Treatment of waste H₂SO₄with 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 NO(3)(-)-intercalated Mg-Al layered double hydroxide (NO(3)•Mg-Al LDH) was used to treat H(2)SO(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(2)SO(4).