Synthesis of Lanthanum-Modified Natural Magnetite: Characterization and Valorization for Phosphorus Recovery from Aqueous Solutions

In this research work, a natural sample from an Omani magnetite (MG) deposit was used for the synthesis of a magnetite decorated with ferrihydrite (MG-Fh), and two lanthanum (La)-modified materials at mass percentages of 5% (MG-Fh-La-5) and 15% (MG-Fh-La-15). These materials were first characterized using various analytical techniques. Then, their phosphorus (P) recovery efficacy from aqueous solutions was studied in batch mode under a wide range of experimental conditions. The characterization results show that compared to the raw feedstock, MG-Fh, MG-Fh-La-5, and especially MG-Fh-La-15 have improved structural, textural, and surface chemistry properties. Adsorption tests indicate that due to the deposition of high contents of lanthanum oxides on its surface, the MG-La-15 exhibited a large P uptake capacity (34.5 mg g⁻¹), which is significantly superior to those determined for MG-La-5 (24.3 mg g⁻¹), MG-Fh (12.4 mg g⁻¹), and various engineered materials published in the literature. Moreover, these materials retain an interesting ability to recover P from real wastewater with a highest adsorbed mass of 27.3 mg g⁻¹, observed for MG-La-15. The P recovery seems to involve both physical and chemical mechanisms, including electrostatic interactions and complexation. This research work shows that La-modified magnetite can be considered a promising and eco-friendly material for P recovery from liquid effluents.