The influence of aluminum on morphologies and crystallization
kinetics
of hemihydrate calcium sulfate (HH) in the hemihydrate process of
phosphoric acid production was investigated. X-ray diffraction analyses
showed that Al3+ ions can be adsorbed onto the crystal
surface and incorporated into the crystal lattice. The crystal growth
rate first increases and then decreases due to the dual role of Al3+ ions in a mixed suspension mixed product removal (MSMPR)
crystallizer. For the first time, the effect of Al3+ ions
on nucleation kinetics of HH at 93 °C was investigated by focused-beam
reflectance measurement (FBRM). The results indicate that Al3+ ions retard the nucleation by increasing the interfacial tension
values (γ).
The wet-process production of phosphoric acid by the nitric acid method is considered as a promising technology with great development prospects due to no production of the byproduct phosphogypsum. However, the traditional nitro-phosphate fertilizer producing process cannot separate nitrogen and phosphorus thoroughly, which limits its applications. The key to solving this problem is to remove nitric acid from the crude phosphoric acid product obtained in the nitric acid wet process by evaporation. Therefore, it is important to measure the vapor−liquid equilibrium (VLE) data of the nitric acid + water + phosphoric acid + sulfuric acid quaternary system under different pressures and concentrations. In this study, the VLE data of the following systems were measured at 10, 20, 40, 60, 80, and 97.4 kPa by the quasistatic ebulliometric method: (1) nitric acid + water; (2) nitric acid + water + phosphoric acid; and (3) nitric acid + water + phosphoric acid + sulfuric acid. The electrolyte non-random two-liquid parameters for the following pairs were correlated with the VLE data by using Aspen Plus as a tool: HNO 3
The solubility measurement of potassium dihydrogen phosphate (MKP) in a water−methanol system is of great significance for the salting-out crystallization of MKP. The solubility of MKP in the H 2 O−CH 3 OH solution was determined by the static equilibrium method in the range of 283.15−343.15 K, and the molar fraction of CH 3 OH varied from 0.0588 to 0.6923. The mixedsolvent electrolyte model (MSE) was used to regress the experimental results, and new parameters were obtained. Based on it, the thermodynamic model of the H 2 O−CH 3 OH−MKP system was established, which is in good agreement with the experimental results, with a relative average absolute deviation of 6.46%. Then, the change in the ion concentration and the activity coefficients in the system were predicted by the thermodynamic model. Finally, the Pixact Crystallization Monitoring (PCM) system and a scanning electron microscope (SEM) were used to observe the crystallization process and the morphology of MKP in the H 2 O− CH 3 OH system, respectively.
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