Study On The Process And Mechanism Of Extracting Lithium From Hydrochloric Acid Leaching Solution Of High Alumina Coal Fly Ash By Solvent Extraction

The present work used solvent extraction method to extract lithium from hydrochloric acid leaching solution of high-alumina coal fly ash.The extraction system,single factor experiment and extraction process were studied,and the extraction mechanism was discussed.In extraction stage,an extraction system was determined with tributyl phosphate as extractant,sulfonated kerosene as diluent,and FeCl₃ as co-extractant.And the optimum conditions were explored:TBP:sulfonated kerosene(volume ratio)=7:3,phase ratio(O/A)=1:4,Fe/Li molar ratio 1.6,extraction time was 5 min at 20?.Under this condition,the extraction efficiency of lithium reached 90.49%in single-stage extraction and 99.26%in Two-stage counter-current extraction.In scrubbing stage,loaded organic phase was scrubbed with 6 mol·L^-1 HCl at O/A=40:1 to remove Al³⁺,then the loaded organic phase was scrubbed by three-stage counter-current scrubbing with 5.5 mol·L^-1Li Cl-0.5 mol·L^-1 HCl at O/A=30:1 to remove Ca²⁺.In stripping stage,99%of Li⁺in scrubbed organic phase was stripped by five-stage counter-current stripping with 6mol·L^-1 HCl at O/A=10:1,the lithium in stripping liquor was enriched to 17.526 g·L^-1,and the total concentration of impurity ions was 0.57 g·L^-1.In regeneration stage,2mol·L^-1 Na OH was used as regenerant to remove free acid and exchange H⁺of extractive compound.There were no third phase,emulsification and solid deposition during the whole experiment.Therefore,the organic solvent extraction is a promising method to recover lithium from hydrochloric acid leaching solution of high-alumina coal fly ash.Mechanistic investigation of lithium extraction from hydrochloric acid leaching solution of high-alumina coal fly ash with the TBP-sulfonated kerosene-FeCl₃ extraction system found that:the structure of extractive compound was Li[FeCl₄]·TBP,and its extracted complex ratio was 1.Both extraction enthalpy?H and the extraction free energy?G were negative,which indicated that the extraction process was exothermic and spontaneous.Therefore,the experiment should be performed at normal or low temperature.