Study On Preparation And Application Of High-Strength Gypsum From PG

The high-strength gypsum can be applied in ceramics, investment casting, medical treatment and paintingas as a kind of binding material because of its advantages such as high strength, high hardness, excellent wearability, clear outline and good mode l. The traditional method need to be improved due to complex process, high cost, quality fluctuate. The author prepared high-strength gypsum powders using half-liquid method from phosphogypsum(PG) that 1d dry compressive strength surpass 50 MPa and studied the mechanism of crystal modifier on morphology regulation.This paper studied the physical and chemistry properties of PG. The lime was used to pretreatment PG, which the dosage and neutralize time was studied. The inspiration of half-liquid method come from the advantage of hydrothermal method and steam pressure method,respectively. The experiment result showed:The pH of original PG is 2.9,and the pH increasing with the increase of lime dosage as well as neutralize time. The pH can be controlled at7.4-8.5 when the dosage of lime is 0.5%-0.7%, which is in favour of the growth of ?-hemihydrate gypsum(?-CSH) crystal. The overmuch lime will destroy ?-CSH crystal morphology as well as compressive strength.The autoclave temperature is counted as the most important element,excess temperature will lead to smaller crystal generating and decreasing hydration speed. The optimal technologic conditions of half-liquid method is autoclave temperature140?, autoclave time 3h, lime dosage0.5%, neutralization time 24 h, slurry concentration 25%, average grain diameter 22.4-69.5?m. The compressive strength can reach 28.1MPa for2 h and 52.3MPa for 1d respectively, and flexural strength 6.8MPa for 2h under the optimal technologic conditions.Crystal modifiers exert important effect on the crystal growth habit.The excessive and lesser dosage of crystal modifiers would form clubbed or amorphous. The maleic acid can control the crystal growth towards short columnar effectively. The compressive strength can exceed 50 MPawhen 0.1%-0.2% maleic acid is used. There is no chemical bonding forming to change phase of ?-CSH, and the adsorption-desorption mechanism was confirmed.Foam concrete can be prepare with density 371kg/m3 and compressive strength 0.8MPa when 0.3% latex powder, 0.6% sodium stearate and 0.3% hydrogen peroxide(mass ratio of hydrogen peroxide:lime is 7:1). The water absorption approximate to 2% for600kg/m3 foam concrete with exterior coating organosilicone. The foam concrete with density 747.9kg/m3 and 4.0MPa, water absorption approximate to 1% can be prepared with the admixing amount of cement and fly ash is 20% and 40% respectively.