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I would like to use non-food grade $\ce{NaOH}$ for $\ce{pH}$ water treatment. Any problem with this mixing with water that contains iron?

The $\ce{NaOH}$ will be pumped into a well. As a $25\%$ solution. Then sent through an ozone filter and a water softener. Eventually, it will be used for pet and human consumption.

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In addition to what thomij has already pointed out, note that $\ce{NaOH}$ etches glass and will degrade various polymers (PET and polycarbonate, among others). –  Greg E. Aug 20 at 0:33
    
What about passing the water through calcium carbonate or magnesium hydroxide to raise pH? –  brinnb Aug 20 at 1:10
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Non-food grade sodium-hydroxide can (and most often do) contains heavy metals. Also, it is pretty corrosive, so you may yourself generate different carcinogens or poisonous side-products inside the well during this process. If you want to use this for human / pet consumption, you may want to consider other solutions, e.g. @brinnb's suggestion. –  Greg Aug 20 at 3:19

2 Answers 2

up vote 5 down vote accepted

Iron hydroxide is insoluble, so it will precipitate out. If there are other metals that aren't alkali metals or alkaline earth metals heavier than calcium, they will also precipitate out. Most of these reactions will release some heat, but if the concentration of the metal ions is low, that shouldn't matter too much.

If you plan to drink the water, using non-food grade $\ce{NaOH}$ might cause a problem, because you won't know what else is in there.

If you add more details, we can probably tell if there are any other things to be concerned about.

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In addition to the other answers, I'd like to add a comment about the risks:

A 25% solution of NaOH in large quantities is very very dangerous. On drop in the eye and you will be permanently blind. It is much worse than acid. Acid causes something akin to a burn that keeps the acid away from the unburned tissue below. NaOH on the other hand dissolves the tissue and penetrates very deeply. The drop in your eye will liquefy your eye.

When you pump it you'll have a lot of pressure, the solution might corrode the plastic and suddenly you have a leak that sprays corrosive lye all over you.

When you mix NaOH with water, it will heat up. Maybe enough to make it boil explosively. Hot NaOH solution is even more corrosive.

I don't know much about well treatment, if you really need to use NaOH, use at least both a full face shield and safety goggles + raingear and have someone stand by with a water hose to wash of any spills quickly. Keep kids and pets away.

I suggest you check if using a carbonate or hydrogen carbonate (e.g. sodium carbonate, sodium hydrogen carbonate) would work. These are much safer.

For the non-food grade, I would be careful. Some industrial stuff is just as clean, some is heavily contaminated. Maybe the people selling it have an analysis of the batch. In any case, make sure you rinse your system very well afterwards.

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