Non-Chemical precipitate

[champ110]

what is a good way to get the precipitate after dropping from solution?

 

[Harold_V]

I don't care what method you try, the one that will work best is to simply leave the gold powder in the beaker in which it has been precipitated and wash it after decanting the barren solution from which it came. Lots of good things come from this. One of them is that there is no risk of losing any of your gold, which should be washed before handling, anyway.

The real benefit of doing what I suggest is that gold that has precipitated from questionable solutions often comes down as very fine powder, hard to gather well, and often very slow to settle. By washing properly, the gold will begin to clump up and settle much quicker, so you not only improve the quality of the gold, you also improve it's handling characteristics.

If you follow proper washing procedures, when the gold is finished and dried, it can be handled perfectly well, without fine particles clinging to the container. If gold doesn't behave as described, it's not pure. I experienced that problem routinely when precipitating gold from bench filings. They were not melted and inquarted, simply boiled first in nitric, then dissolved in AR. Quality was always suspect, but the gold was also refined a second time to insure high quality.

I'm very narrow of mind where this subject is concerned. Handling your precipitated gold by any other means makes no sense unless you enjoy the struggle.

Harold

 

[Paige]

Harold_V

I know you use Sodium dioxide.

I can't get it, so I use SMB. Do you subscribe to the theory that subsequent AR then droppings to purify should utilize different precipitants?

Like 1st time use SMB
2nd use Oxalic acid
3rd use ???
4th go the DMG routew/ Oxalic acid again?

Other precipitants sound as though they might introduce additional metals in, which you are going to have to take out.

Paige

 

[Harold_V]

Harold_V

I know you use Sodium dioxide.

I can't get it, so I use SMB.

Same thing. I used sulfur dioxide, not sodium dioxide. As I understand it, SMB yields sulfur dioxide, which is actually doing the precipitation.

Do you subscribe to the theory that subsequent AR then droppings to purify should utilize different precipitants?

While I rarely practiced that process, yes, I subscribe to it. It makes sense, and could have solved one problem I had for all the years I refined.

When I processed (jewelry) bench waste, certain customers material always included something that followed the gold. I was never able to identify what the substance was (I'm not a chemist and had exhausted my bag of tricks) so I learned to use that gold as my added gold that was used in evaporation. The melting process seemed to eliminate the majority of what ever it was, but it was obvious it was there. The gold would melt with a little activity, with tiny sparkles flying off the powder as it melted.

If I simply re-refined this gold, the substance precipitated with the gold with each refining, although not completely. I assume that if I was to refine the gold several times, it would slowly be eliminated, but I was pleased with the process I was using, which, for me, was important, for it served a purpose and solved the problem at the same time.

The substance of which I speak showed in the wash as a brown liquid. It was far more soluble in water than it was in acid----the majority of it would wash out in the rinse instead of the acid boil. It was brown in color, and nothing I tried to determine what it was yielded an answer.

I would suggest to you that if you precipitate gold a second time, but do your preliminary functions properly, you should get very high quality gold, assuming you follow my washing procedures. I can't imagine the need for more than two refinings.

The most valuable thing any of you can learn is to precipitate gold from the cleanest possible solution. If there is no garbage to drag down, none will be. Dissolving base metals with gold, then expecting the gold to come down clean makes no sense. Look at it like this. If you drop an object in a bucket of mud, can you pick it out and expect it to be clean? By sharp contrast, if you drop the same object in a bucket of clean water, it might be wet, but you won't have added anything to make it dirty.

If you follow good work practice, you should be able to approach 4 9's quality by refining your gold a second time, even using the same precipitant. Just keep things as clean as possible in all cases----

You reach a point of no return, where regardless of how many times you refine gold, it will not get any cleaner because you're contaminating it in other processes. How you wash, handle and melt your gold is as important as how you precipitate the powder. Work with clean tools---including the torch tip. Keep one that is used solely for melting pure gold, and clean it often. Do not let it oxidize to the point where it sheds bits of oxide.

Like 1st time use SMB
2nd use Oxalic acid
3rd use ???
4th go the DMG routew/ Oxalic acid again?

My honest opinion?

Use SMB, working with clean solutions as I've already recommended. I wasn't thrilled with oxalic acid, so I tried it only once. Didn't like the results. If I was to recommend anything aside from SMB, I'd suggest you use ferrous sulfate for the first precipitation, the SMB for the second. I used only SO2 for years and got very acceptable results.

Other precipitants sound as though they might introduce additional metals in, which you are going to have to take out.

I agree. There are many substances that will precipitate gold, but they may or may not be selective. The field of choices is narrowed because we try to recover only the gold.

I wouldn't hesitate to use ferrous sulfate. I used it with good results, and found it washed out easily by my cleaning procedures. I moved away from its use only because it added so much volume to my processes. When you refine from beakers instead of plastic buckets, and you have a hot plate covered in beakers, with more waiting for a spot on the hot plate, you learn to conserve space so you can keep up with the work. Using SO2 from a bottle added nothing to my solutions, and allowed me to operate with greater levels of concentration. My solutions were so highly concentrated when I started the precipitation process that I had to use ice, otherwise the soluton overheated and the gold ceased to precipitate. It wasn't uncommon to precipitate 18 ounces of gold from a 4 liter beaker. The vessel, with roughly one liter of solution within, was filled with ice before introducing the gas. When the gold was down, the solution was warm. In this process, it is important that an ammonium hydroxide wash be included, to eliminate traces of silver chloride.

Once again, I'm posting a picture of gold that I refined. This gold was refined two times, both times precipitated with SO2. It was washed by the method I propose, and needed no pickle after melting except to insure that there were no traces flux that followed the gold when it was poured to make shot. It has to be very close to that magic 4 9's we all seek to achieve.

Harold

 

[Platdigger]

Wow! That is some nice looking gold there Harold. Do you remeber about how many ounces that was?
Randy

 

[aflacglobal]

Welcome platdigger. Harold, your making me hungry again. :wink:
Now where did i put that spoon and milk. :?:

 

[Platdigger]

Thank you for the welcome aflac. Great forum!

 

[Harold_V]

Wow! That is some nice looking gold there Harold. Do you remeber about how many ounces that was?
Randy

No, I have no clue. You can safely assume there's no less than 25 ounces there, however. It was poured from a container that holds 150 troy ounces. I poured enough for a good showing when I took the photo to send to a friend when we were discussing gold, and what I used to do.

Gold, when allowed to reflect light from one surface to another, repeatedly, takes on a beautiful color, as you may have noticed. That happens only when the gold is of high purity, with no oxides showing on the surface. Otherwise it is dull and dark.

My purpose in posting the photo was to emphasize that if the instructions I endorse are followed, each and every person on this forum can achieve a level of excellence that is to be admired. What better proof than to see the results of following the advice?

Welcome aboard!

Harold

 

[Platdigger]

Thank you Harold. I can tell from reading your posts, you are a very good mentor for anyone interested in this buisness. I apreciate your time given to helping others learn.
Randy

 

[EVO-AU]

Harold:
Enjoy your posts immensley. Only been into leaching about ten months. Circuit boards do not interest me. At present I am working with clay. I read about using coffee filters and like the sound of your read, but I do not lose anything - so far as I know - filtering the precips. Any ideas about the use of coffee filters ?

Thank you much, EVO-AU

 

[Harold_V]

Any ideas about the use of coffee filters ?

Depends on the application. I used S&S sharkskin filters for some operations, but I wouldn't consider them, or coffee filters, for filtering final solutions, where you're attempting to remove anything that is not in solution. The sharkskin filters and coffee filters are about identical, aside from size. I used 32 cm filters.

When I processed, I used a Whatman #2 for general filtration of my chloride solutions, and a Whatman #5 when I re-refined. They are expensive, but the do what's expected of them. The sharkskin filters were generally used when filtering polishing wastes and floor sweep wastes. The resulting solution was then evaporated, then filtered a second time with a Whatman #2 prior to precipitation.

When working with solutions that are difficult to filter, a #5 makes it impossible to filter, and a #2 isn't a lot better. They are extremely good at trapping minute particles, and plug easily. If you choose to use them, you must learn to keep your materials clean, which should by your objective, anyway. When you are against a solution such as I describe, a coffee filter, or a sharkskin, will often bail you out----but -----remember-----it's allowing unwanted substances to follow the solution. That is contrary to the purpose of filtration.

If you're working with solutions that are difficult to filter, there's a wonderful trick you can use to eliminate the problem. Take note that incineration is very much a part of the process.

Prior to dissolving your material in AR, but after having dissolved base metals with nitric acid, incinerate to eliminate any carbonaceous materials, then heat until there are no signs of fumes coming from the lot. When the contents have cooled, my usual procedure was to run them through a screen to remove any large items that may require inquartation, then to give the balance of the material a boil in HCL. You don't recognize that much happens, but the process dissolves and holds in suspension troublesome compounds that make filtration difficult. This very process is highly recommended when processing gold filled materials, which often contain traces of tin and lead. Tin, in solution, can be nothing short of a bitch to filter.

After boiling for a reasonable period of time (10 minutes), stirring occasionally to prevent the material from burning to the bottom of the beaker (that happens easily with materials such as polishing wastes), remove the beaker from the burner and fill it with tap water, stirring well to dilute the acid. After it has settled well, decant by siphoning, and repeat the rinse cycle with tap water. There is no need to filter the solution, which can be discarded after testing (with stannous chloride) for values. By incinerating, all traces of other acids should have been eliminated, so the HCL shouldn't dissolve anything of value, palladium oxide being an exception.

Coffee filters are a cheap and readily available filter, but not necessarily well suited to filtering solutions of precious metals. That becomes very obvious when a Whatman #2 is used. In defense of using a coffee filter, it is better than nothing.

Harold

 

[scavenger]

Hi Harold, Just a question about the brown liquid u mention in a previous post.

The substance of which I speak showed in the wash as a brown liquid. It was far more soluble in water than it was in acid----the majority of it would wash out in the rinse instead of the acid boil. It was brown in color, and nothing I tried to determine what it was yielded an answer.

I get this a lot. I thought it was fine powder so I let it settle. Needless to say my washes take along time. Also concerning the ammonia wash, after I do one the ammonia darkens and takes ages to clear. Is there a faster way and is there a danger of explosion from ammonia and silver chloride, if so what is the best way to make it safe? Sorry about all the questions but u seem to have all the best answers. Much appreciated. Dave

 

[lazersteve]

Dave,

If I may interject a handy treatment for the ammonia washes which contain silver chloride.

After pouring the wash of brown ammonia solution thru a layer of 3-4 coffee filters, add HCl to the brown ammonia solution and viola the silver chloride drops out as a nice fluffy white powder and the solution clears quickly. This develops a little heat so perform acid the addition slowly. After filtering the settled silver chloride out the clear solution is merely ammonium chloride in water.

Steve

 

[Platdigger]

So Steve,
At this point are you saying the silver is safe? No chance of forming explosive silver ammonia complexes?
Randy

 

[lazersteve]

If you add the enough acid to drop all the silver out as silver chloride soon after filtering you are safe. The acid drops the silver as silver cholride almost instantly. It takes a short time for the silver chloride to settle.

The first time I ever did it I was amazed at how fast and completely the solution cleared.. the miracle of chemistry!! :lol:

Steve

 

[Harold_V]

Hi Harold, Just a question about the brown liquid u mention in a previous post.

The substance of which I speak showed in the wash as a brown liquid. It was far more soluble in water than it was in acid----the majority of it would wash out in the rinse instead of the acid boil. It was brown in color, and nothing I tried to determine what it was yielded an answer.

I get this a lot. I thought it was fine powder so I let it settle.

In your case, it very well may be. The material of which I speak does not settle----it is something dissolved, a part of the solution.

Needless to say my washes take along time.

I've stressed the importance of precipitating from clean solutions. Your prolonged wash cycles is one of the good examples of why you should.

When you precipitate gold from dirty solutions, it's far less likely to agglomerate, and usually doesn't. Very dirty gold is difficult to wash, and never achieves a level of purity that may be desired, although it is well improved by the wash cycle.

By following prescribed procedures, you can eliminate a lot of the garbage that is now going into solution with your values. A part of that is learning to incinerate and do proper washes prior to dissolving the gold. The alternative is to precipitate from dirty solutions, secure in the knowledge that you're recovering your gold for further processing. Wash it well enough to eliminate the majority of the impurities, then re-process it with AR. The second precipitation will usually provide gold that is light in color and agglomerates well.

Any of the gold I washed after a second precipitation was never a problem. It agglomerates fully, so there is nothing to settle. The final wash cycle, HCL and water, didn't even change color. It came out as clean as it went in. Remember-------even under this condition, I do not claim to have achieved 9999 quality. I was close, of that there is no doubt, but it's very difficult to eliminate that last tiny bit of contamination, or to keep it out as you handle your gold.

Also concerning the ammonia wash, after I do one the ammonia darkens and takes ages to clear.

That pretty much confirms my hunch. My ammonia washes, at worst, turned a hint of blue, exposing the presence of traces of copper. The gold, as precipitated, was much cleaner than that which you describe.

Is there a faster way and is there a danger of explosion from ammonia and silver chloride, if so what is the best way to make it safe? Sorry about all the questions but u seem to have all the best answers. Much appreciated. Dave

I was never concerned about the value of the traces of silver, and disposed of the ammonium hydroxide immediately. I knew that at best there would be nothing more than traces, and not worth the effort to recover them, particularly when you consider that silver, for the most part, used to be valued quite low. If, in the process of washing my gold, I discarded more than an ounce of silver through the years, I'd be very surprised.

As to the safety of recovering it from ammonia, I'd suggest that Steve has provided far more information than I'd have been able, considering I never experienced the process.

Harold

edit: changed spelling to correct typos.

 

[scavenger]

Thanks for your answers Harold. This computer scrap can be difficult to thoroughly clean. I have read that adding sulphurous acid to AR will kill the nitric and drop the gold as well. It focuses only on the gold unlike SMB which
will drop everything if to much is added. Have you had any experience with this? Cheers Dave.

 

[EVO-AU]

Harold:
Whew, going to take some digesting of your post. As I am a rank beginner, ( leaching and smelting, anyway ) I am going over your words very carefully. I've read some of your other posts and do admire your knowledge and willingness to help others.

Thanks much and I'll get back to you. Phill