Abstract
Lithium-rich geothermal waters are considered as an alternative source, and further concentration of lithium is required for its effective recovery. In this work, we have simulated a three-stage lithium recovery process including the brine softening by precipitation Ca2+/Mg2+ cations with sodium carbonate (calculated in PHREEQC), followed by an integrated system consisting of membrane distillation unit (water evaporation), crystallizer (NaCl precipitation), and membrane extraction (Li+ recovery), which was simulated in Simulink/MATLAB. It was shown that the deterioration of membrane performance in time due to scaling/fouling plays a critical role in the performance of the system resulting in the dramatic increase of the replaced membrane modules by a factor of 5. Low cost membranes are required. The process simulation based on the experimental and literature data on the high salinity solutions with the membrane distillation revealed that the specific productivity can be achieved in the range of 9.9–880 g (Li+) per square meter of membranes in the module used before its replacement. The increase of energy efficiency is needed. The mass-flow-rate of saline solution circulated to the crystallizer was set at its almost minimum value as 6.5 kg/min to enable its successful operation at the given parameters of the membrane distillation unit. In other words, the operation of the integrated system having 140 kg of saline solution in the loop and a membrane module of 2.5 m2 for concentration of lithium presence from 0.11 up to 2.3 g/kg would be associated with the circulation of about of 259 tons of saline solution per month between the distillation unit (60 °C) and the crystallizer (15 °C) to yield of up to 1.4 kg of lithium ions. The comprehensive summary and discussion are presented in the conclusions section.
Highlights
The development of new technologies over the past decade has been associated with a sharp increase in lithium consumption, which is evident by a tenfold increase in lithium production from 1995 to 2019, reaching about 80,000 tons per year [1]
Lithium-rich geothermal waters are considered as an alternative source, and further concentration of lithium is required for its effective recovery
The high salinity of such geothermal brines including the presence of magnesium cations hinders their wide utilization
Summary
The development of new technologies over the past decade has been associated with a sharp increase in lithium consumption, which is evident by a tenfold increase in lithium production from 1995 to 2019, reaching about 80,000 tons per year [1]. The membrane prepared from 30% EVAL showed a Li+ flux of 6.8 g/m2·h at a Li+ feed concentration of 0.7 g/L These membranes possess limited stability under operation conditions (extractant regeneration by strong hydrochloric acid). Such treatment is associated with scaling and salt deposition due to high initial salinity and the pronounced presence of calcium and magnesium in some cases, which would result in the drop of membrane productivity, deterioration of heat and mass transfer, and the increasing of hydraulic resistance [27]
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