Selective nitrate removal from aqueous solutions by a hydrotalcite-like absorbent FeMgMn-LDH

FeMgMn-LDH, a type of potential environmental remediation material, has been synthesized via a co-precipitation method, and its adsorption characteristics for nitrate were investigated in this study. It's shown that the prepared FeMgMn-LDH is a promising adsorbent for anions removal, which has high buffer capacity (final pH remained between 9 and 10) and high reversibility, and can remove nitrate ions selectively though an anion-sieve effect. The maximum amount of nitrate adsorption is 10.56 N-mg g^-1 at 25 ℃. The removal rate of nitrate ions can reach 86.26% with the adsorbent dose of 5 g/L in a real water. The competition order of coexisting anions on nitrate adsorption by FeMgMn-LDH is CO₃^2- > PO₄^3- > SO₄^2-. The negative values of ΔG⁰ (from - 27.796 to - 26.426 kJ mol^-1) and ΔH⁰ (- 6.678 kJ mol^-1) indicate that the nitrate adsorption process on the FeMgMn-LDH is spontaneous and exothermic. The main adsorption mechanisms of nitrate removal from aqueous solutions by FeMgMn-LDH are electrostatic attraction and ion exchange.