Equilibrium and non-equilibrium states of systems Na 2 O–Al 2 O 3 –H 2 O and K 2 O–Al 2 O 3 –H 2 O are crucial for establishing key technological parameters in alumina production and their optimization. Due to a noticeable discrepancy between experimental results and thermodynamic calculations based on materials of individual researchers the necessity of systematization and statistical processing of equilibrium data in these systems to create a reliable base of their physicochemical state, analysis and mathematical modeling of phase equilibria is substantiated. The tendency to a decrease of the hydration degree of solid sodium aluminates with increasing temperature and the transition of systems from the steady state of gibbsite to equilibrium with boehmite is revealed. The paper contains approximating functions that provide high-precision description of equilibrium isotherms in technologically significant area of Na 2 O–Al 2 O 3 –H 2 O and K 2 O–Al 2 O 3 –H 2 O concentrations. Approximating function can be simplified by dividing the isotherm into two sections with the intervals of alkaline content 0-0.25 and 0.25-0.4 mole/100 g of solution. The differences in solubility isotherms for Na 2 O–Al 2 O 3 –H 2 O and K 2 O–Al 2 O 3 –H 2 O systems provide are associated with changes in the ionic composition solutions that depends on concentration and temperature, as well as differences connecting with alkali cation hydration, which is crucially important for thermodynamic modeling of equilibria under consideration.
The scientific justification and development of the method for industrial synthesis of complex aluminates of alkaline earth metals is an innovative solution that determined several directions in the development of technology for complex processing of nepheline raw materials. It ensures the production of high-quality metallurgical alumina, the effective utilization of nepheline sludge and production of new types of multipurpose by-products. The modern development of these technical solutions is associated with ensuring the energy efficiency of the synthesis of hydrafed calcium carboaluminates (HCCA) and increasing the level of purification of aluminate solutions. The conditions for synthesizing HCCA with the use of calcareous materials of natural and technogenic origin have been experimentally determined, which makes it possible to isolate the average particle diameter as one of the determining factors of this process. The effect of the turnover of the hydrogarnet sludge on the removal of kinetic limitations in the process of deep desalination of aluminous solutions is theoretically justified. The conditions of a two-stage dosage of HCCA are experimentally determined. It is shown that the optimum ratio of the amount of the reagent supplied in the first and second stages is about 3: 2. At the same time, the maximum degree of precipitation of silica provides the production of aluminate solutions with a silicon module at the level of 95,000, which is achieved by using a HCCA synthesized based on chemically precipitated calcium carbonate in the processing of wastes from the production of mineral fertilizers.
Power consumption across the globe is constantly increasing for a variety of reasons: growing population, industrialization and fast economic growth. The most widespread gaseous fuel – natural gas – has the low production cost. It is 2-3 times cheaper than liquid fuel production and 6-12 times cheaper than coal production. When natural gas is transported to distances from 1.5 to 2.5 thousand km by the pipeline, its cost with account of transportation is 1.5-2 times less than the cost of coal and the fuel storage facilities are not needed. Plants powered by natural gas have the higher efficiency as compared to the plants operating on other types of fuel. They are easier and cheaper to maintain and are relatively simple in automation, thus enhancing safety and improving the production process flow, do not require complicated fuel feeding or ash handling systems. Gas is combusted with a minimum amount of polluting emissions, which adds to better sanitary conditions and environment protection. But due to depletion of major energy resources many experts see the future of the global energy industry in opportunities associated with the use of solid energy carriers. From the environmental perspective solid fuel gasification is a preferred technology. The use of synthetic gas was first offered and then put to mass scale by English mechanical engineer William Murdoch. He discovered a possibility to use gas for illumination by destructive distillation of bituminous coal. After invention of the gas burner by Robert Bunsen, the illumination gas began to be used as a household fuel. The invention of an industrial gas generator by Siemens brothers made it possible to produce a cheaper generator gas which became a fuel for industrial furnaces. As the calorific value of generator gas produced through gasification is relatively low compared to natural gas, the Mining University studied possibilities to use different types of low grade process fuel at the Russian alumina refineries as an alternative to natural gas, access to which is restricted for some of the regions.
The paper presents theoretically based requirements for the activation of synthetic gibbsite for maximum solubility of the activated product. The article describes the methodological foundations of gibbsite thermal activation and its effectiveness evaluation in terms of aluminate solutions decomposition. It is shown that to obtain high-saturation aluminate solutions, activation should provide generation of the reagent with highly-developed surface area, which is not identical to the structure of the deposited gibbsite. As a result of high-gradient thermal activation of synthetic gibbsite, it has been found that the targeted product develops predominantly an amorphous structure with a specific surface area up to 256 m2/ g, preserving its primary particle size. Activation products were investigated using modern methods of physical and chemical analysis. The experimental results confirmed the possibility of the activated product dissolution in the aluminate solution with a metastable compound and their spontaneous decomposition with aluminum hydroxide formation, characterized by high dispersion ability. It is shown, that a significant difference in kinetics and decomposition rates of solutions is connected with the use of a seed material with different particle size composition, which leads to the development of competing mechanisms, resulting in seed recrystallization, homogeneous and heterogeneous nucleation.
One of the problems to be solved in the course of exsolution of crystal sediments is to re-ceive products with desired technological properties. Two fundamentally different approaches can be applied for its resolution depending on method of supersaturation and requirements to the crystal sediments quality. In case of high supersaturation growth centers arise spontaneously and their number determines the properties of the final product to a large degree. The crystallization in the metastable region of solutions prevents spontaneous crystal nucleation and an introduc-tion of the seed phase becomes inevitable in this case. The nature of this phase determines the properties of the final product to some extent. During the real process there are mechanisms that disrupt the normal growth of crystals, causing distortion, leading to heterogeneous nucleation and recrystallization with degradation of seed material even. The line between these trends is the limiting supersaturation value, attrib-uted to the unit of phase interface. In this case the development of appropriate growth mecha-nisms is proportional to the deviation of the specific supersaturation of the solution from its value limit. The traditional source of heterogeneous nucleation is the mechanical interaction of the particles. The interaction probability is proportional to their concentration. Particles’ mass and their size becomes the most significant heterogeneous nucleation factor for seed particles of the same nature and morphology at the conditions of reproducible stream turbulence. Mathe-matical description of these trends has allowed to establish the dependence of the final particles’ size on the seed concentration in the feed pulp and to show the existence of a minimum number of particles of the final product. Experimental study of the of chemical sediments’ properties that depend on the seed amount, was carried out in relation to the breaking-up of aluminate solutions of alumina production. The process of selection of aluminum hydroxide has allowed to establish the amount of the seed aluminum hydrox-ide, resulting in a product of maximum size, and thus to confirm the theoretical conclusions.
The results of synthesis hydrocarboalyuminates of calcium (GKAK) using carbonate reagents of different nature and size distribution. A high activity of the lime sludge from causticising soda and food processing conversion of phosphogypsum, which allows us to recommend them for use in the process of obtaining GKAK. Installed limiting stage of interaction of internal diffusion of the reactants.
The materials physical and chemical analysis of the reasons of instability particle size distribution of productional of aluminum hydroxide in the processing of bauxite by Bayer process. Shown that the frequency of changes in the properties precipitate Al(OH)3, formed during the precipitation of aluminate solutions determined by the dependence of the growth processes on the relative supersaturation of the system per unit area of the seed. Found determines the influence of concentration injected seed aluminum hydroxide and its active surface (which varies under the influence of impurities in the aluminate solution) on the parameters of the periodic changes in the properties of sediment.
The results of the technical and mineralogical studies of washability of low quality bauxites of North Onega deposit are presented. The experiments of determination of the grindability of raw materials including without ball grinding and assessment washability bauxite by magnetic separation and flotation were conducted. These ores are very complex object for enrichment, as characterized by extremely thin impregnated aluminum-containing minerals, as well as the similarity of their properties. Further work of to conduct experiments using chemical enrichment (as soon as the chemical enrichment, and in combination with the physical methods of enrichment) is planned.
Materials of calculation of solubility of aluminum hydroxide in the system Na2O – K2O – Al2O3 – H2O, by data of the solubility in the private sections of this system for a wide range of compositions aluminate solutions by the content of alkaline components are presented. It is shown that the solubility of aluminum hydroxide in the range of concentration of alkaline components from 1,29 mol/l to 1,94 mol/l is a linear function of the mol fraction of one of them. The results of experimental researches on decomposition of aluminate solutions are given. Significant increase of the degree of decomposition of aluminate solutions in per cents of the theoretical values with growth of mol fraction of K2O in a mixture of alkaline components has been established.
The materials of mass transfer kinetic analysis of complicated by the establishment of adsorption equilibrium, during alumina liquor precipitation of alumina production. It is shown that the presence of strongly adsorbing impurities is one of the determinants of the intensity of the aluminum hydroxide chemical precipitation. The results of experimental studies on the alumina liquor precipitation with the participation of adsorption active components.
The role of thermodynamic and kinetic factors in the formation of the real structure of chemical precipitation. On the example of gibbsite precipitation from alkaline aluminate solutions is set to take place in parallel crystallization processes in the formation of production (rheological) properties of the solid phase formed during the chemical interaction is presented.
The materials of the pilot study, which establishes the dependence of the kinetics of mass crystallization of aluminum hydroxide on the extent of metastable alkaline aluminate solutions. Shown that changes in the level of metastability of the environment of crystallization is the lag in time from changes in state parameters of physico-chemical system. The theoretical a justification of the transition from one level of the metastable state to another due to time constraints, changing the structure of unstable solutions.
Experimental results of thermal deposition of crystal hydrates of magnesium sulfate from a solution containing sulphates of alkali metals. Set of indicators as a function of the kinetically relevant factors. It was shown possible to describe the crystallization kinetics equation of magnesium sulphate topochemical processes and identify its characteristics.
Materials of the kinetic analysis of multistage mass-transfer process at decomposition of aluminate solutions in alumina production are presented. It is shown that in the mass-transfer equation concentration indicators which take into consideration distribution of reagents and products in a diffusive layer can play a role of effective concentration. Results of experimental researches of crystallization streams on a various fraction structure are resulted.
The paper describes the theory and practice of low-temperature decomposition of alumina solutions. Scientific substantiation of the use of activated nepheline solution as an inoculum for HASN crystallization is given. Materials of experimental study of chemical equilibrium and kinetics of the decomposition process in the system activated nepheline alcohol - aluminate solution are presented. The possibility of achieving technological low-temperature factors of the process sufficient for the subsequent complete deposition of silica is shown.
Materials explaining the mechanism of spatial differentiation of solution composition with the participation of the gas phase and its role in the creation of non-equilibrium conditions that ensure recrystallization of solid products are presented. Calculations of equilibrium in a number of systems of alumina production are presented. Indicators of non-equilibrium of solutions and their dependence on the leading technological parameters of the process are established.
The mechanism of mass crystallization of synthetic gibbsite at decomposition of aluminate solutions is proposed. The leading role of nucleation and supersaturation in the formation of granulometry of aluminum hydroxide precipitate is shown. The methodology and experimental results of induction period determination during gibbsite precipitation from aluminate solution are presented. The surface energy of solid phase formation during carbonization of aluminate solution as a function of critical nucleation size is determined.
