Study On The Mechanism And Process Of Removing Calcium And Magnesium From Lithium-containing Solution With Organic Phosphoric Acid

Lithium,as the most ideal "energy metal",was widely used in glass,ceramics,batteries,lubrication,nuclear industry,medicine and metal smelting and other fields.At present,lithium has become a strategic reserve resource by many countries.With the rapid development of new energy vehicles,lithium products are in short supply and lithium extraction technology also affects the supply of lithium salt.During lithium extraction in ore or brine calcium and magnesium were the main impurities,which must be removed before or after lithium recovery process.The impurities removal technology has several shorts including greater process complexity and cost.Therefore,it is great significance to develop a new impurity removal methodIn this paper,organic phosphoric acid was used as extractant to remove calcium and magnesium from original brine and pre-concentrated salt lake brine with low magnesium-lithium ratio.The control variable method was adopted to explore the effect of saponification degree,phase ratio and extraction stage number to extraction performance.The whole process of extracting calcium and magnesium from low magnesium-lithium ratio brine was studied in separation funnel and mixer-settler.The process of extracting calcium and magnesium from brine with P204 was investigated by DFT theoretical computation,and the kinetics of extracting lithium and magnesium with P204 was studied via Lewis Cell method.The main results are as follows.(1)Three organic phosphoric acids(P204,P507 and C272)extracting metal ions were in the sequence of Ca2+>Mg2+>Li+>K+≈Na+.P204 was selected as the optimal,and it was proved that the extraction of calcium and magnesium by saponification P204 follow an equal molar extraction,and that it could be used to remove impurities from brine with different concentrations by controlling the saponification degree and phase ratio.(2)The P204 with 66%saponification was subjected to a six-stage countercurrent full-flow process experiment in a separation funnel.The extraction rate of Ca2+and Mg2+in the raw brine reached 99%,and the remaining amount of Mg2+in the raffinate was 5.91 mg·L-1 and the remaining amount of Ca2+was only 0.1 mg·L-1.The extraction coefficient of impurities in the pre-concentrated brine was more than 99%,and the remaining amount of Mg2+in the original brine was 2.54 mg·L-1 and the remaining amount of Ca2+was only 0.1 mg·L-1.Li+loss coefficient was about 7%in all the above processes.(3)P204 with 60%saponification was applied to a "1 stage saponification-4 stage extraction-3 stage reverse extraction" process experiment in a mixer settler.By controlling the process parameters,the calcium and magnesium total concentrations in the original brine and pre-concentrated brine with low magnesium-lithium ratio were removed to 10 mg·L-1,and the Li+loss coefficient was only 7%,and all the experiments was run for over 50 hours with high process stability.Compared with the method of precipitation,the method of solvent extraction has lower consumption of alkali and easy to operate.(4)The sequence of metal ion extracted by organic phosphoric acid extractant was determined comprehensively by the ion charge,hydration and its interaction with organic phosphoric acid extractant.The hydration energy of monovalent ions was significantly smaller than that of divalent ions,thus the divalent ions were more easily extracted by organic phosphoric acid.The Gibbs free energy of reaction of extraction alkali metal ions was significantly smaller than that of divalent metal ions.(5)The extraction of Li+by saponification P204 taken place at the contact interface of two phase,and the extraction reaction was controlled by both diffusion and chemical reaction.In this extraction reaction,the reaction order of Li+and NaA was first.The initial extraction rate equation of saponification P204 extraction of lithium was RLi,int=(0.0048±0.0007)·nLi·nNaA at 298K.For Mg2+,the extraction reaction was diffusion controlled,the reaction order of Mg2+was first,and the number of reaction order of NaA was second.The initial extraction rate equation for extraction of Mg2+by NaA was RMg,int=(0.1805±0.0084)·nMg·(nNaA)2 at 298 K.The investigation in this thesis not only could supply new thought and process route to the calcium and magnesium impurities removal in the lithium extraction techniques,but also could lay a science foundation for the improvement of the impurities removal by extraction with organic phosphoric acid extractants.