CONICET | Buscador de Institutos y Recursos Humanos

Lithium has attracted interest in recent years due to application in batteries for mobile devices and electrical vehicles, pharmaceuticals, nuclear fuels, and other industrial applications. LiCl and Li2CO3 , are obtained from Li-containing Li-Al silicate (spodumene) or from Li-rich brines from high altitude salt lakes such as the Salar de Atacama (Chile), Salar de Uyuni (Bolivia), and Salar del Hombre Muerto or Olaroz (Argentina). The current soda lime method for the extraction and purification of Li from brines relies on evaporation in open shallow ponds to concentrate the salts and fractional crystallization of Li, Na, K, Mg chlorides. Then, Li2CO3 is precipitated by addition of Solvay and the lithium-depleted brine is discarded. The chemical process is relatively simple, however, it has a high environmental impact since it takes place at 4,000 meters above sea level where water is scarce and ecosystems are fragile.An alternative electrochemical extractive method from brine or sea water has been developed recently in our research laboratory. This electrochemical method is fast, efficient, has low environmental impact and low energy consumption. In a first step, brine is in contact with a lithium deficient LixMn2O4 ( 0 x  1) cathode and a chloride reversible poly(pyrrole) (PPy) anode; LiCl is selectively extracted spontaneously. In a second step after rinsing the cell, a low lithium concentration recovery electrolyte replaces brine and the cell potential is inverted, with the resulting recovery of LiCl. The electrode reactions at the LixMn2O4/brine interface during the extraction and release of LiCl from brine within the cubic LiMn2O4 structure are: (1)while at PPy chloride reversible electrode, oxidation of polypyrrole occurs with simultaneous uptake of chloride anions to compensate the excess positive charge in the polyions. (2)We report the performance of the LiMn2O4 /PPy battery cell using natural brine from Salar de Olaroz (Argentina) and KCl recovery solution. LiMn2O4 electrodes were cast from a LiMn2O4 (80% w/w), 10% PVDF and 10% Vulcan carbon X-72 (Cabbot Corp.) slurry dispersed in N-methyl pyrrolydone onto flat carbon Poco and dried at 105C. Natural brine from Salar de Olaroz in the province of Jujuy, Argentina was used. The chemical composition was determined by ICP: Na+ 115.600 ppm (5M NaCl), K+ 10.780 ppm (0.28 M KCl), Mg2+ 2.618 ppm, Li+ 975- 1280 ppm (0.18 M LiCl), B 1.440 ppm, dynamic viscosity of 2.077 Cp, density 1.2710 g.cm-3 and conductivity 0.1735 S.cm-1. The Cl-PPy counter electrode was obtained by electrochemical polymerization of an aqueous 0.1 M pyrrole solution on large surface area platinum mesh (Goodfellow) in aqueous 1.2 M HCl under potential control at 0.8-1 V vs. Ag/AgCl, 3M KCl, during 1 hour.The insertion/release of lithium and chloride at LiMn2O4 and PPy electrodes respectively has been studied by repetitive current pulses and from the E vs, Q (charge), the energy per mole of LiCl extracted could be estimated. A comparison of polypyrrole counter electrode with carbon felt or Pt electrodes has been done. For the LiMn2O4/ PPy extraction cell the cell potential was lower than 0.8 V unlike carbon felt and platinum counter electrodes, the latter with the additional caveat of chlorine evolution.We have carried out repetitive anodic and cathodic current pulses for more than 200 pulses, (500 A.cm-2), following simultaneously the potential at both cathode and anode and found high stability of the extraction electrodes. These studies have been complemented with ICP and ionic chromatography of Li+ extracted at different charge depth. The surface composition of the LiMn2O4 has been studied by XPS at different potentials and electrolyte composition using a special electrochemical cell and a transfer system between the electrochemical an UHV environments.