Treatment of waste H₂SO₄ with Mg−Al oxide obtained by calcination of NO₃⁻−intercalated Mg−Al layered double hydroxide: Kinetics and equilibrium

Abstract

Mg−Al oxide obtained by calcination of NO₃ ⁻-intercalated Mg−Al layered double hydroxide (NO₃•Mg−Al LDH) was used to treat H₂SO₄, acting as both a neutralizer of the acid and a fixative for SO₄ ²⁻. The fraction of SO₄ ²⁻ removed increased with time and with increasing Mg−Al oxide quantity and temperature. The rate of SO₄ 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 SO₄ ²⁻ removal by Mg−Al oxide proceeded under chemical reaction control. Furthermore, the adsorption isotherm of SO₄ 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 SO₄ ²⁻ from H₂SO₄.

Keywords:

• H₂SO₄
• Mg−Al oxide
• NO₃ ⁻−intercalated Mg−Al layered double hydroxide
• treatment
• kinetics
• equilibrium