Processing anode slime from parting cells?

[peter i]

The fun is in the slime (that goes for literature as well as parting cells), but how do you get it out?

My system uses a combustible bag in the basket of my little silver parting cell, and my strategy so far is:

- Let it drip as dry as possible
- Dry it in the oven at low heat (not the wife’s, but an old toaster oven, dedicated for playing)
- Ignite the bag (anything combustible soaked in any nitrate and being thoroughly dry should respond well to fire)
- Treat with dilute cold AR to dissolve gold selectively
- Treat with hot, strong AR to get the PGM’s

Is there a better method than this?

 

[Harold_V]

You're going to have to address the residual silver that makes up the majority of the slimes. Otherwise, the silver will have a tendency to precipitate dissolved values, and, in general, make a mess of things. Much of it will slowly convert to chloride, so you may as well eliminate it first.

I mentioned in a different thread that the big boys boiled their slimes in cast iron kettles. I chose a different route. I'm not suggesting, even for a moment, that it is the best way to go, but it worked for me.

I started with water and nitric, and dissolved the silver. Because it's finely divided, it goes readily. Problem is, so, too, will any palladium that may be present, and some platinum. In order to prevent an endless recycling of the metals, I'd filter the solution, or allow it to settle well, then decant. I then introduced HCl to the solution, and precipitated the silver as a chloride. That was well washed to remove the traces of platinum and palladium. I boiled the slimes until everything that would dissolve did, then rinsed them well, with the rinse added to the other solution already separated. Once the slimes were free from silver, I dissolved them in hot AR, then did the customary evaporation, including the solution from the silver chloride, which contained some of the pt. group, as mentioned, above.

I tended to remove gold from the solution first, but only because it's far easier to wash precipitated gold than the salts of platinum and palladium.

The metals that come from this process are rarely very clean, so a re-refining is in order if purity is a concern.

It might be interesting to hear how you pursue your values. Remember, I'm not educated in chemistry, and came up with solutions with the limited knowledge I had. My method may well be very poorly directed.

Harold

 

[peter i]

Thanks, that changes the strategy to:

Slime:
- Let it drip as dry as possible
- Dry it in the oven at low heat
- Ignite the bag
- Dissolve as much as possible in dilute nitric acid, part in liquid and solid phase.

Liquid:
- Precipitate silver as chloride, wash, test water phases for platinum/palladium* (isolate if any is found)
- Reduce silver chloride once enough is pooled

Solid phase:
-Treat with AR to dissolve gold and remaining PGM’s
-Discard insoluble rest (ash, carbon and dirt)
-Remove excess nitric acid
-Dilute
-Reduce
-Wash and dry
- Refine “gold” further once a sufficient amount is collected.

Cold dilute AR should not dissolve platinum, but does this apply with finely divided platinum?

*Shor: "Platinum group metals will also show up on the stannous chloride test. Platinum turns red, palladium turns orange and iridium turn blue-black".

 

[Harold_V]

Thanks, that changes the strategy to:

Slime:
- Let it drip as dry as possible
- Dry it in the oven at low heat
- Ignite the bag
- Dissolve as much as possible in dilute nitric acid, part in liquid and solid phase.

Good so far, but when you ignite the bag, it won't burn as well as you suppose. Much of the silver nitrate appears to be reduced to elemental silver---which impedes burning.

I'll interject my logic here, which will address one of your comments, below. Be certain to heat the bag to the point of complete combustion, including eliminating any traces of carbon. Heat it with a torch if you must, but try to not leave any carbon behind.

Liquid:
- Precipitate silver as chloride, wash, test water phases for platinum/palladium* (isolate if any is found)
- Reduce silver chloride once enough is pooled

If, by chance, you find no palladium or platinum in solution, you are better served to recover the silver with copper. Precipitate the silver as a chloride only if it is contaminated with the Pt. group. Test with stannous chloride.

Solid phase:
-Treat with AR to dissolve gold and remaining PGM’s
-Discard insoluble rest (ash, carbon and dirt)

When you say discard, I would suggest you NOT discard, but dry, incinerate (to consolidate to a small volume, but most importantly---to eliminate acid fumes that will corrode cherished items in the proximity). If you save these substances, you'll be pleasantly surprised to find they will yield considerable value. It's nearly impossible to wash all values from such materials, but easy to recover them via furnace. Remember my comments on a savings plan?

There is one real good reason to never discard anything that touches precious metals. There will be times when some of it will not be totally dissolved, and often the mud contains traces of silver chloride. There are also instances where you have evaporated the solution well and it is unstable to the point where there will occur some spontaneous precipitation of values. That was not a regular occurrence, but I witnessed it on several occasions. You may not see it if there is considerable flocculence, so it could be easily lost. That material is perfect as a mix, for recovering values. By reducing the chloride (by furnace), the silver becomes the collector, and forms what often is an almost perfect alloy for parting. After more than 20 years, I recovered several hundred troy ounces of alloy. As I said, it was an excellent savings plan.

Carbon, if active, is commonly used to strip gold from cyanide solutions. Allowing carbon to remain when you incinerate has the potential to absorb some of your values. It is for that reason that I suggest you incinerate until it has been totally consumed.

Cold dilute AR should not dissolve platinum, but does this apply with finely divided platinum?

When finely divided, platinum will also dissolve, albeit at a slow rate. You likely know that platinum in the presence of silver is also slightly soluble in nitric. Separating silver from the platinum group can be interesting, with some recycling of your recycled material involved. I never tried for perfect separations, choosing instead to remove that which came easy, then allowing the remains to be recycled with the silver once again. Eventually you recover all the values.

I might suggest you do not allow the pt. group to concentrate too highly, especially if your silver contains gold as well. If the slimes are not free to fall from the anode as it digests, but form a shell instead, when the condition becomes severe enough, you'll deplete your electrolyte, then start dissolving palladium. I'm not sure if it co-deposits with the silver, or not, but it gives you cause to start over. Should you experience this condition, one of the indicators is a rather obvious shift in the color of the electrolyte.

Should you find yourself in that position, it isn't necessary to melt the contaminated crystal. It can be placed in the basket for a second refining, assuming you can make a good electrical connection. I accomplished that by placing an anode on top, with my "doorknob" on top of the anode. It works well. I did it a few times when I found my silver slightly contaminated with copper----not stopping soon enough to change electrolyte. The yield, especially if you make all new electrolyte, is exceptionally clean silver.

Back to the anode, which may contain a percentage of other values, it often will create a hard, black shell as the silver is transferred. I had a policy of scraping my anode each time I knocked down the crystals. I used a porcelain spatula, cleaning the bottom surface of the anode well, then I'd remove the slimes from the basket using an acid dipper. Using the dipper demanded a filter material that did not permit the slimes to penetrate the bag. I used a commercially prepared cotton filter material that appeared to qualify.

Scraping the anode was a necessary step for me because I intentionally used my silver as the carrier for the Pt. group. Most of it came as traces, and was not possible to recover directly. By inquarting, it automatically followed the silver, even the platinum, which I already mentioned would dissolve with just nitric in the presence of silver.

You may experience different reactions if you work cold. I heated all my solutions, needing all the speed I could muster. Otherwise my work would not get done as scheduled. You may have the luxury of working cold and slowly if you're just doing small personal lots, with no deadlines to meet.

*Shor: "Platinum group metals will also show up on the stannous chloride test. Platinum turns red, palladium turns orange and iridium turn blue-black".

Might I suggest to you that you divorce yourself from Shor? I have no axe to grind, but any time you use proprietary systems, you are locked in with buying their products, which are often very high priced. If that is not the case, no problem.

When testing with stannous chloride, the reactions you will see will not be the same as above. Gold will be purple to black, but will leave a purple stain on a spot plate. That's a sure way to discern the presence of gold, which can be confused with palladium under strange circumstances. In such a case, a test with DMG for palladium, and one with ferrous sulfate (for gold) can detail what is present.

Palladium can vary from green through blue to brown, depending on concentration and the relative condition of your stannous chloride. Platinum resembles coffee in color, and can test lighter, depending on concentration and the condition of your stannous chloride.

Hope some of this helps if you change your procedures.

Harold

 

[peter i]

Thanks.

I did not wash the filters, but just lifted them out, allowed them to drip, then dried them at a very low heat (50°C), and ignited them over a steel bowl.
Before drying them actively, the stayed moist. Probably the combination of salts and fibre was more or less hygroscopic. When moist, they probably would not have burned.

They burned surprisingly well! Not quite “I may have burned down the lab, but I got some nice data”-burn, but far more vigorously than I expected.
Exhaust running, working over a bowl and holding them with a pair of tweezers, there was no risk and no loss, just a WOW! It was comparable to cloth impregnated with potassium nitrate.

There was a nice grey ash left behind. I’ll store it until I have finished this round of electrolysis, and then refine it all in a single batch.

I used to have a jar marked “Noble Gunk” for anything that was impure, but could have a valuable content. You have convinced me, that I should have that again (I’ve been a little too busy for a couple of years to do any refining worth mentioning).

If there is no PGM’s I’ll precipitate with copper, that’s a good point! Thanks

I never married Shor, but I’m always happy to glean information from wherever possible. When a chemical is sold under a smart name like “Storm precipitant” it is a sign to me, that it must be available in bulk at a low cost. The MSDS tells you what it is, and off we go.

 

[Harold_V]

They burned surprisingly well! Not quite “I may have burned down the lab, but I got some nice data”-burn, but far more vigorously than I expected.

Mine burned well too, even when damp. The only problem I recall was incomplete combustion, leaving behind some carbon. I won't discount the fact that it has been many years since I last did any of this ---spring of '94, in fact. Old age and time may well be taking a toll on my memory. I may be recalling something totally unrelated

There was a nice grey ash left behind. I’ll store it until I have finished this round of electrolysis, and then refine it all in a single batch.

That's certainly what I'd expect. If you see no signs of carbon, the job was done, and very well.

I used to have a jar marked “Noble Gunk” for anything that was impure, but could have a valuable content. You have convinced me, that I should have that again (I’ve been a little too busy for a couple of years to do any refining worth mentioning).

I certainly understand a busy schedule---as mine once was.

By incinerating and storing the wastes, they aren't troublesome, and having a reasonable volume of them to process makes it worth while. That's why I highly recommend storing instead of processing regularly. Besides, if you haven't had the pleasure of reducing such things with a furnace, I'm sure you'd really enjoy the experience. To give you and idea of how much you might expect from waste such as this, simply clean a badly contaminated melting dish, using soda ash. Make it one that has had values melted regularly, with black, sticky slag remaining. The small button of metal that magically appears from what you'd swear was barren is always fun to experience.

While I respect your education in chemistry, I think I can be of assistance in providing you with an excellent recipe for flux. I did a lot of reading before I concluded what would work for me in that situation, and achieved a recovery that was so good that my slag was too low in value to process with litharge. I know it's a good one as a result.

If there is no PGM’s I’ll precipitate with copper, that’s a good point! Thanks

Welcome. I wanted to clear the air, because my first comments could have easily been misconstrued. I didn't want to suggest you jump through hoops that were not necessary. It's always easier and faster to recover silver with copper, so I followed the alternate only if there was platinum group included and I wanted them sorted.

I never married Shor, but I’m always happy to glean information from wherever possible. When a chemical is sold under a smart name like “Storm precipitant” it is a sign to me, that it must be available in bulk at a low cost. The MSDS tells you what it is, and off we go.

Sigh! That's where I envy you your education. I could read those charts and glean very little.

Have you used the Shor system for refining? While I'm familiar with its existence, I don't have a clue. The only thing I can comment on is that one of my old customers is now refining his own gold. He started out with what I believe to be the Shor system, but quickly abandoned it in favor of nitric and AR. Thus far, he's been able to buy nitric, although I haven't talked with him for about a year now. That may have changed.

Harold

 

[peter i]

I have not used the Shor system, considered it once, but dropped the idea again and stuck with AR. The problem was, that I could not find any independent sources evaluating it, and to some degree, it seemed like they didn’t tell the whole story. I have not refined that much, I guess it will not sum up to more than approx 4 kg gold in total.

Education is good, if it is taught with sense and a purpose. Unfortunately the focusfar too often is on the tests, not the application and solving of real problems. Far too many of our young students have high grades and little practical sense. They solve theoretical problems concerning drugs, toxins and explosives without knowing it!
Those who have both brains and hands have no problems finding a job.

… and I’d love to hear about the flux!

Regards
Peter

 

[peter i]

Dissolved as much as possible in nitric acid, and had no positive test for platinum or palladium, so I precipitated with copper.

Treated the insoluble remains with AR until solution until no longer tested positive for gold, neutralised the nitric acid with urea and precipitated with SMB.

Washed with water, ammonia, muriatic and water to end up with 0.2 grams of light brown gold powder.

It seems my silver was "cleaner" than I expected. At least i now know, that my silver is very pure.

 

[Harold_V]

… and I’d love to hear about the flux!

It appears I overlooked this somehow.

I've posted the flux formula before, but you may have missed it. Here's a repeat:

(3) parts waste material
(1 1/2) parts silica sand
(3 1/2) parts soda ash
(1/2) part fluorspar
(2) parts borax
water

A little experimenting will tell you how much water. It isn't critical. I mixed the components, then introduced enough water to make a slurry. It reacts fairly quickly, setting hard. That serves to lock the values within the flux so they are not lost to turbulence in the furnace. In my case that was important because I melted in a reverberatory furnace, with the flame impinging directly on the charge.

Once the slurry was created, I poured the material inside old plastic lids from ice cream buckets. The idea is to allow them to dry before introducing them to the furnace. The resulting cake was easily broken in smaller pieces, so they would fit the discharge vent of the furnace. Dusting is virtually eliminated.

Your circumstances may be different, but charging the material to a crucible would work similarly. Do allow for some heaving as the material melts. Once the conversion is completed, the charge will settle down and be tranquil. Pouring to a cone mold is a definite advantage.

Any sulfide layers that come from this process should be re-melted, with scrap iron added. A couple lengths of rebar serve the purpose well. What ever is chosen must be able to be removed when the conversion is completed. This process will liberate any values that may have reported in the sulfide material. It stratifies when you pour the original heat, with slag on top, sulfide layer next, then the dorê at the bottom. The layers are typically very easy to separate, especially when a cone mold is used.

Do remember, I had a considerable amount of silver chloride in my waste material, which was intentional. I used it as the collector of greater values. Your material may behave totally differently.

Harold

 

[Macgiver]

Hello Harold,

Based on what I have read so far I feel I should address you as Grand Wizard Harold.

The flux slurry you suggested solves a huge hurtle of our 200-600 mesh material getting sucked out of the furnace. THANK YOU. I will let you know how it goes.

I have another question for you... do you see any difference (other than the obvious) is using an electric or a tort furnace as far as the results you will see in recovered values? Some of the old timer miners in the area swear by one or the other as the ONLY way to get values out our ore. Would the current or EMF or the alignment of the milky way and the heavens above have anything to do with the ability to drop the metals? In my mind if the metal is there... it is there and you should not need any magic furnace to deliver. Am I on track?

Thank you again.

CW

 

[Harold_V]

I have another question for you... do you see any difference (other than the obvious) is using an electric or a tort furnace as far as the results you will see in recovered values? Some of the old timer miners in the area swear by one or the other as the ONLY way to get values out our ore. Would the current or EMF or the alignment of the milky way and the heavens above have anything to do with the ability to drop the metals? In my mind if the metal is there... it is there and you should not need any magic furnace to deliver. Am I on track?

My experience in processing as I discussed is limited to gas fired furnaces, but logic tells me the heat source shouldn't make much difference. I did not rely (knowingly) on the flame for any specific function aside from providing heat. However, the flux in question is very aggressive and is likely to destroy a fire brick furnace, which is typical construction of electric furnaces. If you can control the amount of heaving that I spoke of, you may be safe in using one. I highly recommend your first attempt be with very little material, leaving at least 250% room for expansion. Once the operation is complete, it's very tranquil, but it's quite reactive while being melted.

Harold

 

[Macgiver]

Thank you.