Magnetized vermiculite loaded with waste polishing powder to recover phosphorus in waste water

Abstract

In view of the phosphorus pollution in water bodies and the shortage of phosphate rock resources, the preparation of cheap, accessible and easy-to-recycle adsorbents for the recovery of phosphorus in sewage has attracted much attention. In this study, waste rare earth polishing powder (WP) was doped with magnetized vermiculite (Mev) at a mass ratio of 1:1 through acid leaching and advection precipitation method to prepare the magnetic Mev-WP composite material for adsorbing and recovering phosphorus in the water. The results show that Mev-WP is easy to be separated from water by an external magnetic field and the main reason why Mev-WP specificity can adsorb phosphorus is that the rare earth elements of La and Ce in the polishing powder are loaded on the flake magnetized vermiculite in the form of La (OH)3 and Ce(OH)3. The phosphorus adsorption process of Mev-WP is an endothermic mono-layer chemical adsorption that includes boundary layer diffusion and internal diffusion, of which the boundary layer diffusion is the rate-limiting step, which can complete rapid adsorption within 30 min. Except for HCO3− ions, other coexisting anions in the water have no significant effect on adsorption, but the adsorption capacity is greatly affected by pH. At pH 11 to 3, the material is a stable and environmentally-friendly adsorbent, and with the decrease of pH, the adsorption capacity increases significantly. When the pH is 3, at 25 °C, the adsorption capacity can reach up to 63.79 mg/g. The phosphorus adsorption mechanism of Mev-WP is electrostatic attraction and ligand exchange between -OH on La-OH and Ce-OH and phosphate groups in the water to generate La-O-P and Ce-O-P coordination complexes to remove phosphorus. After 5 times desorption and recycling, the phosphorus recovery rate of the material reaches 65 %, and the deep phosphorus removal verification in urban sewage is effective. Studies have shown that Mev-WP is a promising specific phosphorus recovery agent.