Non-Chemical percipitate question

[Lino1406]

May I suppose new leadless
solder will enable getting
rid of tin at the beginning
of reclammation process,
before any HNO3 is introduced?
Lino1406

 

[eagle2]

Hi Lino; I think I have heard of it. Do you know the composition of metals in it?

Still tin will be on old boards your scrapping. Most times tin or nickel is also plated on copper, then a gold plate is put on. So you still have to contend with Tin.

I think most go the easier route and just melt whatever is precip. and accept whatever their refiner reports. I fuss too much with my precips. I try to send 99.9+ to mine. Then I know I`m not getting ripped off. ---- Al

 

[eagle2]

Going back to the mystery white powder, If you used sulfuric acid to make nitric, there would be Sodium Sulfate in solution.

Besides Tin, The white powder could be free Sulfur. Maybe reduced by your SMB. I`m not sure of this, but you could test this by drying the precip and heating it. Sulfur melts and burns easily, the gas produced is SO2 (poisonous). The similar smell you get when using SMB. Be very careful with this. Use only a small sample. Sulfur is a part of old gunpowder formulas! -- Al

 

[eagle2]

Just want to add, if you didn`t use SMB yet, Its probably not sulfur.

 

[Harold_V]

I hate to filter! This is the first place you start to lose gold.

Only when you discard the filter.

Harold

 

[eagle2]

Hi Harold. Thank You. I must have 20 pounds of filters I`ve been saving for years.

I recently bought a large cheap household SS bowl. I guess you add a little alcohol and burn the filters and then AR the residues. Didn`t someone say you need to muffle this or cover this somehow, so the ash dosn`t float away? ----- Al

 

[Harold_V]

I had a different approach, but my refining conditions were likely very much unlike yours. The vast majority of material I used to process was waste from the jewelers bench. As a result of processing alloyed gold, I inquarted routinely, and had traces of silver chloride in all my wastes. Rather than get involved in recovering the traces of gold chemically, I saved all my wastes, which were well incinerated, then stored dry. That's important if you don't want a rusty environment.

To make a long story short, just before closing the doors on my refining business, I ran my many years of accumulated wastes by furnace reduction. The traces of silver chloride served perfectly well as a collector of accumulated values and helped affect a very good recovery. An assay of my slag indicated a value so low that it was not worth further processing----not even with litharge. The recovery of values over that long span of time was staggering---more than 200 ounces of gold, but bear in mind I processed a huge volume of gold annually. The losses, per filter, were relatively small.

Regards incineration-----my process was to heat the filters in a shallow pan, in my fume hood, using a gas hotplate. Once the material burned, I raised the heat on the pan until the bottom was red, at which time carbonaceous residues were consumed. It's virtually impossible to get compete combustion otherwise. It was much like watching charcoal burn, albeit in much smaller quantities.

You are correct in thinking that there will be some losses due to smoke and other discharges. My hood was filtered, and was cleaned about every second year. The recovery of gold from the hood alone was well worth the effort. Losses to dusting should be expected----but--again, remember, I processed a lot of material annually. On a hobby basis, the losses would not be significant, although certainly worth recovering if possible.

Given your circumstance, it might be logical to incinerate as best you can, then process with AR after a good wash with HCl. That will insure that the material will filter easily. Otherwise, you may discover that your gold chloride, recovered from the residues, won't filter worth a damn. I've had a liter of chloride solution take more than three days to filter-----which is the reason I came up with the HCl wash process. I never again suffered with filtration problems.

In reality, there will never come a point where you should discard filters, or anything that makes intimate contact with your values. If nothing else, incinerate them and store them for the future, at which time you may do a furnace reduction as I did. You will be pleasantly surprised and rewarded for your efforts.

Edited to include:
As an add-on-----a bowl isn't very good for incineration. You'll find the contents don't get enough oxygen. A fairly shallow pan serve much better. Go to any of the second hand stores (Goodwill, for example) and look for old fry pans. Steel pans work, but shed oxidized iron and don't have a long life. Stainless pans last for considerable time. Do not try aluminum-----it will melt at the temperatures involved in proper incineration.

I removed the handle to avoid doing stupid things, like picking one up while it was blistering hot, and used a wheel weight pliers to handle my pans. The one I had was an early tap, with no hammer on the end. The strange offset of the pliers worked very well, and was the best thing I discovered for the purpose.

Avoid even trying cast iron pans. Their mass will make it impossible to achieve a red heat, and it will likely crack from uneven heating in any event. Once you've given this a try, it will all make sense.

Hoke talked of "pouring on the gasoline"------which is, of course, absolutely stupid. Do not use any accelerants----just get the pan hot and allow it to burn on its own. Also, be careful if you happen to incinerate any of the plastics, such as garbage bags. They appear, at first, to not burn well. They are reduced to oil upon heating, then when they're hot enough, they burn with a vengeance. Early in my learning curve, I set my garage on fire by that process. It resulted in building a fire-proof hood. Be careful!

Harold

 

[eagle2]

Thank You. Many good points. No doubt from hard experience.

Your HCl wash. Did you use concd HCl or diluted like 6 Molar? Did you heat and filter that from a beaker, or soak and stir, then decant the solution. The PM`s would still be in the residues and anything that dissolved would be base metals?

Also the carbon and the heat produced in the incineration would have reduced many compounds to their metals. So the HCl could redissolve some base elements.

I wonder if a bit of H2O2 added to the HCl wash would improve the dissolution of the base elements?

Or did you just use the HCl wash to float away any fine ash that remained that would plug up the filter?

Al

 

[Harold_V]

Your HCl wash. Did you use concd HCl or diluted like 6 Molar?

Because I lack proper education, my approach was more of one from the perspective of a person following a recipe. Many of the things I did I did because I was so instructed. Perhaps that will help you understand that I did little of this from a scientific standpoint, although I was eager to follow prescribed procedures. So then, in answer to your question, I used tech grade hydrochloric for everything but the final wash when I re-refined my gold. As far as washing materials like your filters, I'd have incinerated them, screened to remove any potential large items, swept a small magnet through to remove any magnetic particles (which were all dumped in the stock pot), then the material would be placed in a beaker, and covered with roughly 50/50 HCl and tap water. I would then boil the lot for a period of time, usually simply making visual observations that the material had been changed. It's usually obvious. One thing to remember. When you're processing a large amount of material that is akin to dirt, it often will cook dry on the bottom of the beaker, which then forms a very hard deposit, a combination of previously dissolved elements and solids. That usually results in a broken beaker, so my advice to you if you decide to pursue this as I suggest, be certain to keep stirring your material as it heats, and even when it is boiling. Even then, the occasional hot spot will overheat the beaker, which will crack when stirred.

Did you heat and filter that from a beaker, or soak and stir, then decant the solution.

Once satisfied that I had dissolved anything that would, the beaker would be removed from the heat and filled with tap water, stirred well, and allowed to settle. Once settled, the solution would be decanted (siphoned, not poured, otherwise you stir up the solids), and rinsed (tap water) at least once, more if necessary. I allowed the color of the rinse water to determine if more rinses were required. My experience indicated that if the solution was reasonably free of color, the gold chloride solution that came from the next step was easily filtered, and that was my objective.

The PM`s would still be in the residues and anything that dissolved would be base metals?

You may even find some traces of base metals after the fact, but the majority of them appeared to be removed in that the gold chloride solutions from such an operation tended to be yellow, not green or brown. This system was very effective in removing base metals as well as compounds that were unknown to me that made filtration difficult. It's entirely possible some of them were not even metallic in nature, although I have no way of knowing that.

Also the carbon and the heat produced in the incineration would have reduced many compounds to their metals. So the HCl could redissolve some base elements.

I have to assume that's correct. For sure, you'd remove copper and iron. If the color was blue, I never bothered to test----secure in the knowledge that anything I processed would not be found in a blue chloride solution.

I wonder if a bit of H2O2 added to the HCl wash would improve the dissolution of the base elements?

You'd likely have to talk with one of the fellows that are well versed in chemistry. My personal advice, based on not knowing, is to not do so. What I did worked very well---and I can't see where anything you might do would improve the results. It was, for all practical purposes, trouble free. I used this method even when processing large volumes of eye glass frames, which can be very trying when run in concentrated solutions.

Or did you just use the HCl wash to float away any fine ash that remained that would plug up the filter?

As I've said, there are many substances that are dissolved, many of which I likely didn't understand.

Remember----as long as you've incinerated well, nothing of value aside from palladium oxide can be dissolved in straight HCl (I'm open to correction if I'm wrong), so don't be shy about just attacking the lot as I described. If there's anything of value dissolved, it can be recovered easily in the stock pot, so you can't get in trouble with this process.

When you boil and stir material of this nature, your stirring rod will tend to scratch the hell out of your beaker. If you have a variety of beakers (or other containers), it might be in your best interest to set one aside to be used strictly for operations of this nature. Once scratched, they are not well suited to precipitation. Gold tends to adhere doggedly to the scratches, making total recovery difficult.

Harold

 

[eagle2]

Your remarks match my experiences, too. Gold does tend to start precip on scratches in the beaker!

I`m not a chemical graduate, but I did study my college chemistry books.

50/50 HCl and water is close enough to 6 molar for HCl.

If you heat a solution with a lot of heavy residue or heavy gold precip, in the bottom to near boiling, It will "bump", so you better stir anyway. I`ve lost gold when a bump spurted a bit half way up the wall! Needless to say, I like to cover those beakers with a watch glass now. If you stop stirring for a moment keeping the stirring rod sitting in the beaker does help reduce this.

Thanks for all your help! Happy holidays!

Al

 

[Lino1406]

Hello Al,
Sorry if I was misunderstood. I meant
lead is preventing tin dissolution by HCl
and therefore the new formulas may
help. Some that I saw include Sn-Bi
or Sn-Ag, where the co-element consists
less then 5%, against 37% of lead in
the classic solder.
Lino1406

 

[eagle2]

Hi Lino: Oh I think I see what you`re referring to. Doing the base dissolution with HCl instead of Nitric acid. Its not done with solid base metals, because its slow and many metals don`t dissolve. With just plated pins with a bit of solder on them nitric or a electro-strip cell is still my choice. You might try an experiment on the new solders and see if HCl will work.

I didn`t know lead in solders was inhibiting dissolution in HCl. Merck`s index states lead and tin dissolve in hot concd HCl. I think, any silver in the solder would interfere or slow or stop this, anyway.

You will still run into Tin plate under the gold plate and some Tin alloyed in the Copper.

Boiling dilute Hydroxide will clean your scrap and prepare the surface for acid treatments. But you`re getting into so many pretreatments, a batch will take forever to finish.

Al

 

[Palladium]

8) 8)