| Arsenic-alkali residue is a kind of hazardous solid waste which is formed fromantimony smelting enterprises.It is he waste residue generated in the process ofantimony smelting. Arsenic and its compounds in arsenic-alkali residue are highly toxicand easily soluble in water. Pollution incident with arsenic is easily happened if it is notkept safe improperly. And sodium sulfate is one of the by-products of arsenic-alkaliresidue. In industry, sodium sulfate is also widely used in papermaking, textile,medicine, fuel, glass, synthetic fiber and so on. Besides, sodium sulfate with differentparticle size is very necessary in industry. The study of sodium sulfate on crystallizationprocess is propitious to resource recovery for arsenic-alkali residue. It has importantscientific and practical significance to meet the demand of different particle size ofsodium sulfate. In this paper, thermodynamics, nuclear dynamics and crystal growthkinetics of crystallization process of sodium sulfate were comprehensively studied.1. Solubility curve and super-solubility curve were measured in blank conditionand ultrasonic field by laser measurement system. On the other hand, the effect ofultrasonic time and power on sodium sulfate were researched. According to theexperiment results, the solubility of sodium sulfate has an inflection point at34℃in oursystem. Different substances were found around34℃. When the temperature is higherthan that of the inflection point, the solubility curve shows a slow downward trend.Below34℃, Glauber salt (Na2SO4·10H2O) is separated out from the supersaturatedsolution. According to the principle of thermal equilibrium, the heat is more likely tomove to the endothermic direction with increasing temperature. Thus, with increase oftemperature, there is increase of sodium sulfate concentration. When the temperature isabove34℃, the dissolution of sodium sulfate crystal becomes exothermic. Thus withtemperature rise, there is a decline in the concentration of sodium sulfate. There is heatabsorption during the dissolution of Glauber salt. It is explained that the solubility curveis special. The solubility increases with the increasing of ultrasonic time until thebalance. And it is increasing firstly with increasing of ultrasonic power but thendecreased. In a word, the influence of ultrasound on the solubility of sodium sulfate cannot be ignored.2. Metastable zone width and the induction period were determinated by laser. Themetastable zone width is reduced in ultrasound. Factors such as cooling rate, agitatingrate, ultrasonic time, power and frequency on the effect of the metastable zone or the induction period were investigated. The crystallization nucleation equation andnucleation orders were determined based on the relationship oflnborlnNandln(ΔTmax). The graph of two-line was obtained according to therelationship between(lnS)2and lntind. And then, the surface tension and the surfaceentropy factor are determinated on the basis of the slope of the line. Thus, crystalgrowth of sodium sulfate is continuous growth mode since f <3.3. In the experiment of crystal growth kinetics, crystal growth of sodium sulfate isthe size-dependent based on a random experiment. The equations of nuclear dynamicsand growth kinetics of sodium sulfate were measured according to ASL model.Meanwhile, the effects of saturation, stirring intensity, ultrasonic parameters and otherfactors on the growth kinetics of crystal were also considered. Results show that, thenucleation rate and growth rate will increase with saturation increasing; the average sizeof the crystal and CSD is smaller with the increasing of the stirring intensity andultrasonic time or power. People should choose appropriate conditions to get therequired crystal according to the laboratory of theoretical research which in industrialcrystallization or in the laboratory through these experiment results. |
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