# Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning

Pyrometallurgy: Roasting, Smelting, Refining & Electrowinning 2017-04-21T02:33:06+00:00
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## leaching of coal fly ash (2 replies and 3 comments)

ely.thar
5 months ago
ely.thar 5 months ago

we conducted a bacisity test on the coal fly ash sample resulting to a ph of 12.01, how can we calculate the volume of our lixiviant needed to add in the sample to reach a ph of 0.8?

mikerockandel
5 months ago
mikerockandel 5 months ago

Probably infinite. If coal ash is highly alkaline, huge dilution, 100s of times what you used may get you to 8.0. You really want 0.8? You will have to add acid lixiviant

ely.thar
5 months ago

if we use H2SO4 as our lixiviant, what should we prefer a two stage leaching or a single stage? knowing from our sample has a ph of 12

mikerockandel
5 months ago

Not sure 2stage helps you. But does depend on your objective. Imagine flyash moving left to right and acid solution opposite. 2stage would possibly give you a near neutral aqueous effluent with the flyash stream exiting at 0.8 pH. Cant avoid testing, the solid-liquid separations may be hardest part of design.

RUHRIN
5 months ago
RUHRIN 5 months ago

I think this is correct.

Need to know the average formula weight (F) for then fly ash.  This is obtained by chemical analysis.

If one adds 100 gm of fly ash to 1 liter of water, then the concentration of [OH]- is approximately

[OH]- = 100 gm/[F gm/mole/lit] of [OH]- = (100/F) moles/lit of fly ash

There is 1 mole of [OH] per mole of fly ash, so there is (100/F) moles/lit of [OH]-

1 mole of H2SO4 can neutralize 2 moles of [OH]-, so:

1/2(100/F) = (50/F) moles/lit of H2SO4 required

Concentrated (98%) H2SO4 contains approximately 18.4 moles/liter of H2SO4, so:

1 lit (50/F mole of fly ash/lit) (1 lit H2SO4/18.4 mole) = (50/F) (1/18.4) liters of H2SO4

ely.thar
5 months ago

is there any way can we get the amount of sulfuric acid needed, if we don't conduct a chemical analysis for the average formula weight of the fly ash sample?

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