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 over-exploitation 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-Fe₃O₄-8.27 % 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.