Quantum Chemistry Investigation On The Physicochemical Property Of Coal Pyrite And Its Inhibitory Regularities

With the harm to the ecological environment and human health caused by the deep processing and utilization of coal,it is imperative to remove the sulfur in coal.Flotation is an economical and effective pHysical method to remove the fine particle size of pyrite in coal.The pHysicochemical property of coal pyrite itself and its corresponding inhibitors are the key factors to determine the desulfurization effect by flotation.Compared with the pyrite,the morpHological structure,surface electronic structure and hydropHobicity of coal pyrite are very different.So the results of the study on the surface properties of pyrite and the related organic inhibitors are not suitable for the coal pyrite.So it is very important for removing the pyrite in the coal and improving the effect of flotation desulfurization to carry out the systematic study on the difference and its mechanism of the surface properties between the pyrite and coal pyrite and to screen out the efficient organic flotaiton inhibitors.The mineralogical properties between pyrite and coal pyrite were compared in the paper.Firstly,the difference of hydropHobicity was compared by contact angle and adsorption heat test.The origin of the difference among the two types of pyrite was explored by advanced analytical methods.The results showed that there existed carbon atom substituted on the coal pyrite and it leaded to that the hydropHobicity changed.And meanwhile the carbon atom undissociated completely in the comminution process and the sulfur atom formed in the oxidation process were also the key factors to affect the hydropHobicity of pyrite surface.With the first-principle method of density functional theory(DFT)and the plane-wave ultrasoft pseudopotential method,it was proved from the simulated view that the substituted and adsorbed carbon atom and the adsorbed atom changed the electronic structrure of coal pyrite surface and its hydropHobicity strengthened.And finally based on the special property of coal pyrite and the adsorptional mechanism of agent on the mineral surface,the effeicient organic flotation inhibitors suitable for the coal pyrite were screened out theoretically combined with the facts.The results was verified by flotation test.The main research results are as follows:1.The experiments on the difference of hydropHobicity and mineral property between pyrite and coal pyrite was carried out.The results were as follows:(1)The results of the contact angle and adsorption heat test showed that the contact angle of coal pyrite was bigger,its adsorption heat was lower so that the hydropHobicity of coal pyrite was stronger.(2)The results of the Inductively Coupled Plasma Optical Emisson Spectrometry(ICP-OES)? X-ray diffraction(XRD)and Scanning Electron Microscope-Energy Dispersive Spectrometer(SEM-EDS)show that there exist sulfur atom substituted by carbon atom on the pyrite surface in the non-stoichiometric form of Fe1-xC.It is put forward that the carbon atom substituted on the pyrite surface makes the hydropHobicity of coal pyrite stronger from lattice defect.(3)The carbon element content of pyrite and coal pyrite are respectively 3.30%-6.00% and 7.08%-23.25%.The hydropHobicity of coal pyrite increases with the decrease of S/Fe mole ratio and the increase of carbon element content.2.With the first-principle method of density functional theory(DFT)and the plane-wave ultrasoft pseudopotential method,the fluence of carbon atom's substitution and adsorption and sulfur atom's adsorption on the electronic structure were carried out and the results are as follow:(1)The optimization results of pyrite cell showed that the calculated cell parameters and band gap were most close to the experiment value under the condition that the 285 eV cut-off energy and PW91 function of Gengeralized Gradient Approximation(GGA).(2)From the view of thermodynamics,it is easiest for the carbon atom to substitute for the high-position sulfur atom on the pyrite surface and then the stable structure is formed,easier to replace the low-position sulfur atom and difficult to replace the iron atom.The band gap decreased the Fermi level declined with the increase of substituted carbon atoms.And it accelerated the transfer of electron.And so it was easyr for the pyrite to be oxided and captured by collector and to float in the flotation.(3)The carbon atom can adsorb right above the iron atom,sulfur atom and Fe-S bond.The adsorption energy on the Fe-S bond was minimum and it was most stable.The carbon atoms adsorbed on the pyrite surface hindered the interaction between water molecule and pyrite and the hindering effect increases with the increase of carbon atom.The carbon atoms adsorbed on the surface of coal pyrite and it seemed that the surface was covered by a large of symbiotic carbonaceous substance.It leaded to that the partial surface of pyrite was similar to the coal and the hydropHobicity of pyrite surface was enhanced generally.(4)The sulfur aslo adsorbes on the different sites of pyrite surface and the adsorption energy right above the iron atom is maximum.The sulfur atom adsorbed on the pyrite also hinder the interaction between water molecule and pyrite and the hindering effect also increases with the increase of sulfur atom.And the hydropHobic sulfur adsorbed on the pyrite surface made its hydropHobicity stronger.3.On the basis of mineral property and electronic structure properties of coal pyrite,the model of coal-pyrite was build.The effect of substituted carbon atoms,adsorbed carbon atoms and sulfur atoms on the water molecule's adsorption was discussed and the microcosmic mechanism about the stronger hydropHobicity of coal pyrite was revealed from the view of quantum chemistry.(1)The adsorption energy of water molecule on different sites of perfect pyrite surface show that water molecule can adsorb on the top of low-position sulfur atom,vertical and parallel to top of iron atom.But it is hard for the water molecule to adsorb on the top of high-position sulfur atom.The equilibrium adsorption of H2 O parallel to top of irom atom with two low-position S-H bond is most stable.After the water molecule adsorbes on the pyrite surface,the 2p orbit of oxygen atom interact with the 3d orbit of iron atom and the Fe-O bond is formed and the weak H-S bond is aslo formed between the hydrogen atom and sulfur atom.(2)Compared with the perfect pyrite surface,the adsorption energy of H2 O on the pyrite surface substituted by carbon atoms decrease with the increase of carbon atoms.The weaker C-H bond is formed between carbon atom on pyrite surface and hydrogen of water molecule.The Fe-O bond is also weaker.So the hydropHobicity of pyrite surface substituted by carbon atoms become stronger.(3)The adsorption energy of H2 O on the pyrite surface adsorbed by carbon atoms become positive from negative value.The forming bond is Fe-C-O bond from Fe-O bond.It can be obtained that the pyrite surface adsorbed by carbon atom become hydropHobic from hydropHilic and the hydropHobicity is stronger with the increase of carbon atom.The mechamism of the influence of carbon atom's adsorption on pyrite hydropHobicity is revealed from the view of quantum chemistry.(4)Compared with the perfect pyrite surface,the adsorption energy of H2 O on the pyrite surface adsorbed by sulfur atoms become positive from negative value.The Fe-S-O bond is formed between pyrite surface,sulfur atom and water molecule.The pyrite surface adsorbed by sulfur atom become hydropHobic from hydropHilic and the hydropHobicity is stronger with the increase of sulfur atom.The mechamism of the influence of sulfur's adsorption on pyrite hydropHobicity is revealed from the view of quantum chemistry.(5)On the same doping or adsorption concentration of impurity atom,the effect of symbiotic carbonaceous on the hydropHobicity of pyrite surface was biggest.The covered sulfur was secondary and the doped carbon atoms was weakest.Macroscopically the hydropHobicity of coal-pyrite accreted with carbonaceous was greater than coal-pyrite covered by sulfur and greater than coal-pyrite doped by carbon atom.4.Based on the conclusion of water molecule's adsorption on the pyrite surface,the relation between structure and property of thiol inhibitors and their adsorption on the coal-pyrite surface were simulated.The adsorption intensity of water molecule and inhibitors were compared.The results are as follow:(1)The structure and quantum chemical parameter of different tpyes of inhibitors is optimized and calculated by the Castep and Dmol3 modular of Materials Studio software.The HOMO of thiol carboxylic acid inhibitor and thiol alcohol inhibitor molecule decreased with the increase of carbon atom and the electron mainly focused on the sulfur atom.It showed that the activity of inhibitors increased gradually.The HOMO electron of thiol aromatic carboxylic acid inhibitor focused on the sulfur atom and benzene ring.And the HOMO of L-QJBJS was minimum and its activity was maximum.So from the view of inhibitors' activity themselves,the inhibition of QJDS,QJDC and L-QJBJS were strongest among the three types of inhibitors.(2)Compared with the water molecule,the adsorption energy of thiol inhibitors were bigger.It illustrated that the adsorption of thiol inhibitors was stronger and had advantage in the competitive adsorption of water molecule.And meanwile it can prevent the kerosene and diethyl pHthalate from adsorbing on the coal-pyrite surface.(3)The order of action energy of inhibitors on the coal-pyrite surface was QJDS>QJBS > QJYS,QJDC > QJBC > QJYC,L-QJBJS > J-QJBJS > D-QJBJS.The inhibition of various inhibitors increased with the increase of carbon atoms.And when the carbon atom was same,the inhibition of thiol alcohol inhibitor was maximum and the thiol aromatic carboxylic acid inhibitor was minimum.So from the adsorbtion intensity of inhibitor on the coal-pyrite QJDS,QJDC and L-QJBJS were the strongest inhibitor.5.The flotation organic inhibitors are screened out theoretically according to their activity and solubility.And then the screened organic inhibitors were tested through the flotation experiments and the pyrite in the coal was removed effectively.(1)The results of monomineral self-induction flotation indicated that it was easier for pyrite and coal-pyrite to float in the acidic environment.The native floatability of coal-pyrite was stronger than the pyrite.(2)The results of monomineral flotation with inhibitor added illustrated that the order of inhibition to the clean coal was QJBS>QJBC>FZSN>L-QJBJS>CaO,to the coal-pyrite was QJBC>QJBS>L-QJBJS>CaO>FZSN,which was consistent with theoretical screening results of organic inhibitors.(3)The pyrite of clean coal declined a little under the flotation inhibitors and the sulfur of clean coal exceeded the standard.The coal-pyrite in the Gongwusu primary slime had extremely fine dissemination size through the SEM analysis.And the new technology of flotation must be explored to remove the pyrite under the condition of deep crush.