Identification And Removal Of Coloring Substances In Phosphogypsum

The main component of phosphogypsum as a by-product of the acid industry is Ca SO₄·2H₂O,and its resource utilization is a worldwide problem today.Phosphogypsum contains a variety of impurities,resulting in gray,which seriously limits the resource utilization of phosphogypsum.In order to solve the whiteness problem of phosphogypsum resource utilization,this paper identifies and removes the coloring matter in phosphogypsum;the content of coloring matter in phosphogypsum is low,so it is impossible to directly analyze phosphogypsum to determine the composition and existing form of coloring matter in phosphogypsum;according to determine the coloring matter in phosphoric acid leaching slurry,the composition and existing form of coloring matter in phosphogypsum is determined.According to the judgment results,the colored substances in phosphogypsum are removed by different methods.The main work is as follows:1.Analysis and identification of coloring substances in phosphoric acid extraction slurry（1）The phosphoric acid leaching slurry is collected in the phosphoric acid production process section in this paper.The solution is obtained after dissolved by N,N-dimethylformamide and n-hexane,the solution is used to judge the composition and coloring of small molecule organic matter by gas chromatography-mass spectrometry.In order to collect the solid,Phosphoric acid and salt substances are removed by running water.The solid is used to determine the composition by XRD and XRF;the composition and content of organic matter is determined by TG and FTIR Spectrometer;the existence of samples is determined by FESEM.The experimental results showed that the main coloring material is a complex composed of Fe S₂and organics,its existence form is organic matter incompletely encapsulating Fe S₂.The content of Fe S₂is 10.70%（based on Fe）and the content of organic matter is 2.39%.2.Removal of coloring matter in phosphogypsum（1）Impurities is removed by using foam separation method in phosphogypsum.When the dosage of catcher is 3 kg/t and the amount of foaming agent is 300 g/t,the coloring matter of phosphogypsum in phosphogypsum is well removed,and the whiteness of phosphogypsum is 38.9.（2）Impurities is removed by using extraction method in phosphogypsum.When the ratio of liquid to solid is 3:1,the extraction temperature is 50℃,the dosage of 1-dodecanethiol is 15 ml,and the extraction time is 80 min,the decolorization and impurity removal effect of phosphogypsum is the best.The whiteness of phosphogypsum is 40.7.（3）Impurities is removed by using calcination method in phosphogypsum.When the calcination temperature is 600℃and the calcination time is 80 min,colored substances of phosphogypsum is removed,the whiteness of phosphogypsum is 60.（4）Impurities is removed by using pickling method in phosphogypsum.When the liquid-solid ratio was 3:1,the pickling temperature is 80℃,the mass fraction of hydrochloric acid solution is 25%,the pickling time is 100 min,the decolorization and impurity removal effect of phosphogypsum is the best,and the whiteness of phosphogypsum was 48.8.（5）Impurities is removed by using oxidation method in phosphogypsum.When the liquid-solid ratio is 2:1,the oxidation temperature is 70℃,the concentration of hydrogen peroxide is 25%,and the oxidation time is 100 min,the decolorization and impurity removal effect of phosphogypsum is the best,and the whiteness of phosphogypsum is 49.5.（6）Impurities is removed by using complex method in phosphogypsum.The complex method of hydrochloric acid pickling and hydrogen peroxide oxidation is used to decolorize and remove impurities in phosphogypsum.When the mass fraction of hydrochloric acid is 25%and the concentration of hydrogen peroxide is25%,the decolorization and impurity removal effect of phosphogypsum is the best,and the whiteness of phosphogypsum is 64.5.