Development of Polyelectrolyte Complex Nanoparticles for Direct Lithium Extraction from Oilfield Brines

Abstract This paper details the formulation and characterization of a novel nanoparticle system composed of polyethyleneimine (PEI) and dextran sulfate (DS) for direct lithium extraction (DLE) from bulk oilfield brines sourced from North America. Different mass ratios of solutions of PEI and DS at varied concentrations (1 -10wt%) were prepared in the presence of 150 ppm Li concentration to yield nanoparticle systems that electrostatically entrap the Li ions in the solution. The nanoparticles produced were characterized by their size, zeta potential (charge), polydispersity index, and count rate with a particle size and zeta potential analyzer equipment. Inductively coupled plasma optical emission spectroscope (ICP-OES) and Total Organic Content-Total Organic Nitrogen (TOC-TON) analyzer equipment were coupled to analyze the Li entrapment efficiency within the nanoparticle systems. Results indicated that the final pH, size, and charge of the nanoparticles were influenced by the mass ratio of PEI and DS. Particle size exhibited a decreasing trend with increasing PEI: DS mass ratios from 1 to 5, while the opposite trend was observed for mass ratios lower than 1. Zeta potential generally became more positive with higher PEI: DS mass ratios. Meanwhile, negatively charged nanoparticles were observed at lower ratios. The extraction efficiency was optimum between 10 and 9 wt.% concentrations of PEI and DS with positively charged nanoparticle systems exhibiting greater entrapment. The maximum observed entrapment efficiency was approximately 48%, achieved through bilayer deposition. Integrating this innovative nanoparticle-based DLE method into existing lithium treatment processes can significantly enhance lithium recovery rates, either in combination with membrane extraction techniques or as a standalone methodology following the removal of divalent cations in the pretreatment phase.