lazersteve said:
Harold,
You are a valuable asset to this forum. Regardless of your level of formal education you have the hands on experience. You know what works and that counts for a lot.
You can save yourself a lot of trouble if you'll trust me on these operations. I have no axe to grind, just trying to help people learn ways of refining that are tried and proven through years of use, almost in all cases by those that went before me. I made my share of stupid mistakes when learning, so if I can pass along some things to avoid, I'd certainly be remiss if I failed to do so.
If I say something and don't offer an explanation for why I make a particular suggestion, I certainly am open to questions. I don't mean to leave out pertinent information, but this discussion can drag out until it literally fills volumes of books. There's so much to know in order to refine properly that it simply can't be covered in a few sentences.
I'm going to purchase a copy of Hokes book tonight.
I fully expect that when you receive it and start to digest the incredibly good information contained within, that you will quickly come to realize why I promote the book so heavily. Aside from particular information I own about advanced PM group refining, and some of the silver processes I used, everything I know came from Hoke's book, along with guidelines pertaining to gold extraction from ores from Rose's book. It won't take you long to come to terms with how little you understand about precious metal refining, and how valuable Hoke's book will be to you. I still have my copy----and wouldn't dream of parting with it. In truth, it represents what I have become-----including my early retirement.
On the subject of the sterling you mention some of the other base metals. Are these other metals recommended or just okay to use if they are laying around?
I avoided using anything but known silver. Brass should be avoided at all costs. It often contains tin, which makes filtration difficult in succeeding operations. When you find you have a solution that refuses to filter, it generally contains tin. There are ways to avoid the problem, which I'll discuss when appropriate.
There's nothing wrong with using your silver over and over again aside from the fact that as you do so, if you deal with dental golds, or jeweler's wastes, it will gradually accumulate a lot of the platinum group metals. You can usually tell when they're present, for they come down last, after the silver, and always darken the silver. Once the silver has been precipitated, testing the solution with stannous chloride will tell you if you have values present, or not. The solution is generally green in color if so, not blue as you might expect. The solution will turn blue when the PM group has been precipitated. A little experience in that regard will be most revealing for you. Bottom line----it's far cheaper to reuse silver, time and again, than to add other types of scrap to the operation. You're better off to sell the scrap copper alloys and buy silver.
On that note------do not sell pure copper. It's a valuable asset in refining---it's the way you recover your silver. Avoid using wire-----you'll likely eventually end up with a melting furnace that will permit you to melt it and cast large bars that you'll use for silver recovery. I used to do that routinely, using old buss bar from which silver contacts had been removed. That way the small amount of silver that was left behind in the way of silver solder or silver plating on the copper was recovered as the copper replaced silver in solution. In the end, you can even recover the copper if desired, using scrap steel. Don't use aluminum-----sell it for scrap----it's worth a lot more than steel. Or, use it to convert silver chloride to elemental silver. There is no easier way.
I have the silver and it's no problem to go with straight sterling (silver and copper alloy typically). I noticed while I was making the tutorial on separating gold from silver how easily nitric chews thru silver, much easier than copper or brass.
Exactly! Just keep applying that logic and you'll enjoy outstanding success.
American silver coinage is 90% silver. Canadian silver coinage is typically 80% silver. You already know that sterling is 92.5% silver, balance copper. Foreign flatware is often less than sterling, so it is not referenced as sterling. It's not uncommon to find flatware that is as low as 72% silver, but higher tends to be the norm. Scandinavian countries appeared to favor a much lower silver content, so always check them for silver, even when they don't say they're sterling. Look for numbers, anything with three digits should be suspect. Examples might be 720, 850, or 925 (Sterling). If in doubt, file a notch in the object with the corner of a file. Apply a drop of nitric acid to the filed notch. If it doesn't turn green almost instantly, it very well may be silver. If it does, it's plated. Time is critical in this test. Left to stand long enough, if it is silver, the traces of copper included will eventually turn your solution green. It's that first reaction to watch.
Are you familiar with silver testing solution? We can talk about that if you wish. It's a fool-proof way to test for the presence of silver, and can even be used to a minor degree in determining percentage, although I never relied on it for that.
Should I cornflake the gold/silver alloy before using the acid on it?
Absolutely! That breaks it down to large surface areas and thin cross sections, insuring that everything will properly digest in a timely fashion. That may not be an issue if you're just refining for pleasure, but when you have a hot plate covered with beakers of customer gold, you have to make time. Besides, Hoke recommends it!
You mentioned using AR in the inquarting process, everywhere else I've read mentions dilute nitric, which is the most efficient?
I'm sorry, I may have said something that doesn't have great continuity. Rather than go back and try to find what I said, let me say it here, properly. Once you have inquarted your gold and poured it into water to make the "corn flakes" I like to mention, the next operation is to apply nitric acid and water. Tap water is very acceptable. You'll generate a tiny amount of silver chloride, but that will not be lost-----it will appear somewhere in the operation and eventually be recovered. DO NOT apply AR. Because of the presence of silver, you won't accomplish anything aside from cleaning your shot very well!
While it works somewhat
faster, pure nitric (reagent grade) is not the best choice. Here's a great little demonstration of why not. I made my own electrolyte for my silver parting cell. I started with 30 ounces of pure silver crystal, product of a previous refining. That was placed in a 4000 ml beaker, then nitric acid applied. While I had reagent grade, I used a tech grade for almost all operations, reserving the much more expensive reagent grade for use in standard and testing solutions. Modern production methods pretty much insure that nitric is not polluted with chlorine, which would be your chief concern. Remember that I did everything in a fume hood and on a hot plate. Once the acid was added to the silver, it did very little. However, the moment I added water (distilled, of need), the silver immediately started to dissolve.
It has been explained to me that when water is added to nitric acid, hydrogen from the added water provides the necessary hydrogen to form the hydronium ion. That not only accelerates the dissolution, but also extends the capacity of the acid.
Economically speaking, dollar for dollar, tech grade nitric will outperform reagent grade.
Lastly, is a second dissolution of the gold an absolute requirement?
Absolute requirement?
No, it is not. If you do your work well, removing anything that will dissolve in nitric before going to AR, you can precipitate gold of good quality from a single refining. Something in me made me do otherwise, and part of the reason was that I processed filings without melting them. The yield was always quite dirty, but good enough to determine an accurate yield, which became the basis for settlement for the customer. That gold, after melting to form a button, was then used as my added gold when refining, during the evaporation process to remove nitric.
You'll know if you should re-refine, or not, when you melt your gold. When it's pure, there is no sign of frosting on the surface, the color is an astounding gold one, there is no discoloration (oxidation), and if you pour an ingot and don't apply heat as it cools, it will pull a very deep pipe. If you intend to market your gold as industry standard purity, I'd strongly advise that you refine a second time. You'll be amazed to see signs of copper and other elements in the solution after the gold had been precipitated.
If you choose to not do so, and you sell to other refiners, that's what they'll do with it, anyway, so no need. The decision is yours------there is no right or wrong answer, depending on your objective. Mine was to be known as the best damned refiner the customer had ever used!
Harold
Edit: changed the word slower to faster---and added the phrase Economically speaking, dollar for dollar, tech grade nitric will outperform reagent grade.
