Warning: Hydrochloric acid is corrosive. The resulting metal chlorides are toxic or carcinogenic.
You will need:
3% or more concentrated Hydrogen peroxide
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.
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.