The massive discharge and stockpiling of phosphogypsum became an increasingly severe issue on environment. The transformation of phosphogypsum into fibrous alpha-type hemihydrate gypsum (α-HH) with high L/D(ratio of length-to-diameter) is one of the effective routes to achieve the high-valued utilization. In this work, six types of cationic surfactants, including CTAB, STAC, CHEC, CGG, CPAM and PDDA were selected to investigate their different effects on shape of α-HH crystals through hydrothermal method under the condition of 160 °C(0.6 MPa saturated vapour pressure) for 3 h. The results showed that the introduction of all selected surfactants can increase the length-to-diameter (L/D) ratio of α-HH crystals. As the concentration of surfactants increases, the L/D ratio first increases and then decreases, and the highest L/D ratio of 171.3 was obtained by using CTAB at 0.6 %. The mechanism of regulated growth of α-HH crystals into fibrous structure following in the presence of six cationic surfactants was also demonstrated. Moreover, the adsorption mechanism of cationic surfactants on the α-HH surface was investigated by molecular dynamics simulation and theoretical analysis. It is found that the order of binding energy (E) between the addition and α-HH crystal faces is E(10) > E(110) > E(200) > E(002). This work provides insightful guidance from both experimental and theoretical perspectives for controlling the crystal form of α-HH and preparing high-strength gypsum.

中文翻译：

---

阳离子表面活性剂辅助磷石膏晶型转变机理的实验与理论研究

磷石膏的大量排放和堆存成为日益严峻的环境问题。将磷石膏转化为高L/D（长径比）的纤维状α型半水石膏（α-HH）是实现高值化利用的有效途径之一。本工作选择了CTAB、STAC、CHEC、CGG、CPAM和PDDA 6种阳离子表面活性剂，在160 ℃（0.6 MPa饱和条件下）通过水热法研究了它们对α-HH晶体形貌的不同影响。蒸气压）3小时。结果表明，引入所有选定的表面活性剂都可以增加α-HH晶体的长径（L/D）比。随着表面活性剂浓度的增加，L/D比先增大后减小，使用0.6%的CTAB时得到的最高L/D比为171.3。还证明了在六种阳离子表面活性剂存在下，α-HH 晶体调节生长成纤维结构的机制。此外，通过分子动力学模拟和理论分析研究了阳离子表面活性剂在α-HH表面的吸附机理。结果发现，加成晶面与α-HH晶面之间的结合能(E)顺序为E(10)>E(110)>E(200)>E(002)。该工作从实验和理论角度为控制α-HH晶型和制备高强石膏提供了富有洞察力的指导。