Facile preparation of dual La-Zr modified magnetite adsorbents for efficient and selective phosphorus recovery

•Magnetic La-Zr adsorbent was prepared by one-step coprecipitation.•La content in bimetallic adsorbent increases P adsorption capacity.•Desorption efficiency declines with the La increasing content.•High performance was remained after 5 treatment cycles with fish farm sludge. Phosphate (P) is an irreplaceable resource for the growth of all living organisms, and the impending exhaustion of minable P rock arouses the demand of P recovery, which further promotes the novel technologies development. To reclaim the P from wastewater or sludge conveniently and efficiently, a novel magnetic adsorbent with La-Zr bimetallic modification (La-Zr@Fe3O4) possessing a high affinity to phosphate and rapid separation was proposed in this study. Adsorption tests showed that the adsorption capacity of P on La-Zr@Fe3O4 increased with La content, reaching the maximum value of 49.3 mg/g at pH 3 by L1Z2. Whereas, the addition of La resulted in the decline of desorption efficiency from ~85% to ~60% in the pH range from 3 to 6, except pH 2. The kinetics of P adsorption on the La-Zr@Fe3O4 was described well by the pseudo-second-order model, while the isotherm of P adsorption was fitted well by the Freundlich model. Besides, the adsorbent exhibited high selectivity towards P over other coexisting ions (Cl−, NO3−, SO42−, Mg2+, and Ca2+). The feasibility of P recovery from the solid phase was investigated and confirmed by P recovery from fish farm sludge. The 90% removal efficiency of P and 88% desorption efficiency in cyclic adsorption/desorption experiments evidenced the stability and reusability of La-Zr magnetic adsorbent. The analysis of X-ray diffraction, Fourier transform infrared spectrum, and X-ray photoelectron spectroscopy revealed the replacement of OH− with phosphate via the ligand exchange was the adsorption mechanism. This work demonstrated that the highly efficient, rapidly separable, and repeatable La-Zr@Fe3O4 has the potential for phosphate sequestration and recovery.