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July 6 2011 4 06 /07 /July /2011 13:52

Warning: Hydrochloric acid is corrosive. The resulting metal chlorides are toxic or carcinogenic.

 

You will need:

 

Alnico magnet

Hydrochloric acid

3% or more concentrated Hydrogen peroxide

Sodium bicarbonate

Sodium hypochlorite

Ammonia, concentrated

Sodium hydroxide

 

Alnico magnets are made of an iron-aluminium-nickel-cobalt alloy. The process for separating them is detailed here.

 

Add hydrogen peroxide to concentrated hydrochloric acid in a 1:1 ratio. Add the alnico magnet. Bubbling is observed and a colored solution is formed. This solution contains these components:

 

Iron(III) chloride, yellow

Nickel(II) chloride, green

Cobalt(II) chloride, blue (in this HCl concentration)

Aluminium(III) chloride, colorless

 

Here are some properties of the chlorides:

 

Iron(III) chloride: Forms alkali-insoluble hydroxide, is not oxidized by bleach, hydroxide does not dissolve in ammonia

Nickel(II) chloride: Forms alkali-insoluble (at normal temperatures) hydroxide, is not oxidized by bleach, hydroxide dissolves in ammonia

Cobalt(II) chloride: Forms alkali-soluble hydroxide, is oxidized by bleach, hydroxide dissolves in ammonia

Aluminium(III) chloride: Forms alkali-soluble hydroxide, is not oxidized by bleach, hydroxide does not dissolve in ammonia

 

Based on these properties, a separation mechanism is thought out:

 

Add sodium bicarbonate to reduce the pH to around 2.

Add excess sodium hydroxide. Cobalt and aluminium dissolve, while nickel and iron remain behind. Filter.

Acidify the cobalt and aluminium solution to neutral and then add excess ammonia. A cobalt ammine complex will form and the aluminium hydroxide will precipitate. Filter and separate.

Add excess ammonia to the nickel and iron precipitate. Nickel should dissolve as the nickel ammine complex. Filter and separate.

 

Results:

 

Nickel(II) ammine chloride, blue solution

Iron(III) oxide, brown precipitate

Cobalt(III) ammine complex, orange solution

Aluminium hydroxide, white precipitate

 

You have successfully separated an alnico magnet.

 

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Published by LanthanumK - in Experiments
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