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Magnesium hydroxide for pH adjustment

By April 18, 2022May 12th, 2022Chemicals, Pumps, Safety, Tanks

Caustic (NaOH) works great for pH adjustment at a brewery. It works fast, staff are accustomed to working with it, it’s easy to get, and there is usually a lot of it around. But it’s dangerous!
A different and safer option is available to raise the pH of wastewater besides caustic.  Magnesium hydroxide, Mg(OH)2, aka mag. It’s safe enough to drink, there are twice the hydroxide ions per molecule, and can be less expensive. But using it is not something to jump into without good planning.

Mag is a milky, chalky white slurry. It’s non-toxic and generally safe. Imagine a very thin sheetrock joint compound and you get the idea.

The solids will settle without adequate mixing, it can’t let it freeze (even during shipping), and reaction times are a lot longer. It requires a special tank, dosing pump, and even the delivery tubing needs to have constant motion.

Years ago I did a trial without good planning. I had a 1000 gal tank filled it with mag, then I dropped a submersible pump in there for mixing. I used a regular LMI chemical dosing pump. In short order the dosing pump seized with settled solids, the tubing filled with settled solids, and the submersible pump seized with settled solids! But I persisted and received a 2nd order. This froze during transport and I had 4 drums of solid Mg(OH)2 to liquify. It turns out that is very hard to do! To get rid of it I wound up adding chunks of Mg(OH)2 through the top manway of my EQ tank. Years later I went into that tank for cleaning and had to pull all of those chunks back out of the tank. They do not dissolve, soften, or change form in any way.  Let’s just say I am not a fan.

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