Abstract:

Preparation of high-strength gypsum is an important way to recycle phosphogypsum.In order to realize the recycling of phosphogypsum,the method of autoclaved aqueous solution was adopted by using aluminum sulfate,potassium oxalate and their complexes as crystal modifier to prepare α-hemihydrate gypsum under the conditions of autoclaved temperature of 130 ℃,holding time of 6 h and liquid-solid mass ratio of 0.5.The effect of the different crystal modifier on the morphology and mechanical properties of α-hemihydrate gypsum was discussed.The results showed that the morphology of the samples prepared by using aluminum sulfate as the crystal modifier had a tendency to develop from needle-like to long-column,small-grain to large-grain with the increase of crystal modifier content,but the morphology of the samples prepared by potassium oxalate as the crystal modifier was mostly short columnar and the grain size was different.When the total amount of crystal modifier was 0.6% of gypsum and the ratio of aluminum sulfate to potassium oxalate was 5∶1,the sample prepared by the composite crystal modifier had the characteristic of large crystal grain size and regular crystal morphology（hexagonal crystals）.The 2 h flexural strength and 2 d absolute dry compressive strength could reach 5.88 MPa and 36.90 MPa respectively.

Key words: α-hemihydrate gypsum, crystal modifier, aluminum sulfate, potassium oxalate