Study On The Extraction Of Fluoride Ion In Wet-process Phosphoric Acid

Although the wet phosphoric acid process is very mature,it still faces the problem of high impurity and low purification rate in downstream products.Fluorine is one of the main impurities.The separation and purification of fluorine in wet phosphoric acid are studied in this paper.In this paper,the separation of fluorine ions in leaching solution of Weng'an phosphate ore in Guizhou Province was studied.The separation of fluorine ions from phosphate rock leaching solution and scrubbing and stripping of fluorine ions from loaded organic phase were studied by a new liquid-liquid separation method------bubble membrane separation method.The separation system was systematically studied on the sides of reaction mechanism and kinetics.This paper not only has important value for purification of wet phosphoric acid,but also has important theoretical reference value for comprehensive utilization of fluorine-contained phosphate ore in China.The chemical composition of Weng'an Phosphate ore was analyzed.The results show that phosphate rock belongs to high grade phosphate ore,the content of P₂O₅ is32.65%,the content of fluorine is 3.68%and the leaching rate of fluorine ion is 82.8%.The organic solvents used in the separation process were also selected from some alternative organic solvents.The results showed that TP35 and SO17 had the best separation effect,so they were selected as the organic phase of the separation system.TP35 and SO17 were used as a composite organic phase,and sulfuric acid was used as an organic phase treating agent,and the fluorine ions in the leaching solution of the phosphorite were separated and measured.The results show that the volume ratio of the sulfuric acid to the compound organic phase is 1:1,the volume ratio of the TP35 and SO17 is 7:3,the volume ratio of the compound organic phase to the water phase is 1:5,the stirring speed is 200 r/min,the reaction temperature is 90?,When the reaction time is 50 min,the separation rate of the fluoride ion is 98.3%,and the loss rate of P₂O₅ in the leaching solution of the phosphate ore is only 2.21%.The stripping experiment of fluoride ions in loaded organic phase was carried out using sodium hydroxide solution as stripping solution.The results show that when the molar concentration of sodium hydroxide solution is 2 mol/L,the volume ratio of sodium hydroxide solution to organic phase is 10:1,the reaction time is 30 min,the reaction temperature is room temperature,and the stirring speed is 200 r/min.The stripping rate of fluorine ion reaches 90.2%,and the compound organic phase is able to reuse,and the fluorine ions are recycled.The reaction mechanism of the separation system was studied.The results show that the separation system is different from the conventional liquid-liquid extraction separation.It is a bubble diffusion process based on bubble membrane separation.The bubble formation in the reaction process is studied by bubble theory and its diameter is calculated.Based on the results,a reaction process model was established.The reaction kinetics of the separation system was studied by establishing the reaction kinetics model.The results show that the separation system is a mixed control process?diffusion control and interface reaction control?.The apparent activation energy of the reaction process is calculated to be 21.6 kJ/mol.The macroscopic kinetic equation of the separation system is obtained finally.