I recently did a test involving chloride to perchlorate using the new MMO which is resistant to both Cl2 and O2 evolution with no errosion.
The cell was 1st operated in buffered pH controlled conditions till 78% conversion as per my usual protocol. Then it was let to run without pH control
to convert most of the chloride. The reason is because the buffer CaCl2 fails at around 78% conversion or when too much chlorate is dissolved and the
Ca(OH)2 starts going back into solution. regardless after the no pH control run and it reaches mostly chlorate with some hypochlorite in equilibrium.
The cell is acidified with H2SO4 and persulfates are added to keep the pH at around 2-5. This allows all remaining hypochlorite and chloride to escape
as Cl2. Once the pH stabalizes around 5 the current density is cranked up and its let to run.
This however yielded no perchlorate after 5 days which means that its simply not active enough to produce perchlorate. This is the 2nd time I repeated
this experiment and the results were the same with more controlled conditions.
IMPORTANT- DO NOT USE Ir-Ru MMO FOR PERCHLORATE OR 100% chlorate conversion it leads to emission of toxic RuO4 gas.
This project was done in collaboration with pyrochems
Pictures below of test cell and final result
The final pic of precipitate is chlorate because it was not instantaneous and a similar run using PbO2 on Ir-Ta electrode swap yielded mostly
perchlorate after a few days while this run yielded nothing after 5 days.
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