I've been focusing a lot on aluminum hydroxide recently, or specifically breaking it down into its base components. I know that when aluminum hydroxide dissolves in nitric acid it forms aluminum nitrate ($\ce{Al(NO3)3}$), which decomposes when it boils into aluminum and nitrogen dioxide. The end goal of this process is to recover the aluminum from the aluminum hydroxide, but that can't be done until the aluminum hydroxide dissolves into the nitric acid. I don't know if aluminum hydroxide readily reacts with nitric acid or not. Can aluminum hydroxide react with nitric acid readily? Or does it need to be catalyzed, or should I use a different reaction to isolate the aluminum?

  • $\begingroup$ At the right ratios, you should end up at same compound. $\endgroup$ Feb 29, 2016 at 13:39
  • $\begingroup$ I have heard that a passive layer of oxide forms on aluminum instead of forming a nitrate $\endgroup$
    – Aditya Dev
    Feb 29, 2016 at 14:25
  • $\begingroup$ @AdityaDev that works in air, but acids degrade this coating, I believe. $\endgroup$ Feb 29, 2016 at 14:37
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    $\begingroup$ I'm fairly certain that the atmospheric oxide layer is stripped away in nitric acid $\endgroup$
    – Sigismund
    Mar 1, 2016 at 16:37
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    $\begingroup$ Aluminium metal is hard to produce. Industrial processes consume vast quantities of electricity to electrolyse molten aluminium salts. If there were easy ways to do this, they would be used industrially. There is a big incentive to find better ways but yet none have appeared. That suggests your proposed method of aluminium recovery won't work. $\endgroup$
    – matt_black
    Nov 12, 2016 at 11:30

2 Answers 2

  1. Aluminum oxide could be the product of fusing Al(NO3)3 at high enough temperature. Aluminum metal would not be a product, in water or in fused salt.

    2.Aluminum metal does not readily dissolve in nitric acid because of formation of passive oxide/hydroxide film. The nuclear power industry had need of large amounts of aluminum nitrate, and it was made by dissolving aluminum metal in hydrochloric acid (very fast) and treating the solution with nitric acid, boiling off the HCl.

    1. Aluminum metal is often prepared for welding by removing the oxide film with dilute hydrofluoric acid. The aluminum surface is bare metal for, oh, maybe a microsecond, before oxidizing back to the oxide. But the aluminum oxide film will be very thin for a few hours and easy to weld. The oxide film grows thicker in air as it ages.

Industrial preparation of Al using electrolysis of molten $\ce{AlF3/AlO2}$ mixture at $\pu{1500 ^\circ C}$ is done not because they like using high temperatures, but because there are no other good ways to make Al. Hydrolysis of aqueous solutions of aluminum salts will not yield metallic aluminum.

Can $\ce{Al(OH)3}$ react with $\ce{HNO3}$? It really depends. Fresh $\ce{Al(OH)3}$ will dissolve in dilute $\ce{HNO3}$. Old $\ce{Al(OH)3}$ ages to $\ce{Al(OH)3}$ and is much less reactive.

Electrolysis of water solution of aluminum salt will not yield metallic aluminum. Hydrolysis of $\ce{AlCl3}$ yields $\ce{H2 + O2/Cl2}$. $\ce{Al(NO3)3}$ will be reduced by forming hydrogen, so you well get a a mix of products: $\ce{NO2}$, $\ce{NO}$, $\ce{H2}$, but not aluminum metal. If this were easy, industry wouldn't bother with hydrolysis of molten $\ce{AlF3/Al2O3}$.

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    $\begingroup$ What you mean by:-1."Old Al(OH)3 ages to Al(OH)3 and is much less reactive" 2."Would it be this easy plants wouldn't bother with hydrolysis of molten AlF3/Al2O3" $\endgroup$ Jul 15, 2016 at 3:49
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    $\begingroup$ Please explain how old aluminium hydroxide ages to aluminium hydroxide — the same compound. $\endgroup$
    – Jan
    Oct 8, 2017 at 15:13

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