| Chalcopyrite and molybdenite often coexist closely.Flotation technology is a common method for the separation of chalcopyrite and molybdenite,but flotation separation is extremely difficult due to the similarity of floatability of the two minerals.The commonly used depressants for the flotation separation of chalcopyrite and molybdenite includes sodium sulfide and sodium hydrosulfide,which have the disadvantages of large dosage,inferior selectivity,and producing toxic gases.As a biodegradable,inexpensive and green resource,starch has the potential to contribute to the sustainability of mineral flotation separation.The effects of native and modified starch on the flotation behavior of chalcopyrite and molybdenite were investigated in the paper.The mechanisms of the interaction between starch and chalcopyrite were revealed by contact angle measurements,adsorption isotherms,gel permeation chromatography(GPC),infrared spectroscopy,zeta potential and X-ray photoelectron spectroscopy(XPS).(1)The effects of native rice,corn and wheat starch on the flotation behavior of molybdenite and chalcopyrite were investigated.At low dosage,wheat starch had little effect on chalcopyrite flotation.When the amount of starch was high,wheat starch can effectively depress the flotation of chalcopyrite,but had little impact on the flotation of molybdenite,and the recovery difference was more than 58%.In the presence of rice starch and corn starch,the recovery difference of chalcopyrite and molybdenite was 27%and 19%,respectively,and the selective depression effect was inferior.The depression mechanisms of three native starches for chalcopyrite were revealed by various experiments.The three native starches had the same adsorption form.Hydroxyl groups in the native starches interacted with copper and iron hydroxyl/hydroxides on the surface of chalcopyrite.Wheat starch exhibited the best depression performance,followed by rice starch,and the worst is corn starch.(2)Native wheat starch significantly and selectively depressed chalcopyrite.At starch dosage of 67 mg/L and kerosene dosage of 80 mg/L,wheat can reduce the recovery of chalcopyrite to about 13%,while molybdenite still had a recovery of over70%.The mechanisms of starch interaction on the heterogeneous surfaces of chalcopyrite and molybdenite were clarified when native wheat starch was used as the study object.The protonated hydroxyl groups of native wheat starch molecules were heterogeneous adsorbed on the surface active sites of chalcopyrite and the edge planes of molybdenite by specific chemical(acid-base)interactions and hydrogen bonding,rather than on the hydrophobic sulfur-rich sites on the surface of chalcopyrite and the hydrophobic basal plane of molybdenite through hydrophobic interactions.The adsorbed starch macromolecules shield the hydrophobic surface sites on chalcopyrite and prevented the adsorption of kerogen chains.Only a small number of starch molecules extended to the adjacent basal plane of molybdenite,which had less effect on the interaction between molybdenite and kerosene.(3)The native wheat starch was modified to obtain modified wheat starch.The modified wheat starch exhibited superior depression properties than the native wheat starch.The modified wheat starch could reduce the recovery of chalcopyrite to less than5%,while the recovery of molybdenite remained above 70%.Modified starch acted mainly on the polar sites on the chalcopyrite surface and on the edge surfaces of molybdenite,while it had poor adhesion on the hydrophobic base of molybdenite.The oxidation modification disrupted the native granular structure of wheat starch and broke the polymer chains,resulting in a lower molecular weight and viscosity,and solubility increase at room temperature.Some carboxyl groups replaced the hydroxyl groups on the starch units during the oxidation process,thus changing the structure and properties of the native starch molecule and making it more favorable for the starch functional groups to interact with the mineral surfaces. |
PDF Full Text Request