Preparation of α-hemihydrate gypsum whiskers from phosphogypsum using atmospheric pressure nitrate solution

A substantial stockpile of phosphogypsum (PG) not just consumes land resources, but also poses environmental contamination risks. Herein, the conversion of PG into high-value α-hemihydrate gypsum (α-HH) whisker by the atmospheric pressure salt solution method with simple process, high efficiency and low energy consumption was investigated. Sodium nitrate was found to accelerate the conversion of PG into α-HH, and sorbitol could modify the α-HH into rod-like morphology with high aspect ratios. The α-HH whiskers with an average length of 96.28 µm and an average aspect ratio of 25.47 were prepared within 1.5 h under the optimal parameters of 80 ℃, sodium nitrate-30 wt%, PG-12 wt%, and sorbitol-1 wt%. The modulation mechanism was that hydroxyl groups in sorbitol formed strong hydrogen bonds with the sulfate groups on the lateral of the crystals, which promoted the growth of α-HH along the c-axis. Moreover, the filtrate could be effectively recycled by adding salt medium and crystallization modifier. Such technique provides a theoretical basis for the high-value utilization of PG.