RESUMO
Lithium recovery from brines has become a hot topic. The current evaporitic technology is slow, and serious environmental concern has been raised regarding the large volumes of water used, relating both to brine concentration through evaporation, and intensive pumping of fresh water needed in the fine chemical processing to produce high purity lithium carbonate. In this work, an experimental and theoretical analysis of brine desalination using a double-slope Solar Still was carried out. The Solar Still was installed right next to an existing lithium mining facility in northwest Argentina, and was tested with native high salinity lithium rich brine for a continuous year under the typical weather conditions of lithium deposits: high altitude, large thermal amplitude between day and night, strong winds, and high solar radiation. The performance of the solar still as an evaporator was compared with that of a PAN evaporimeter class A, and correlated to experimentally determined weather parameters. While the performance of the Solar Still for brine concentration was below that of open air evaporation, the Solar Still allowed for the production of an average of 2 L day-1 m-2 of distilled water, in marked contrast with current practice. Numerical simulations allowed us to quantify heat exchanges in both the Solar Still and the open air system.
Assuntos
Lítio , Purificação da Água , Água Doce , Sais , Luz SolarRESUMO
Lithium extraction from continental brines involves the evaporation of large amounts of water in open air ponds, in order to concentrate the brine. The evaporitic technology implies the evaporation of large water volumes, raising environmental concerns. If we envision the use of desalination processes for the concentration of lithium-rich brines, then fresh water production/recovery becomes a process well integrated with lithium extraction. Here we apply the Pitzer thermodynamic model with effective molality to estimate activity coefficients for 8 different native brines, and for the resulting concentrated solutions produced by a hypothetical advanced desalinization technique. In all cases, rational activity coefficients deviate considerably from unity. We calculate next the least work of separation for a hypothetical desalination process for the 8 different brines. Because of the large total salinity, the calculation shows that the least work of separation ranges from 18 until 42 kJ kg-1 at nil recovery ratio, and escalating from those numbers as more water is recovered. We can also predict the boiling point elevation, the vapour pressure lowering, and the osmotic pressure. Our calculations show that results are not strictly proportional to the total dissolved solids. Results are strongly dependent with the specific chemical composition of each brine, with the amount of divalent ions (Mg-Ca-SO42-) in particular strongly influencing calculations. Fresh water and lithium minerals production could be part of a single integrated production system.