Depressing Capability And Mechanism Of Starch Derivatives In The Reverse Flotation Desilication System Of Hematite

Starch,as a depressant of hematite,is widely used in reverse cationic collector floatation and reverse anionic collector floatation.However,there are some shortcomings in production practice,such as complex preparation and poor separation sharpness for fine-grained minerals.Starch derivatives have good solubility.It has been shown that starch derivatives can be used as depressants in reverse flotation desilication of hematite.However,there are few studies on the effect of substituents and degree of substitution on the depression performance of starch derivatives.In this study,two typical systems of cationic collector reverse flotation and anionic collector reverse flotation were studied,covering flotation tests,starch derivatives and minerals surface adsorption,and the influence of starch derivative on collector adsorption.With cassava starch,phosphate starch and carboxymethyl starch as depressants,the depression effect and mechanism of substituents and degree of substitution of starch derivatives on fine hematite and quartz were investigated.In the reverse flotation test with dodecylamine as the collector,when the degree of substitution of starch derivative substituent increased,and its depression to hematite and quartz decreased.The phosphate starch with low degree of substitution can depress the hematite,but has little effect on quartz,so it is superior to the original starch in reverse cationic collector floatation.In the reverse flotation test with sodium oleate as the collector,the increase in the degree of substitution of starch derivative led to stronger depression on hematite,and showed depression on quartz when the dosage of CaCl2 was too large.Under the appropriate dosage of activator CaC12,the separation efficiency of starch derivative is higher than that of raw starch as the depressant of hematite by anionic collector reverse flotation.The results of calculation with CASTEP module in Materials Studio software showed that the substituents of starch derivatives have strong interaction with hematite surface and weak interaction with quartz surface.The results of quartz crystal microbalance tests showed that the adsorption of starch derivative molecules on Fe2O3 surface belongs to chemical adsorption,and the adsorption layer is compact;whereas on SiO2 surface the adsorption belongs to physical adsorption,the adsorption capacity is about 1/10 of Fe2O3 surface,and the molecular structure of phosphate starch adsorption layer is mostly loose.Because of the negative charge of the substituent group,the negative value of the surface potential of the mineral is increased by the starch derivative adsorbed on the surface of the mineral,and the high degree of substitution starch derivative greatly reduces the surface potential of the mineral.When the degree of substitution of starch derivatives is high,the adsorption on the surface of hematite and quartz promotes the adsorption of dodecylamine.The depression of low degree of substitution phosphate starch is better,which is related to the adsorption difference between hematite and quartz.The proportion of substituent-PO32-in the molecule is small,and it has a strong interaction with the surface of hematite.Because the decrease of the surface potential is small,adsorption of low degree of substitution phosphate starch on the surface of hematite is not conducive to the adsorption of dodecylamine.The interaction of substituent-PO32-with the surface of quartz is weak.Reduction of the adsorption of low degree of substitution phosphate starch on the surface of quartz and reduction of the surface potential of quartz promote the adsorption of dodecylamine on the surface of quartz.With the increase of CaCl2 dosage,the amount hydroxyl compounds of calcium adsorbed on the surface of quartz increases,the adsorption capacity of high degree of substitution phosphate starch increases,while the adsorption capacity of sodium oleate changes little.By flotation with anionic collector,using starch derivatives with high degree of substitution and adding excessive amount of CaCl2 would make more starch derivatives adsorb on the surface of quartz,masking the adsorbed collector on the surface of quartz and thus depressing its flotation.