Phosphate removal from aqueous solutions by nanoscale zero-valent iron

In this study, nanoscale zero-valent iron (NZVI) was synthesized by conventional liquid-phase chemical reduction methods without a support material and then characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effect of NZVI particles on phosphate removal from aqueous solutions was examined. The results showed that the phosphate removal efficiency increased from 34.49% to 87.01% as the dosage of nanoscale iron particles increased from 100 to 600 mg L⁻¹ with an initial phosphate concentration of 10 mg L⁻¹, and the phosphate removal efficiency decreased from 72.89% to 51.39% as the initial phosphate concentration increased from 10 to 90 mg L⁻¹, with 400 mg L⁻¹ NZVI. Phosphate removal efficiencies of 99.41% and 95.09% were achieved at pH values of 2 and 4, respectively, with an initial phosphate concentration of 20 mg L⁻¹ and 400 mg L⁻¹ NZVI. The use of NZVI particles synthesized in a carboxymethyl cellulose (CMC)–water solution significantly enhanced phosphate removal from an aqueous solution compared with the use of NZVI synthesized in an ethanol–water solution. NZVI particles achieved 71.34% phosphate removal, which was remarkably higher than that of microscale zero-valent iron (MZVI) particles (16.35%) with 10 mg L⁻¹ of phosphate and 400 mg L⁻¹ iron. Based on the removal mechanism analysis performed in this study, we recommend that phosphate removal be accomplished by simultaneous adsorption and chemical precipitation. The XRD patterns of the NZVI before and after the reactions indicated the formation of crystalline vivianite (Fe₃(PO₄)₂·8H₂O) during the procedure.

本研究采用传统液相化学还原法合成了未添加载体材料的纳米零价铁（nanoscale zero-valent iron, NZVI），并通过透射电子显微镜（transmission electron microscopy, TEM）、扫描电子显微镜（scanning electron microscopy, SEM）及X射线衍射（X-ray diffraction, XRD）对其进行了表征。本研究考察了NZVI颗粒对水溶液中磷酸盐的去除效果。结果表明：当初始磷酸盐浓度为10 mg·L⁻¹时，随着纳米铁投加量从100 mg·L⁻¹提升至600 mg·L⁻¹，磷酸盐去除率从34.49%升至87.01%；当投加400 mg·L⁻¹ NZVI时，随着初始磷酸盐浓度从10 mg·L⁻¹升高至90 mg·L⁻¹，磷酸盐去除率从72.89%降至51.39%。当初始磷酸盐浓度为20 mg·L⁻¹、NZVI投加量为400 mg·L⁻¹时，在pH为2和4的条件下，磷酸盐去除率分别可达99.41%和95.09%。相较于在乙醇-水溶液中合成的NZVI，在羧甲基纤维素（carboxymethyl cellulose, CMC）-水溶液中合成的NZVI颗粒可显著提升水溶液中磷酸盐的去除效果。当磷酸盐初始浓度为10 mg·L⁻¹、铁投加量为400 mg·L⁻¹时，NZVI颗粒对磷酸盐的去除率可达71.34%，显著高于微尺度零价铁（microscale zero-valent iron, MZVI）的16.35%。基于本研究开展的去除机理分析，我们建议采用吸附与化学沉淀协同作用实现磷酸盐的去除。反应前后NZVI的XRD图谱显示，反应过程中生成了结晶态蓝铁矿（Fe₃(PO₄)₂·8H₂O）。