Nanoparticles Aid Extraction of Lithium From Oilfield Brines

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 221397, “Development of Polyelectrolyte Complex Nanoparticles for Direct Lithium Extraction From Oilfield Brines,” by David K. Danso, SPE, University of Kansas and Tertiary Oil Recovery Program; Jozef Bicerano, Bicerano & Associates Consulting; and Douglas P. Heller, SPE, Sun Specialty Products, et al. The paper has not been peer reviewed. _ 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 were prepared in the presence of 150-ppm lithium (Li) concentration to yield nanoparticle systems that entrap the Li ions in the solution electrostatically. Results indicated that the final pH, size, and charge of the nanoparticles were influenced by the mass ratio of PEI and DS. Integrating this innovative nanoparticle-based DLE method into existing lithium-treatment processes can enhance lithium recovery rates significantly. Materials and Methods Reagents. Polycationic branched PEI with a molecular weight of approximately 25 kDa was used without further purification. Anionic dextran sulfate—sodium salt with a molecular weight of approximately 500 kDa—was used as received. Lithium chloride (LiCl) salt was used to prepare Li brine solution. Hydrochloric acid (HCl) with 37% concentration and sodium hydroxide (NaOH) was used for pH adjustments of PEI. Preparation of PEI Solution. A total of 20 g of PEI was added into 180 g of reverse-osmosis/deionized (RO-DI) water (18.2 MΩ) under continuous stirring at 600 rev/min to yield 10 wt% of PEI stock solution after 30 minutes. The stock solution obtained was further diluted to 9, 8, 7, 5, 4, 3, 2 and 1 wt% PEI solutions. The pH of these solutions was decreased from approximately 11 to a desirable pH by the addition of 37% HCl or 1-M NaOH solution when the target pH was bypassed. Preparation of DS Solution. A total of 20 g of DS was added gradually into the vortex of 180 g of RO-DI water under continuous stirring at 600 rev/min to yield 10 wt% of DS stock solution after 40 minutes. The stock solution obtained was further diluted to 9, 8, 7,6, 5, 4, 3, 2 and 1 wt% DS solutions. Polyelectrolyte Complex Preparation and Characterization. Varied compositions of polyelectrolyte complex nanoparticles were prepared dropwise at a 1,200-rev/min drop. In all formulations, the same percentage by weight of PEI and DS was paired in the complexation reactions. Thus, the mass ratio was rather varied. The order of addition of formulation was PEI first, followed by DS, and, finally, the addition of the 28,401-ppm LiCl solution. A 10-minute interval was allowed for PEI and DS to completely mix and form nanoparticles before the LiCl was added to the glass vial. The pH of the complex was recorded, and 0.2 mL was measured into a cuvette. The cuvette sample was further diluted by a factor of 11 by adding 2 mL of RO-DI water. The new pH was documented for particle-size distribution and zeta-potential measurements.