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I posted this at Virtual Farm show (Canadian) also, & got these responces to explain it. I've been doing it this week in a 100 gal. vat, & it is working GREAT!!! - MAJ ..... I am aware of the chemical processes at work here and used to do the very same thing as a kid with 6 volt lantern batteries. I couldn't make out the sketch, but to confirm, the rusty piece was on the negative terminal - right?
What is happening is that the electolyte - salt - is comprised of sodium (a metal) and chloride (an alkali ?). Anyway, once dissolved, the sodium separates and is transported by the electrons to the positive terminal. The sodium is there to basically keep things moving. Before the electrons leap off the metal onto nearby sodium molecules, they take some of the iron with it. However, this iron is tied up as rust, unless you let it go too far (hence the pitting). The positive side collects all of the junk and is probably black, green, or white after a while. Electroplating works the same way, except you put dissolve a copper, gold, or some other metal salt and put the object of interest on the positive terminal. The metal collects there on the object! This process definately works and is very gentle - hence the longer derusting time. I bet it also produces bubbles. If you are getting bubbles, provide for ventilation as it contains a significant proportion of hydrogen gas. That comes from water molecules be caught up in the process too (hydrogen is chemically a metal). Rust occurs for similar reasons as single oxygen atoms are looking for a spare electron or two. Iron readily has "spares" and the oxygen will attach. Chlorine is even more reactive. I have seen experiments where highway bridges are fed a current that is supplied by solar cells. The chlorine in road salt grabs the free electrons being provided and tend to leave the iron in the bridge alone. It works, but there are practical limits (and off topic here too!). ..... Link
ftp://ftp.pangea.com/pub/people/rock/oldtools/restoration/ElectrolyticDerusting.txt
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