Hierarchical flower-like MgAl layered double hydroxide microparticles as phosphate porter for its recovery from phosphate-contaminated water

Abstract

Layered double hydroxide (LDH) represents an important class of adsorbents for phosphate (P) recovery from water, but the scale application remains challenged by the scarcity of LDH adsorbents with balanced adsorption capacity and settling performance. Herein we developed the three-dimensional MgxAl100-x-LDH microparticles (∼4 μm) with hierarchical flower-like structure and controlled compositions, which delivered fast P adsorption (equilibrium time < 5 min), large P adsorption capacities (108.8 mg g−1 by Mg60Al40-LDH) and better settling performances than the nanoscale LDH counterpart. The mechanistic study revealed that the robust adsorption performance of MgAl-LDH was attributed to the efficient anion exchange of P with the intercalated anions (Cl− and CO32−) in LDH. Owing to the exchangeability of intercalated P with the concentrated CO32− in aqueous solution, we demonstrated that almost all the P adsorbed in LDH could be recovered in 1.0 M Na2CO3 solution, and the cumulative P in solution could reach a concentration of 4.5 g/L after batches of recovery experiments. The Mg60Al40-LDH was further coupled with magnetic particles for P removal from natural lake water. The composite afforded high efficiencies in P removal and adsorbent separation from water (settling time: ∼10 min), but inadequate adsorption selectivity towards P especially in the presence of SO42− and dissolved organic matters. This work is expected to provide a new platform for both the efficient P recovery and adsorbent collection from wastewater.