Pretreatment by recyclable Fe(3)O(4)@Mg/Al-CO(3)-LDH magnetic nano-adsorbent to dephosphorize for the determination of trace F(−) and Cl(−) in phosphorus-rich solutions

The magnetic nano-adsorbent Fe(3)O(4)@Mg/Al-CO(3)-LDH (Mg/Al-type layered double hydroxide) with a CO(3)(2−) interlayer anion has been synthesized successfully on Fe(3)O(4) nanoparticles via a urea hydrothermal method. It is confirmed that the nano-adsorbent can adsorb PO(4)(3−) rapidly and efficiently in multi-ion solutions; meanwhile, it did not adsorb any F(−) and Cl(−), even with a high amount of the nano-adsorbent or a longer adsorption time. This behaviour is beneficial for applications to remove PO(4)(3−) in phosphorus-rich solutions, and especially can be utilized to determine trace F(−) and Cl(−) anions in phosphorus-rich solutions by physical and chemical analysis methods including ion chromatography without serious interference from PO(4)(3−) for trace determinations. Herein, the hydrothermally synthesized Fe(3)O(4)@Mg/Al-CO(3)-LDH was characterized via SEM, TEM, SAED, XRD, FTIR, magnetic hysteresis loop analysis and adsorption–desorption isotherm analysis. The structure and stability, adsorption mechanism, magnetic saturation value, specific surface area, total pore volume, phosphate adsorption capacity and recyclability are discussed. Using the optimized pretreatment conditions, Fe(3)O(4)@Mg/Al-CO(3)-LDH was utilized successfully to adsorb PO(4)(3−) in real samples and determine trace F(−) and Cl(−) accurately by ion chromatography; this would be very beneficial for continuous analysis and on-line tests by physical and chemical analysis methods without interference from PO(4)(3−) in phosphorus-rich samples, leaving F(−) and Cl(−) even if in a trace content.