# Smelting fine carbon ash



## sohwohn (May 29, 2019)

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 (May 29, 2019)

Some photos


----------



## sohwohn (May 29, 2019)

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 (May 29, 2019)

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 (May 29, 2019)

anachronism said:


> 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 (May 29, 2019)

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 (May 29, 2019)

anachronism said:


> 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."
> 
> ...


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 (May 29, 2019)

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? 




Sent from my iPhone using Tapatalk


----------



## anachronism (May 29, 2019)

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 (May 29, 2019)

snoman701 said:


> 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?
> 
> ...


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 (May 29, 2019)

anachronism said:


> 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 (May 29, 2019)

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 (May 30, 2019)

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 (May 30, 2019)

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


----------



## anachronism (May 30, 2019)

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


----------



## sohwohn (May 30, 2019)

anachronism said:


> 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 (May 30, 2019)

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 (May 30, 2019)

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 (May 30, 2019)

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.

Sent from my SM-G950U using Tapatalk


----------



## snoman701 (May 30, 2019)

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. 



Sent from my iPhone using Tapatalk


----------



## rickzeien (May 30, 2019)

snoman701 said:


> 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.
> 
> ...


I resemble that remark. High pollen count + extreme heat + old timer's syndrome = me 

LOL

Thanks 

Sent from my SM-G950U using Tapatalk


----------



## sohwohn (May 30, 2019)

anachronism said:


> 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.
> 
> ...


The essential FeSO4 will be arriving in days so I'll have days to read the materials. Guess I'll be ready.

I ash the carbon using a pot with heat underneath. A electric heating thing, I'll take a photo of it tomorrow.

I think it's very very likely that the carbon isn't completely ashed, since we didn't spend much effort examining this part.

This conversation has reminded me to ash the carbon tomorrow by myself, as this part had been done mostly by someone else. I will try the 'adding KNO3 when carbon is red hot' method which I found on this forum. Then I will smelt the ash again, see if there's a difference.


----------



## sohwohn (May 30, 2019)

snoman701 said:


> 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.
> 
> ...


Sir, your reply has given me a lot of new knowledge. I'm not sure if it is, but I found a lot of white bubbles on the upper-inner part of the crucible, maybe that's KNO3, I don't know. But knowing that the graphite crucible would absorb KNO3, I guess I'll stop using it or find something else to replace it.

Stirring the molten is the another thing I've missed out. Important too. I'll try this with a fire-proof gloves. Thanks!

I've noticed that a lot of Na2CO3 with little SiO2 would make a lot of bubbles. The flux almost spilled out of the crucible today as I was doing experiments. Didn't think of using this as an advantage though. Thank you for your experience talk, I will try that.

The borax/silica part, I assume you mean 2 part borax, 2 part silica, and 1 part soda ash? I always felt like silica would make the molten too sticky, and gold would stick to the slag, so I always put more soda ash than silica. Is this wrong?


----------



## sohwohn (May 30, 2019)

snoman701 said:


> 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.
> 
> ...


I'm new to this. Actually I'm new to this whole industry, and I'm learning from XRF assaying to ores processing to now hydro-metallurgy and fire-assaying.

I thought, graphite was the only option here because, I thought, it was how this 'induction furnace heating the crucible not the quartz cup protection very safe bla bla bla' thing works.

You suggesting SiC crucible and I asked my supplier and they did have it. I suppose in this way I could use KNO3 more effectively? If yes, I'm buying a box.


----------



## rickzeien (May 30, 2019)

In his reply he was talking about my furnaces that are LP not induction. 

I am not sure about crucibles for induction furnace.

Sent from my SM-G950U using Tapatalk


----------



## sohwohn (May 30, 2019)

rickzeien said:


> In his reply he was talking about my furnaces that are LP not induction.
> 
> I am not sure about crucibles for induction furnace.
> 
> Sent from my SM-G950U using Tapatalk


OK ^.^


----------



## Owltech (May 30, 2019)

If I were you I would change Cu for Ag and Na2CO3 for NaOH, also pinch of NaNO3


----------



## snoman701 (May 30, 2019)

You can use SiC crucibles with induction, but 5 kw might be pushing it a bit. I've got 7.5 and the smallest SiC crucible barely gets hot enough for silver, on a good day. You end up dumping a lot of power in to the conductive crucible.


----------



## sohwohn (May 30, 2019)

snoman701 said:


> You can use SiC crucibles with induction, but 5 kw might be pushing it a bit. I've got 7.5 and the smallest SiC crucible barely gets hot enough for silver, on a good day. You end up dumping a lot of power in to the conductive crucible.


I see. So that's not an option for me.


----------



## sohwohn (Jun 1, 2019)

I found that the factor which affect me most was how well the carbon was ashed. Adding KNO3 during ashing when the carbon started to become red hot surely speeded up the process, but the carbon I was using was around 1-2mm large so only the surface of it ashed rapidly. Most part of the carbon was still not-burnt.

So, I started grinding the gold-bearing carbon, in order to get cleaner ash. I know there would be great loss of gold during grinding. I feel like the first step to find out the problem is to make sure it's not about ashing. Or, problem solved.

Will be updating my results tomorrow.


----------



## anachronism (Jun 1, 2019)

I'm not certain why you would add acid during ashing.

What temperature and time are you taking and what equipment are you using?


----------



## Platdigger (Jun 1, 2019)

Potassium nitrate may be acidic in a smelt, but I would not say it is an acid.
But yes, why add anything when ashing. I think he meant to use it as an oxidizer.

I had a high temperature "ashing" furnace made just for this type of work.
It was plumbed to were you could add pure oxygen during ashing of the sample.


----------



## Owltech (Jun 2, 2019)

sohwohn said:


> I found that the factor which affect me most was how well the carbon was ashed. Adding KNO3 during ashing when the carbon started to become red hot surely speeded up the process, but the carbon I was using was around 1-2mm large so only the surface of it ashed rapidly. Most part of the carbon was still not-burnt.
> 
> So, I started grinding the gold-bearing carbon, in order to get cleaner ash. I know there would be great loss of gold during grinding. I feel like the first step to find out the problem is to make sure it's not about ashing. Or, problem solved.
> 
> Will be updating my results tomorrow.



Replace Na2CO3 with NaOH or KOH


----------



## sohwohn (Jun 2, 2019)

I found the problem, guys!

I used nitric acid to dissolve the copper button.

The residue was assayed by XRF.

It had almost 95% of the original gold value from ash.

To conclude, I did manage to condense all gold value into the copper button. It was the surface of copper button having low readings, now that I can assume the inner part of the button is more condensed with gold.

So it is now I understand that I failed the assaying because I missed out one procedure showed in our guidebook: I need to compress the oval-shape copper button into a form of plate. I guess this will force the inner part of the copper button show up.


----------



## Hurc (Jul 2, 2022)

sohwohn said:


> I found the problem, guys!
> 
> I used nitric acid to dissolve the copper button.
> 
> ...


Is it possible that smelt button have different composition on surface and different in inner part. I heard that button have same composition through out. Can some one confirm Is it normal that button have different composotion at surface and different in inner part?


----------



## Yggdrasil (Jul 2, 2022)

Hurc said:


> Is it possible that smelt button have different composition on surface and different in inner part. I heard that button have same composition through out. Can some one confirm Is it normal that button have different composotion at surface and different in inner part?


Depending on melt time, temperature and such parameters it may happen that the button can be poorly mixed. 
I think.... maybe. 
Like a solder operation if all metals do not melt properly, but more braze together.

But in normal conditions they should be more or less uniform, unless you have alloys that don't play well together.
The surface can have impurities from slags, oxides and such though.


----------



## orvi (Jul 2, 2022)

Hurc said:


> Is it possible that smelt button have different composition on surface and different in inner part. I heard that button have same composition through out. Can some one confirm Is it normal that button have different composotion at surface and different in inner part?


Depends on what you are smelting. It is obvious when one look to the phase diagrams of metals which are melted. Some - like AgPd system has nice phase diagram without any eutectics (but that doesn´t mean it will stay homogenous after melting). Others, like Fe-C are much much different and difficult.
One of the most crucial things for preparing homogenous button is cooling time. If you left the bead to cool slowly, it has plenty of time to establish equilibriums and create various crystalline phases inside - which ultimately result in different composition eg on the surface and inside the button.
I had plenty of experience with this phenomena on PGM alloys. XRF was sometimes practically useless for assessing the composition... Also AgCu tend to alter the composition, despite being melted at higher temperature and poured into the mold.


----------

