基于密度泛函理论研究磷建筑石膏晶体表面吸附丁二酸转晶机理

The Crystal Modification Mechanism of Phosphogypsum by Surface-adsorbed Succinic Acid:a Density Functional Theory Study

基于密度泛函理论的第一性原理,对磷石膏晶面及吸附物丁二酸构型进行了优化,通过丁二酸与晶体表面的吸附模型计算模拟了丁二酸以三种不同的吸附方式分别与晶面发生反应,结果发现丁二酸最可能的吸附方式为丁二酸羧基中双键氧原子被晶面上的Ca原子垂直吸附,且为化学吸附。采用扫描电镜、X射线衍射和X射线光电子能谱分析了丁二酸对磷石膏晶体形貌及表面电子结合能的影响,并测得不同掺量丁二酸作用下磷石膏的抗折、抗压强度。研究发现,丁二酸中羟基与磷石膏晶面Ca元素发生了表面化学作用,与模拟结果基本一致,丁二酸吸附于磷石膏晶面的作用机理表现为丁二酸中O的2p和H的1s轨道中的电子向晶面上Ca的3d轨道发生了迁移。在杂质预处理过程中,丁二酸添加量为磷石膏用量的0.2%时磷石膏的抗折、抗压强度最大,分别为6.9 MPa和31.6 MPa。

Geometric and electronic structure of phosphogypsum surfaces and succinic acid were optimized by density functional theory.The reactions corresponding to three different adsorption modes of succinic acid on phosphogypsum surfaces was simulated,indicating that the most tentative adsorption mode is the vertical adsorption of double bond oxygen atoms in the carboxyl group onto the Ca atoms.The effects of succinic acid dosage on the crystal morphology and surface electron bonding energy of phosphogypsum were analyzed by scanning electron microscopy,X-ray diffraction and X-ray photoelectron spectroscopy,meanwhile the flexural strength and compressive strength of the phosphogypsum were measured.The simulation results coincided well with the experimental results,and verified the the surface chemical interaction between hydroxyl and Ca.The action mechanism of succinic acid adsorption on phosphogypsum crystal surface was revealed by the electron transfer from O 2 p and H 1 sorbitals of succinic acid molecules to 3 d orbitals of Ca atoms on the crystal surface.During the process of impurity pretreatment,the maximum flexural strength and compressive strength,6.9 MPa and 31.6 MPa respectively,can be obtained while the succinic acid phosphogypsum mass ratio is 0.2%.