Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning

Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning 2017-04-21T02:33:06+00:00
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Overreactive Smelting Flux (4 replies)

6 months ago
EcoBlu 6 months ago

In an RDO induction furnace, we are trying a new flux recommended by a friend who is supposedly having success with it.  The ingredients are: 1# Silica, 1# Lime, 1# Soda Ash, 1# Anhydrous Borax, 400g Baking Soda, 4 teaspoons Potassium Nitrate, and 4 teaspoons Fluorspar.  This is mixed 3-1 with our 100-mesh ore and slowly added to the crucible.  The problem is that the mixture never allows a high power setting and continuously froths to the point of boiling over -- similar to a vinegar/baking soda reaction (high school volcano).  It has taken over an hour and a boil-over to get just 1/3 of the material added.  Any ideas of what is wrong?

6 months ago
lostsierra 6 months ago

What's the ore have in it? Also, I don't care for the formula. Lime and Fluorspar do about the same thing. I use Chapman flux to smelt, right out of the bucket. I use it on black sand cons, IC chip powder. Works fine. Chapman has mang. dioxide as an oxidizer. Not Pot. Nitrate. I must have half a dozen smelt formulas but not that one you use. 

6 months ago
Bhaduri 6 months ago

Incrementally lower baking soda by 50-g per batch & observe boil over tendency; do you have hi-sulfides in the feed? if not, you could also lower niter content sequentially AFTER you determine response to baking soda adjustments,,,

6 months ago
David 6 months ago

A friend in the business commented the following to me:

"First reaction is you are using Borax Decahydrate instead of Anhydrous Borax (Decahydrate has 10 water molecules in the crystal structure and you are boiling off the water. There is also a pentahydrate with 5 water molecules.

Designing fluxes is straightforward if you have analysis of the feed. But it is silly to just take someone else's flux unless the material is the same. When you say 200 mesh ore does do you mean Ore or some sort of concentrate because ore would have Silica in it (probably) and thus you would not add silica in the flux, whereas a concentrate may have a lot of pyrite in it, in which case you would need silica and maybe more nitre (sodium nitrate).

Incidentally Soda Ash and Baking Soda are the same thing... Lime is I assume CaO but may be Ca(OH)2 or CaCO3. In either case Soda Ash, Baking Soda, Nitre and possibly Lime all potentially produce gas on heating and the whole flux mixture is very Alkali.

I think you may be using Borax Decahydrate even though you say it is Anhydrous."

So, is it straight ore you are refining?

Maybe I would eliminate the baking soda and lime.
Are you putting it into a hot furnace?

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Sugar Watkins
6 months ago
Sugar Watkins 6 months ago

The recipe sounds like baking cookies, pretty bizarre. Too many elements competing with each other. The flux would be suited to reducing an impure iron ore, not much else. Boiling over is likely caused by the KNO3 and CaOH.

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