| The new type series of a-ammonolyzed fatty acids(a-AFAs)-insertion of imino group and a hydrophilic oxygen atom into the a-position of aliphatic acid were firstly designed based on organic structural chemistry theories and principles of molecule structural design of flotation collectors.By using Materials Studio 8.0 quantum chemistry program,the collectors’ molecular parameters such as bond length and bond angle etc.have been obtained from the optimum geometric molecular structures which could prove the design of collectors’ molecular structures is feasible and reasonable.The eight above a-AFA collectors with different carbon chain length of et-her amino and carboxyl group-2-((2-(hexyloxy)ethyl)amino)hexanoic acid(O4H9 CH(NH(CH2)3OC6H13)COOH,HHEA),2-((2-(octyloxy)ethyl)amino)hexanoic acid(C4H9CH(NH(CH2)3OC8H17)COOH,HOEA),2-((2-(decyloxy)ethyl)amino)hexanoic acid(C4H9CH(NH(CH2)3OC10H21)COOH,HDEA),2-((2-(lauryloxy)ethyl)amino)h-exanoic acid(C4H9CH(NH(CH2)3OC12H25)COOH,HLEA),2-((2-(hexyloxy)ethyl)a-mino)lauric acid(C10H21CH(NH(CH2)3OC6H13)COOH,LHEA),2-((2-(octyloxy)et-hyl)amino)lauric acid(C10H21CH(NH(CH2)3OC8H17)COOH,LOEA),2-((2-(decylo-xy)ethyl)amino)lauric acid(C10H21CH(NH(CH2)3OC10H21)COOH,LDEA),2-((2-(1-auryloxy)ethyl)amino)lauric acid(C10H21CH(NH(CH2)3OC12H25COOH,LLEA)we-re firstly synthesized by α-ammonolyzed reaction from 3-alkoxy-1-propanamine(3-hexyloxy-1-propanamine,3-octyloxy-1-propanamine,3-decyloxy-1-propanamine,and 3-lauryloxy-l-propanamine)and a-bromo-saturated fatty acids(a-bromohex-anoic acid and a-bromolauric acid),respectively.The results of chemical eleme-nt analyses,Fourier transform infrared spectrometer(FT-IR),nuclear magnetic h-ydrogenand carbon measurements(1H-NMR and 13C-NMR)reveals that the pro-ducts arethe target α-ammonolyzed fatty acid products.The basic flotation behavior of pure quartz,hematite and magnetite using a-AFAs as the collectors were investigated by single mineral tests at pulp temperature 15.0 ℃,and the influence of the carbon chain length of ether amino and carboxyl group on flotation properties were studied.The flotation results indicate that the collecting ability order for the three minerals is quartz>hematite>magnetite.The longer of carbon chain length of ether amino and carboxyl group,the wider flotation pH ranges and stronger collecting abilities were obtained.While,the flotation recoveries decreased with increasing carbon chain length on account of the solubility and dispersity of the a-AFA collectors which containing carbon atom numbers between 6 and 15 in the chain decreased with increasing chain length at low temperature.Under the flotation conditions of pulp temperature 15.0℃,a-AFA dosage 20.0 mg·L-1,the flotation results showed that the collecting abilities for quartz,hematite and magnetite minerals are in the order of LDEA>LOEA≈ HLEA>HDEA ≈ LHEA>HOEA>LLEA≈ HHEA,HLEA>LLEA≈LDEA>HDEA>LHEA>LOEA≈HOEA>HHEA and HLEA>LDEA>LOEA>LHEA>HDEA ≈ LLEA>HOEA>HHEA,respectively.The quartz-hematite-magnetite artificial mixed minerals flotation tests under the conditions of pulp temperature 15.0℃,pulp pH 8.00,depressor starch dosage 8.0 mg·L-1,and collector LDEA dosage 20.0 mg·L-1,the concentrate total ferrum(TFe)grade of 65.51%and TFe recovery of 9%have been obtained which demonstrates that the a-AFAs are the new collectors with a preferable collecting and separation ability for reverse flotation to remove quartz mineral from iron ores at a relatively low temperature.The adsorption mechanism of the new type collector α-AFAs on pure quartz,hematite,and magnetite mineral surfaces were established by zeta potential measurements,FT-IR,XPS(X-ray photoelectron spectroscopy),molecular dynamics(MD)and quantum chemistry simulated calculations,in conjunction with the results of single mineral micro-flotation tests at 15.0 ℃.The study reveals that the a-AFA collectors had been adsorbed on the surface of quartz surface at pulp pH 10.00 in the forms of electrostatic interaction and hydrogen bonding adsorption based on the results of zeta potential measurements,FT-IR spectra,and XPS.While,on the surfaces of pure hematite and magnetite chemical adsorption occurred besides the electrostatic interaction and hydrogen bonding adsorption.The adsorption process of a-AFAs on quartz’s surface at a molecular level in vacuum shown that the a-AFA collectors could adsorb on quartz’s(101)surface as the H atom of collectors a-AFAs moved closer to the O atom of quartz(101)surface.With the increase of carbon chain length of ether amino and carboxyl group,the adsorption energies decreased gradually within a small range which indicates that the carbon chain length of nonpolar group mainly influences the hydrophobic abilities of a-AFA collectors.The results of the equilibrium configurations and adsorption energies of collector LDEA on quartz’(101)surface in aqueous under different pH revealed that the optimum pulp pH for LDEA adsorption on quartz’s surface is at neutral to weak alkali(pH 6～10)environment.That is to say,it was difficult for LDEA adsorption at the weak acid environment and strong alkali condition on quartz(101)surface.The flotation condition experiments,open-circuit flotation experiment,and closed-circuit flotation experiment for Anqian mixed magnetic concentrate were accomplished using LDEA as the collector.The closed reverse flotation experiment of one roughing-three scavenging obtained the iron concentrate with TFe grade of 68.08%,TFe recovery of 88.20%,while the grade of tailing was only 12.32%.The experiment demonstrates that LDEA was an effective flotation collector with good collecting and separation ability on Anqian ores at comparatively lower temperature.The results will lay the foundation for developing floating collectors used in lower temperature in iron ore flotation,which would not only enrich the flotation reagent theory,but also solve the high energy consumption problems in iron ore flotation. |
