Crystal modifier is a significant factor in preparation of α-hemihydrate gypsum (α-HH) from phosphogypsum (PG). The influence of maleic acid, reaction temperature, time, and solid-liquid ratio on the preparation of high-strength α-HH from PG was systematically studied herein. The optimum condition for α-HH prepared by hydrothermal autoclave method was pH of 4, temperature of 140 °C for 2.0 h with solid-liquid ratio of 4:5. Crystal modifier of maleic acid can effectively regulated the crystal morphology of α-HH. SEM-EDS and FTIR analysis suggested that maleic acid could preferentially absorbed on the top face of α-HH crystals that decreased the growth rate of α-HH along the c-axis, resulting in the morphology of α-HH crystals transformed to hexagonal prisms, and the regulatory mechanism was estimated by molecular dynamics (MD). When maleic acid (0.1%) was added, the obtained α-HH showed aspect ratio of 1.2, and the flexural and compressive strength of the hardened α-HH could reach to 14.79 and 46.24 MPa, respectively. All of these results will help to design long-term effectiveness of phosphogypsum recycling strategies.

Heavy metal pollution by both uranium and arsenic has become a major environmental problem associated with uranium mining worldwide. At present, physical, chemical and biological technologies are available as the main remediation techniques. Among them, phytoremediation is relatively low cost, hinders more pollution and allows for fast recycling of the uranium as compared to other techniques. However, suitable phytoremediation depends critically on the better choice of plant species. In this study, field sampling of soils and plants surrounding a uranium mine was conducted, and atomic emission spectrometry of samples performed, in order to characterize the distribution of heavy metal pollution and to provide a scientific basis for the phytoremediation of uranium mining sites. Soil uranium concentrations were found to be highest in open-pit mine sites, followed by ore dressing investigation sites and also the river confluence sites. Uranium did not migrate from active mining areas and the highest uranium concentration measured 232.70 mg×kg-1. In contrast, arsenic regularly migrated downstream, with soil concentrations averaging 47.26 mg×kg-1 , two times the limit set by the Three Grade Standard of Soil Quality in China (GB 15618-1995). Rumex nepalensis accumulated high levels of uranium, with a bioconcentration factor of 3.60 and a transfer factor of 3.61. Polygonum viviparum was able to accumulate arsenic, with a root transfer factor of 3.69, and also uranium as indicated by a bioconcentration factor greater than one. Thus, our investigations improved the understanding of the potential role of Polygonum viviparum and Rumex nepalensis involved in phytoremediation of uranium or uranium-arsenic pollution.

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