[bnelson907]

Thanks for any help that can be provided! My inorganic chemistry is pretty weak, so I am sorry if these questions are poorly presented. My questions are regarding the rehabilitation of the aqueous portion that remains after you precipitate talc out of Step 2, below. In other words:

1. I think that the aqueous "remainder" after filtering the talc is NO₃^- in H₂O. Is this correct?

2. What is the best way to convert the NO₃^- into HNO₃ so it can be reused and how much energy is required?

3. If this in not the right forum, can anyone suggest where I should go to get help?

Step 1: Dissolve magnesium carbonate in nitric acid (reaction in H₂O solution)
MgCO₃ + 2 HNO₃ → Mg(NO₃)₂(aqueous)+ CO₂(gas)+ H₂O(liquid)

Step 2: Precipitate out talc by adding silica (reaction in H₂O solution)
3 Mg(NO₃)₂ + 4SiO₂ + H₂O → 3MgO(SiO₂)₄H₂O (solid) + 6(NO₃)^-(aqueous)

[Borek]

1. I think that the aqueous "remainder" after filtering the talc is NO₃^- in H₂O. Is this correct?

No, and it can't be. This reaction equation:

3 Mg(NO₃)₂ + 4SiO₂ + H₂O → 3MgO(SiO₂)₄H₂O (solid) + 6(NO₃)^-(aqueous)

is not balanced - properly balanced equation have not only same amount of atoms on both sisdes (no idea whether atoms are balanced, I have not checked it) but also identical charge on both sides - and obviously you have -6 on the right, 0 on the left.

[bnelson907]

I'm sorry if I wasn't perfectly clear as I realize that the second equation is not balanced - part of my question should have been, "what is balancing the NO3^-?". Everything I've found states the precipitaion occurs and the precipitate can be removed, so the talc (3MgO(SiO₂)₄H₂O) is gone as a solid.

So what balances the NO3^-? Since its in H₂O, does the water counter-balance by creating H₃O⁺, releasing some oxygen in the process? This doesn't make much sense to me as it would mean the acid (HNO₃) is automatically revitalized/regenerated as a result of the precipitation - and I haven't found a source that explains this part of the reaction.

As I said before, my chemistry is weak, so any help is appreciated.

[Borek]

You are not using SiO₂ - at least IMHO.

[bnelson907]

I know its SiO₂ - its 99.9% pure from Sigma Aldrich. Is it possible the NO₃^- or some portion of it (NO/NO₂?) is converting to a gas? None of the equations I've seen suggest this, but then they don't really address it very well at all.

[Borek]

If anything, logic calls for

3Mg(NO₃)₂ + 4SiO₂ + 4H₂O -> H₂Mg₃(SiO₃)₄ + 6HNO₃

but I find it extremally unlikely that SiO₂ will react with anything in solution.

Then, I am known to be occasionally wrong