Preparing ammonium hexafluorozirconate

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Ammonium hexafluorozirconate - (NH4)2ZrF6 - is prepared by dissolving freshly precipitated Zr(OH)4 in concentrated ammonium bifluoride - NH4HF2 - solution in a polypropylene beaker. A 10 % excess of ammonium bifluoride is used:

Zr(OH)4(s) + 3 NH4HF2(aq) → (NH4)2ZrF6(aq) + NH3(aq) + 4 H2O(l)

The reaction is accompanied by heat generation. Gently simmer the solution on steam bath to obtain full dissolution. If the solution is still turbid, hot-filter to clarity.

On cooling and chilling overnight, well-formed crystals of ammonium hexafluorozirconate are obtained.

Hexafluorozirconate and hexafluorohafnate were used in the first separation of these elements by fractionated crystallisation of solutions of these salts.

Pyrolysis of ammonium hexafluorozirconate yields anhydrous zirconium tetrafluoride:

(NH4)2ZrF6(s) → ZrF4(s) + 2 NH4F(g)