# Couple Hokes questions



## Radiobender (Apr 21, 2014)

First of all, good reads all around here. Im new, but read alot and just read Hokes guide, well, got 30 pages left, but I need some clarification on a few things.

He has some old techniques Im assuming, talking about asbestos and mercury...hope noone uses this stuff!

Im assuming nitric acid is always a 35% concentration, is this correct? He is very vague sometimes saying things like "add a bit of water if you want". I just dont want to do something stupid and get a face bath.

Also, Im trying to undestand the best way to remove tin and lead, as these seem to be the most problematic. From his guide, Id like to get some feedback on his suggested method of washing your gold powder afterwards in nitric acid, then water, again. This seems to be the most efficient, as one would use the least amount of chemicals, and thats my goal, cause they arent cheap! I will have a problem with lots of solder in my scrap. Ive been saving for a long time, and learning this now, I wish Id been a little more diligent in keeping the solder out of my pile. But at this stage, his suggestion seems fairly simple, cheap and effective! With this method, Hokes always refers to evaporating his nitric acid, instead of neutralizing it for the most part. Ive already bought a bunch of Urea so I might as well use it. Is it adviseable to use the Urea in a nitric acid wash with my gold powder at the end, then wash and go from there? Any other proven methods that wont cost me another 2L of nitric acid? I just dont want to have to wash my gallons of scrap with so much chemicals itll cost me a ton. 
As well, the smelting process using a sodium nitrate or potassium to remove any base metals. I think its around chapter 15 or 16 he says you should end up with a high grade gold using his method of washing your powder with his process, coupled with a flux/borax. Seems to make sense from the way I understand it. Any advice on his process?

Oh, and he doesnt say much on sulfuric acid to drop any base metals, or maybe I missed it, but I dont believe he refers to sulfuric acid specifically. I know theres alot of mention about this method on youtube, or other internet tutorials, so much so thats its the only method known. Any tips on this?

Thanks in advance. I will be doing very small batches to start, and would love to post my findings by multiple methods. I have much of the exact same scrap that I would like to break into the exact same size batches to see different results.


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## dannlee (Apr 21, 2014)

If this was a quiz it'd be red ink time :roll: Hoke is not a 'he'... :mrgreen:


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## g_axelsson (Apr 21, 2014)

I can give you a quick answer on the nitric acid at least. Often nitric is found in 70% concentration but very often it is diluted to 30-35% as it is more effectively when diluted and it goes further when diluted. (NOx is oxidized and reabsorbed into water which creates new acid for the reaction.)

When you start to experiment, try to keep down the nitric acid volume, it is easy to add more acid if needed but when you already have added the acid it's a lot harder to get rid of it. If you can control your nitric acid volume then you don't need any urea or evaporating off the nitric acid.
You are better served to learn the correct way to refine and skip the urea than to "Ive already bought a bunch of Urea so I might as well use it."

If you really need to have a chemical way to remove nitric acid then sulfamic acid is the preferred way today. Personally I don't use either of them, I try to control the amount of nitric and evaporate off any excess when the need arises.

Most texts talk about 1 ml nitric acid for a gram of gold but I have managed to dissolve 53g of gold with only 32 ml of nitric (but with excess hydrochloric acid). I always start off with only half the nitric and then I try to make an educated guess at the end on how much additional acid I need.

Göran


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## Geo (Apr 21, 2014)

Ms. Hoke was a very accomplished woman at that, metallurgist, chemist, jeweler, refiner, teacher. Keep in mind that she wrote her books so that the common man (of the time around the turn of the last century) would be able to understand and follow along. Things like using gasoline to incinerate and dissolving metal in an open window may have been the norm at the time. Her books are not meant as a step by step per se but more of a guide showing what you may expect from a certain type of reaction. There was no such thing as electronic scrap in her time so there is no reference to it in any of her books. As long as you understand the process and can use "common sense" when she tells you that a solution will taste bitter and not check to see for yourself and take her word for it.


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## butcher (Apr 21, 2014)

Radiobender,

You are off to a good start reading Hoke's book, keep reading, and rereading it, as you go along.
the forum will be helpful as you read it, much of Hokes book will begin to make more sense to you.

I suggest you do the getting acquainted experiments in Hoke's book, this will be tremendously helpful when doing recovery of electronic scrap, or basically any type of scrap, and learning how to deal with lead and tin, by doing these experiments you gain a knowledge of the reactions of metals and acids, by doing the experiments you will gain an understanding of how to deal with the troublesome metals, this way you begin to understand many of the basic principles needed.

I suggest begin your learning curve with a simple material, with only two primary metals like gold and copper (and traces of nickel), closely trimmed computer memory fingers, with no solder (tin or lead), using the copper II chloride leach (also called AP or acid peroxide method) to recover the gold from the circuit board and other metals, after recovering the higher grade gold foils start with the HCl and sodium hypochlorite (household bleach) to dissolve the gold foils (much easier that using aqua regia)...

Starting with these simpler methods, you will also learn a lot, and gain much needed experience, that will help you with other processes that can be much more complicated, and for electronic scrap these methods will be tools you will use often.

Keep studying the forum, you have just begun a study that can take many lifetimes to learn, but as you learn a little you will be hungry to learn more.


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## FrugalRefiner (Apr 21, 2014)

Radiobender,

As has been mentioned, Hoke wrote her book over 70 years ago. She mentions a number of procedures and chemicals that are not favored today. The versions of her book in my signature line include an introduction that points out some of the most hazardous. Download a copy and read through the introduction to get an idea of things that have changed.

Dave


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## Radiobender (Apr 24, 2014)

Excellent, I did alot of experiments the last few days. I dissolved a couple grains of 24k and got well aquainted with stannous testing on a pure AR solution so I know what to look for. I even tried making my own with Sulfuric acid and solder. So now Ill properly drop my gold with no waste. Its so very true, experience is the best teacher!

That was a good piee of adivce on how much gold per solution, sorry dont know how to quote responses. I learnt that one the hard way, even after reading it, so there ya go, you really do have to experiment and see for yourself. Ive always been a hands on guy so especially so with me. 

I think I whipped up a good batch. Did a SMB wash as per a post on here...the one with 3 rinses, then HCL, boil off etc. worked well! Its settling now, then may need to repeat. I took some pics along the way, hope to get some up if I can figure out how.

Im a little hesitant on taking my powder and washing with nitric acid as per Hokes chapter 15 or 16 I think. After all this work, Im getting a little impatient to see my pretty yellow ball, but Ill do some more reading. 

I did some tests with tin/lead in AR, 70% and 35% NA, just to see what Id be looking for. Its really nice to finally be at this stage after all the studying and saving of my scrap for so long. Thanks again for the responses. Ill try the bleach solution someone mentioned, curious on that one. I had done some HCL/peroxide stripping before, but wouldnt have worked for all the different types of scrap I had. When I get a proper scale, I want to do some comparative tests for yields per LB/CPU types etc. Ill need some more equipment for that though. I see that question alot, guys asking how much gold is on certain types of CPUs. Id like to put that one to rest! Heh.

Anyhow, Ill keep it short and clean for now. If anyone has anymore tips on refining tin/lead Id love to hear em.

Cheers~


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## butcher (Apr 24, 2014)

You do not want to get tin in solution with gold, it will make a colloidal gold solution, making recovery of gold just about impossible.
Doing some research on colloidal gold will help you understand this problem better.

Tin is basically a problem in many solutions for the refiner; this is one of the metals that can really give us a hard time if we do not understand how to deal with it properly.

Tin is a thief that can rob you of gold.

With tin and lead (solder) it is best to remove them before dissolving the gold.

In your above post I believe you meant to say HCl and tin to make the stannous chloride solution to test for gold, not sulfuric and tin (If I understand what you were saying).

Note the reaction of stannous chloride and the gold chloride solution in the method for testing gold, which gives a purple solution of colloidal gold, the gold in this solution is reduced, which means the gold is an elemental metal, and is no longer an ion of gold in solution, so you cannot reduce the gold from this colloidal solution with a chemical like SMB, FeSO4 or other chemical precipitant selective for gold.
You cannot cement this gold from solution with copper, or some other reactive metal, with the gold in this solution already being reduced back to a metal (that will not precipitate, or settle) and being held in solution by electrostatic charge, this gold already has all of its electrons in its outer shell, and will not take electrons from a precipitant or metal, these tiny clumps of gold atoms will not combine enough of these atoms to form a precipitant, the repelling forces of the colloid keep the colloid from growing large enough for the gold to drop as a precipitate of gold, the colloids force each other around, forcing each other around stirred up in solution, this repelling action keeping them from combining, or settling, it is very difficult to recover that gold from the purple solution, or to break the colloid to recover this gold. This is the problem with tin and gold in solution.
Except when we are testing for gold in solution with the tin chloride salt, where the tin is useful for us to see whether or not we have gold in solution, by the Purple of Cassius color.


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## g_axelsson (Apr 24, 2014)

That's great news! 8) It sounds like you have come along well.



Radiobender said:


> Excellent, I did alot of experiments the last few days. I dissolved a couple grains of 24k and got well aquainted with stannous testing on a pure AR solution so I know what to look for. I even tried making my own with Sulfuric acid and solder. So now Ill properly drop my gold with no waste. Its so very true, experience is the best teacher!


I'm sure this is a typo, you make stannous chloride with hydrochloric acid, not sulfuric. :mrgreen: 

Göran


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