Getting pure gold (shining)

[Noxx]

Hello,
I would like to know what I must add/change to a standard AR process to get pure gold after melting it. Most of the gold buttons I get are not completly shining and seem to have a very thin layer of impurties. How can I correct that ?
Thanks

 

[darkelf2x1]

try an acid wash after the melt down to clean up the gold, but your probably better off waiting for the pros on the board

 

[Noxx]

No acid wash won't help...

 

[Fever]

Try increasing your surface area prior to AR cleansing. You can do this by "shotting" your gold, which essentially means to pour your molten gold into water so that it forms BB's similar to rifle shot. This would allow the acids to interact with more of the gold surface. Just an educated guess really, hopefully some of the heavyweights will chime in on this....

Fever

 

[Harold_V]

It has everything to do with how you're refining.

There are NO shortcuts. If you want pure gold, you MUST follow accepted practice. Remember, those that went before us have gone through this time and again----and have perfected a process that will yield good quality------so if you're interested in achieving that level, follow instructions that are at your disposal. Don't experiment-----leave that for others with time on their hands that are content to re-invent the wheel. This is particularly important for you, considering you're trying to establish a refining service.

Depending on what you're starting with, you may have a hard time achieving a good level of purity the first time through. That's to be expected. Part of the problem is mechanical drag-down, where you're working with very heavily contaminated solutions, part of which follow the gold. They're not always easy to wash out, even when boiling with HCL.

My advice to you is this:

Process your gold the first time, using conventional means. Allow as little in the way of contaminations (metals) as is humanly possible, to be included with the gold. Use only clean vessels. Wash them well between operations-----and use BonAmi cleanser if necessary to remove stubborn stains. Do not use other cleansers, for they scratch the glass. Filter before precipitating, and insure that the filter does not allow particulate matter to pass. If it does, re-filter, or go to a better filter grade. A Whatman #2 does an outstanding job for first refined metals, although they are not cheap. I used them exclusively for filtering first run gold chloride. I felt they were worth the extra money. At all times, keep your beaker covered with a watch glass of appropriate size, to prevent contamination from other sources.

Precipitate your gold using conventional methods, collect it and wash it well. It's best to use a precipitant that does not add contamination. I preferred SO2, but there are others that work equally as well, I'm sure.

First wash should be in boiling HCL and tap water. Boil for a prolonged period of time. Take up the solution with tap water, decant after the gold has settled, then rinse with tap water, which should again be brought to a boil. After it has boiled for a period of time, add more tap water to cool the lot, then decant as before. Rinse again, and do it until the wash water comes off clear. Next, wash the gold with ammonium hydroxide and tap water. Heat it until it boils. You'll notice that the solution gets discolored. How much is determined by how dirty your gold was when you started. The ammonia evaporates fairly quickly, so you can't boil very long. Add tap water to cool, decant, and follow up with a tap water rinse, again, boiling the water. Add tap water to cool, then decant. You now repeat the HCL and tap water wash. You'll be amazed that suddenly more contaminants will come off. Boil well, add water to cool, decant, repeat the water rinse, decant, then, and this is important-------start the refining process all over again by dissolving the well washed gold powder in aqua regia. I'll talk about that in a minute, but these are indicators you should have observed along the way, aside from the fact that you could see contaminants being washed from your gold powder.

The gold powder, which started out quite dark, is now much lighter in color.

It may have been rather loose and flocculent, but now is eager to agglomerate, so it forms lumps and settles quickly.

While these instructions sound like a lot of wasted time, when you process what you think is pure gold, you'll see evidence in the remaining solutions that it was not. The evidence of which I speak will be in your solution when you've extracted the gold for a second time. It's a lot of work which is why I re-refined my gold in large lots, often as much as 200 ounces at each refining, so the time spent yielded a large return.

When you precipitate for a second time, one of the things that you can do to help eliminate unwanted elements is to use a different precipitant than the first time. I never bothered with that, but it's good advice if you're fighting with a given contaminant and can't get rid of it by other means. That was never a problem for me.

Wash the gold powder the second refining by the same methods and sequences as the first refining. Make sure all your equipment is scrupulously clean. Force dry the gold when it's washed by heating the beaker at a very low heat for a long period of time. Avoid allowing the beaker to achieve boiling temperature---you get minor steam explosions that blow gold out of the container. As the gold dries, it's a good idea to swish it around the beaker occasionally, which prevents the gold from bonding to the beaker. The residual matter in water tends to form around the gold and bond it to the beaker. While it's a contaminant of sorts, it does NOT alloy with your gold, so it is not a source of lowering the fineness unless you have strange elements in your water. For me, it was not a problem.

Once dry, you can then melt your gold. A clean, never used for anything but pure gold, dish can be used. It should be covered with a coating of borax, but nothing else. DO NOT USE ANY SODA ASH. If there are any oxides present, they'll be reduced and absorbed by the molten gold instead of locked in the flux.

Your torch should be cleaned of loose crud before melting your gold. Run fine abrasive cloth over it until it's very clean, then wipe it down with a damp cloth to remove any traces of dust. Think clean every inch of the operation-----otherwise you undo all the hard work you've done getting your gold pure.

Your other option is to operate a small gold cell, but you must have several ounces of pure gold for the electrolyte.. That is likely not a viable choice for you at this point in time.

Harold

 

[Harold_V]

Try increasing your surface area prior to AR cleansing. You can do this by "shotting" your gold, which essentially means to pour your molten gold into water so that it forms BB's similar to rifle shot. This would allow the acids to interact with more of the gold surface. Just an educated guess really, hopefully some of the heavyweights will chime in on this....

Fever

Gold is NOT cleansed via AR----that dissolves the gold, and it makes no difference if you start with melted gold or not, although melted gold dissolves at a much slower rate, so it's a good idea to not melt unless you are striving to eliminate something that comes out upon melting. However, melting, alone, will not yield pure gold. You can remove traces of oxides by a sulfuric pickle, but if you re-melt the gold, you quickly discover they are not gone. The contamination isn't a surface thing, it's throughout the gold. Thus, you can't wash melted gold and improve it's quality to any degree----the contaminants must be left behind when the gold is precipitated from solution, then the gold powder washed well to eliminate dragdown.

Harold

 

[goldsilverpro]

Harold,

Did you pre-mix the aqua regia. If so, did you use urea or did you boil it down to syrup to get rid of the nitrates?

OR,

Did you use the two acids separately to keep from using excess nitric, thus eliminating the need for urea or boiling down?

I think you told me the latter but, I can't exactly remember. That's the method that I prefer.

 

[Harold_V]

No one in their right mind premixes aqua regia. It gasses considerably once mixed, so it is nearly impossible to store without problems. That's not to say you can't, but why would you? It takes but seconds to combine the acids, and there are no hazards involved regards heat reactions. What would anyone gain by pre-mixing?

The only exception to that might be for making testing solutions, which are normally created in very small volumes, so the problems associated with storing them are correspondingly smaller as well.

When I dissolved gold, it was rarely done blindly. I had a reasonable idea of the amount of gold present, and had concluded that an ounce of nitric (tech grade) with no less than 4 ounces of HCL would dissolve a troy ounce. An excess of HCL presented no serious problems, but it had to be evaporated due to my particular method of refining, so I tried to hit the proper volumes as closely as possible. I always started slightly low, and allowed the acid to work until totally exhausted. I'd take the beaker to the state of boiling. Once there were no further signs of brown fumes, I'd add a little more HCL to the mix to see if there was any further action. If not, the evaporation process was started, assuming there was no gold left undissolved. If all the gold hadn't been dissolved, I'd add a calculated amount of nitric to the mix and watch for a reaction. If there was none, I'd add a little HCL. You get pretty good at it, so you don't use too much.

Key to success is working in a fume hood, where you can heat the acids and get instant results. If a guy is working for pleasure and doesn't care if it takes a day or two, whole different story, but I had to get things done. I often had as many as ten batches of gold in process at one time, with more waiting in the wings. Refining time had to be short, without short-cutting quality.

I used no shortcuts for the evaporation process aside from using a button of once-refined gold to consume any extra added nitric that wasn't needed. I didn't use urea, and I wouldn't use urea now if I was refining. I see no need. The button was weighed before it was introduced to the lot, and weighed when it was removed in order to trach the amount of added gold. Unused nitric was consumed without adding volume to the container by this method.

I used the evaporation process for more than one reason. I wanted my solutions as concentrated as possible, especially when re-refining. Precipitation, being an exothermic reaction, there wasn't enough cooling capacity for the process to be successful without icing -----so I used concentrated solutions (well evaporated, so they didn't destroy the filter paper) and added ice to the beakers for precipitation. That step was very important to success. You may recall that I used SO2 to precipitate. I was very pleased with it-----but you do need a fume hood.

Although sue considered my operation a knee jerk affair, I processed thousands of ounces of gold over the years. I'd put my quality up against that of any major refiner------unless they were parting in a cell. I don't think I'd claim four nines, but one of my customers had my gold assayed and reported that that particular lot was found to be 9997. I was pretty proud of that. I have no doubt that some of my results would have been 9999, but I also think it wouldn't be routine.

Harold

 

[goldsilverpro]

Harold,

I guess I had misunderstood you earlier. I thought you were alternating acids to prevent excess nitric, as I was. But, both ways work.

I probably haven't evaporated an AR solution in 28 years. I have never used urea in aqua regia solutions. This is because I never have any excess nitric, ever. The first few drops of my precipitating agent dropped gold. This is the proof of no excess nitric. If you have excess nitric, the precipitant reacts with the nitric before it drops gold. I started out following Hoke to the letter and, in 1979, I worked for a guy that was the greatest refiner I have ever known. He showed me the trick. I've covered this several times but, no one seemed to pay attention. I've never heard of anyone else doing this. The last time I owned a refinery, I shipped gold weekly as 99.99% and got top dollar. This was spectroed several times and always was up to par. I never had a lot rejected.

(1) As you did, I calculated, approximately, how much of each I needed and measured them out. For uninquarted Karat gold, this was about 125-150 mL of HCl and 25 mL of HNO3. My mentor didn't measure anything out. He just poured the acids back and forth from gallon jugs and never overadded

(2) Put the gold in a beaker or pyrex coffee pot and put this in a 5 quart white Corning Ware dish, in case of breaks and dribbles. Cover the gold with the HCl and heat it until steaming. I usually also add about 5% - 10% water. To make things easier, try to make sure you've added a little more HCl than necessary. This extra won't cause any problems.

(3) Add a small amount of nitric and let it work until the reaction slows down. Give it a slow stir and then another addition. Repeat this until there is no reaction with a fresh addition. Note: At the first addition, the reaction is vigorous and then, it slows down quickly - this addition is consumed quickly. The next addition will be less active at first and will take longer to complete - and, so on. When you first learn this, you might overshoot the nitric. After doing it a few times, you'll hit it right on the button. You have to get used to how it feels. At first, if you add too much nitric, you can always use urea but, it'll never be as pure.

(4) Add a bit of HCl, let it heat up, and watch for a reaction. If there is no reaction, you are finished. If you started with an excess, this will be the case. If there is a reaction, add some more HCl and let it heat up.

(5) If the HCl reacted, add a bit more HNO3 and watch. If there's a reaction, wait until it stops and add a bit more. Repeat until no reaction and try the HCl again.

(6) The idea is to go back and forth until you've hit the exact amount of nitric and, at least enough HCl. If you added a slight excess of HCl to start with, however, you won't have to go back and forth much. I rarely used all of the nitric that I had initially measured out.

Towards the end, go very easy on the nitric additions and give them a long time to completely be consumed. Towards the end, the pieces will be well caked with silver chloride and the acid penetrates slowly. Towards the end, keep it real hot - just below boiling. Towards the end, stir often. Also, during the process, stir before each addition. Always keep the beaker or pyrex coffee pot covered with a watch glass or a kitchen saucer when you're not stirring or adding. Never boil the solution. If you do, you can't tell the difference between fizzing and boiling.

When it's finished, transfer to a clean bucket. Add 3 times it's volume of tap water. This dilution will precipitate about 99% of the silver as silver chloride. To about 4 gallons of dilute aqua regia, add about 60 mL of battery acid and stir. This precipitates the lead. Allow to settle.

I'll go over the precipitation later.

NOTES:
(1) For Karat Gold, this direct dissolving could take as much as 8 hours. You will probably dissolve only about 98% of the gold, on the average. The remaing undissolved gold should be inquarted.

(2) To speed things up and dissolve 100% of the gold, you can first inquart the karat gold (reduce to 25% gold) with copper or silver, dissolve in nitric, pour off the nitric and rinse a few times, and treat the remaining gold powder in a much smaller amount of aqua regia. This process will take about 4 hours, after the gold has been shotted.

(3) If you only have 10Kt gold, or less, you can leach all of the silver, copper, zinc, etc., with nitric, without inquarting. Keep it quite hot.

(4) This method will do about 5 tr.oz. of karat gold in a coffee pot and about 10 oz. in a 4 liter beaker. I keep the amount of gold low to keep the solution levels low. Once the solution level is more than about 3" deep, the reaction is slower. I usually had 8 or 10 setups working at the same time.

It was late and I was tired when I wrote this. I'll look it over tomorrow to check for errors.

 

[Harold_V]

Harold,

I guess I had misunderstood you earlier. I thought you were alternating acids to prevent excess nitric, as I was.

I think we're not communicating well, or I may have stated what I did in a poor fashion. While I may have worked slightly differently from what you described, the objective was the same. I did alternate acids, and I never premixed my AR---it was mixed on demand. Our processes were very much alike.

The problem with your method, and mine as well, is that you can introduce too much nitric. I was always careful to not do so, evidenced by the amount of added gold in each batch (from the button used in evaporation), and always evaporated to full expulsion. I routinely added additional HCL a couple times as the solution reduced to heavy concentration, which insured that the nitric was consumed. A small amount of the added gold being dissolved assured me that all the gold in the lot had been digested, that there was none left behind. That was to insure that the customer wasn't cheated.

Your method would have been in serious conflict with my procedure-----I had to keep the level of concentration very high, as I outlined. The one advantage to yours is that you worked with much more dilute solutions, so mechanical dragdown was likely reduced. Had I not re-refined my gold, that would have been a problem. I've mentioned it before, but I'll do it again. When I re-refined my gold, I ran it in large lots, starting with 75 ounces. That was split in four beakers for precipitation. Each beaker was a 4000 ml----that started with a liter of gold chloride. To that I'd add ice to bring the level up to a full beaker. I then immediately precipitated the gold. When the gold was down, the solution was hot. As I said, precipitation is an exothermic reaction, which gives up all the heat energy used in dissolving the gold.

One comment on 10K. While it does process without inquartation, you can inquart and process far faster. I processed school rings by the pound------and wouldn't dream of not inquarting. The difference in process time is hours------hours I couldn't waste.

Harold

 

[goldsilverpro]

Harold, I'm very glad to know that you use the acids separately. Most people don't. How did you learn to do this? I haven't read Hoke for awhile but, I don't remember her doing it.

I'm glad that this all important thread finally occurred. This stuff is hard to explain but, is very straightforward in practice. Hopefully, the readers can understand what we're saying. If not, they should ask specific questions until they understand the mechanisms used in both our processes. Also, those others who are producing good gold should participate and detail their processes. Every good refiner uses the same basics but, all vary in the details. The more variations we know, the better we can settle on our own excellent process.

We both understood early that, besides getting all of the gold, high purity had to be the main goal. This is what separates the men from the boys, in this business. It's just as easy to produce good gold as it is to produce bad gold. The basic steps are the same. It's all in the details - the tricks.

Harold, you're right. It's always possible to add too much nitric. At the start, I did it more than a few times. More nitric makes things go faster and there's a tendency to overadd. However, when I discovered that I had to pay the piper, down the line, I developed more patience. Urea produced less pure gold and I avoided boiling down like the plague. With a little experience, I learned to avoid overadding and it got to the point that it didn't happen.

There's one thing I don't understand, Harold. How did you get rid of the silver? You obviously did, but I can't see how. When I first started, I ran experiments to find out how much silver would dissolve in aqua regia. I found that silver was quite soluble in concentrated aqua regia but most of it dropped out at a dilution of 3 to 1. After that, the curve flattened out and further dilution didn't drop much more. I found that, if I didn't dilute at the start, the silver would come out later, when the aqua regia was diluted by the rinses. This would combine with the dropped gold and contaminate it.

Sometimes, when my one furnace was tied up, I ran the karat gold scrap as is. Usually, though, I inquarted. Inquarting gives several advantages. It is faster in the long run, although there are additional steps. The aqua regia dissolving is very fast, the solution gives much less volume to work with, and the solution is mainly gold, since most of the other metals are eliminated by the nitric. This higher purity aqua regia makes it easier to end up with pure bars. And, maybe the most important, you don't have to deal with that nasty silver chloride that sets up like concrete on the stuff you're trying to dissolve.

I don't remember the nitric leaching of 10KT gold taking that long. I would guess 3 or 4 hours. I usually did it on large batches of class rings. I had a couple of class ring manufacturers that gave me their scrap.

In recent years, I rarely had to redissolve and go through the aqua regia process twice. The times I remember involved the first drop being contaminated with platinum group metals. I eventually learned to get rid of the Pt. gp. early on.

 

[lazersteve]

I eventually learned to get rid of the Pt. gp. early on.

What do you mean by 'early on' ? Please explain how you would remove the PGM's.

 

[Harold_V]

Harold, I'm very glad to know that you use the acids separately. Most people don't. How did you learn to do this? I haven't read Hoke for awhile but, I don't remember her doing it.

Two things lead me to work that way. One was the fact that there is little agreement on what constitutes the proper ratio of HCL and nitric when making AR. I've read a ratio of 3/1 and up to 5/1. Armed with the idea that too much HCL does no harm, I started adding more HCL almost at the outset of my learning curve. Still used too much nitric, because I wasn't familiar with the behavior of the chemicals, but as my skill increased, the excesses diminished.

Understand that I relied on a small overage. It was my way of insuring the customer wasn't cheated. If, when I evaporated, the button of gold I added to the dish didn't give up some weight, there was a distinct possibility that I had left behind some of the customer's gold. That's not hard to do if you're running filings, or if your shot, from inquarting, was run poorly in the nitric operation.

We both understood early that, besides getting all of the gold, high purity had to be the main goal. This is what separates the men from the boys, in this business. It's just as easy to produce good gold as it is to produce bad gold. The basic steps are the same. It's all in the details - the tricks.

I feel we each develop our own methods, but if you deviate too far from accepted practice, your results can, and probably will, be suspect. I have a lot of respect for those that went before us. They went through all of these things time and again----and, luckily for us, passed on their findings. As far as I'm concerned, only if a person can't acquire a particular chemical is there reason to not follow accepted practices. The sole exception would be if one's hobby is to experiment. If the goal is to extract and purify gold, getting cute and creative is likely to lead to a considerable amount of frustration, and yield less than acceptable quality.

The other point to consider, and it's diametrically opposed to my thinking and logic, is that some of these guys have no interest in the gold-----to them it represents nothing but money. If they can extract (concentrate) the gold, then market it to others at a reasonable price, their objective has been met. Wouldn't work for me, for I have a killer instinct that drove me to perfection----but that doesn't make me, or them, right or wrong.

Harold, you're right. It's always possible to add too much nitric. At the start, I did it more than a few times. More nitric makes things go faster and there's a tendency to overadd. However, when I discovered that I had to pay the piper, down the line, I developed more patience.

That was the best teacher I could get----even though Hoke spoke of the subject, you have to step in that oil before you understand how dirty your shoes will get! :lol:

There's one thing I don't understand, Harold. How did you get rid of the silver? You obviously did, but I can't see how.

Depends. When running filings, which yield very dirty gold the first time through, I simply filtered it from the gold chloride. When inquarting, there was very little left behind, and it was also filtered from the chloride solution prior to precipitation.

When I first started, I ran experiments to find out how much silver would dissolve in aqua regia. I found that silver was quite soluble in concentrated aqua regia but most of it dropped out at a dilution of 3 to 1.

Please accept this comment in the spirit in which it's offered!

That's nonsense! It is common knowledge that silver can not exist in an acid solution in the presence of chlorine. I've yet to read anything that would support what you said, with one exception. Rose discusses the fact that the odd atom of one element will display characteristics of another, in this case he was discussing silver and gold, at least as I recall. Remember, I've been away from this stuff for well over ten years, and as I've stated time and again, all my books are in storage. At any rate, my choride was always taken up with water, although very little. Anything that was willing to precipite did, and was filtered off. I never found traces of silver in the second refining----NEVER.

After that, the curve flattened out and further dilution didn't drop much more. I found that, if I didn't dilute at the start, the silver would come out later, when the aqua regia was diluted by the rinses. This would combine with the dropped gold and contaminate it.

What you're describing sounds like lead, not gold. Unless you had assays run to verify what you experienced, I'd question your observations. I can state with honesty that I never experienced anything like that---but I always insured that I had discharged traces of lead.

Sometimes, when my one furnace was tied up, I ran the karat gold scrap as is. Usually, though, I inquarted. Inquarting gives several advantages. It is faster in the long run, although there are additional steps. The aqua regia dissolving is very fast, the solution gives much less volume to work with, and the solution is mainly gold, since most of the other metals are eliminated by the nitric. This higher purity aqua regia makes it easier to end up with pure bars. And, maybe the most important, you don't have to deal with that nasty silver chloride that sets up like concrete on the stuff you're trying to dissolve.

Before you prime newbies with the idea that they can run karat gold that way, with success, please try to remember that silver is not soluble in AR. It converts to a hard, impenetrable crust that stops AR dead in its tracks. I've done my share of experimenting in that regard, and know all too well that you can literally boil 14K gold in AR for days and not have it dissolve. Readers should understand right off that if there is a content of sliver that exceeds 10%, you're likely to have great difficulty dissolving gold unless the cross section is so thin that the metal has been fully penetrated before the chloride layer has been fully formed. That's why it was a successful method for running filings, although even in that case they were first treated to a prolonged boil in nitric, to remove as much silver and base metal as was possible. Karat gold was my bread and butter-------I ran it daily in multiple batches.

I don't remember the nitric leaching of 10KT gold taking that long. I would guess 3 or 4 hours. I usually did it on large batches of class rings. I had a couple of class ring manufacturers that gave me their scrap.

Yes----3 or 4 hours. Inquarting made that a half hour, and eliminated the follow up operation, whereby you had to melt the bits that refused to dissolve, inquart, and start over. It delayed the batch too long. It was just plain faster, easier and better to inquart at the outset.

In recent years, I rarely had to redissolve and go through the aqua regia process twice. The times I remember involved the first drop being contaminated with platinum group metals. I eventually learned to get rid of the Pt. gp. early on.

You're not going to try to convince me you achieved 9999 that way, are you? Nothing I've ever read indicates that's a reasonable expectation, and my personal experience, and I'm damned thorough and careful, lead me to believe that it's nearly impossible. I do think you can achieve 9995 with reliability----as long as you're not processing filings that have not been melted and inquarted.

I agree with you in that if one is to refine, setting the goal for anything less than 9999 makes no sense, but achieving it isn't easy. Only parting properly with a cell will yield consistent results, and then you're at the mercy of your support equipment. Something as simple as a dirty torch tip can lower the fineness (they shed copper oxide). I wasn't willing to settle for less than the industry standard of 9995, and worked hard to exceed it. I was very happy with my results, and think I would be less than truthful if I was to claim consistent 9999.

Harold

Edit: changed words so they made sense

 

[lazersteve]

whereby you had to melt the bits that refused to dissolve, inquart, and start over.

Harold,

I experienced this same situation even after inquarting? :? Is this because I didn't get the gold to fully alloy with the silver?

What is the accepted process for alloying gold and silver for inquarting
( i.e.: 3 parts silver, 1 part gold, melt gold, add in silver, mix (?), etc.).

Thank you for your valuable input.

Steve

 

[lazersteve]

I do think you can achieve 9995 with reliability----as long as you're not processing filings that have not been melted and inquarted.

Harold,

Am I correct to conclude that this to means inquarting is a precusor to higher purities?

I have adopted the purer is better mentality lately. The thing I noticed right off of the bat was the additional work involved in attaining the higher purity product. I think it's worth the extra work if you really want the purest gold possible. My goals are sort of a cross between yours and some of my own. I'm not processing gold for the money, but for the future value. I've sold a few ounces of my gold early on, but now I'm stockpiling it as a retirement plan. Knowing it will be worth more when it is the pureest possible, I'm driven to attain the highest purity I can.

On the flip side, time is of no concern for me as it was for you. You had many customers waiting in the wings, where I have only my curiosity and desire to learn as my driving force. Since I have more time to ponder the philosiphy of gold refining, I tend to be creative and try out some uncharted territories along the way. Granted I waste some time doing so, but I too must step in the oil to realize how dirty it is! :wink:

Keep up the great post Harold, I sincerely feel you are the heart and soul of this forum.

Steve

 

[goldsilverpro]

That's nonsense! It is common knowledge that silver can not exist in an acid solution in the presence of chlorine.

Harold,
One of the first things I learned was that silver chloride is soluble is strong aqua regia. Not a lot but, certainly enough to severely affect the final purity of the gold. It reacts similarly to lead but, to a lesser extent. Before dilution, the filtered solution is perfectly clear. Upon dilution, the dissolved silver chloride precipitates. Therefore, the standard way of precipitating it is to dilute the aqua regia. Some say 2 volumes. Some say 4. My experiments said 3. I was quite surprised that you didn't agree with it. Nearly every refining book I've ever read states this fact. And, it is a fact. I don't have a copy of Hoke any more but, I seem to remember that she mentioned it. You might check your copy.

My experiments were simple. I cooked some AgCl in standard 3/1 aqua regia, filtered it, most probably through glass fiber filter media, and then analyzed the silver dissolved in the aqua regia by atomic absorption. Then a I diluted it a bit, filtered it, and again ran it on the AA. I repeated this several times and then plotted it on a graph. Three dilutions removed most of it.

I only have 4 refining books left. Two didn't mention it. The first edition of Ammen (pp117) said to dilute it 3 or 4 times but, didn't say why.

I did find more than a mention of it in the last book. This was in a an IPMI (International Precious Metals Institute) book of the papers that were given at the 1980 IPMI Symposium on Recovery, Reclamation, and Refining of Precious Metals, held in San Diego. I was an IPMI member at the time and attended. The IPMI is probably the most prestigious PM organization in the world. In the papers, is a long article entitled "Silver Chloride". Here's a quote from that paper, page 3. The author documents these statements but, I won't supply the references unless you want them.

"It (silver chloride) is somewhat soluble in concentrated HCl and heavy metal chlorides. Solubility in these increases with temperature and concentration. Solubility in chlorides appears to be by the formation of complex chloroargentate ions.... Solubility in HCl and heavy metal chlorides is of interest because of how it relates to aqua regia systems. In aqua regia dissolution the liquid consists of a very concentrated mixture of heavy metal chlorides, usually at elevated temperatures. These are ideal conditions for the dissolution of AgCl. Even small amounts of silver chloride, if left in solution, can have a marked effect on the purity of the gold produced. This is especially true for the third and forth decimal places of fineness. Fortunately most of the AgCl can be removed with water. One to two volumes are usually recommended for this dilution during the clarification stage."

So, what I said is true.

I've thought about your process to try and determine why you had no silver problems. (1) If you always inquarted, your aqua regia would have much less heavy metal chlorides so, less AgCl would be retained. The experiments I ran, however, showed some retention with no heavy metal chlorides but only aqua regia alone. (2) After boiling down, I assume you added water (diluted) and filtered. This is probably where you got rid of it.

Before you prime newbies with the idea that they can run karat gold that way, with success, please try to remember that silver is not soluble in AR. It converts to a hard, impenetrable crust that stops AR dead in its tracks. I've done my share of experimenting in that regard, and know all too well that you can literally boil 14K gold in AR for days and not have it dissolve.

Although neither of us likes the direct aqua regia process, without inquaration, it is the standard aqua regia process that most refiners use. You and I are in the minority. As I understand, one reason you used it was because you wanted to get every milligram of gold dissolved so you could be honest in accounting with your customers. Most refiners could give a damn about 100% honest accounting. They know that, sooner or later, it'll all come out in the wash. Of course, by that point, it would belong to the refiner. In my case, when using direct aqua regia, it was on already purchased material. I rarely worked on a recovery basis. I preferred inquarting because, as one of your reasons, I hated fighting with the silver chloride. If you reread my post, you will see that I never promoted direct aqua regia. I just showed how it was done.

You're not going to try to convince my your achieved 9999 that way, are you? Nothing I've ever read indicates that's a reasonable expectation, and my personal experience, and I'm damned thorough and careful, lead me to believe that it's nearly impossible.

What do you mean by 'early on' ? Please explain how you would remove the PGM's.

Early on in life, Steve.

In 1969, I was head chemist for a large refinery in L.A. Our Wohlwill Cell (gold purification cell) solution was often too contaminated with base metals and required frequent solution changes, in order to maintain high purity gold. I started experimenting with ways to extend the life of the solution. We had a well stocked lab and had quite an assortment of chelating agents. Most were variations of EDTA. Chelate comes from the Greek word Chelos, which means "claw". It grips metals in several places, like a claw, and holds them in solution. I figured that, if I added EDTA to the solution, it would chelate the base metals and prevent them from plating out with the gold.

When I added the specific type of EDTA to asample of cell solution, all of the gold dropped out. Surprise, surprise. For about a hour, I was very disappointed. I really thought it would work. Then, it dawned on me that I might have a new precipitating agent for gold. I started doing lots of experiments and maximized the process. We melted several batches of gold dropped from heavily contaminated aqua regia, under pristine conditions, and sent off samples to be analyzed for all impurities. To my amazement, none were under 99.99% pure. Some approached 99.999%, believe it or not. Some of these aqua regia solutions were intentionally contaminated with all of the platinum group. Still, the gold was above 99.99% pure, with only one drop. I'm not saying that the company always shipped 99.99% gold, because they could introduce impurities during the melt. I am saying that the powder was most always 99.99%.

None of the company experts could figure out why it worked. Later, I concluded that formaldehyde, a common gold precipitant, was released when the EDTA product neutralized the aqua regia. You could smell it. The base metals were tightly held into the solution and didn't come out with the gold. I never could figure out what happened with the silver and platinum group but, somehow, they were held into the solution. The company pretty much shut down the Wohlwill operation and went with my invention for everything. We called it EZ-Drop. I was a hero based on a failed experiment. The company was running about 10,000 ozs/month and ran the process for several years, until they were bought out by a big conglomerate.

When I left, I continued using it until about 1980, although I always kept some around for gold containing platinum group. From the late '80's though the mid '90's, when I owned my last refinery, I had no need for EZ-drop. I specialized in recovering 80/20, gold/nickel braze from military and commercial jet engine parts. Another reason I stopped using this product was that chelating agent wastes, with their tightly bound heavy metals, are very difficult to waste treat. The EPA hates them. Also, the EDTA product was expensive. In 1969, it cost about $650 per drum, of which, under optimum conditions , you could drop about 3000 ozs of gold.

Note to Harold I am correcting something in the third from the last paragraph. When we sent out the EZ-Drop samples, we didn't melt them. We sent them out in powder form. The melted samples were for another project. It's been 38 years and I remembered wrong.

 

[Harold_V]

That's nonsense! It is common knowledge that silver can not exist in an acid solution in the presence of chlorine.

Harold,
One of the first things I learned was that silver chloride is soluble is strong aqua regia. Not a lot but, certainly enough to severely affect the final purity of the gold. It reacts similarly to lead but, to a lesser extent. Before dilution, the filtered solution is perfectly clear. Upon dilution, the dissolved silver chloride precipitates. Therefore, the standard way of precipitating it is to dilute the aqua regia. Some say 2 volumes. Some say 4. My experiments said 3. I was quite surprised that you didn't agree with it. Nearly every refining book I've ever read states this fact. And, it is a fact. I don't have a copy of Hoke any more but, I seem to remember that she mentioned it. You might check your copy.

Well, your comments are certainly in keeping with what Rose had to say about random silver atoms behaving as if they're gold. Just checked my Merck index, which clearly states that it is "superficially attacked by HCL", which likely explains the entire subject, particularly when I read your comments below. .

I'm going to quote your entire statement, below, thinking that what you have to say is very important, but most of all, revealing. Good stuff, Maynard!

My experiments were simple. I cooked some AgCl in standard 3/1 aqua regia, filtered it, most probably through glass fiber filter media, and then analyzed the silver dissolved in the aqua regia by atomic absorption. Then a I diluted it a bit, filtered it, and again ran it on the AA. I repeated this several times and then plotted it on a graph. Three dilutions removed most of it.

I only have 4 refining books left. Two didn't mention it. The first edition of Ammen (pp117) said to dilute it 3 or 4 times but, didn't say why.

I did find more than a mention of it in the last book. This was in a an IPMI (International Precious Metals Institute) book of the papers that were given at the 1980 IPMI Symposium on Recovery, Reclamation, and Refining of Precious Metals, held in San Diego. I was an IPMI member at the time and attended. The IPMI is probably the most prestigious PM organization in the world. In the papers, is a long article entitled "Silver Chloride". Here's a quote from that paper, page 3. The author documents these statements but, I won't supply the references unless you want them.

"It (silver chloride) is somewhat soluble in concentrated HCl and heavy metal chlorides. Solubility in these increases with temperature and concentration. Solubility in chlorides appears to be by the formation of complex chloroargentate ions.... Solubility in HCl and heavy metal chlorides is of interest because of how it relates to aqua regia systems. In aqua regia dissolution the liquid consists of a very concentrated mixture of heavy metal chlorides, usually at elevated temperatures. These are ideal conditions for the dissolution of AgCl. Even small amounts of silver chloride, if left in solution, can have a marked effect on the purity of the gold produced. This is especially true for the third and forth decimal places of fineness. Fortunately most of the AgCl can be removed with water. One to two volumes are usually recommended for this dilution during the clarification stage."

So, what I said is true.

I've thought about your process to try and determine why you had no silver problems. (1) If you always inquarted, your aqua regia would have much less heavy metal chlorides so, less AgCl would be retained. The experiments I ran, however, showed some retention with no heavy metal chlorides but only aqua regia alone. (2) After boiling down, I assume you added water (diluted) and filtered. This is probably where you got rid of it.

I had to think about that for some time. The method I pursued could have easily included traces of silver as chloride, based on your quoted comments, for which I thank you.

Incidentally, I have the loose-leaf from the same symposium you mentioned (IPMI), but mine is dated March 10-13, 1981, San Diego.

I obviously eliminated silver chloride, although unbeknownst to me, when I did my wash with ammonium hydroxide. I knew it was removing copper that didn't come out with the first HCL wash, but had not considered that I might also be removing silver. If that is not the case, then my gold certainly must have contained traces. While I diluted my solutions, they were never diluted by three times (I already covered that in my previous post)-----but I can clearly see that there is a benefit in doing so. I never had my gold assayed, and had a customer not done so, I'd have never had a clue. I just worked on my quality until it would melt without traces of oxides, and had a great surface. It think we're in lock step in that regard----those qualities come only from very pure gold.

Although neither of us likes the direct aqua regia process, without inquaration, it is the standard aqua regia process that most refiners use. You and I are in the minority. As I understand, one reason you used it was because you wanted to get every milligram of gold dissolved so you could be honest in accounting with your customers.

I've never had the privilege of touring a major refinery----so I'm not at all up to speed in what they do,and how they do it. I stand to learn a considerable amount in that regard.

I'm held captive by my trust in Hoke's book. I had messed with my gold in the hopes that I could produce clean gold without jumping through all the hoops. My first button was frosty, leaned somewhat green, and was obviously not pure. I tried to dissolve in in AR by boiling for hours, which turned into days. The silver content was way too high to permit dissolution, and the button ended up with a very ugly coating of silver chloride. It may be soluble in AR, but not enough to permit refining without reducing it to respectable levels. As I said, I boiled my button for hours on end in AR, and dissolved no gold in the end, once the impervious layer of chloride had formed.

I finally read the book and resorted to inquartation. Miracle of miracles, I ended up with relatively pure gold once I followed the instructions and quit being cute and creative. That's why I always recommend the newbie follow good and accepted practice. It's not because I do it that way, and there's no other way-----it's because it's very simple to do, and best of all, it works, and works every time. I fully realize there are other ways, perhaps some of them even better, but it's pretty hard to beat the basic process Hoke presents-------and they can be done without expensive equipment. I assume major refiners are heavy into contained vessels of sorts, where they can conduct these dissolutions at elevated temperatures and can deal with the resulting fumes, likely recycling them to the source of origin. Care to comment on that?

In 1969, I was head chemist for a large refinery in L.A. Our Wohlwill Cell (gold purification cell) solution was often too contaminated with base metals and required frequent solution changes, in order to maintain high purity gold. I started experimenting with ways to extend the life of the solution. We had a well stocked lab and had quite an assortment of chelating agents. Most were variations of EDTA. Chelate comes from the Greek word Chelos, which means "claw". It grips metals in several places, like a claw, and holds them in solution. I figured that, if I added EDTA to the solution, it would chelate the base metals and prevent them from plating out with the gold.

Excellent explanation of a process snipped ------

That certainly explains your position,and I thank you for that. Clearly, what I had to say is true----first refined gold is unlikely to exceed 999-----and is often far worse. Your process was and is very impressive.

On that subject, the IPMI literature I have in my possession addresses pretty much the same thing, but in refining the platinum group. Instead of precipitating the platinum from dirty solutions, they precipitate the base metals, then go after the values. I don't recall any of the details----it's been well over 12 years since I last read the papers, but, once again, your concept is well supported by the endeavors of others.

I hope readers have learned something from this long drawn out post. I know I have.

Harold

 

[Harold_V]

Harold,

I experienced this same situation even after inquarting? :? Is this because I didn't get the gold to fully alloy with the silver?

What is the accepted process for alloying gold and silver for inquarting
( i.e.: 3 parts silver, 1 part gold, melt gold, add in silver, mix (?), etc.).

Not being fully alloyed would certainly be one of the things to consider. The other would be if you had used enough nitric acid, or not. If you're working your metals cold (no hotplate), it's a lot easier to achieve the results you did. Heating makes a huge difference in that the turbulence tends to keep the insoluble in suspension and keeps the solution in action, better exposing the metal to the acid. Hot acids work much faster than cold acids.

Gold and silver will eagerly combine, but you do have to give them a reason. My normal procedure was much the same as a manufacturing jeweler would use, which is to simply stir the heat with a carbon rod. You can buy them from a jewelry supply store, or you can even use a carbon rod that is used for air arcing metals. Welding supply stores sell them, although you might have to buy a box. Any good sized welding shop would probably have them and sell you a couple. They're not very expensive. A buck should buy you a rod. They last a long time, slowly burning away where they contact the molten metal. So you'll know, they break fairly easily, so get the largest one you can find, for strength. I used ½" diameter rods. They're a bit "clunky" at first, but the end burns away to form a taper, so you end up with a small end that works for small lots.

The stirring takes only a second or two, but be advised that the carbon transfers heat quickly. I held my carbon rod with a pair of wheel weight pliers----which doubled as the gripping device to pour the molten mass into my container of water (I used clay melting dishes for small lots). The angle of the pliers was perfect for that purpose, but a bit of a compromise for stirring. No matter, you do it only briefly, anyway.

When you pour your metal into water, there's no better way than to simply pour out of the lip of your melting dish in a fine stream. Move about over the water so you don't concentrate the metal in one spot. When I poured large heats, it wasn't uncommon to end up with a large mass otherwise. Pouring this way doesn't yield shot-----it yields what I like to call corn flakes. They are thin and irregular, and dissolve quickly.

It's important to keep the gold content around the 25% bracket. You won't always be successful, for there are surprises. If you get involved with a lot of dental gold, for example, you have to add a serious amount of silver to offset the higher gold content. By sharp contrast, if you run a batch of 10K, particularly old 10K, that is actually borderline 9K, it takes very little. My policy was to add about 105% in silver of the weight of the mixed scrap gold I'd process. It kept me in the ballpark. Considering 14K is 58.3%, you ended up quite close to 25% gold content.

The problem with inquarting too low (under 25% gold) is that you risk the gold breaking into fine powder. That's not a problem, all you have to do is wait for the stuff to settle before decanting. For me, that wasn't a good thing because of the need to turn the gold quickly.

If you don't use enough silver, the nitric process will not be successful in that the gold is so dense that it eventually isolates the undissolved metal from the acid. In that case, all you can do is give the stuff a prolonged boiling in nitric, and hope you penetrate to the center. If you start over, you have to add a huge amount of silver because you're dealing with near pure gold on the exterior. I think you see where I'm going with this.

The other negative of not having enough silver is that you don't get a clean extraction with the first operation, so the metal you dissolve isn't as clean as it otherwise may have been. As you might imagine, the cleaner your solution, the cleaner the gold will be that precipitates. It's also important that the precipitant you use is very selective Some reagents have a propensity to precipitate other elements to some degree, and there's always the problem of drag down. Washing the gold well after precipitation is key to improving the quality, but a second refining really does the trick. By then, your contaminants are very few, and if you don't add anything to your solutions to yield a color (I didn't), you can see what is left behind by the second refining. It was always a proud moment when my solution was clear. A sure sign that my first refining had been carried out well.

It might not hurt to mention that not all gold needs to be inquarted. White gold, for example, can be directly dissolved in AR with success (no silver), but you miss out on the first operation, where you remove base metals. I don't recommend the procedure, but it does work.

The gold you're recovering from your cell needs no inquarting, as I'm sure you know. Just don't melt it. If I was to refine it, I'd incinerate it, papers and all, getting it hot enough to convert carbon to CO2. Avoid heating to the point of forming prills. I'd then give it a wash in boiling HCL, rinse, and go straight to AR. The gold from that operation would, in all likelihood, not need a second refining. The HCL wash should remove anything that's questionable. Be sure to keep Hoke's recommendation in mind to add a few drops of sulfuric when evaporating, if you go that route. You may not need it, but it does no harm. If you go the urea route, I'm afraid I'm not much help-----I never used it, nor would I if I was refining now.

Tonight I may have learned something that should have been obvious to me. GSP had claimed that some silver goes into solution in AR. Rose had discussed that to some degree in his book, but there was no explanation as to the cause. GSP provided that information. I suggest that if you refine in small quantities, that you dilute your solutions. If you run concentrated solutions like I did, be certain to do an ammonium hydroxide wash to remove traces of silver chloride that get through the operation.

I'd like to comment on your quest for pure gold. I'm very pleased to hear you talk that way. There is no doubt in my mind, to do anything less, particularly in your situation, where your intention is for retirement, you couldn't make a more sound decision (it worked for me!). You open the door to selling your gold to any consumer, and at full value. Otherwise you'd be locked in to selling to a refiner, or to a recycling source. You can always fall back on that in an emergency. No reason you shouldn't put that money in your pocket, and the reward from turning out ultra pure stuff is worth the effort in personal satisfaction. My proudest moments were always when I was finished with re-refining large batches.

When the day comes that you can melt your gold and not have oxidation, you'll know you're getting close. It's not all that hard, Steve. Take it slow and easy, as you have, and it will turn out fine. Pay strict attention to your washing cycles, and keep your vessels clean. Keep your vessels covered with the appropriate watch glass, too. I washed my glassware with BonAmi to remove any traces of staining. You have to have a different mindset when you strive for better than 9995!

Harold

 

[Harold_V]

I do think you can achieve 9995 with reliability----as long as you're not processing filings that have not been melted and inquarted.

Harold,

Am I correct to conclude that this to means inquarting is a precusor to higher purities?

In my opinion, yes. It stands to reason that anything you do to remove unwanted substances from your gold before it goes into solution will decrease the contaminants that come down with the gold. They need not precipitate to contaminate------they hitch a ride mechanically---and don't always wash out well. Eliminate them and there is nothing to ride with the gold.

You also have to keep in mind that some things simply don't contaminate gold. Water, for example, that has no heavy metals contained within, will not add negative things to your process. That it contains other elements is obvious, but they just ride through the process. They don't report in the final product.

I have adopted the purer is better mentality lately. The thing I noticed right off of the bat was the additional work involved in attaining the higher purity product. I think it's worth the extra work if you really want the purest gold possible.

I've already commented on your quest-----and I wish you luck. Trust me, Steve, the pure gold is its own reward! It's worth the effort, especially for guys with a hint of perfectionism. :wink:

Harold

 

[lazersteve]

The other would be if you had used enough nitric acid, or not. If you're working your metals cold (no hotplate), it's a lot easier to achieve the results you did.

I'm sure I used enough nitric (70% Lab Grade). I even poured off the first batch and added more to be sure. I didn't get much more action. I think heating is the issue. Since I don't have a fume hood yet I do everything cold and just wait it out. As I've stated many times, I'm in no hurry.

Oddly enough the inquarting I filmed for the Separating Silver from Gold tutorial worked fine with no heating. Maybe I didn't get quite enough silver in the alloy on this batch? The last possiblity is the amount of powder gold that has formed, it almost seems as though it's preventing the nitric from contacting the alloy. I've been stirring the solution on a regular basis and it still seems to be SLOWLY eating away the last tiny bits of the alloy. Hoke mentions in one of the early chapters of her book to go thru the gold powder after inquarting looking for bits that have not dissolved. She recommends adding them to future inquartation batches.

Thanks Again Harold,

Steve