Interaction Mechanism And Molecular Simulation Of Coal-based Humic Acid With Cr(Ⅵ)

In this paper,Yunnan Huanning lignite was extracted and modified by alkali-soluble acid precipitation method,and three kinds of humic acid and modified humic acid materials were obtained.the three humic acid-based adsorption materials were soluble humic acid（HA）,thermal modified humic acid（IHA）and bentonite modified humic acid（BHA）.The influencing factors and mechanism of Cr（VI）removal by humic acid and its modified materials were studied systematically by means of adsorption experiment and molecular simulation.Adsorption experiment showed that under the acidic condition of p H=2,HA had the highest removal rate of Cr（VI）,and the order of saturated adsorption of Cr（VI）by three adsorbents was HA>IHA>BHA.Compared with HA and BHA,IHA,Cr（VI）can be treated effectively in a wider range of p H.The BHA,prepared from bentonite（mainly montmorillonite）and HA with a mass ratio of 8:1 has lower manufacturing cost and better dispersibility in water under the condition of little difference in treatment effect.The adsorption kinetics analysis shows that the adsorption process of Cr（VI）by HA and BHA accords with the Mckay quasi-second-order kinetic model,and the main factor affecting the adsorption rate is the chemical adsorption process,while that of IHA is more consistent with the Langergren quasi-first-order kinetic model,and the mass transfer resistance is the main factor affecting the adsorption rate.From the point of view of thermodynamics,the adsorption isotherm of HA accords with the Freundlich adsorption isotherm model,while the adsorption isotherms of IHA and BHA are more consistent with the Langmuir adsorption isotherm model.Structural parameters of HA and IHA were calculated by elemental analysis,infrared analysis and 13C solid-state NMR,and the molecular models of HA and IHA were constructed.Then the infrared spectra of the model were calculated and verified by Gaussian 09W software,which showed that the structure of the molecular model was reasonable.The molecular formula of the HA molecular model is C90H63O48N,the relative molecular weight is 1925,and the simplest molecular formula of the IHA molecular model is C₇₃H₄₆O₃₅N,and the relative molecular weight is 1447.Simulation of the adsorption kinetics of HA on the 001 and 100 surfaces of montmorillonite shows that HA can be adsorbed on the 001 and 100 surfaces of montmorillonite with strong adsorption.Consistent with the changing trend of adsorption experiments,the adsorption process was simulated by Monte Carlo using Materials Studio 2019.The results show that the saturated adsorption capacity of HA,IHA and BHA for Cr（VI）is 12,6,and 8molecular/u.c.,respectively.The molecular dynamics simulation shows that the adsorption of Cr（VI）in HA and IHA structure is more stable than that in BHA,and mainly interacts with C=O and COOH in molecular structure by hydrogen bond and van der Waals force.There are 53 pictures,32 tables and 88 references in this paper.