Preparation Of Nano-CaSO₄ From Phosphogypsum

Phosphogypsum?PG?is a kind of solid waste discharged in the wet process of phosphoric acid production.Its utilization rate is not high,and the pollution to the environment is an urgent problem to be solved.At present,the resource utilization and high-value utilization of phosphogypsum is one of the research hotspots in the phosphorus chemical industry.In this paper,anhydrous nanometer calcium sulfate?anhydrous nano-Ca SO₄?with dimensions less than 100 nm was prepared with phosphogypsum as raw material through modification and crystal control,and added to HDPE material to improve its performance.The main research results are as follows:?1?The preparation process of anhydrous nano-Ca SO₄ was studied.With phosphogypsum as raw material,the effects of the amount of HNO₃ and H₂SO₄,the amount of ethanol/glycerol and CTAB,and the reaction temperature on the morphology of anhydrous nano-Ca SO₄ prepared from phosphogypsum were studied by means of SEM,TEM and XRD.When the volume ratio of glycerol to ethanol is2:1,and the solid-liquid ratio of PG:CTAB:HNO₃:H₂SO₄ is 4:1:4:4,anhydrous nano-Ca SO₄ with a cubic structure with dimensions less than 100 nm can be prepared at 140°C.?2?The formation mechanism of anhydrous nano-Ca SO₄ was studied.By means of TG-DSC,FTIR and XPS,the formation mechanism of anhydrous nano-Ca SO₄crystal morphology under different processing conditions was studied.With the increase of reaction temperature,when the concentration of Ca²⁺andSO₄^2-ions in the system reaches the supersaturation of Ca SO₄,anhydrous Ca SO₄ crystal nucleus are formed;The addition of HNO₃ and H₂SO₄ can reduce the supersaturation of Ca SO₄ and inhibit the precipitation of whiskers,which will hinder the growth of Ca SO4 along the c-axis.The same ion effect ofSO₄^2-in the solution will inhibit the dissolution of Ca SO₄·2H₂O;By the combination of glycerol/ethanol/CTAB,the growth of nano-Ca SO₄ along the c-axis was inhibited,and the ratio of length to diameter was reduced.?3?The effect of adding anhydrous nano-Ca SO₄ on the properties of HDPE was studied.Nano-Ca SO₄ was modified by KH570 and stearic acid,respectively.The structure and crystallization behavior of HDPE composite with nano-Ca SO₄ were studied by SEM and DSC.When nano-Ca SO₄ is modified by KH570 and added to HDPE,the ester group in KH570 molecular chain increases the polarity of the matrix and forms hydrogen bond,and the intermolecular force increases,which makes nano-Ca SO₄ more evenly dispersed in the matrix and reduces the stress concentration and crystallinity.When the addition amount of nano-Ca SO₄ modified by KH570 is3%,the tensile strength of modified HDPE is 18.51%higher than that of pure HDPE,and the melt strength is 2.25 times higher,which shows that the modified nano-Ca SO₄has a better effect on HDPE.