Smelting fine carbon ash

[sohwohn]

I tried smelting 10g carbon ash with following flux:

10g carbon ash
40g Borax
20g Na2CO3
10g SiO2
25g CuO
5g Ascorbic Acid

The resulting copper button only gives 18-33% of the gold value from original carbon ash.

I've tried reducing or adding chemicals I put bit it was not very effective..

Wonder what I did wrong.

I used 5kW induction furnace and smelting was done in 15/20mins.

 

[sohwohn]

Some photos

 

[sohwohn]

Carbon ash loading varies from 1% to 70%. Mostly 0.5-2%.

Average 1%, or 10kg/ton, or 10000ppm.

I've done 10+ experiments, with different ash sources.

All of them come with 18-33% recovery rate....

Really wonder what I've done wrong..

 

[anachronism]

If you used 40g of Borax a fair amount of your gold is locked up in the borax.

Also did you use a graphite crucible?

 

[sohwohn]

If you used 40g of Borax a fair amount of your gold is locked up in the borax.

Also did you use a graphite crucible?

Yes. I did use graphite crucible.

I tried 1:1 ash to borax, it didn't work better

 

[anachronism]

Ok you've got two problems then. You've got gold on your graphite crucible and in your borax.

I ash carbon too. I prefer to take it up in AR and refine it rather than try to melt it "as is."

If you're going to do this, a good strong long hard boil in HCl gets a lot of the base metals out of the ash.

Hope that helps

Jon

 

[sohwohn]

Ok you've got two problems then. You've got gold on your graphite crucible and in your borax.

I ash carbon too. I prefer to take it up in AR and refine it rather than try to melt it "as is."

If you're going to do this, a good strong long hard boil in HCl gets a lot of the base metals out of the ash.

Hope that helps

Jon

Thank you. I suppose I will try AR if I can't get any further with direct smelt before this weekend.

I found another flux:

10g ash
1g Na2CO3
2g Borax
0.5g SiO2
1g KNO3
0.1g NaCl

Guess I will try this soon.

Also I'm thinking smelting without borax.
10g ash
10g Cu2O
2g Ascorbic acid
5g SiO2
15g Na2CO3

 

[snoman701]

Post a picture of your slag. Is it solid and glassy or porous and chalky? Is it liquid at pour? If not, add a gram or two of fluorspar. It will be hard on your crucible though.

Are you milling your flux together prior to loading it in the crucible?

The carbon is completely ashes?

How much are you mixing? Even though induction provides mixing currents in the metal, you still have to make sure you are mixing the slags like crazy.

Are you collecting in a cone?




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[anachronism]

Add as much Flourspar as you like but you're still locking up gold prills (that you can't see) in your flux.

Best route is clean chemically, refine and then melt.

 

[sohwohn]

Post a picture of your slag. Is it solid and glassy or porous and chalky? Is it liquid at pour? If not, add a gram or two of fluorspar. It will be hard on your crucible though.

Are you milling your flux together prior to loading it in the crucible?

The carbon is completely ashes?

How much are you mixing? Even though induction provides mixing currents in the metal, you still have to make sure you are mixing the slags like crazy.

Are you collecting in a cone?




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Some was glassy and solid, some was porous and chalky. I noticed those porous and chalky were badly smelted. Thanks!

Yes, it was liquid at pour.

I have not milled my flux but they came in AR so it was kind of fine already.

Not sure carbon was completely ashed. I found that if not, it would greatly affect the smelting. I will see what I can do on this poart.

I'm mixing the flux chemicals in a plastic bag. I think it's well mixed.

I'm not collect in a cone but a bullion mold one-side lifted.

 

[sohwohn]

Add as much Flourspar as you like but you're still locking up gold prills (that you can't see) in your flux.

Best route is clean chemically, refine and then melt.

Very indeed.

Somehow, I found assaying raw ores using the mentioned flux was extremely effective.

The thing is, as you mentioned, the gold particles in activated carbon ash were too-too-fine.

As shown in one picture in my post, I used 12-50x scope to examine the ash and still the spread gold particles were like pencil dots. I thought it was like gold salts but it wasn't, it was smaller than gold salts, I guess.

I suppose 60% of the gold particles are in the slag. As I assayed the slag by direct XRF, there was very very small but still clear gold readings.

I will try the-chemical-way eventually, but I don't have a fume hood right now and I fear much acid boiling.

My goal is to reach 80% recovery by smelting.

Now that I'm planning to smelt ash without SiO2 (forming metal oxides) and more Ascorbic acid (encourage reduction). Or plan B, smelting ash without slag-formation, i.e. using only Cu2O and C6H8O6.

 

[sohwohn]

Another thing I've just noticed, was that, the top side of the button, had higher gold value than the bottom side of the button. Maybe, it's another indication that most gold still trapped in slag.

 

[sohwohn]

I've tried smelting ash with just copper. The recovery rate is even lower. The only possible explanation to conclude all experiments that I've done by far is that the gold is carried away by 'smoke'?

 

[sohwohn]

No matter how I smelt. Glassy slag, solid button, clean pour. I still couldn't get more than 30% recovery rate.

 

[anachronism]

Can't recover more than 30% by smelting? Use the method I suggested then.

 

[sohwohn]

Can't recover more than 30% by smelting? Use the method I suggested then.

FeSO4 is shipping to me. I need to read some articles to make AR.

I have both HCl and HNO3. I suppose I just mix them with 3:1 ratio and soak the ash?

 

[anachronism]

I would recommend, that as you suggested, you read up on AR. That's a good plan.

Using 3:1 will leave you with a load of Nitric to deal with. You are best using small additions.

I mentioned boiling your ash hot and hard for a good period of time in HCl before using AR to take away a lot of the contaminants. That's the first step.

Edit: Also how exactly are you ashing your carbon? In what? At what temperature? For how long?

Jon

 

[snoman701]

It doesn't matter if you are leaching with AR or smelting, your carbon has to be fully ashed. In the smelting route, you could normally use nitre to finish the oxidation, but doing so in a graphite crucible will be difficult as the nitre will be consumed by the graphite walls.

You absolutely have to be mixing the flux pool when molten. The molten prills will only coalesce to a certain extent, so you have to mix them so that they make contact with each other, join together, and keep joining until they finally join with the bulk of the melt.

In general, you want your borax/silica to bone ash ratio to be 2:1, but I like to add my bone ash in increments while mixing. It instantly thins the flux and gives you a ton of bubbles and mixing action, and if you mix through this, you get good movement.

A collection cone is also necessary. This is your final chance in the melt, it causes a pressure differential, forcing the more dense materials together.

If you go with AR, do NOT just add 3:1 HCl/HNO3 to your ashed carbon.

 

[rickzeien]

What crucible do you recommend?

Do you stir the melt or use sparge?

You use bone ash rather than sodium carbonate?

Once the melt is liquid do you hold at that temperature for a period of time?

Thanks.

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[snoman701]

Soda ash....sodium carbonate...not bone ash. Brain dead Benadryl head from too many blood sucking vampire mosquitoes.

For your purposes, order your silicon carbide crucibles directly from Morgan. Just order enough to meet their minimum...at $100/crucible it won’t take long.

They don’t make a crucible that will fit his melter...and sparging might be a bit difficult as well.



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