Efficient and sustainable phosphate removal and recovery from wastewater with zinc-substituted magnetite

Excess phosphorus in water causes significant environmental issues, such as algal blooms, while the overexploitation of phosphorus ores has raised concerns about phosphorus depletion. To address both the removal and recycling of phosphate efficiently and cost-effectively, a Zn isomorphically substituted magnetite (Zn-Fe3O4) was synthesized by incorporating Zn(II) into the Fe(II)/Fe(III) lattice of Fe3O4, targeting phosphate adsorption from wastewater. Key parameters, such as initial phosphate concentration, adsorbent dosage, adsorption time, and pH were optimized to maximize phosphate adsorption. Based on the Langmuir isotherm model, Zn-Fe3O48.27 % demonstrated a maximum phosphate adsorption capacity of 111.5 mg P/g. Selective adsorption tests showed that Zn-Fe3O4-8.27 % had a higher affinity for phosphate than other interfering anions and dissolved organic matter. After eight adsorption-desorption cycles, Zn-Fe3O4-8.27 % retained 80 % of its initial adsorption capacity, successfully recovering over 70 % of the phosphate, with only an 11 % loss of of Zn(II). This significantly lower Zn(II) loss compared to other zinc-based adsorbents, enhancing its reusability. This high efficiency in adsorption and recycling is attributed to strong electrostatic attraction and inner-sphere complexation between Zn(II) and phosphate. Consequently, Zn-Fe3O4-8.27 % emerges as a promising adsorbent for phosphate removal from wastewater.