Destroying Chlorate with chemicals

When making Perchlorates from Sodium Perchlorate you must have pure Perchlorate. The only sensible and feasable way to purify Sodium Perchlorate from Chlorate contamination is to destroy all traces of Chlorate by chemical treatement. 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 crystallising 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.

See here for a detailed description of Chlorate removal from Potassium Perchlorate by Swede.

Chemicals for the destruction of Chlorate
Sodium Metabisulphite Na2S2O5Also called di-Sodium Disulphite or Sodium Disulphite or Sodium Pyrosulphite. This can be got at the local wine making store in the form of 'Campden tables' where it is used in wine making and sterilising. It is used as a food additive, E223. It is similar to Sodium Bisulphite, Metabisulphite being the dehydrated derivative of two molecules of Bisulphite.
Sodium Bisulphite NaHSO3Also called Sodium Hydrogen Sulphite. It is used as a food additive, E222.
Sodium Sulphite Na2SO3 It is used as a food additive, E221.
Sulphur Dioxide SO2 Used in US Patent No. 2,392,769. It can be generated by burning sulphur or you can purchase in a cylinder. It is also used as a food preserver and disinfectant.It is a suffocating gas.
Ferrous (II) Sulphate FeSO4:7H2O
+ Sulphuric Acid
Common names are Copras, Iron Sulphate, Green Vitriol. It is use for killing moss in lawns and can be got at the local garden store.
Ferrous Ammonium Sulphate (NH4)2SO4 .FeSO4:6H2O
+ Sulphuric Acid
Also called di-Ammonium Iron (II) Sulphate. It is somewhat expensive. Similar to Iron (II) Sulphate
AcidsHCl and others. Easy to obtain. You need to be careful of the ClO2and Cl2 gases produced.
HeatThe solid product can be heated so that all remaining Chlorate is converted to Perchlorate and Chloride
Temperature control need to be accurate and the heating needs to be for the required time.

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
Use K compounds if you need to keep Na out of your final product.

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 <----> 2Na+ + 2H+ + 2SO32-
The Sulphite then reacts with Chlorate:

3SO32- + ClO3 - => 3SO42- + Cl-
The overall reaction is:

3Na2S2O5 + H2O + 2NaClO3 => 3Na2SO4 + 3H2SO4 + 2NaCl
There is more info. here on dissociations.

You can then neutralise the solution using Sodium Hydroxide which will give you more Sodium Sulphate and water.
H2SO4 + 2NaOH ==> Na2SO4 + 2H2O

2.68 grams of Bisulphite is required per gram Sodium Chlorate for complete destruction to occur.

Sodium Bisulphite

Similar to Metabisulphite

Sodium Sulphite

Similar to Bisulphite

Sodium Disulfite

Similar to Bisulphite

Sulphur Dioxide

See US Patent No. 2,392,769
The chemical equation would be:
SO2 + H2O ===> 3H2SO3 + ClO3 - ===> Cl- + 3SO42-
Sulfur dioxide gas can be generated by a number of means including adding HCl to Sodium Bisulfite and gently heating.
A good way to make SO2 is to add Sulphur (55g) to Sulphuric acid (120ml) + 2 grams of Fe2O3 as catalyst and heat strongly. (Thanks to GarageChemist for that).
The solution should be neutralized when all Chlorate has gone.

Ferrous Sulphate + H2SO4

This is cheap and easy to obtain. The reaction products should not be a problem. The Sulphate should be dissolved in the acidified water (the acid will stop Iron Hydroxide form forming, it is also necessary for the reaction that destroys the Chlorate) first and then added to the solution that is being treated.
6FeSO4 + NaClO3 + 3H2SO4 ====> 3Fe2(SO4)3 + NaCl + 3H2O
Keep the pH below 3 for the reaction to proceed and the solution should be heated/boiled.
For every gram of Sodium Chlorate that needs to be destroyed you need 1 * 6 * 3.66 = 22 grams of FeSO4 :7H2O, quite a large amount. (3.66 is the ratio of the molecular weights). If using anhydrous Ferrous Sulphate you would need 8.6 grams.

Ferrous Ammonium Sulphate + H2SO4

Same as Ferrous (II) Sulphate but it is more expensive and harder to get. Does not oxidise in air as Ferrous (II) Sulphate does and won't form Hydroxide when added to water. Keep solution below pH 3 for destruction reaction to proceed. Heating or boiling should be used. You will need quite a lot per gram Chlorate.

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.

2KClO3 + 4HCl ===> 2KCl + 2H2O + 2ClO2 + Cl2

This yellow gas is ClO2 and is explosive at concentrations above 10%. It is also very toxic, as is the Chlorine gas, and should not be inhaled under any circumstances. If using HCl, any excess acid can be gotton 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.