共晶磷对石膏性能的影响及其作用机理

共晶磷是磷石膏中仅次于可溶磷的有害杂质,影响了磷石膏的应用性能。采用分析纯模拟共晶磷的生成条件制取共晶磷含量较高的石膏样品,经煅烧成半水石膏后加入到天然建筑石膏中,进行物理力学性能试验,并利用扫描电镜、原子吸收光谱、红外吸收光谱结合化学分析的手段,研究了共晶磷对石膏性能的影响及其作用机理。结果表明:共晶磷明显降低了建筑石膏的水化率,使二水石膏析晶过饱和度降低,晶体粗化,结构疏松,硬化体强度降低。在二水石膏煅烧成半水石膏的过程中共晶磷并没有发生变化,仍存在于石膏晶格中;在建筑石膏水化过程中,共晶磷从晶格中溶出,变成可溶性磷HPO42-溶解在浆体中,HPO42-电离出H+和PO43-,其中PO43-又迅速与溶液中大量存在的Ca2+结合,转变为难溶性Ca3(PO4)2覆盖在晶体表面,阻碍了石膏的进一步水化,从而导致硬化体强度降低,而富余的H+则导致了浆体pH值的降低。

Influence of P2O5 in Crystal Lattice on Gypsum Properties and Its Mechanisms

P2O5 in crystal lattice, which is the second harmful impurity in phosphogypsum except for the water soluble P2O5, affects the application performance of phosphogypsum. The gypsum samples with a high content of P2O5 in crystal lattice were prepared with analytical reagents under simulated conditions of P2O5 in crystal lattice formation. Then they were calcined to hemihydrates and added to the natural building gypsum to progress the physical and mechanical properties testing of their hardened pastes. The influence of P2O5 in crystal lattice on the performance of gypsum and its mechanisms were studied by scanning electron microscopy, atomic absorption spectrometry, infrared spectroscopy combined with chemical analysis methods. The results show that: P2O5 in crystal lattice significantly reduces the hydration rate and the crystallization supersaturation of dihydrate gypsum, makes crystals thick and structures loose, makes the strength of hardened paste reduced. The P2O5 in crystal lattice does not change in the process of calcination, still exists in the gypsum crystal lattice. In the hydration process, the P2O5 in crystal lattice continuously dissolves from the crystal lattice, changes into water soluble HPO42-, which ionizes to H+ and PO43-, PO43- quickly binds with Ca2+ in the solution, changes to Ca3(PO4)2 which covers on the crystal surface, hinders the gypsum further hydration, results in the strength reduction of hardened paste, and the surplus of H+ will lead to a decrease in pH value of the slurry.