Study On Properties And Mechanism Of Phosphogypsum Purification And Its Preparation Of PVC Composites

With the rapid development of china’s industries, the output of industrial solid waste is increasing. At present, the accumulated pile quantity of phosphogypsum in our country is over250million tons, its annual increment exceeds55million tons, but its utilization rate is only30%. Therefore, using phosphorus gypsum as inorganic filler is one of the efficient utilization ways.Based on phosphorus gypsum as raw materials, this thesis investigated the purifying-whitening preparation process of phosphogypsum and the influence on material properties when filled polyvinyl chloride (PVC) with the phosphogypsum, discussed the phosphogypsum surface modification to the compound materials mechanics performance influence and the phosphogypsum superficial modified mechanism, and studied the processing rheological properties of high filling phosphogypsum/PVC composite materials.First of all, the process conditions of impurities removal and whitening of phosphogypsum was studied. The result showed that iron and organic matter had a greater impact on the whiteness of phosphogypsum, and using the acid soluble-roasting methods could effectively remove these impurities. Under the same concentration of acid, the iron removal result of hydrochloric acid is better than sulfuric acid, and the product turned into the short stick anhydrous calcium sulfate with average particle size of6.67micrometer. The organic compounds were removed when the sintering temperature was above600℃. The whiteness of the product reached up to97.0under the conditions of pickling temperature60℃,20wt%concentrations of hydrochloric acid, pickling time3.0h, sintering temperature800℃and sintering time2.0hSecondly, the surface modification of the pickling-calcined phosphogypsum and applying it to the preparation process of PVC composite were studied. The results indicated that the filler content of phosphogypsum, the surface modification of phosphogypsum and PVC additives had the more significant effect on the mechanical behavior of phosphogypsum/PVC composite. The phosphogypsum after the surface modification improved the mechanical properties of composite. The flexural strength, bending modulus, tensile strength and impact strength of the composite respectively reached62.76MPa and 2949MPa,32.60MPa,26.60kJ·m-2when the filler content of phosphogypsum was60phr and the adding amount of silane coupling agent KH-550was1.0%. After surface modification, there was the physical absorption or chemistry reaction between the coupling agent and phosphogypsum. In addition, ACR and CPE of the PVC additives could improve the impact strength of the composite.Finally, the performance of PVC composites prepared with the high packing phosphogypsum was researched. The results indicated that the blending temperature, surface properties of phosphogypsum and PVC processing additive of PVC had the important effects on processing rheological property of phosphogypsum/PVC blend system; the plasticizer of DBP could significantly improve the rheological properties of PVC, formed the chemical bonding with PVC and increased the PVC molecular spacing. At the conditions of blending temperature190℃,20phr of DBP and350phr of phosphogypsum filled amount, PVC/phosphogypsum composite with the bending strength28.4MPa was prepared.