First-princisples Calculation On The Crystal Structure And Surface Adsorption Behavior Of Monazite And Fluorite

The rare earth mineral monazite and calcium-containing mineral fluorite have a close symbiotic relationship.Fluorite is easy to mix into monazite flotation concentrate in large quantities,so it is difficult to achieve flotation separation of the two minerals.The genetic characteristics of minerals,such as crystal structure,surface structure and surface anisotropy,can affect the surface reactivity,wettability and adsorption capacity of reagent,and have a great influence on the flotation behavior of minerals.Quantum chemical calculation can be used to study the related properties of mineral crystal and its surface from the atomic level.Therefore,the first principle calculation based on density functional theory is used in this paper to study the crystal and surface properties of monazite and fluorite and the mechanism of their interaction with flotation reagent from the atomic level,so as to provide theoretical guidance for the flotation separation of monazite and fluorite.In this study,the related properties of mineral crystal and its surface were calculated by material studio 2017 software,combined with XRD test results to determine the common cleavage surface and exposed surface of the two minerals;the interaction mechanism of octylhydroxamic acid and oleic acid with the common exposed surfaces of monazite and fluorite was studied,and the difference of the interaction between the reagents and different mineral surfaces were analyzed.The conclusions are as follows:When the exchange correlation function was GGA-PW91,the cutoff energy was 450eV,and the K point was 3×3×3,the total energy of monazite and fluorite was the lowest,and the structure was the most stable.Through calculation,it was found that monazite and fluorite were both non-conductive minerals;O and Ce atoms in monazite and F and Ca atoms in fluorite were the most active.The surface energy and broken bond density of monazite（100）and fluorite（111）were the least,which were the most common cleavage and exposed surfaces of monazite and fluorite,respectively.The 2p orbit of two O atoms on the carboxyl group of the anion functional group of OA was near the Fermi level,and its activity was strong.OA could replace H₂O on the surface of fluorite（111）to form a stable adsorption form of a four-membered ring with a single-core and two-coordinate configuration,and its adsorption energy was the largest,-268.325kJ/mol.After adsorption,the density of state peaks of O and Ca atoms moved to the direction below Fermi level,and strong resonance appears in the range of-8⁰ ev.The adsorption results showed that OA had a stronger interaction with fluorite than OHA.The 2p orbit of the two O atoms on the oxime group of the OHA anionic functional group were near the Fermi level,and their chemical properties were active.OHA could replace H₂O to form a five-membered ring with the most stable adsorption form on the surface of monazite（100）in a mononuclear double coordination configuration,and its adsorption energy was the largest,-466.863 kJ/mol.After adsorption,the density of state peaks of O and Ce atoms moved to the direction below Fermi level,and strong resonance appeared in the range of-10⁰ ev.The results showed that OHA had stronger interaction with monazite than OA.Therefore,OHA could be used as a selective collector to separate monazite and fluorite by flotation.