Transformation of phosphogypsum (PG) into α-hemihydrate gypsum (α-HH) in sodium salt solution is disturbed by the doping of Na, which causes the frost of Na doped α-HH. In this study, the content evolution of Na impurities into α-HH was clarified during the hydrothermal process at 95 ℃, the frost phenomenon of hardened gypsum containing Na impurities was observed and controlled. The results show that increasing the initial NaCl concentration from 5 % to 25 % can promote the phase conversion of PG into α-HH within 30 min, but this will increase the NaO content in the product from 0.08 % to 4.37 %, which is due to the formation of the undesirable phase NaSO·5CaSO·3HO. The content of Na impurities entering α-HH presents a non-linear increase with the NaCl solution concentration and reaction time, which can be well described by Boltzmann function. An obvious frost phenomenon of the hardened plaster of Na doped α-HH can be observed after curing 3 d, and the frost is identified as NaSO. This work further demonstrates the feasibility that the addition of CaCl in NaCl solution is an effective approach to control the doping of Na into α-HH, the NaO content decreases to 0.97 % in the mixed solution of 17.5 % NaCl and 10 % CaCl, this helps to eliminate the frost phenomenon and improve the mechanical strength of α-HH.

中文翻译：

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NaCl溶液制备α-半水石膏过程中的钠掺杂及控制


Na的掺杂干扰了磷石膏(PG)在钠盐溶液中向α-半水石膏(α-HH)的转化，导致Na掺杂α-HH的霜化。本研究阐明了95 ℃水热过程中Na杂质向α-HH的含量演变，观察并控制了含Na杂质的硬化石膏的霜化现象。结果表明，将初始NaCl浓度从5%增加到25%可以促进PG在30 min内相转化为α-HH，但这会使产物中NaO含量从0.08%增加到4.37%，这是由于形成不良相NaSO·5CaSO·3HO。进入α-HH的Na杂质含量随着NaCl溶液浓度和反应时间呈现非线性增加，这可以用Boltzmann函数很好地描述。 Na掺杂α-HH石膏固化3 d后可观察到明显的结霜现象，经鉴定该结霜为NaSO。这项工作进一步证明了在 NaCl 溶液中添加 CaCl 是控制 Na 掺杂到 α-HH 中的有效方法的可行性，在 17.5 % NaCl 和 10 % CaCl 的混合溶液中 NaO 含量降低至 0.97 %，这有助于消除结霜现象，提高α-HH的机械强度。