I have a set-up were I have a bottle with water (DI water, 0.8uS/cm). To that bottle I have added some MgO nanopowder, at a concentration of ~ 0.08mg/ml. It appears that the white powder is dissolving and a standard water hardness titration results in a steady increase of Mg over time: about 1 (mg/L)/Day in a very linear way.

From what I know, MgO is bearly soluble in water, and now it has reached ~40% dissolution according to the test, over the couse of ~3 weeks.

there is no other material in the water.

What could cause this steady dissolution? could it be a slow reaction to form Mg(OH)2 and than a reaction with CO2 from the air/water to dissolve the Mg(OH)2. or is there something I dont know about MgO nanoparticles?

Thanks!