(381d) Phosphate Removal and Recovery from Aqueous Solution Using Polyelectrolyte Modified Lignin-Magnetic Nanoparticles

Wastewater treatment for different contaminants, including nutrients such as phosphorus and nitrogen, is a global problem that has garnered much research for the past decades. Phosphorous in wastewater may exist at different concentrations and in several forms, such as orthophosphates (H₂PO₄^-, HPO₄^2-, and PO₄^3-), polyphosphates, and inorganic phosphates, depending on the source. Conventional water-purification treatment methods, such as membrane filtration, are proven but often exhibit low flow rates, hindering their application in processing large volumes of water. Magnetic nanoparticles have recently been evaluated as adsorbents for water treatment due to their large surface area, numerous adsorptive sites, and functionalization ability. However, they face some challenges as researchers investigate methods to effectively develop an economically and technically feasible route for large-scale commercial production of adsorbents with an optimal removal capacity and high removal efficiency.

In this study, magnetic nanoparticles grafted with lignin biopolymer and strong polyelectrolytes are synthesized and assessed for phosphate adsorption capabilities. MNP-lignin particles were synthesized via chemical co-precipitation of Fe²⁺ and Fe³⁺ in the presence of lignin in an inert atmosphere. The polyelectrolytes, poly (vinyl ethyl imidazolium bromide) and poly (diallyl dimethyl ammonium chloride) were polymerized from the MNP-lignin surface through a free radical polymerization using lignin hydroxyl groups as polymerization initiation sites. The resultant MNP-lignin-polyelectrolyte particles were then characterized through a suite of techniques to determine their material properties, including dynamic light scattering (DLS), zeta potential (ZP), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). Phosphate adsorption experiments were conducted to evaluate the removal of various phosphorous species from wastewater as a function of time, initial phosphate concentration, and co-anion presence. Adsorption isotherms and kinetics were also evaluated to determine the fundamental adsorption mechanism between phosphate and the lignin-graft-polyelectrolyte surface chemistry. Magnetic separation and regeneration of the adsorbents were also assessed to evaluate recyclability.