| The existence of fine clay minerals is one of the main reasons in coal slurry treatment.Clay minerals form highly stable suspensions in water due to the strong electronegativity of clay mineral surfaces.Metal electrolyte salts are usually used to increase the electrolyte content,thereby reducing the electronegativity of the surface of the fine clay mineral particles,in order to achieve the purpose of adjusting the water quality of the system.However,the main role is undertaken by metal cations and their complexes.Kaolinite is the main clay component of mineral processing wastewater such as slime water while aluminum salt is commonly used as coagulant.Up to now,the microscopic mechanism of aluminum salts on the kaolinite surfaces has not been studied in-depth,especially the adsorption mechanism analysis between the hydrolyzed components and the kaolinite surfaces at the molecular/atomic level.Furthermore,in the nature,Al3+and Si4+in the crystal structure of kaolinite are easily replaced by lattice defects or other positive ions,which can change the properties of the fracture surface of kaolinite.Therefore,it is of great significance to study the adsorption process and adsorption mechanism of aluminum salts on different exposed surfaces of kaolinite.Based on density functional theory(DFT),these were calculated that the adsorption process and stable adsorption configuration of the monomer components Al(OH)2+,Al(OH)3,Al(OH)4-and the hydrated aluminum ion(i.e.Al(H2O)63+)on the ideal kaolinite surfaces and the replaced kaolinite surfaces by impurity atoms Fe(?)and Mg.Then the adsorption stability and adsorption mechanism between the substance and the surface from the aspects of bonding analysis,charge transfer,and density of states analysis were analyzed.Meanwhile,this thesis takes the high-purity kaolinite and coal-measure kaolinite as the research objects,and explores the adsorption characteristics of Al3+ ion the surfaces of ideal kaolinite and coal-based kaolinite in different pH solution environments by graphite furnace atomic absorption spectrometry.The main research findings are as follows:(1)The kaolinite(001),(001)and(010)surfaces are common exposed surfaces after the dissociation of kaolinite crystals.After the substitution,the charge on the impurity atoms and that on the adjacent surface oxygen atoms are rearranged to form a new bond.After Fe(?)Al is substituted,the bond between Fe(?)and adjacent oxygen atoms shows strong covalentness,while after replacement by MgAl,the bond between Mg and adjacent surface oxygen atoms has strong ionicity.Furthermore,the result showed that Fe(?)Al substitution is relatively easier to occur than MgAl substitution.(2)Al(OH)2+,Al(OH)3 and Al(OH)4-can be adsorbed on the ideal kaolinite surfaces,and the adsorption on the ideal kaolinite(001)and(010)surfaces are better.When adsorbed on the ideal kaolinite(001)surface,the best adsorption sites are located above the oxygen atoms in the hydroxyl groups parallel to the kaolinite(001)surface.The adsorption between Al(OH)2+and Al(OH)3 and the kaolinite surfaces is mainly based on hydrogen bonding,and the interaction between Al in the adsorbate and surface oxygen atoms,and the latter is the main one.The adsorption of Al(OH)4-on the kaolinite surface is mainly based on hydrogen bonding.When Al(OH)2+,Al(OH)3 and Al(OH)4-are adsorbed on the kaolinite surfaces replaced by Fe(?)/Mg,the adsorption energy are lower than that on the ideal kaolinite surfaces,and the adsorption is more stable.When adsorbed on the kaolinite Fe(?)Al-(001)and MgAl-(001)surfaces,the adsorption sites of the best stable configuration are located in the hydroxyl group adjacent to the substitution position(that is,the hydroxyl group parallel to the surface).This is because the activity of oxygen atoms near the impurity atoms is enhanced after substitution.When Al(OH)4-is adsorbed on the replaced kaolinite(001)and(010)surfaces,the adsorption energy are-310.40 kJ/mol and-435.93 kJ/mol,and that were the lowest and the adsorption were more stable.(3)The reasonable coordination number of water molecules of Al3+is less than or equal to 6.In addition,when the coordination number is 6,it is the most stable hydrated aluminum ion complex.When Al(H2O)63+is adsorbed on the outer layer of the kaolinite surfaces,the strength of the adsorption mainly depends on the hydrogen bond between the adsorbate and the surface,the magnitude of the electrostatic attraction between the two,and the adsorption posture.When Al(H2O)63+single tooth adsorption on the inner layer of kaolinite surfaces,the adsorption mainly depends on the hydrogen bonding between the adsorbate and the surface and the bonding of Al-Os atoms.The Al-Os is the bonding between A1 3p orbitals in the adsorbate and Os 2p orbitals of the oxygen atom on the kaolinite surface.The order of adsorption stability of Al(H2O)63+is the same when it is adsorbed on the outer layer and inner layer of kaolinite respectively.However,when Al(H2O)63+is adsorbed on the outer layer of the kaolinite surface,the adsorption energy is lower than that single tooth adsorption on the inner layer of kaolinite surfaces,,and the adsorption stability is better.In addition,when Al(H2O)63+is adsorbed on the kaolinite surface of Mg substituted,the adsorption energy is lower than that when it is adsorbed on the kaolinite surface of Fe(?)substituted,and the adsorption is relatively more stable.(4)The measurement of the properties of the samples found that,in the same particle size grade after dissociation,the fine-grained particles in the coal-measure kaolinite are more distributed,and the flatness of the surface layer structure is relatively low.Combined with the measurement of the adsorption amount of aluminum ions,the turbidity removal rate and the comparison of the coagulation effect,the results show that the adsorption effect of Al3+ on the coal measures kaolinite is better than that on the pure kaolinite,which is consistent with the theoretical calculation results.In summary,through the combination of quantum chemical simulation and adsorption tests,the microscopic adsorption mechanism and macroscopic adsorption characteristics of the hydrolyzed components of the aluminum salt of the commonly used coagulant in different solution environments were explored on the ideal/actual kaolinite surface.It can provide a theoretical basis for the development and design of aluminum-containing reagents and the optimization of the pharmaceutical system.Figure[86]:Table[37]:References[161]... |
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