[Removal of Fe(Ⅱ), Mn(Ⅱ), and NH₄⁺-N by Using δ-MnO₂ Coated Zeolite]

δ-MnO₂/zeolite nanocomposites were prepared with natural zeolite, potassium permanganate, and manganese sulfate by oxidation-reduction precipitation, which were used to simultaneously remove Fe²⁺, Mn²⁺, and NH₄⁺-N from groundwater. To investigate the performance and mechanism of Fe²⁺, Mn²⁺, and NH₄⁺-N removal from groundwater by δ-MnO₂/zeolite nanocomposites, static batch experiments were conducted under different environmental conditions in a zero-oxygen atmosphere using SEM, TEM, Zeta potential, FTIR, and XPS techniques. The experimental results showed that the manganese-oxide-coated natural zeolite was δ-MnO₂, and Fe²⁺, Mn²⁺, and NH₄⁺-N adsorption on the δ-MnO₂/zeolite nanocomposites could be best described with the pseudo-second-order kinetic model and the Langmuir model. In addition, the maximum adsorption capacities of Fe²⁺, Mn²⁺, and NH₄⁺-N were calculated to be 215.1, 23.6, and 7.64 mg·g^-1, respectively. The removal mechanism of NH₄⁺-N from the solutions by zeolite was via the action of ion exchange, and the adsorption and oxidation catalysis of δ-MnO₂-coated zeolite were responsible for the removal of Fe²⁺ and Mn²⁺. This research indicates that δ-MnO₂/zeolite nanocomposites could be used as highly efficient adsorbents to simultaneously remove Fe²⁺, Mn²⁺, and NH₄⁺-N from water.