Solvent Extraction Of Lithium From Hydrochloric Acid Leach Liquor Of Coal Fly Ash By TBP

Coal Fly ash?CFA?is a solid waste produced in the coal combustion process.A large amount of CFA accumulated,bringing about serious environmental pollution and ecological damage.The main chemical composition of CFA is alumina?Al₂O₃?,silica?SiO₂?,iron oxide?Fe₂O₃?and calcium oxide?CaO?.In addition,it also contains trace rare metals such as lithium?Li?,gallium?Ga?,vanadium???,rare earth elements,among of which,the content of Li in CFA is about 250¹400 ?g/g.It will be of great value if Li in CFA can be recovered.At present,many technologies have been developed to recover and utilize Al and Si from CFA and achieved good progress.This provides significant technical support for high-value utilization of CFA.It will be cost-effective and promising if Li???can be recovered during the separation and utilization of Al and Si from CFA.The commonly used methods of recovering Li???include precipitation,adsorption,solvent and extraction,most of which focus on neutral and alkaline systems.Few research has been reported on the selectively extraction of Li???from acidic systems,especially from acidic leach liquor of CFA.The coexistence of multi ions involving Fe???,Al???,Ca???in the CFA acid leach liquor cause much difficulties in the selective extraction of Li???.This work aims at the difficulty of selective extraction of Li???from CFA simulated hydrochloric acid?HCl?leach system.Solvent extraction technique was used to investigate the extraction behavior and mechanism of Li???from Li???/Al???/Fe???-HCl-H₂O system by tributylphosphate?TBP?and dichloromethane?DCM?.Subsequently,the selective extraction of Li???from simulated CFA hydrochloric acid leach liquor was performed under the optimum conditions.The stripping of Li???in organic phase and the reuse of TBP were also investigated.The main research contents and conclusions are as follows:?1?The effect of HCl concentration,Fe/Li molar ratio,O/A ratio and TBP concentration on the extraction and selectivity of Li???were studied byusing TBP and DCM extraction system.The optimum conditions for extracting Li???from Li???/Al???/Fe???-HCl-H₂O system were obtained.The results showed that approximately 90.0% of Li???was recovered from the solutions containing 0.4 mol/L HCl,3:1 Fe/Li mole ratio,2 mol/L Al???using 1.85 mol/L TBP with a 1:1 of O/A ratio after a single stage of extraction.The maximum loading of Li???for 1.0 mol/L TBP was 2.2 g/L,where the molar ratio of TBP:Li:Fe was 3:1:1.AlCl₃ can enhance the extraction of Li???significantly by its salting-out effect.Under the optimum conditions,the solvent extraction and enrichment of Li???from CFA simulated hydrochloric acid leach liquor was conducted.The extraction efficiency of Li???was about 90.0%.?2?The extraction mechanism of Li???from Li???/Al???/Fe???-HClH₂O system was investigated using ultraviolet visible spectroscopy?UV-Vis?,infrared spectroscopy?FT-IR?and electrospray ionization mass spectrometry?ESI-MS?.The organic phase before and after extraction was characterized.The results showed that Li???was transferred into organic phase by the synergistic effect of the electrostatic interaction between [FeCl₄]-with the complex cation and the coordination reaction of TBP with Li???.The existing form of the Li???complex in organic phase was [Li?TBP?n?H₂O?m]+·[FeCl₄]-?0<n?3,0?m?1?.[Li?TBP?₃]+·[FeCl₄]-was the main form.?3?The way for effective stripping of Li???from Li-loaded organic phase was further developed.Taking H₂SO₄ and HCl as stripping agents,the effect of stripping agent concentration,O/A ratio on the stripping of Li???was investigated.The results showed that HCl was more effective stripping agent.More than 70.0% of Li???can be stripped from Li???-loaded organic phase under the optimum conditions which were 2:1 of O/A,6 mol/L of HCl after one stage of stripping.After two-stage of stripping,Li???in organic phase can be stripped and the extractant can be reused after washing the organic phase.In this paper,TBP was investigated as extractant to extract Li???from simulated CFA hydrochloric acid leach liquor.The extraction behavior of Li???from Li???/Al???/Fe???-HCl-H₂O system by TBP was studied and theextraction mechanism was also revealed.TBP can be reused after stripping and washing.This work provides an alternative technology for the selective extraction of Li???from CFA hydrochloric acid leach liquor.