Aspect ratio-controlled preparation of α-CaSO(4)·0.5H(2)O from phosphogypsum in potassium tartrate aqueous solution

In this study, a simple and efficient strategy is developed to synthesize rod-shaped α-CaSO(4)·0.5H(2)O crystals with tunable aspect ratio from industrial phosphogypsum only in potassium tartrate aqueous solution at a low temperature. Industrial phosphogypsum can be effectively converted into rod-shaped α-CaSO(4)·0.5H(2)O crystals with the assistance of potassium tartrate, and the aspect ratio of α-CaSO(4)·0.5H(2)O crystals gradually decreases from 52 : 1 to 1 : 1 with increasing the concentration of potassium tartrate. The formation process of the rod-shaped α-CaSO(4)·0.5H(2)O crystals in this system involves the dissolution of CaSO(4)·2H(2)O and nucleation of α-CaSO(4)·0.5H(2)O crystals. The tartrate ions from potassium tartrate in this system preferentially bind to (001) and (002) facets of α-CaSO(4)·0.5H(2)O crystals, inhibiting the growth of α-CaSO(4)·0.5H(2)O crystals along the c-axis and controlling its morphology and aspect ratio.