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Destroying Chlorate by chemical means

When making Perchlorates from Sodium Perchlorate you must have pure Perchlorate. The only sensible and feasible way to purify Sodium Perchlorate from Chlorate contamination is to destroy all traces of Chlorate by chemical treatment. When 'raw' Sodium Perchlorate is removed from cell liquor it will be contaminated with some Chlorate. There must not be too much Chlorate in the product or it will be wasteful and foolish to attempt to destroy a large amount of Chlorate by chemicals.
The Perchlorate should be dried and weighed and then re dissolved so you can then destroy all traces of Chlorate before going on to make other Perchlorates.
If you have a solution of Perchlorate that has been obtained by letting your cell run for long enough to convert nearly all of the Chlorate to Perchlorate then you can proceed with the destruction of the Chlorate without crystallizing out the Perchlorate. The absence of Chlorates should be checked for by using a sensitive test for Chlorate after the destruction step has been completed. See Tests for Chlorate and Perchlorate.
There should be NO Chlorate. A Perchlorate that contains ANY Chlorate must be treated as if it WAS Chlorate in regard to dangerous combinations with combustibles, like for example Sulphur. You also have the extra problem of Chlorate contamination if you are going to make Ammonium Perchlorate, you don't want any Ammonium Chlorate forming.

Note: Sulphite can be spelt either as said or as Sulfite.
Sulphate can be spelt either as said or Sulfate.

should be checked for using some of the sensitive tests for Chlorate. HCl acid can be purchased at the builders providers and is used for cleaning cement.

All the chemicals below work by reducing the Chlorate ion. The sulphites have the same reducing power in dilute acidified solutions as sulphur dioxide. All the sulphite and sulphur dioxide reactions take place in a similar manner. You can test for the presence of Chlorate in your product as per US Patent No. 2,392,769

Sodium metabisulphite

The solution should first be acidified to pH 3 or so using sulphuric or HCl acid. The sulphite added and the solution heated strongly or boiled

The Sodium Metabisulphite reactions take place according to:

First, the Metabisulphite dissociates:

Na2S2O5 + H2O <-> 2NaHSO3
The sulphite then reacts with Chlorate:

3SO3.2- + ClO3- => 3SO4.2- + Cl-
The overall reaction is:

3Na2S2O5 + H2O + 2NaClO3 => 3Na2SO4 + 3H2SO4 + 2NaCl

You can then neutralize the solution using Sodium Hydroxide which will give you more Sodium Sulphate and water.

H2SO4 + 2NaOH ==> Na2SO4 + 2H2O

Sodium Bisulphite

Similar to Metabisulphite

Sodium Sulphite

Similar to Bisulphite

Sulphur Dioxide

See US Patent No. 2,392,769

Ferrous Sulphate

This is cheap and easy to obtain. The reaction products should not be a problem. The sulphate should be dissolved in acidified water (the acid is to stop Iron Hydroxide form forming) first and then added to the solution that is being treated.
Reaction Equation: 6Fe+2 + 6H+ + (Cl+5O3)- ------> 6Fe+3 + Cl- + 3H2O

Ferrous Ammonium Sulphate

Same as Ferrous (II) Sulphate but it is more expensive and harder to get. Does not oxidize in air as Ferrous (II) Sulphate does and won't form Hydroxide when added to water.

Strong acids

HCl is the best acid to use. Wouters page explains the process and is thus:
Acid is added to the solution to be treated and the solution is boiled. Yellow gas is released (the more Chlorate the more gas) as the Chlorate is destroyed. This gas is ClO2 and is explosive at concentrations above 10%. It is also very toxic and should not be inhaled under any circumstances. If using HCl, any excess acid can be gotten rid of by boiling. There should not be large amounts of Chlorate present (as with all the other methods) when adding acid. The solution is them basified with NaOH (or appropriate hydroxide or carbonate if you are concerned for the final colour that the produce will make when burned) and the presence of Chlorate should be checked for using some of the sensitive tests for Chlorate. HCl acid can be purchased at the builders providers and is used for cleaning cement.