Treatment of waste H ₂SO ₄ with Mg-Al oxide obtained by calcination of NO ₃ ^-intercalated Mg-Al layered double hydroxide: Kinetics and equilibrium

Mg-Al oxide obtained by calcination of NO ₃ ^-- intercalated Mg-Al layered double hydroxide (NO ₃̇Mg-Al LDH) was used to treat H ₂SO ₄, acting as both a neutralizer of the acid and a fixative for SO ₄ ^2-. The fraction of SO ₄ ^2- removed increased with time and with increasing Mg-Al oxide quantity and temperature. The rate of SO ₄ ^2- removal followed first-order kinetics with apparent rate constants of 2.0 × 10 ^-3, 4.4 × 10 ^-3, and 5.3 × 10 ^-2 min ^-1 at 10, 30, and 60°C, respectively. The apparent activation energy was 52.1 kJ mol ^-1, confirming that the SO ₄ ^2- removal by Mg-Al oxide proceeded under chemical reaction control. Furthermore, the adsorption isotherm of SO ₄ ^2- by Mg-Al oxide obeyed the Langmuir equation. The maximum adsorption amount was 2.0 mmol g ^-1, or 4.0 meq g ^-1, indicating that Mg-Al oxide has a large capacity for uptake of SO ₄ ^2- from H ₂SO ₄.