Ammonium sulfate, ammonium bisulfate and ferric oxide are mixed at a molar ratio of 8:5:13 and heated in high temperature muffle furnace or fluidized bed at different temperature. To the sample, the thermal gravimetric (TG) analysis is used, the reaction residue is analyzed by fourier transform infrared spectroscopy (FT-IR) and chemical analysis, the generated gas is qualitatively analyzed as well. The process of thermal decomposition for ammonium sulfate and ammonium bisulfate via addition of Ferric oxide has four stages-the decomposition of ammonium sulfate, the formation of ammonium ferric pyrosulfate, the decomposition of ammonium ferric pyrosulfate, and the decomposition of ferric sulfate. The ammonium ion in sample is completely decomposed at about 500°C. The decomposition ratio of sulfate ion or bisulfate ion is up to 99.8% above 800°C.
Possible ways to remove fluoride from phosphoric acid are extraction,but there are always generated a second organic phase ,where still have small amounts of impurities such as fluoride,sulfate,iron,aluminum and heavy metals. The traditional process using pure water or dilute phosphoric acid washing the organic phase to get phosphoric acid ,but the impurities removing rate is not obvious.This study explore a new way to changes the washing detergent,using dilute alkali solution to reduce fluoride content of stripping in phosphoric acid.The optimization of experimental conditions is dilute alkali mass fraction 20%,dosage 0.4%,temperature 45°C,the defluorization rate can be 67.75% and phosphorus pentoxide yield rise to 95.50%.This study provides a new idea to improve defluorination rate in industrial production.
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