Mechanistic insight and rapid co-adsorption of nitrogen pollution from micro-polluted water over MgAl-layered double hydroxide composite based on zeolite

Abstract

Layered double hydroxide composites for water treatment have been widely studied for their advantages of high adsorption capacity, stability, and reusability. However, little is known about the co-adsorption potential and mechanism of these composites for ammonium and nitrate. In this study, based on the Box-Behnken response surface optimization design, the MgAl-layered double hydroxide@zeolite (MgAl-LDH@zeolite) composite that can rapidly co-adsorption ammonium and nitrate was synthesized via a two-step modification method. The co-adsorption process quickly reached equilibrium within 10–30 min and achieved over 80% efficiency in the initial 3 min. Besides, the MgAl-LDH@zeolite showed a low pH dependence in a wide pH range (4–8). The physico-chemical structure of MgAl-LDH@zeolite was characterized, and on this basis, the effects of pH, dosage, and coexisting ions on co-adsorption were investigated. Ion exchange, electrostatic attraction, hydrophobic sorption, and metal-bonded bridges contributed substantially to the immobilization. The ions competition simulation experiments and five regenerative cycle experiments adequately demonstrated the high selective adsorption ability and recyclability of the MgAl-LDH@zeolite. In addition, the adsorption efficiency of ammonium and nitrate in natural river water were both above 97.62%, which further confirming the application potential of the MgAl-LDH@zeolite. Overall, this work presents a new multifunctional adsorbent for nitrogen removal in the micro-polluted source water.