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 alpha-hemihydrate gypsum (alpha-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 alpha-HH, and sorbitol could modify the alpha-HH into rod -like morphology with high aspect ratios. The alpha-HH whiskers with an average length of 96.28 mu m and an average aspect ratio of 25.47 were prepared within 1.5 h under the optimal parameters of 80 degree celsius, 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 alpha-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.