Rust removal from Iron

I was shown an interesting technique today for removing rust from  large intricate steel and iron  objects .

First a plastic container large enough is required  , to this was fitted four lenghts of re-bar ,each lenght of bar was connected together by a copper band at the top , each bar goes from the top to the bottom of the container ,  the object you wish to de-rust is placed  submerged in water mixed with 'Soda' ( need to check back to find out exactly what chemical was used )  . Now you apply 24vdc from an old style battery charger ,anode + connected to the copper band and iron bars , cathode - connected to the work piece , switch it on and its starts to fizzle and bubble , after a time the iron oxide leaves the work surface and ends up in the water , after that iron proper starts to be lost from the work piece , once your done a quick rub down with a wire brush  ,allow to dry ,then a wipe with a rag moistened with white spirit , and voila your ready to apply your primer , pretty neat I have to say 

Citric acid works a bit faster. Lots of stuff can be used, even plain salt. Some need warm water. Soda and citric acid work well with cold water.

Yeah I guess its about making the water a bit more conductive to get ions exchanging  .

It's important to mention that the workpiece should not touch the rods or you'll just short out the battery.

The opposite chemical reaction to oxidation (rust) is called reduction... I have seen it done with heat and water, but more common to use mild acids, like vinegar.

JR

The reaction is just a few volts. 24V seems wasteful. I have seen it done with 6V.

The guy that showed me it is ex army where I guess 24Vdc systems were most common , he's most likely been doing that way so long its just not worth trying to teach the old dog new tricks.