Effect of Additives on Calcium Sulfate Hemihydrate Whiskers Morphology from Calcium Sulfate Dehydrate and Phosphogypsum

The influence of P2O5 on the whiskers morphology of CaSO4 · 0.5H2O was discussed by using CaSO4 · 2H2O as raw materials and the hydrothermal process at 140°C for 2 h. The result indicated whiskers were obtained by adding 0.2% P2O5, with a smooth surface, uniform diameter (∼1–3 µm), and an aspect ratio of about 45. The aspect ratio of whiskers decreased as the addition amount of P2O5 increased. Raw phosphogypsum (PG) was ground by using a planetary ball mill and then washed using distilled water in order to reduce the P2O5 content. Washed PG constituted ∼50% of the sample, with an agglomerate size of 32.6 µm, and contained 0.43 wt% P2O5. The influence of glycerol on the morphology of CaSO4 · 0.5H2O whiskers was investigated by also using the hydrothermal method. The aspect ratio of whiskers first increased and then decreased while the amount of glycerol increased. The whiskers were also prepared by using added 1.3 wt% calcium oxide (CaO) PG at 140°C for 2 h and the effect of phosphorus on whiskers growth can be decreased.