| The flotation of wolframite&cassiterite and the selective separation of scheelite have always been one of the most difficulty problems for the exploitation of tungsten&tin resources.The high selective flotation collector is the key to solve these problems.Based on the characteristic of crystal structure and surface properties of wolframite,cassiterite,scheelite,fluorite and calcite,together with the analysis of structure-activity relationship of chelating collector,as well as the establishment of QSAR model,targeted-molecular design techniques of flotation chelating collector,which was guided by quantum chemical calculations,molecular orbital theory and group electronegativity theory,was putted forward in this thesis,owing to the high-speed progress of modern computing technology and the fast development of modern molecular designing theory of flotation reagents.Three new hydroxamic acid collectors designed for the flotation separation of scheelite and calcium gangue minerals,and an unsaturated phosphonic acid collector used for the folation of wolframite and cassiterite were designed and synthesized.The examination of elemental analysis,IR and NMR characterization,as well as flotation research for designed collectors were carried out.The adsorption and flotation mechanism of collectors were also studied by flotation solution chemistry theory,quantum chemical calculations and molecular dynamics simulation.The main research results are listed as follows:The influence of crystal structure on the surface properties and the characteristic of crystal structure and surface properties of wolframite,cassiterite,scheelite,fluorite and calcite were analyzed by the energy band theory of solids,quantum chemistry theory and molecular orbital theory.The results show that the bottom part of conduction band of wolframite and cassiterite cleavage surfaces is mainly composed of the electron orbits of surface metal atoms,Sn atoms and Mn/Fe atoms are the active atoms of casiterite and wolfmaite surfaces,respectively.However,these was a strong bonding interaction between oxygens and metal atoms.the activity of metal atoms is not high.Scheelite,fluorite and calcite are ionic crystals,and have the same surface active calcium ions,resulting in the separation difficulty.The difference in crystal structure leads to different way of collector targeted-molecular design for this two types minerals.Wolframite and cassiterite which have different active atoms from their gangue minerals,only need to looking for polar functional groups that have specific interaction with the active atoms.However,the selective collectors for scheelite have to consider the spatial effect and the key-matching principle between collector and mineral surface structure.The effects of polar and nonpolar structure on the reactivity and flotation performance of collectors were analyzed by quantum chemistry calculations,molecular orbital theory and group electronegativity theory.The thesis found that the hydroxamic acid is a suitable high selectivity collector for scheelite,and the phosphonic acid polar functional groups was suitable for wolframite and cassiterite floatation.The nonpolar group has also a great influence on the floatation performance,reaction activity and surface hydrophobicity of collector.The carbon chain length and carbon chain isomerism have little effect on the activity of molecules,but the hydrophobicity and molecular surface area.The presence of benzene ring or ring structure or double bond,and electron withdrawing groups or electron donating groups in the nonpolar groups will have a great impact on the performance of collector.Study on the selectivity of hydroxamic acid and phosphonic acid by quantitative structure activity relationship research(QSAR)method.Based on the Genetic Function Approximation(GFA)method,with the sample capacity of 18,the QSAR model for the separation selectivity of scheelite-fluorite flotation was successfully established by using fast molecular descriptors and quantum chemical descriptors.The optimal model 5 of the selectivivity index ? with model correlation coefficient R2 of 0.900 and Rcv2 prediction coefficients of 0.852,was obtained.Internal reliability validation of this model was performed using leave-one-out cross validation approach,with R2 of 0.929.To validate predictive abilities of models,an external validation was conducted for test sets with the average absolute deviation was 0.146.The reliability and predictive ability of model 6 is good,which can be used to predict the selectivity of hydroxamic acid.The results showed that the charge of O atoms in hydroxyl group and Aux_density parameters of molecular are the key factors affect the selectivity of hydroxamic acid.The presence of benzene ring and double bond in nonpolar groups is conducive to the increase of collector selectivity.Due to the unreasonable distribution of data,it is impossible to establish an effective QSAR model for the selectivity of phosphonic acid.Based on above results and the molecular design theory of modern flotation reagents,three new kinds hydroxamic acid used for the separation of scheelite:6-(1,3-dioxoisoindolin-2-yl)-N-hydroxyhexanamide(BHHA);6-(1,3-dioxo-1,3-dihydro-2H-benzo[f]isoindol-2-yl)-N-hydroxyhexanamide(NHHA),6-(1,3-dioxooctahydro-2H-isoindol-2-yl)-N-hydroxyhexanamide(HHHA)and a new unsaturated phosphonic acid collector,(1-hydroxy-2-methyl-2-octenyl)phosphonic acid(HEPA)used for wolframite and cassiterite flotation were designed and prepared.These collectors were characterized by elemental molecule analysis,infrared spectrum,nuclear magnetic resonance(NMR)examination and quantum chemistry calculations.Flotation performance of new chelating collectors were investigated by pure minerals flotation experiments,comparative flotation experiments with conventional reagents and actual ore flotation experiments.The micro-flotation test results show that these new hydroxamic acids have good selectivity for calcium minerals.These three have better collecting ability for scheelite than that for fluorite and calcite.The selectivity sequence of three new collectors for scheelite is NHHA>BHHA>HHHA.Using NHHA as collector,the effect of adding modifier in the flotation was investigated.The addition of inhibitors,such as water glass,CMC and citric acid,can effectively improve the separation efficiency of scheelite and fluorite,calcite.Lead nitrate,which can activate flotation,can also improve the recovery rate of scheelite.With the same concentration,HEPA has a much wider operating pH range and a much stronger collecting ability for wolframite and cassiterite than SPA.The HEPA was demonstrated to be an efficient flotation collector for fine cassiterite and wolframite.The NHHA and HEPA were respectively used for the actual ore flotation of scheelite and cassiterite,and both that obtained good results.The flotation test,zeta potential measurement and infrared spectroscopy,combined with flotation solution chemistry theory and quantum chemistry calculation,molecular dynamics simulation was used to investigated the flotation and adsorption mechanism of new collectors.The research results show that the adsorption mechanism of phosphonic acid collector was mainly attributed to the chemical adsorption between the monoanion of HEPA and metal atoms on mineral surface.The calculation results of phosphonic acid adsorption onto cassiterite were highly consistent with the actul results.The space key-matching principle is the very good interpretation for the results that these new hydroxamic acids have the best selectivity for scheelite and the selectivity of NHHA is better than those of BHHA and HHHA. |
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