胶磷矿与白云石界面水化特性的分子模拟研究

Molecular Simulation Study on the Hydration Characteristics of the Mineral-Water Interface of Collophanite and Dolomite

以胶磷矿为研究对象,研究了胶磷矿和白云石的界面水化特性,通过密度泛函理论(DFT)和分子动力学模拟(MDS)研究了单个水分子在氟磷灰石(001)面和白云石(104)面的吸附构型和水溶液中矿物表面的水化作用,并对矿物界面形成水化膜的结构和性质进行分析。DFT结果表明,水分子会与氟磷灰石(001)面和白云石(104)面发生相互作用,水分子在氟磷灰石表面与Ca1位点的吸附能为-128.19 kJ/mol,在白云石表面与Ca和Mg位点的吸附能为-62.30 kJ/mol和-54.89 kJ/mol,水分子的O与氟磷灰石和白云石表面的Ca/Mg位点作用形成弱化学吸附,水分子与白云石表面Ca位点作用强于Mg位点,水分子的H与两种矿物表面的O作用形成氢键吸附。氟磷灰石/白云石-水体系MDS结果表明,两种矿物表面水分子密度沿z轴方向出现明显分层,靠近矿物表明的水分子密度较大,这层水分子即为水化膜。水化膜内的水分子呈定向、密集排列,氟磷灰石和白云石表面均能形成水化膜。通过相对浓度分布和扩散系数分析发现,氟磷灰石和白云石表面水化膜结构分为有序层、过渡层和本体水,靠近表面的有序层水分子与表面作用较强,水分子有序排列,外层水分子主要受氢键作用,水分子随着与表面距离增加趋于混乱无序,氟磷灰石表面水化膜厚度为0.56 nm,白云石表面水化膜厚度为0.68 nm。

The interfacial hydration characteristics of collophanite and dolomite were studied.The adsorption configuration of a single water molecule on the(001)surface of fluorapatite and(104)surface of dolomite and the hydration of mineral surface in aqueous solution were studied by density functional theory(DFT)and molecular dynamics simulation(MDS).The structure and properties of the hydration film formed at the mineral interface were analyzed.The DFT results indicate that water molecules will interact with the surfaces of fluorapatite(001)and dolomite(104).The adsorption energy of water molecules on the surface of fluorapatite with Cal site is-128.19 kJ/mol,and the adsorption energy on the surface of dolomite with Ca and Mg sites is-62.30 kJ/mol and-54.89 kJ/mol.The O of water molecules forms weak chemical adsorption with the Ca/Mg sites on the surface of fluorapatite and dolomite,the interaction between water molecules and the Ca site on the surface of dolomite is stronger than that of Mg site,and the H of water molecules forms hydrogen bond adsorption with the O on the surface of two minerals.The MDS results of the fluorapatite/dolomite water system show that there is a significant layering of water molecule density on the surface of the two minerals along the&-axis direction,and the water molecule density near the minerals is higher,which is the hydration film.The water molecules inside the hydration film are arranged in a directional and dense manner,and the hydration film can be formed on the surfaces of fluorapatite and dolomite.Through analysis of relative concentration distribution and diffusion coefficient,it was found that the surface hydration film structure of fluorapatite and dolomite is divided into ordered layers,transition layers,and bulk water.The ordered layers near the surface have strong interactions with water molecules,and the water molecules are arranged in an orderly manner.The outer water molecules are mainly used by hydrogen bonds,and water molecules tend to become disordered with increasing distance from the surface.The thickness of the hydration film on the surface of fluorapatite is 0.56 nm,the thickness of the hydration film on the surface of dolomite is 0.68 nm.