me, the advantage of speed is of greater value. But if your goal is ultra-pure gold, then evaporation is the way to go.

Having excess nitric acid in the auric chloride - even a little bit - contributes greatly to allowing other, non-gold metals, dropping down with the pure gold powder when using sodium metabisulfite as your precipitant.

Also, excess nitric acid greatly increases the chance of a boil over when precipitating the gold with sodium metabisulfite. The reason for this; as the sodium metabisulfite is added to the auric chloride solution and the gold precipitates, any unused nitric acid will immediately redissolve the precipitated gold back into solution and generate lots of heat.

The bottom line is this, removing excess nitric acid is critical. You can see here how important it is not to use too much nitric acid to begin with.

More to come later - kadriver

AndyWilliams said:

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.

Click to expand...

Hoke's 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 expel 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 it's got to be played!

kadriver

mikeinkaty said:

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 contaminants?

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

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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

The Moderators would like to thank all of the members who contributed to the original thread that this post was based on, as well as those who asked questions showing what was missing. Because of the extra length and interest in this thread we have created the above, consolidated version making for an easier read. We encourage all members to read, comment, and ask questions in the original thread, Refining gold from karat scrap step by step beginner

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