α-hemihydrate (α-HH), known for its exceptional mechanical properties, is a widely used building material. Despite its advantages, the traditional method of producing α-HH through regular pressure brine poses significant drawbacks. These include substantial industrial salt demands, high production costs, and water pollution. A more environmentally friendly α-HH preparation process has been developed to counteract these issues, combining FGD gypsum and concentrated brine. This study delves into the effects of the principal ions present in concentrated brine on the phase transition process and the microstructure of the final product. Our findings reveal that the reaction rate accelerates with increased concentrations of Ca, Mg, K, and Na in concentrated brine. However, excessive Na concentration can alter the phase transition process, converting the product to β-HH. Additionally, an overly high concentration of KCl may prompt a part of the K to engage in the reaction, leading to the formation of isomeric potassium gypsum. This process can disrupt the original structure of hemihydrate gypsum. The addition of maleic acid to the salt solution was found to foster anhydrous gypsum formation. In contrast, succinic acid can decrease the crystals' aspect ratio, resulting in the growth of short columns, thereby enhancing the product's strength performance. Our research also identified that the reaction rate elevates as the pH value declines. However, an acidic environment diminishes the size of the crystal and counteracts the crystal modifier's effects. Lastly, incorporating CaCl and MgCl into concentrated brine with a low Na concentration can convert FGD gypsum into high-strength α-HH. This transformation results in a product boasting a 1-day compressive strength of 40.5 MPa.

中文翻译：

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制备α-半水石膏协调处置烟气脱硫石膏和电厂浓盐水

α-半水合物 (α-HH) 以其卓越的机械性能而闻名，是一种广泛使用的建筑材料。尽管有其优点，但通过常规压力盐水生产 α-HH 的传统方法存在显着的缺点。其中包括大量的工业盐需求、高生产成本和水污染。为了解决这些问题，我们开发了一种更环保的 α-HH 制备工艺，将 FGD 石膏和浓盐水相结合。这项研究深入研究了浓盐水中存在的主要离子对相变过程和最终产品微观结构的影响。我们的研究结果表明，随着浓盐水中 Ca、Mg、K 和 Na 浓度的增加，反应速率会加快。然而，过量的 Na 浓度会改变相变过程，将产物转化为 β-HH。另外，过高浓度的KCl可能会促使部分K参与反应，导致异构钾石膏的形成。这个过程会破坏半水石膏的原始结构。发现向盐溶液中添加马来酸可促进无水石膏的形成。相反，琥珀酸可以降低晶体的长径比，导致短柱的生长，从而提高产品的强度性能。我们的研究还发现，反应速率随着 pH 值的下降而升高。然而，酸性环境会减小晶体的尺寸并抵消晶体改性剂的作用。最后，将CaCl和MgCl加入低Na浓度的浓盐水中可以将​​FGD石膏转化为高强度的α-HH。这种转变使产品的 1 天抗压强度达到 40.5 MPa。