ADSORPTIVE REMOVAL OF NO_2~- FROM AQUEOUS SOLUTION BY CALCINED Mg-Al LAYERED DOUBLE HYDROXIDES

The calcined Mg-Al layered double hydroxides (Mg-Al CLDH) for removal of NO-2 from aqueous solution was investigated. The results show that Mg-Al CLDH is an effective adsorbent for the removal of NO-2 from aqueous solution. The mechanism is followed memory effect.At the initial concentration of 15 mgN·l-1 for NO-2, the equilibrium concentration is lower than 1 mgN·l-1.The maximum adsorption capacities of NO-2 on Mg-Al CLDH from 293 to 323 K are 17.24 to 29.94 mgN·g-1, which are much higher than those obtained for other adsorbents.The adsorption processes are endothermic.The adsorption data are well fitted to the Langmuir isotherm model.The adsorption rate is increased considerably with temperature.The activation energy is 109.94 kJ·mol-1.The adsorption processes are chemical adsorption and well fitted with the pseudo-second-order kinetic model.The removal rate is influenced insignificantly at the initial pH of 4.0 to 9.0.The adsorption capacities are decreased with the increasing concentrations of competitive ions. The orthogonal array design shows that the initial concentration of solution is the most important factor.