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The Liquid-solid Equilibria Of The System Na~+, K~+, Mg~(2+)//Cl~-, SO4~(2-), NO3~--H2O At 298.16 K And Its Application

Posted on:2009-03-12Degree:DoctorType:Dissertation
Country:ChinaCandidate:X L HuangFull Text:PDF
GTID:1101360242967125Subject:Chemical processes
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In this work, the liquid-solid equilibria of the hexa-component system Na+, K+, Mg2+//Cl-, SO42-, NO3--H2O, to which the nitrate brine close to Lop Nur of Xinjiang belongs, and its subsystems are studied at 298.16K. Study on them can provide theoretical guidance for the comprehensive utilization of the nitrate deposits in Xinjiang.The isothermal isobaric phase behavior for the system Na+, K+, Mg2+//Cl-, SO42-, NO3--H2O saturated with NaCl at 298.16K can be used to guide technology. As a result, the free-solvent and free-NaCl projection for the hexa-component system at 298.16K can be plotted in form of regular tetrahedron or trigonal prism. The unit of J(?)necke index for this diagram is mol/mol(2K++Mg2++SO42-+2NO3-) or mol/mol(2K++Mg2++2NO3-). The values of water and NaCl are obtained by insertion according to principle of phase diagram.At 298.16 K, the phase diagram of Na+, Mg2+//SO42-, NO3--H2O system consists five invariant points, eleven univariant curves which divide the phase diagram into seven regions of crystallization with one salt; the phase diagram of the system Na+, Mg2+//Cl-, NO3--H2O includes four crystallization regions with one salt, five univariant curves and two invariant points; the phase diagram of the system K+, Mg2+//Cl-, NO3--H2O at 298.16K includes five crystallization regions with one salt, which are being separated from each other by seven univariant curves which intersect in three invariant points; in the phase diagram of Mg2+//Cl-, SO42+, NO3--H2O, there are two invariant points, five univariant curves and four regions of crystallization with one salt; in the phase diagram of Na+, K+, Mg2+//NO3--H2O, there are one invariant point, three univariant curves and three regions of crystallization with one salt.In the phase diagram of Na+, Mg2+//Cl-, SO42+, NO3--H2O system at 298.16K there are six invariant points, and ten regions of crystallization with one salt. The phase diagram saturated with NaCl consists of eight crystallization regions with two salts, thirteen univariant curves and six invariant points.The phase diagram of the system Na+, K+, Mg2+//Cl-, NO3--H2O saturated with NaCl at 298.16K, consists of four invariant points, nine univariant curves and six crystallization regions with two salts.In the phase diagram of the system Na+, K+, Mg2+//Cl-, SO42-, NO3--H2O saturated with NaCl at 298.16K, there are twenty-five invariant points with five salts and fifteen crystallization regions with two salts. One invariant point is co-crystallizing point, the others are reaction points.Based on the studies above and isothermal evaporation experiment, the sequences of salt crystallization during evaporation process at 298.16 K were determined for two kinds of the nitrate brine. At the earlier stage, the sequence of crystallization is NaCl→NaCl+Na2SO4→NaCl+Na2SO4+Na2SO4·MgSO4·4H2O; at the later stage, the sequences of salt crystallization are different due to different composition of brine.During the isothermal evaporation experiment at 298.16K and natural evaporation experiment, at the earlier stage, the sequence of crystallization and the changes of composition of liquid are close to the analysis of phase diagram to a great extent for two kinds of typical brine. Metastable phase equilibrium behavior exists in the system Na+, K+, Mg2+//Cl-, SO42-, NO3--H2O.Under the guidance of the results, basis technological process of comprehensive utilization for the nitrate brine was dertermined. For the sunning process of the brine, a model, in which the lose ratio of NO3- is function, the number of the solar ponds and the concentration in the solar ponds are independent variables, has been established by material balance and phase diagram calculation. Combining with industrial data, and utilizing the optimizing method of MatLab, the model has been optimized, the regulation of concentration distribution in the solar ponds has been obtained, and the effect of the number of the solar ponds and the quantity of the brine carried by the salts deposited on the lose ratio of NO3- has been also discussed.
Keywords/Search Tags:Brine, Potassium nitrate, Hexa-component system, Liquid-solid phase equilibrium
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