Molecular Design And Interaction Mechanisms Of Desulfurizing Collectors For Bauxite

With the development of alumina industry,the supply problems of high grade of bauxite resources become increasingly severer.The utilization of the high-sulfur bauxite(sulfur content is greater than 0.7%)has been aroused a special concern.Sulfur in the high-sulfur bauxite mainly exists in the form of pyrite,which would cause a lot of negative effects on alumina production.Therefore,it is necessary to desulfurization before the bauxite being used in the process of alumina production.Flotation has proved to be a particularly suitable method for the desulfurization of high-sulfur bauxite in term of flexible operation and economic technology.Notably,flotation reagents are key factors in the fotation process.In this work,the physical and chemical characteristics of high sulfur bauxite were firstly investigated.Then,based on the molecular design theory,several mercaptoimidazole reagents were first designed and prepared using direct method to be used as pyrite collectors in the flotation desulfurization of high-sulfur bauxite.Frontier orbital energy for the interaction of reagent and minerals including pyrite,muscovite and diaspore was calculated according to the density functional theory(DFT)of quantum chemistry.Then,the flotation behavious of single minerals using new reagents as collectors were investigated,and the structure-function relationship of mercaptoimidazole reagents were established.Adsorption behaviors and interaction mechanisms of four new reagents onto pyrite were studied through adsorption experiments,molecular dynamics simulation,EDLVO theory and advanced analysis techniques.Flotation desulfurization and desilicication of high-sulfur bauxite were achieved using new reagents as pyrite collector through orthogonal tests and single factor experiments.The main contents are as follows:The analysis results from XRF,XRD,SEM and metallographic microscope show that the valuable mineral of high-sulfur bauxite used in this work is diaspore,the sulfur-containing mineral is mainly pyrite,and silicon-containing mineral is muscovite.These minerals are complexly and tightly embedded in each other.The aluminum to silicon ratio(A/S)of this sample is 3.36,and the content of sulfur is 2.87%,which is belong to refractory high-sulfur bauxite.The minerals in high-sulfur bauxite were well liberated through crushing and grinding.The amphoteric mercaptoimidazole reagents abbreviated as M1,M2,M3 and M4 were constructed through designing the polar group of mercaptoimidazole and the nonpolar groups of quaternary ammonium salt with different carbon chain structrue and geometric dimension.The nonpolar group of M1 reagent contains long carbon chain and narrow dimension,while M2 reagent contains long chain and wide dimension,M3 reagent includes short carbon chain and hydroxyl group,and M4 reagent includes short carbon chain and carboxylate.The DFT calculation results indicates that the reactivities of four reagents in the form of molecurel are higher than there ioned forms.The reactivity of four reagents follow the order of M2>Ml>M4>M3,and the bonding atoms are primarily N atom in imidazole ring and S atom in S-H group.The frontier orbital interaction energy ?E1 between mercaptoimidazole reagent and pyrite is lower than that of muscovite and diaspore,which demonstrats that the mercaptoimidazole reagents show stronger interactions with pyrite than muscovite and diaspore.The mercaptoimidazole reagents were successfully synthesized by the direct method.The structure and property of four regens were characterized by FTIR,NMR,UV-Vis,and TG-DSC.UV-Vis spectra of four reagents is smilar with mercaptobenzimidazole having ultraviolet characteristic absorption at 300 nm.TG-DSC results indicate that the mercaptoimidazole reagents possess good thermostability.The recovery of pyrite using mercaptoimidazole reagents as collector is higher than that of muscovite and diaspore due to the higher adsorption capacities on pyrite.Amoung the four collectors,collector M2 with long carbon chain and wide geometric dimension presents higher adsorption capacity and flotation performance on pyrite than other three collectors,in consistant with the DFT results.The suitable condition for four collectors to flotate pyrite are respectively acidic,alkaline,strong alkaline,and neutral.Under the slurry pH 9,higher flotation recovery of pyrite was obtained through decresing the dosage of collectors Ml and M4,while increasing the dosage of collectors M2 and M3.The adsorption process of collector M2 on pyrite follows pseudo-second order kinetic model,wich is a nonspontaneous and endothermic process.The isotherm adsorption of collector M2 on pyrite is fitted to Freundlich isotherm,and higher temperature is beneficial to adsorption.The results of SEM,FTIR,XPS,contact angle tests and Zeta potential analysis indicate that the adsorbed mercaptoimidazole reagents are evenly distributed on the pyrite surfaces.The hydrophobicity of pyrite increases and the negative charges on pyrite surfaces decreses after interacting with mercaptoimidazole reagents.The interaction mechanisms of mercaptoimidazole collectors with pyrite surfaces are principally chemical reaction and chelation through forming C=N-Fe-S coordination ring,which is in accordance with DFT calculation results.EDLVO results indicate that mercaptoimidazole collectors increase the hydrophobic force and hydrophobicity of pyrite partices which accelerate the flocculation flotation of pyrite particles.The flotation desulfuration of high-sulfur bauxite indicate that mercaptoimidazole collectors present good desulfuration performance,especialy the collector M2 with long carbon chain and wide geometric dimension.Synchronous desulfuration and desilicication were achieved through adding desilicication collector and diaspore depressant.The optimized condition are 10%solid density,particle size of-74?m of 75%,pulp pH 9,temperature 30 ?,depressant dosage of 50 g/t,activator dosage of 20 g/t,collector M2 dosage of 120 g/t,CTAB collector dosage of 100 g/t,and terpenic oil dosage of 120 g/t.Under the optimized conditions,the sulfur content of concentrate was 0.27%,with A/S of 8.09 and Al2O3 recovery of 76.41%.The novel and effective mercaptoimidazoles collectors of pyrite designed and prepared in this work and synchronous flotation desulfuration and desilicication of high-sulfur bauxite would provide theoretical and practical fundation for developing novel flotation reagents and efficient separating of high-sulfur bauxite.