Relationship Between Structure And Performance Of Humic Substances Based Binder For Iron Ore Pellets

Abstract:Binder is indispensable in the production of iron ore pellets, which can dramaticly influence the quality of finished products. Humic substances as a type of organic macromolecule polymer consist of carboxyl groups and hydroxyl groups, which should be further researched because of their ideal adhesive molecular conformation. At present, functional mechanisms of humic substances on the surface of iron ore is not fully clear. Furthermore, structure-performance relationships of humic substances based binder have not yet been clearly established because of few researches on their physical and chemical properties especially on the structure characteristics.A type of humic substances based binders are prepared from lignite and weather coals. The binders mainly consist of two active fractions including fulvic acid and humic acid. The properties of binder active fractions and their functional mechanisms were studied by adopting infrared spectroscopy (FTIR), environment scanning electron microscope (ESEM), atomic force microscope (AFM), thermogravimetric-differential thermal analysis (TG-DSC) and X-ray photoelectron spectroscopy (XPS) et.al; The energy criterion△ETRT between binder and target minerals were calculated using the density functional theory (DFT), molecular functional assembly and binder molecular model; And most of all, the technical requirements for humic substances based binder are proposed based on the structure-performance relationships of binder active fractions. The main conclusions of this research are summaried as follows:(1) There are obvious differences in physical and chemical properties between binder active fractions (fulvic and humic aicds). Compared to humic acid, Fulvic acid is characterized by better dispersibility, relatively low degree of aromatization and small molecular weight but relatively high content of oxygen-containing functional groups. Humic acid processes good thermal stability and wider thermal decomposition range. (2) Chemical adsorption occurs between binder active fractions and iron concentrate surface, indicating the adsorption of fulvic acid is stronger. The adsorption of binder is more accord with Freundlich model and second order kinetics. The theoretical maximum adsorption amount of fulvic and humic acids is respectively8.92×10-3mg·cm-2and2.70×10-3mg·cm-2. Electronic binding energy variation of Fe2p3/2after adsorption of fulvic and humic acids are-1.12eV and-0.57eV, respectively. The net desorption energy of fulvic and humic acids is respectively-87.0J/g and-26.7J/g. The active fractions adsorbs on the surface of iron concentrates in the shape of net, fibrous or clusters. The adsorption of humic acid can be enhanced by fulvic acid.(3) DFT calculation demonstrates that, compared to phenolic hydroxyl group, carboxyl group performs better solid-affinitive capability. The solid-affinitive capability of binder increases with the increase of the number of polar groups. For binder molecule, the enlargement of non-polar aromatic hydrocarbon can enhance the capacity of chemical adsorption, but also result in decrease of electrostatic forcing.Reagent active equation and energy criterion demonstrates that binder molecule adsorbs on mineral surface with chemical reaction as deciding effort. The order of solid affinitive capability of binder with three target minerals follows FeTiO3> Fe3O4> Fe2O3. For interaction between binder and target minerals, the contribution of positive covalent coordination bond△E2RTT to energy criterion△ETRT is biggest, while electrostatic forcing△E1RT is smallest.(4) The adsorption and subsequent binding strengths are negative correlation with E4/E6of fulvic acid. The performance of fulvic acid is increased with increasing its molecular weight. The adsorption and binding strengths are positive correlation with E4/E6of humic acid. The performance of humic acid is increased with decreasing its molecular weight. The molecular weight which is too large or too small is unfavorable to the adsorption and binding strengths of humic substances. The performance of active fractions performs better when the molecular weight of fulvic acid and humic acids is respectively600Da and1500Da. The idea range of molecular weight of humic substances is from1410Da to1490Da.The technical requirements for humic substances based binder are proposed by following:1) E4/E6of humicsubstances should be close to3.86;2) The content of humic substances should be in the range of40%to50%;3) For magnetite, V-Ti containing magnetite and hematite, the mass ratio of humic acid to fulvic acid should be close to8:2,7:3and6:4.(5) For magnetite, V-Ti containing magnetite and hematite concentrates, three kinds of binders are prepared. Compared to those pellets prepared with2.0%bentonite, the pellets with0.75%novel binder are characterized by1.0%higher TFe grade, better compression strength and the similar metallurgical properties.