Study On The Adsorption Mechanism Of Polysaccharide Inhibitors On Talc Surface By Density Functional Based Tight Binding

Talc is one of the most common gangue minerals in sulphide ores such as chalcopyrite and molybdenite.Due to its strong natural floatability,talc is easy to float up with bubbles in the flotation process,which will affect the grade of flotation concentrate.In addition,talc is easily grinded and muddied,resulting in slime covering on the surface of the target mineral,which makes it difficult to separate from the target mineral and greatly increases the difficulty of subsequent metal smelting.At present,talc inhibitors used in mineral flotation mainly include sodium silicate,sodium hexametaphosphate,Guar gum and carboxymethyl cellulose.Among these inhibitors,several polysaccharides have been widely used due to their characteristics of wide variety,low price,green environmental protection and strong talc inhibition.At present,most of the studies on the effect of polysaccharides inhibitors on talc surface are conducted by flotation test,potential test and adsorption capacity test,etc.,but it is rare to use density functional theory to study the mechanism of their inhibition on talc from the micro level.In this work,the effect of lattice defects on hydrophilic and hydrophobic properties of talc(001)surface was studied from the microscopic point of view based on density functional theory.The adsorption model of xanthan gum(XA),Guar gum(GG),Pululan polysaccharide(PU),maltodextrin(MA),carboxymethyl chitosan(CC)and chitosan(CH)on the surface of ideal talc(001)was established,and the interface bonding was analyzed.The inhibition effect of polysaccharides on talc was studied by means of microthermal test,flotation test and contact angle test.The adsorption mechanism between talc and polysaccharides inhibitors is interpreted from multiple perspectives,and the research results are as follows:(1)The Castep module based on DFT theory was used for geometric optimization of talc protocell.Lattice parameters of talc protocell were obtained as a=5.33(?),b=9.21(?),c=9.46(?),and the error was 3.5%compared with the experimental value.The results show that the ideal talc is an insulator with a band gap of 5.29eV,and the 2p orbital of oxygen atom in talc contributes the most to the total electron density of talc.(2)The simulation results of lattice defects on(001)talc show that the degree of substitution of Mg atoms by several impurity atoms is Fe>Ca>Al>Ni>Mn.The electron density of Si atoms on the surface of talc(001)decreases slightly due to lattice defects.The Mulliken overlapping population of bond formation shows that the impurity defect makes the charge density overlap region of Si-O_b bond on the surface of talc(001)smaller than that of Si-O_b bond connected to Mg atom,which weakens the covalency of the bond and enhances the ionic property,thus changing the hydrophilic and hydrophobic properties of talc(001)surface.The impurity defects of Fe,Mn and Ni significantly reduce the surface band gap width of talc(001)to less than 2eV and enhance the gold properties of talc surface,indicating that the three impurity defects have an effect on the surface conductivity of talc(001).(3)Matsci-Mg.skflib parameter library,which can calculate talc system,is established by using DFTB+module based on density functional theory tight binding method.The structure and properties of guar gum,chitosan,carboxymethyl chitosan,Pullulan polysaccharide,maltodextrin and xanthan gum,as well as their adsorption mechanism on talc(001)surface,were calculated steadily and efficiently in this database.The results show that the adsorption of polysaccharides inhibitor molecules on talc(001)surface mainly depends on hydrogen bonding.The order of adsorption on talc(001)is xanthan gum>Guar gum>Pullulan polysaccharide>maltodextrin>carboxymethyl chitosan>chitosan.Among them,xanthan gum has the strongest adsorption capacity,the shortest hydrogen bond length and the largest bond Angle.As can be seen from the state density diagram,the electron orbital of oxygen atom on talc(001)surface is more stable after the adsorption of polysaccharide inhibitor molecule.(4)The results of pure mineral flotation experiment show that xanthan gum can inhibit talc at low concentration and reduce its flotation recovery from 90%to about10%.The inhibitory effect of six polysaccharide inhibitors on talc was in the order of xanthan gum>Guar gum>Pullulan polysaccharide>maltodextrin>carboxymethyl chitosan>chitosan.The results of contact angle test showed that the wetting contact angle of talc surface decreased with the adsorption of six polysaccharides inhibitors,and the wetting contact angle of talc surface decreased from 79°to 44°with xanthan gum and 46°with guar gum,respectively.Other polysaccharides inhibitors reduced the wetting contact angle of talc surface to less than 60°,indicating that the hydrophilicity of talc surface was significantly enhanced after adsorption of polysaccharides inhibitors.(5)The results of microthermal kinetics experiments show that the adsorption of xanthan gum and guar gum on talc surface is exothermic process,and the maximum values of?G_?^?are 57.834kJ·mol^-1 and 57.811kJ·mol^-1 at 308.15K,respectively.The maximum reaction rate coefficient of xanthan gum was 1.020×10^-3(/s)at 298.15K,and the maximum reaction rate coefficient of Guar gum was1.024×10^-3(/s)at 303.15K.The activation energy(Ea)of xanthan gum adsorbed on talc surface was 0.756kJ/mol^-1,which was slightly lower than that of Guar gum(0.913 kJ/mol^-1).Under the same conditions,xanthan gum was more easily adsorbed on talc surface.The experimental results are consistent with the calculated results,which shows that the model is scientific and reasonable.