Laser-induced breakdown spectroscopy for quantitative lithium monitoring in geothermal brines for lithium extraction

We introduce an innovative optical measuring device based on laser-induced breakdown spectroscopy (LIBS) for the quantitative analysis of Li in geothermal brines for Li extraction. LIBS allows for contactless and in-situ monitoring of dissolved Li. In the presented technique, we induce plasma on the surface of artificial high saline fluids under flow. We utilize a nanosecond Nd: YAG laser operating at 1064 nm wavelength and 6 ns pulse duration. The pulse laser energy is set to 26 mJ. For each sample, we perform 50 shots at a repetition rate of 1 Hz, and the acquired spectra are averaged. By carefully selecting the parameters of our LIBS system, we achieve efficient measurements on the liquid surface, minimizing common phenomena such as splashes, bubbles, or ripples. We calibrate our system using artificial samples over a wide range from approximately 10 to 1300 mg/L, for Li I line at 670.8 nm, and we derive a calibration curve exhibiting an R2 value of 99.98%. Our LIBS implementation on the flowing fluid surface, coupled with the calibration of the system, enables accurate quantification of Li in high saline fluids with an average relative uncertainty of less than 2%. The precision of our measurements, compared to reference values obtained using ICP-OES, is high, with a percentage difference ranging from 0.1% to approximately 7%. Our findings demonstrate precise quantification of Li in high saline fluids. The accurate Li monitoring achieved through our presented technique, combined with the fast, contactless, and in-situ capabilities of LIBS, paves the way for its integration into Li extraction facilities in geothermal power plants.