Synthesis of large plate-like gypsum dihydrate from waste gypsum board

This paper reports the synthesis of large plate-like gypsum (calcium sulfate) dihydrate generated from waste gypsum board via a wet process. Gypsum hemihydrate was formed by dehydrating waste gypsum board in a sodium sulfate solution at 100 °C for 1 h to form needle-like crystals. The large gypsum dihydrate was formed by lowering the temperature of the gypsum hemihydrate suspension below 80 °C. The large plate-like gypsum dihydrate was obtained by adding seed crystals to a suspension cooled at 80 °C. When 40 μm seed crystals were added at 0.5 mass%, the large plate-like gypsum dihydrate crystals obtained from waste gypsum board had average dimensions of 250 μm length × 100 μm width × 35 μm thickness.