High-capacity structured MgO-Co adsorbent for removal of phosphorus from aqueous solutions

Structured MgO-Co adsorbents synthesized with a template-free method were developed for removing phosphorus from aqueous solutions. The adsorbents had petal-like folds, specific surface areas of more than 200 m2/g, and phosphorus adsorption capacities of ca. 240 mg/g with removal efficiencies of 99% after 5 cycles of reuse. Adsorption of phosphorus onto the material occurs by ligand exchange, Lewis acid-base interaction and electrostatic attraction with mechanistic features varying according to solution pH. In the adsorption mechanism, electrostatic attraction is important for pH values from 1 up to the zero point charge (pH = 12.8), while ligand exchange is dominant for solution pH values from 1 to 11, while Lewis acid-base interactions become dominant at solution pH values greater than pHzpc. Mg(H2PO4)2 and MgHPO4 are the main adsorption products. Structured MgO-Co materials have high efficiency for phosphorus adsorption, require few chemical steps for synthesis, are readily immobilized or recovered with magnetic force and are applicable to recovery of phosphorus from actual wastewater streams.