Fe₃O₄/MgAl-NO₃ layered double hydroxide as a magnetically separable sorbent for the remediation of aqueous phosphate

The separation of a spent sorbent from treated water after remediation is one of the major difficulties associated with industrial scale water treatment methods. Fe₃O₄ particles offer an easy magnetic method for the separation of used sorbent from water. Due to its low sorption capacity, magnetic Fe₃O₄ particles were first modified with Mg₂Al-NO₃-LDH prior to use in phosphate remediation. The Fe₃O₄/Mg₂Al-NO₃-LDH composite materials showed a maximum sorption capacity of 33.4 mgP/g while Fe₃O₄ particles alone recovered only 4.6 mgP/g. The kinetics of phosphate sorption onto Fe₃O₄/Mg₂Al-NO₃-LDH follows the pseudo-second order kinetic model supported by the best linear regression coefficient value (R² - 1.00). Sorption isotherm studies indicated that it follows the Langmuir monolayer sorption isotherm. The effect of pH and competing anion studies indicate that this material is highly efficient in a wide pH range (pH 3-10). Selective sorption of phosphate on Fe₃O₄/Mg₂Al-NO₃-LDH was observed in the presence of excess sulfate, as well as from sea water enriched with phosphate. Fe₃O₄/Mg₂Al-NO₃-LDH composite material offers easy separation of spent sorbents due to magnetic property. The retention of sorption capacity in a wide pH range, and selectivity in the presence of competing anion, as well as from sea water suggests that these composite magnetic materials will be effective for wastewater remediation.