Preparation and Application in HDPE of Nano-CaSO4 from Phosphogypsum

Nano-CaSO4, a good cubic structure with dimensions of no more than 100 nm, was first prepared from phosphogypsum (PG). The effects of different reaction conditions on PG morphology, achieved by optimizing the reaction temperature, the concentrations of HNO3, H2SO4, and cetyltrimethylammonium bromide (CTAB) and other factors, were discussed. PG dissolved in HNO3 was reassembled after c-axis growth was inhibited by the common ion effect of SO42–. The morphology of CaSO4 was regulated by a guiding agent, namely, a mixed solution of glycerol, ethanol, and CTAB. The optimal morphological conditions of a smooth surface and structural integrity were established at 140 °C. The solid–liquid ratio of PG, CTAB, HNO3, and H2SO4 was 4:1:4:4, and the volume ratio of glycerol to ethanol was 2:1. The mechanical properties of nano-CaSO4 in linear high-density polyethylene (HDPE) were investigated, and it was found that a low content (3%) of nano-CaSO4 had a significant reinforcing effect on the mechanical properties. Nano-CaSO4 (3%) can increase the melt strength by nearly 2 times and increase the tensile strength and elongation at break by 9.16 and 31.43%, respectively; thus, this method is economical and applicable for the comprehensive utilization of PG.