Molecular Structure Effect And Applied Mechanism Of Depressant Starch In The Reverse Flotation Of Hematite

China’s iron ore resources are rich in reserves and widely distributed.With longterm exploitation and utilization,the beneficiation of complex poor fine iron ore enrichment is becoming increasingly apparent.Flotation is the most commonly used method in the industry to deal with fine-grained refractory hematite ores,of which reverse flotation has become the mainstream.As a key reagent in reverse flotation,it is urgent to study the mechanism of starch depressants in the reverse flotation process.However,the existing research has only revealed the relationship between starch inhibiting ability and solution p H,and given the acid-base theoretical explanations.There is a lack of direct evidence and computational simulations to support the relevant conclusions.Therefore,the use of experimental analysis and computational simulations to visualize the mechanism of acid-base interaction of starch depressants with mineral surfaces and to explain the molecular structure effect of starch depressants in hematite reverse flotation has become a high priority.In this paper,the mechanism of acid-base interaction between starch depressants and mineral surfaces were visually revealed,whether the starch molecular structures affected the flocculation ability of starch depressant on minerals were investigated,and the molecular structure effect of starch depressants in hematite reverse flotation were thoroughly demonstrated.The structural model and bonding mechanism between starch molecules and mineral surface were investigated,and the traditional "acid-base interaction theory" was extended to the "interface matching mechanism" between starch molecule structure and mineral surface structure.The main findings are as follows.(1)Acid-base theory analysis of the action of starch depressants on mineral surfaces.Based on the application of acid-base theory in the flotation process of hematite,we investigated the effect of starch depressant(NS)on the bonding of mineral surface under different p H conditions,and clarified the adsorption mechanism and mechanism of acid-base interaction at the interface between them.At p H 6.0 and p H10.0,starch chemisorbed with hematite surface,Fe and O atoms may be present as the interacting masses,while no interaction occurred in quartz surface.This conclusion was further verified using AFM morphological scans and force curve measurements in conjunction with a DLVO computational model.In addition,the anomalous force traction curve of the starch and hematite surfaces at p H 4.0 and the comparable force on withdrawal to that at p H 6.0 provide further insight into the inference that weak chemisorption and hydrogen bonding occurs at the interface between them and is dominated by hydrogen bonding.(2)Interfacial matching mechanism between starch molecular structure and mineral surface structure.The inhibition effect of three starch depressants on minerals during flotation was compared at p H 10.0,extending to changes in mineral surface properties and particle flocculation behaviour,and then an interfacial matching model was developed at the atomic level to verify the molecular structure effect.Zeta analysis,XPS testing and AFM force curve measurements revealed that the molecular structure of starch does not affect its chemisorption to the surface of hematite,but the intensity of the effect varies,with the lower the straight chain/branched chain ratio,the stronger the chemical effect,i.e.WS>NS>G50;for quartz,starch does not chemically interact on its surface,but hydrogen bonding may be present,which in turn has an effect on the mineral surface properties.In addition,starch molecular structure and the flocculation phenomenon of hematite were investigated in terms of the settling behaviour,turbidity and micromorphology of the mineral particles,and it was found that starch affects the agglomeration size of the mineral particles,which in turn affects the settling rate of the particles and the turbidity of the slurry suspension.Finally,based on quantum chemical calculations and molecular dynamics simulations to optimise the mineral cell and surface structure,the starch molecules were structurally optimised and their frontline molecular orbitals calculated,and a starch-mineral surface structure model was constructed to calculate the surface adsorption energy.The difference in adsorption energy presents results consistent with the chemical interaction described above,strongly elucidating that starch is chemically adsorbed on the surface of hematite due to the different ease of its participation in chemical reactions and the intensity of its action: WS>NS>G50;while the adsorption energy of the three starch species with the surface of quartz is relatively small and does not differ significantly,and its adsorption energy is in the range of hydrogen bonding(25-40 k J/mol),deeply interpretation of the relevant conclusion that no chemical interaction occurs at the interface between the two,but the interaction may exist in the form of hydrogen bonding.