How do lime and caustic react with (NH4)2SO4?

Question

Consider a large volume of water with (NH4)2SO4 at 30 g/L and pH 4.21. Various metals at low concentrations as well.

I need to increase the pH to 8 so much of the metals precipitate out.

What reaction would happen with the (NH4)2SO4, in the following two scenarios:

1. CaCO3 is used to raise the pH.

2. NaOH is used to raise the pH.

Much appreciated!

Answer 1

1. CaCO3 is used to raise the pH.

the H+ ions from the hydrolysis of (NH4)2SO4 should combine with the CO3)-2 ,

as that happens more Ca+2 should go into solution, as CaCO3 's equilibrium shifts into Ca+2 & CO3)-2,

that increased Ca+2 should precipitate out some of the SO4)-2 as CaSO4

2. NaOH is used to raise the pH.

I expect the increased OH-, to combine with NH4+ & produce NH3 & H2O