Metastannic Acid Experiment

[jeneje]

I have been doing some low grade pins in HNO3(nitric), as we know it creates Metastannic Acid and it is hard to get the gold foils. I have found an easy way to rid the Metastannic and its works for me. Here is the process i used today along with pics, The steps are as follows,

Put the gold bearring Metastannic into the reaction vessel.
Add water to just above the material about 1/2 inch.
Add 1/2 teaspoon of lye.
Heat solution(DO NOT BOIL) you will see a reaction of the lye change colors it will cheese up to a fluff and then change to a brown material and settle to the bottom.
While warm decant and filter the solution as much as you can. It will be Brown.
Add water to the remaining solution NOT MUCH.
Add HCL to the solution, this will change to a yellow / green.
Decant and filter - your trapped gold will be free and settle in the filter. Use the same vessel and filter as before to decant in.

Hope this helps someone.
Ken

update; Using the procedure above will put gold into solution, just done a test with stannous and its positive, Done a bigger amount and it works for a leach solution on Metastannic for micro gold removal. More tests are needed to confirm.

 

[Lino1406]

Well done!

 

[NobleMetalWorks]

Nice trick...

I recently had to deal with gold foils in a copper/Metastannic Acid solution.

Metastannic Acid doesn't dissolve in AR, HNO3 nor HCl.

I digested contacts in Nitric Acid, I did not know there was tin under the copper that was under the gold. I ended up with Metastannic Acid. I filtered off the Copper Nitrate, washed the solids which were metastannic acid and gold foils. Once the solution was free of copper nitrate, I then dissolved everything in AR, then filtered the Au pregnant solution, rinsed the material in the filter with water to make sure all values are out, rinse the Metastannic Acid into another beaker with water, test for Au, if positive, then let the Metastannic Acid settle to the bottom of the beaker, decant the liquid, wash, rinse, repeat as many times as needed. I used 5 gallon buckets with plastic cullenders that fit across the mouth of the bucket perfectly with small handles on either side that prevent it from falling into the bucket. I use restaurant size coffee filters for are about as big around as the 5 gallon bucket, a little larger, but fit perfectly in the cullenders. Far better to filter this way than small filters. You are able to easily rinse the Metastannic Acid this way.

Scott

 

[Geo]

that is a round about way to do it chemically. there is one simpler way to rid material of H2SNO3 (hydrated tin oxide) besides removing tin before processing, is incinerating the material. when you heat the material to a red heat, it will drive off the extra oxygen and reduce the tin oxide back to metallic form. then it can be removed with hcl.

 

[goldsilverpro]

that is a round about way to do it chemically. there is one simpler way to rid material of H2SNO3 (hydrated tin oxide) besides removing tin before processing, is incinerating the material. when you heat the material to a red heat, it will drive off the extra oxygen and reduce the tin oxide back to metallic form. then it can be removed with hcl.

When you incinerate metastannic acid, SnO2 is produced. The ore, cassiterite, which is mainly SnO2, is the main source of tin. The SnO2 is reduced to tin metal by heating at about 2500F with carbon, coke, carbon monoxide, etc. No way are you going to reduce it to tin metal by ordinary incineration.

Metastannic acid is not soluble in HCl. However, according to Hoke (page 72), if you wash it well and don't allow it to dry, it is soluble in warm 50/50 sulfuric. Of course, the problem is washing it well.

I read in several places that, if you boil metastannic acid in HCl, a tin chloride compound is formed which is soluble in water. I assume you would have to rinse out the HCl before this would work.

 

[Geo]

thanks GSP for the clarification. i wasnt sure how the mechanics work and now im not sure it works at all, but i was told a long time ago to incinerate and use a hcl boil to remove the tin. it seemed to work but it could have been just as easily the water washes that followed.

 

[kurt]

Incineration converts the metastanic acid (tin paste) to tin oxide which is then removed with hot HCL washes (at least that is my understanding & it works for me)

I would assume Kens method of using lye along with heat in the process is doing the same reaction (converting tin paste to tin oxide)

I have tried using lye but without heating it & that did not work so I guess the heat is the trick with that.

personally I will stick with incineration - its quik & easy with less chemical waste & washing

Kurt

 

[jeneje]

Incineration converts the metastanic acid (tin paste) to tin oxide which is then removed with hot HCL washes (at least that is my understanding & it works for me)

I would assume Kens method of using lye along with heat in the process is doing the same reaction (converting tin paste to tin oxide)

I have tried using lye but without heating it & that did not work so I guess the heat is the trick with that.

personally I will stick with incineration - its quik & easy with less chemical waste & washing

Kurt

Kurt you and Geo are right here, incentration is the best way to go, first if you add to much lye you will dissolve some gold, which will require you to add HCL to re acidify and then use copper bus bar to reclaim you gold.

Second, heating lye can be very dangerous, with that said, breathing fumes put off by hot lye can cause a host of medical prolbems some of which can cause death weeks after inhalation. Before using lye one should read up on the dangers of it.
Ken

 

[kurt]

(1)Top pic is foils before incineration

(2) incinerating foils in stainless steal pot on single burner propane camp stove

(3) foils after incineration - the green/gray stuff is the tin paste that has coverted to tin oxide

(4) treating incinerated foils with hot/warm HCL

(5) foils after HCL treatment

stirring the foils several times in this process is important - the foils at the bottom of the pan get the needed red hot but the oxygen for convertion doesn't get to them & the foils on top don't get the needed red hot - so you need to stir several times to move foils from bottom to top & top to bottom of pan to insure complete convertion

Kurt

 

[kurt]

As an added note I would like to thank Harold for impressing on me the importance of not skipping this step - it has made a world of difference in the out come of my gold bars processed from foils

Kurt

 

[butcher]

I will take a cup of coffee, that looks good in the filter.

 

[kurt]

Those are the large restaurant coffee filters so have a full pot of coffee on me :lol: got a 28 gram bar out of that batch

Kurt

 

[Eaheisler]

Bravo

 

[yvonbug]

I know it's been a long time since this post, but i was just wondering what other people were coming up with in answers to the blue goo problem. And I thought back to when I first encountered it. I was living in the Bay Area in the heart of silicon valley. I had started to do my own backyard refining. And I ran a batch that had this hideous blue paste that was holding alot of my gold! I was pissed! So I left the filtering process alone for the night. The next day I checked out the filter, and saw that the liquid had finally gone thru but that paste was pretty thick on the filter. So I set it out in the sun to dry, wondering what to do with it. After it had dried, it looked like dried mud, all curled up and split apart and kinda burnt looking. So I crushed it up even more and stuck it in a plastic jar ready to shelve it. Then I got to playing around with the powder seeing what might desolve it. Alcohol, acetone, hot water, paint thinner, MEK...nothing really did anything to it. And then I got around to some sulfuric acid I had. Not wimpy electrolyte, industrial strength. I got a small beaker of it and set it out in the sun and went and got my powder. When I finally got back out there, the sulfuric was pretty well warmed up by the sun. But I sprinkled my yukky blue powder into it and WOW! the blue powder just kinda swirled and disappeared into solution and my gold just floated on top or sank to the bottom! So I grabbed that beaker and poured it thru another filter and there was my gold! The blue goo had just washed thru. I was so happy! Actually, there was alot more gold in there than I had thought. And it looked so good there in the filter w/o that crap. So, thats my old story of the blue goo and I've stuck with it ever since. I have gone on here to find other methods of dealing with it, but this was easiest in my opinion.

 

[Smack]

Reno Chris had a good post on the subject. http://goldrefiningforum.com/phpBB3/viewtopic.php?f=52&t=20477

 

[kurtak]

If you want true success getting rid of the stannic tin in your foils follow the instructions for incineration & "hot" HCl treatment as I posted above in this thread :!:

I have tried both hydroxide treatment & sulfuric treatment & I will "never" use ether of those method "ever" again :!:

I will stick to what works - & works VERY well :!:

Kurt

 

[Topher_osAUrus]

I will "never" use ether of those method "ever" again :!: [/u] :!:

Sorry to bring up a dead thread. But, Kurt, I have to ask.

Why do you not like the sulfuric solution to the tin paste problem?

 

[kurtak]

I will "never" use ether of those method "ever" again :!: [/u] :!:

Sorry to bring up a dead thread. But, Kurt, I have to ask.

Why do you not like the sulfuric solution to the tin paste problem?

I missed this question from Topher here in this tread back when he first posted it - so he sent me a PM asking the same question (which I answered in a PM)

Because I provided a link to this thread as part of my answer in another recent question about stannic tin - I thought I would up date this thread with the answer I sent Topher in a PM - that answer (to Topher) was as follows ------------

Hokes page 71 says --- "If you still have some tin paste, left over from an earlier experiment, try the effect of sulphuric acid upon it. . . It dissolves it, whether dilute or concentrated."

But it doesn't --- not really - though it does have "some" effect on the stannic tin it does not actually truly dissolve it - it more or less brakes it down into an ultra fine colloid - much the same as NaOH as explained here by Chris :arrow: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=52&t=20477#p209836

So - if there is just a "small" amount of stannic tin - it will put it into suspension long enough for the foils to settle & then decant it - washing "most" (but not all) off

Or - it makes it fine enough that much of it (but not all) will pass through a filter (can't use a paper filter as the sulfuric will ash the paper)

So - although it will help to "reduce" the amount of stannic tin (if you started with a "small" amount of stannic tin in the first place) it wont eliminate all of it

The reason I know this to be true is that I tried it (about 4 or 5 years ago) on some stannic tin (a LOT of stannic tin - like a couple cups full) that had "some" (very little) "ultra" fine foils tied up in it

So I figured I would (as suggested by Hokes) "dissolve" the stannic tin away with sulfuric --- I started using concentrated sulfuric - it did not dissolve the stannic tin & the foils where so fine that by the time they settled - most of the tin did as well - leaving a somewhat cloudy ( stannic tin in suspense) solution

So I tried diluting it --- same result - thought maybe I just didn't use enough sulfuric to dissolve all the tin (stannic) so added more sulfuric --- same result - tried time with stirring - as well as heat - as well as adding more sulfuric (to concentrate) & then diluting again

After a about a week of messing with it & using up a gallon of sulfuric I ended up with my ultra fine foils still tied up in a bout 1 1/2 cups of stannic tin (so reduced the stannic tin by about 1/2 cup & about 3 gallons of sulfuric waste (from diluting)

With incineration (reduction roasting actually) & as long as you do your roasting to completion (convert all the stannic tin to tin oxide) you can then "eliminate" ALL the tin with the HCL wash/leaching

Conclusion --- if you want to "insure" you have got rid of the tin - incinerate & treat with HCL

Kurt

 

[Lino1406]

Concentrated fluoboric acid HBF4 may help you

 

[richard2013]

Concentrated fluoboric acid HBF4 may help you

That acid is less friendly and far more dangerous than dealing with HCL.