Fig. 3. (A, B) Measured (symbols) Se(IV) sorption isotherms from 1 mM KCl, 1 mM CaCl₂, 1 mM K₂SO₄, and 1 mM CaSO₄ and (C, D) Se(VI) sorption isotherms from 1 mM KCl, 1 mM CaCl₂, 1 mM K₂SO₄, and 1 mM CaSO₄ and corresponding Freundlich sorption model fits (solid lines).