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Hey all, I'm in the process of removing rust from steel by electrolysis. No paint or other coating, so I know no hazardous materials.
Will the iron in the water act to kill moss? green grass? I'm no chemist, so I don't have the knowledge to know whether the iron in the water is in a form that will be available/useful.

Thanks!

What salt are you using in the water? Baking soda? Washing soda?

If so, discard the solution. Sodium carbonate or sodium bicarbonate wouldn't be good for your lawn in any significant quantities; the pH is way too high and you don't want to be dumping sodium into the soil.

Also, depending on the metal you used as an anode, that could be a problem as well. Iron rebar would be no issue. Stainless steel will leach chromium into the electrolyte, and that's going to be hexavalent. That's not good for you or for the lawn.

I wouldn't worry about Cr(VI) too much. It's not the best thing to ingest, but it's not the worst. The whole Erin Brockovitch movie really overplayed this one. Let's compare it to some other materials. EPA drinking water limit for Cr(VI) is 0.1 mg/L. Anybody use 2,4-D? Most of us use it without much worry. The science tells us that 2,4-D is more dangerous to humans, so the EPA's drinking water limit for 2,4-D is 0.07 mg/L. Oral LD50 is around 100 mg/kg for Cr(VI), which is similar to caffeine (127 mg/kg). For the smokers and vapers out there, nicotine's oral LD50 is 3.4 mg/kg.

I think this one's been overplayed a bit.

Let's not forget the fact that it's a known carcinogen. The others you listed were all directly toxic, whereas chromium's toxicity is quite low--and it is, in fact, a required nutrient. Almost all natural chromium is trivalent, not hexavalent.

The EPA's limit of 0.1 mg/L (or 0.1 mg/kg) is for total chromium, not hexavalent. Which is 100 parts per billion. https://www.epa.gov/dwstandardsregulati ... king-water

The EPA does not have a maximum allowable hexavalent limit otherwise. California has established a limit, currently, of 10 PPB. The listed goal is 0.5 PPB.

Even using 100 PPB, 1,000 square feet of soil to a depth of 6 inches or so weighs approximately 50,000 pounds. If you were to follow the water limits in your soil (the two are, of course, not directly applicable to each other), the total limit would be 0.005 pounds, 0.08 ounces, or 2.4 grams.

That's just an example to give a feel for allowable amounts. Actual soil total chromium load is around 37 PPM on average--very nearly 100% of that is chromium-3, which is not at issue.

Salt is washing soda @ 1 tbsp/gal
Anode is rebar.

Thanks for the input.

I have a large area of dense moss that i need to get rid of. Could i use the solution on that? Would the soil have time to recover/dilute the washing soda pH spike? Or is that a "we can't answer that question" question?

Clueless. Honestly, if you want my opinion? Discard the solution. There are too many unknowns, and at least one of the knowns is not good for the soil.