Preparation of anhydrous calcium sulfate whiskers from phosphogypsum in H2O-H2SO4 autoclave-free hydrothermal system

Abstract

The anhydrous calcium sulfate (AH) whiskers were prepared in H2O-H2SO4 autoclave-free hydrothermal system by using phosphogypsum (PG) as raw materials. The influences of solid/solution ratio, reaction time, H2SO4 concentration and maleic acid on crystal growth were detected. The whiskers with smooth surface and high aspect ratio were obtained in a 20 mass% H2SO4 solution for hydrothermal 1 h with 1:60 ratio of solid/solution. The aspect ratio decreased but the amount of whiskers increased in sample by increasing the addition amount of maleic acid. The whiskers were not obtained in 30 mass% H2SO4 solution for hydrothermal 1, 2 and 3 h, respectively, with 1:60 ratio of solid/solution, and the whiskers were also not obtained by adding maleic acid in the solution.