ALL values dissolved in AR

[dgr]

I have a number of screws that had gold plating/splashing on their heads. They're out of a plating machine. The heads are cross drilled so mechanical removal of the metal was not possible. I found that I could dissolve most of the screws in HCL. However, a number of the screws would not dissolve in anything. I finally gave up and when after the gold with AR. This dissolved all the PMs and left what is likely most of the screw material behind. We believe it was stainless although I did find what I believe was a titanium piece.

I hope you're smiling at this point. I am fine with admitting that I didn't know what I was doing. I have since then read Hoke and Harold's refinery handbook. Thank you all for making those available.

On to the questions:
I have a soup of PMs in AR. What is the best way to get them out? If I understand Hoke correctly, I've already created silver chloride. If that is correct, I see no reason to not move forward with removing the nitric acid from the AR and precipitating the gold. However, there could be gotchas involved which is why I'm here.

I feel it's safe to say that the following metals may be in solution at this point: Cu, Ag, Au, and possibly Pd, Pt but I don't think those metals are used in plating.
Here is the solubility information I could find:
CuCl -- soluble in acid. I'm not sure if it is CuCl or CuCl2 I am dealing with.
AgCl -- insoluble in acid
AuCl -- soluble in acid

So here are my thoughts. Proceed with removal of nitric acid. AgCl should form and can be filtered. Precipitate AuCl until solution no longer stains with Stannous Chloride. Rinse precipitate in hot water to remove any Lead Chloride that may be present. Retreat precipitate with Nitric acid and rinse. Redissolve what should now be mostly gold in AR and reprocess with SMB.

What metals will SMB precipitate? I know gold is one but I haven't found the answer on silver. Although it may be irrelevant as I am dealing with Silver Chloride instead. I did find this in Hoke, "The clear solution contains dissolved gold, copper, zinc, etc. If there is much copper or nickel in it, it will be greenish brown." as a lead into the section on precipitating with Copperas. This leads me to believe that only gold with drop out.

Would there be any advantage to using copper to cement everything below copper in the solution and reprocessing at that point or to simply neutralizing the solution so that it is basic and dropping all the values out of solution and starting over?

Thank you for your time. I really do appreciate this community making itself available. And I'm fully prepared to be told I did a dumb thing :mrgreen:

 

[Harold_V]

A great deal depends on how much free nitric is present. If you've used too much, you'd be far better served to recover the gold using copper, then to reprocess.

A couple things to consider.
For all practical purposes, you can not have both gold and silver in the same (acidic) solution. Silver will have already been precipitated as silver chloride, which will be removed by filtration. The only exception to that is the miniscule trace of silver that behaves like gold, a fact that is well documented. It can be removed by cooling of your solution, or by dilution with tap water.

Do not wash gold with nitric acid that has come from a chloride solution. In spite of careful washing, there will be traces of residual nitric present, which will re-dissolve some of the gold. A wash with HCl is more than adequate, and it doesn't dissolve your gold. I'm assuming you do this hot, where any free chlorine is instantly evaporated from the solution. Cold washing isn't recommended, anyway.

Read Hoke before you venture forth. Everything you need to know is there. Concentrate on testing, too. It's very important for you to understand if you expect to be successful.

Harold

 

[dgr]

Harold,
Thank you for the response. I appreciate all the free information you provide. Which isn't really free because you went and earned it. Hoke has so much information in it! It has provided most of the answers I have looked for.

I am going to cement with copper and reprocess. One thing I can't find the answer to is what should the copper look like when it is finisted reacting with the rest of the nitric acid? I did the following with a small portion of my solution:

The solution was filtered, diluted 4:1 with water and copper was added to it. It was warmed and allowed to react. Once finished reacting, the copper wire has been somewhat reduced as expected. However, it was also coated with a loose black crust. What is this compound? Based on my understanding of the cementing process in that it will only drop out metals more noble and my finding that hot HCL will dissolve cuprous chloride, I went ahead and scraped this crust into the solution.
The beaker was decanted and then rinsed with hot HCL and washed. This was followed by a ammonia wash and rinse with water. The precipitate was then dried and melted.

At this point, I am pleased with the results. I am going to soak my button in nitric and look for any reaction. I will then soak in again in HCL and again look for any reaction. I will treat the rest of my solution as above then reprocess it with SMB.

If I'm successful, attached is a picture of my first test.

 

[Harold_V]

One thing I can't find the answer to is what should the copper look like when it is finisted reacting with the rest of the nitric acid?

A great deal depends on the amount of free nitric acid that is present. Given enough, the copper will have been fully dissolved. With a trace present, values will cement, then, with some luck, the copper surface will dissolve enough to shed the values as slimes, yielding a clean copper surface. That doesn't always happen, and that makes the recovery of the values somewhat more difficult (more below).

Once finished reacting, the copper wire has been somewhat reduced as expected. However, it was also coated with a loose black crust. What is this compound?

That's the values. When gold is divided finely, it no longer reflects light in a straight line. It is well diffused, resulting in the color appearing darker, even black. Given the balance of which I spoke, where there's a little free nitric present, it would have continued dissolving the wire, freeing the cemented values.

On that subject, while wire works, it's smarter to avoid its use. Use pieces that can be easily removed and cleaned. Wire breaks up as it reduces in size, making removal difficult. I think you can see that if you have an abundance of wire present, you may have to dissolve a serious amount of unwanted copper, so, in a sense, you're back where you were at the beginning, with heavily contaminated material.

Based on my understanding of the cementing process in that it will only drop out metals more noble and my finding that hot HCL will dissolve cuprous chloride, I went ahead and scraped this crust into the solution.

That was the appropriate thing to do. With a piece (buss bar, for example), that would have been much easier, but the point is that you recovered the values, and that was your objective.

The beaker was decanted and then rinsed with hot HCL and washed. This was followed by a ammonia wash and rinse with water. The precipitate was then dried and melted.

Because of the recovery technique involved, I would have recommended you not melt the powder, but re-refined for greater purity. That, of course, relies on your objective. You may not wish to invest the time it takes to improve the quality. In the case where you had no expectations of re-refining, I'd likely recommend the recovered gold powder be incinerated (to kill any chlorides) then given a wash in hot dilute nitric. I rarely recommend that process because of the risk of re-dissolving some of the gold, but when you cement with copper, the quality will be questionable at best, especially if there's the slightest risk of contamination by any of the platinum metals. After the nitric digest, I would rinse well, then incinerate once again, to kill nitrates. I would then wash with hot HCl, rinse well, wash with ammonium hydroxide, rinse well, then follow up with a final wash with HCl, and a final rinse with water. Given the complexity of these operations, it's just easier to simply wash well, as you did, then to re-dissolve the gold powder. Melting has some value in eliminating a trace of some of the contaminants, but it makes re-dissolution a little more difficult.

At this point, I am pleased with the results. I am going to soak my button in nitric and look for any reaction. I will then soak in again in HCL and again look for any reaction. I will treat the rest of my solution as above then reprocess it with SMB.

You can be justly proud of your button! It looks pretty good, especially considering the process you used. However, any further treatment that does not include dissolving will serve no purpose. The percentage of gold is so high that it will protect any contaminants from dissolution. Even prolonged boiling in nitric or HCl won't alter the button, although if there's any surface discoloration that may be removed. It will have virtually no effect on the overall purity of the button. That was my point about re-dissoving the gold powder before melting.

When you re-dissolve your gold, any base metals that may be included are generally liberated. The barren solution, after precipitation, will be discolored, indicating the nature of the contaminant. It's a great way to determine what is not being eliminated. Values recovered from very dirty solutions tend to drag down a small percentage of the contaminants, which have a way of reporting in the final product. Garbage in, garbage out, so to speak.

Harold

 

[dgr]

Harold,
Thank you for the kudos! And thank you for continuing to steer me down this path. I agree with you about not melting the gold initially. But then I wouldn't have this little button to fiddle with.

There are pmgs in this mixture. I was getting a reaction with stannous and determined it is palladium. Orange-brown that changes to green. I confirmed with the source that gold, nickel, palladium, rhodium were used in the plating process. I don't know if getting the pmgs out right now is worthwhile as I only expect around 100g total of gold.

Following your advice, the button did end up back in the mix with the rest of my solution. The initial melt was only a test to insure my result was as expected. A chemistry lab practical as it were. I went ahead and processed the rest of the solution including a good wash and being redissolved as you outlined and that resulted in just under an oz. of gold that was turned into a button. I may go ahead and reprocess it. Right now, the journey is the goal for me so investing time repeating the process is still educational.

Details of the second time through. The gold was dropped with copper originally. The precipitate was washed with hot water until clear. Then it was washed with HCL and rinsed until clear. Then ammonium hydroxide and rinsed until clear. Then HCL. It was redissolved in AR and dropped with SMB. Again it went through the wash rinse cycle before being melted.

Now that I have reread your post for the 10th (ok, I'm lying, 20th) time I believe that there was a better approach following dropping with copper. You mention simply redissolving the precipitate. My understanding is this would provide a solution with a lower concentration of base metals to be carried along when dropping the gold. From reading Hoke, this forum and my own journey, it seems at this point it would be ideal to roast my precipitate and begin at the beginning. Treat it as high carat gold that has been inquarted except we didn't actually add any silver. It is already finely divided so that it could then be processed from the point of doing a nitric soak. Being that it was dropped with copper, the higher reactivity metals should be gone. Tin and lead should be gone due to the addition of sulfuric when removing the nitric. What we are dealing with at this point is removing the percentages that were caught in the process since I had to approach it backwards.

Is that the proper direction to take when the gold and base metals are already finely divided? Or does one actually need to inquart in order to get than 2nd or 3rd or 4th nine? Or is the shorter path of redissolving and re-precipitating sufficient?

Here's a 30.7 gram button this time around. Sorry for the poor picture quality. The cleaving would have been deeper but I was afraid of it sticking in my melting dish so it was dropped in water and has a pipe on the backside.

 

[Harold_V]

Harold,
Thank you for the kudos! And thank you for continuing to steer me down this path. I agree with you about not melting the gold initially. But then I wouldn't have this little button to fiddle with.

Agreed! That is very much a part of learning the refining process. It's important that we reap a reward along the way. Were you to have seen my first button, you'd have been appalled by comparison. Still, it was the results of my first attempt, and was quite instrumental in forming my future habits. Slowly, ever so slowly, I came to realize that pretty much everything Hoke spoke of was in my best interest. There are times when you learn what to do by doing what you shouldn't do. Nothing shows you why better than achieving less than desired results.

There are pmgs in this mixture. I was getting a reaction with stannous and determined it is palladium. Orange-brown that changes to green. I confirmed with the source that gold, nickel, palladium, rhodium were used in the plating process. I don't know if getting the pmgs out right now is worthwhile as I only expect around 100g total of gold.

You'd be best served to not attempt a proper recovery, using ammonium chloride and sodium chlorate. If your solution is either quite dilute, or it is heavily contaminated with other elements, the resulting palladium will be of questionable quality, if it can be recovered at all. The platinum metals respond very poorly to precipitation when diluted, so it's entirely possible you'd fail, anyway.

What I'd recommend is to recover the palladium with copper, just as you recovered your gold with copper. Do that after you have precipitated the gold with SMB. Be advised that SMB has a tendency to precipitate some palladium, but the second refining you spoke of will generally eliminate the vast majority.

Right now, the journey is the goal for me so investing time repeating the process is still educational.

In truth, I endorse that very process. You learn far more from application than you do from reading----so as long as you understand what to do, and why it is done--the rest is in the doing.

Now that I have reread your post for the 10th (ok, I'm lying, 20th) time I believe that there was a better approach following dropping with copper. You mention simply redissolving the precipitate. My understanding is this would provide a solution with a lower concentration of base metals to be carried along when dropping the gold.

That's correct. Because you will have separated the values from the vast majority of contamination in the precipitation and wash (which should not be eliminated, although it can be limited to just a wash with HCl, followed by a good rinse), the succeeding operation will have precious little in the way of contamination that can be dragged down. In and of itself, a second refining, even one handled poorly, is bound to improve the quality beyond that which is accomplished by carefully washing a once refined gold. I proved that to more than my satisfaction when I spent way too much time trying to improve the quality of the gold I used to dispense when I first refined. It was good enough to be used, but not good enough to satisfy the part of me that tends to have perfectionist tendencies. On a whim, I re-refined a small lot and was pleasantly surprised at the improved quality, plus I could see the contamination that was eliminated (blue coloration of the barren solution, after precipitation). That was all I needed to come to terms with the idea that a second refining was worth the effort, so that became my normal routine.

From reading Hoke, this forum and my own journey, it seems at this point it would be ideal to roast my precipitate and begin at the beginning. Treat it as high carat gold that has been inquarted except we didn't actually add any silver. It is already finely divided so that it could then be processed from the point of doing a nitric soak. Being that it was dropped with copper, the higher reactivity metals should be gone. Tin and lead should be gone due to the addition of sulfuric when removing the nitric. What we are dealing with at this point is removing the percentages that were caught in the process since I had to approach it backwards.

Is that the proper direction to take when the gold and base metals are already finely divided? Or does one actually need to inquart in order to get than 2nd or 3rd or 4th nine? Or is the shorter path of redissolving and re-precipitating sufficient?

In my opinion, the nitric wash can be very useful, and would be my recommendation if you use copper for the first recovery. You would be well served to do the roast you spoke of, to ensure you didn't dissolve any values in the preliminary nitric wash. For the record, you should always test solutions for traces of values, for you never know when you'll find some of the platinum metals, or when you may inadvertently dissolve gold. In traces, all are best sent to the stock pot, where they are recovered without effort. The stock pot will become one of your favorite functions, especially if you find yourself working with mixed values.

Back to the question, it's always easiest to dissolve the well washed (gold) powder than to melt and dissolve. When I re-refined, I did so with reasonably large batches, no less than 70 ounces per session. The gold received a prolonged boil in HCl, then a good water rinse. It was then (force) dried for settlement. I stored the powder until there was sufficient volume to warrant a second refining. Melting with silver may, in some weird way, remove something from the mix, but I liken the idea to washing a car with muddy water. Your objective is to eliminate base metals, along with traces of silver. So long as you keep adding some, you can expect a compromise on the hoped for results. That's not to say that you can't achieve your goal that way, but it creates more work and may or may not improve the overall quality. A direct second dissolution (of the unmelted powder), if for no other reason, should yield better results, simply because you have not included anything intentionally that must be removed.

Keep in mind, the purpose of inquartation is to permit dissolution of gold when there's too much silver present to permit dissolution directly in AR. By increasing the silver content (or it can be done with copper or brass, neither of which I recommend), the percentage of gold is too low to protect the alloy from dissolution with nitric. Your objective, then, is to get the gold in solution, nothing more. Inquartation makes it possible. Once finely divided, it's not really necessary, just as it's not necessary if you re-process a button of pure. It will dissolve directly in AR, it just takes more time than do finely divided particles.

Here's a 30.7 gram button this time around. Sorry for the poor picture quality. The cleaving would have been deeper but I was afraid of it sticking in my melting dish so it was dropped in water and has a pipe on the backside.

Very nice! Well done!

If it's any help, while I poured the vast majority of my gold as shot, making buttons, in particular the first few years, was routine for me. I learned that you could allow the gold to freeze well, then remove the button from the melting dish using a stainless tweezers. I'd use one tip to get under the button, then grip it and plunge the button in cold water. It would then get boiled for a few minutes in dilute sulfuric to remove traces of flux. There's a window of a few seconds before the temperature drops to the point where the flux (borax) in the dish solidifies, bonding the button securely.

Harold

 

[Geo]

wouldnt that be silver nitrate instead of silver chloride?

 

[Harold_V]

wouldnt that be silver nitrate instead of silver chloride?

Your question is not clear to me. Can you direct it to someone, or can you make it more clear what you are asking?

Harold

 

[dgr]

Geo,
Are you referring to this? "I've already created silver chloride."

Unfortunately, the way my gold came to me, it was mechanically locked onto the screw heads. The easiest path to get the gold off of the screws was with aqua regia. My understanding is the CL^- would react with the Ag⁺ and precipitate as solid silver chloride. As silver nitrate is soluble and silver chloride is not, the reaction would have went from Ag + NO₃ + Cl --> AgCl + NO₃. This assumption is substantiated by the test for silver nitrate which as I understand it is to drop a crystal of NaCl into the solution and watch for a precipitate.

 

[Geo]

you said you had a soup in the AR that included AgCl but in a nitrate solution wouldnt it be silver nitrate instead?

 

[Harold_V]

you said you had a soup in the AR that included AgCl but in a nitrate solution wouldnt it be silver nitrate instead?

If the solution in question is AR (aqua regia)---it is no longer solely a nitrate solution-----any silver present will have been precipitated as silver chloride-----aside from miniscule traces. The traces have been discussed endlessly, and are eliminated by dilution or chilling the solution. At that time, the silver precipitates as silver chloride.

A rule of thumb ------in acid, silver and gold can not be in solution at the same time. That is not true of a cyanide solution. That's what makes gold processing so easy, and why cyanide is looked upon as a recovery procedure instead of a refining procedure.

Harold

 

[Geo]

ahh.thank you for the info.i remember reading that someplace now,ill have to to find it and go back over it.hope theres no harm in asking noobish questions.

 

[Harold_V]

ahh.thank you for the info.i remember reading that someplace now,ill have to to find it and go back over it.hope theres no harm in asking noobish questions.

They are to be encouraged, if anything. There's a lot to remember when setting out to refine. We have all the patience and time required to help those that are willing to help themselves, so never hesitate to ask direction when you have applied yourself and may not understand a specific point. Those that refuse to lift a hand in their own betterment aren't going to be so fortunate. I'm (we're?) inclined to suggest they read Hoke.

Harold

 

[dgr]

Harold,
I wanted to follow up on this thread and thank you for all of the information you provided. I feel like my success in getting here is directly related. The assay on my 30 gram button came back at 98.62% Au. I don't have the percent of contaminants. I then processed and melted a 79 gram button. I tried to better follow the key processes you outlined. The assay came back as:

99.13 Au
0.126 Ag
0.256 Cu
0.192 Pt
0.062 Pd

Needless to say, I am tickled with my results. I also see room for improvement in my process. A longer wash in hot nitric will be incorporated in my future processes.

I do have a question on cementing the PGMs. Do these come out as slimes? What I found was it appeared the copper became flash plated with silver coloring. Although I'd say it was paler than silver metal. For now, I am going to drop all the metals out of my solutions, consolidate them and deal with them when I have a quantity.

Thank you again for all the time you give here.

 

[Harold_V]

Harold,
I wanted to follow up on this thread and thank you for all of the information you provided. I feel like my success in getting here is directly related.

Thanks, but credit goes to you for following advice. Many do what they want to do instead of what they are instructed to do. You appear to be able to put your ego in neutral and accept guidance. For that you are to be commended.

Needless to say, I am tickled with my results. I also see room for improvement in my process. A longer wash in hot nitric will be incorporated in my future processes.

You have been working with material that can be challenging. When you have palladium mixed with gold, it's always a little troublesome. I believe that as you progress, you'll come to understand how important proper washing is to the end product, too. Mean time, enjoy your success. You've earned it.

In regards to a nitric wash, my typical comment is to proceed with caution if you introduce nitric to values that have come from a chloride solution. It takes but traces of chloride to form AR, dissolving some of the values. I found that incineration eliminates the problem, but even prolonged rinsing with water may not.

A second refining tends to leave behind the vast majority of contaminants, assuming you use good practice. My second refined gold would typically melt with but a hint of surface irregularity, if that. A clean surface that doesn't oxidize is a good method of determining your degree of success. Also, the color of gold after melting can tell a great deal about purity. I had a small (home brew) ingot submitted that was obviously contaminated, evidenced by its color. Turned out it had but traces of platinum included, discovered upon re-refining.

I do have a question on cementing the PGMs. Do these come out as slimes? What I found was it appeared the copper became flash plated with silver coloring.

I experienced the flash plating with silver on many occasions, so, yes, it's likely that on occasion you'll have that very experience. That's the basis of electroless nickel plating, by the way.
I would assume that you would normally recover the values as black slimes, yes, and that's most desirable, as you can't recover the plating without considerable effort.

I can't really speak from experience in that I recovered the majority of my platinum metals in the stock pot, the only exception being those that were cemented on copper that followed silver. They were always the last to come down, and ALWAYS as a black deposit. It would darken the silver, so it was obvious it was being recovered.

Incidentally, if you are getting a recovery that you described, that may not be a good thing. When silver plated my copper bars, it was often difficult to remove. In some cases, I had to allow the silver to remain, allowing slightly exposed areas to continue recovering silver. Eventually the bar is consumed, liberating the rather substantial sheet of silver. I expect that if you have enough of either of the metals in solution to plate as you described, you may have enough in solution to recover chemically. Could be that evaporating to concentrate the solution may pay dividends. All depends on how much contamination by base metals you must deal with. A concentration of copper, for example, will grow crystals when the solution cools.

Harold