Production Of Industrial Grade Lithium Fluoride By Sodium Fluorosilicate Produced By Phosphate

Phosphate bearing-ores contains 2.5～4.0% fluorine, in wet-process phosphoric acid(WPA),part of fluorine escaped in the form of SiF4 by water absorption,got concentration for 8～15% of fluorosilicic acid solution. In domestic most of phosphate fertilizer enterprises recycled fluorosilicic acid solution to prepare sodium fluorosilicate and sodium fluoride,but as a sodium fluorosilicate,sodium fluoride use narrow, price low and the market capacity small, the products usually dull of sale. In order to improve the value-added of NaF from phosphate fertilizer by-product and solve the problem of NaF poor sale, this experiment take phosphate fertilizer by-product sodium fluoride as fluorine source to explore a new process routes for the preparation of fluoride lithium.The process of preparing fluoride lithium from phosphate fertilizer by-product NaF and LiOH·H2O was discussed in this paper. First, respectively take hydrofluoric acid and alkali sodium hydroxide as desilication reagent to remove SiO2 in NaF from phosphate fertilizer by-product, Compare the effect of desilication, choice the better; then phosphate fertilizer by-product sodium fluoride as fluorine source to explore process routes for preparation of fluoride lithium in water and hydrofluoric acid respectively, Compare two process routes of preparation of fluoride lithium, choice the better, At last collected waste alkali in the reaction,filtrate and washing liquid,adding sodium fluorosilicate preparation of sodium fluoride and sodium silicate, in order to achieve the recycling of resources. Study results showed that:1.Study the effect of desilication on NaF from phosphate fertilizer by-product, Experiments indicate that compare with hydrofluoric acid, take sodium hydroxide as desilication more better in desilication effect, and more economic value. The better desilication process condition is:① T=105℃;② t=10h;③ n(NaOH)/n(SiO2)=4;④ C(NaOH)=1mol/L.In this condition, desilication rate reached 80.79%,the SiO2 content in raw material NaF from phosphate fertilizer by-product is reduced to 0.16%(by mass).2. With water as solvent,the optimum conditions of preparing lithium fluoride is:① liquid-solid ratio=10;② T=90℃;③ washing water dosage is V=50 m3/t;④ n(Li)/n(F)=1.05;⑤ reaction time is 8h;⑥ stirring rate r=120r/min.In this optimum conditions, the purity of LiF reached 98.94%,the yield of LiF over 90% and the quality of LiF met the GB/T22666-2008.3.With hydrofluoric acid as solvent.the optimum condition of preparing lithium fluoride is:① liquid-solid ratio= 10;② T=80℃;③ n(HF)/n(F)=15%;④ n(Li)/n(F)=1.05;⑤ reaction time is 5h;⑥ stirring rate r=150r/min.In this optimum conditions, the purity of LiF reached 99.18%,the yield of LiF over 90% and the quality of LiF met the GB/T22666-2008.4.Compared with two process routes of hydrofluoric acid and water as solvent,Although the product purity of taking hydrofluoric acid as the solvent slightly higher,Considering the cost and equipment corrosion bigger than take water as solvent,comprehensive consideration,select water as solvent to prepare lithium fluoride.5. Collected waste alkali from the process of preparation of lithium fluoride and washing liquid,adding sodium fluorosilicate preparation of sodium fluoride and sodium silicate, the quality of NaF met YS/T517-2006 and the modulus of sodium silicate reached 2.23.The characteristics of this process is to desilicate raw material of sodium fluoride and water alkali (sodium hydroxide) generated in this process can be used for producting sodium fluoride after joining fluorine sodium silicate, not only increase the economic benefits of this technology,also greatly reduces the waste liquid pollution to environment,to achieve the recycling of resources.