Kinetics And Thermodynamics Of Sodium Arsenate During Crystallization Process Under Ultrasound And Magnetic Field

China has the most abundant antimony resources in the word and almost all thearsenic-alkali residues are produced in china. By now, total more than twentythousand tons arsenic-alkali residues stacked in our country and with the growths of800～1000tons per year. The arsenic-alkali residues contain about10%to15%arsenic and the main pollution component is Na3AsO4. If the toxicity arsenic-alkaliresidue expose to the environment, it would be a great threaten to our human. Somearsenic pollution events have happened around our country. At present, the chemicaltechnique is hard to separate toxic component in arsenic-alkali residuse and thetraditional measures such as roasting, landfill would cause serious secondarypollution.One of the key technologies to handle arsenic-alkali residues are to separatearsenic by the measure of crystallize. The existing sodium arsenate evaporation－cooling crystallization technology is a kind of applied separation technology, but thethermophysical property of sodium arsenate is very similarity to other impurities andefficient separation crystallization technology confronts with big challenge. On otherhand the lack of metastable zone width, induction period and other thermophysicaldata make the crystallization process hard to control. Until now, the thermodynamicsproperty of sodium arsenate has not reported and few article studied its crystallizationtheory. In-depth grasp of sodium arsenate related thermal physical properties andstudy the mechanism of the thermodynamics and kinetics of crystallization of sodiumarsenate can fundamentally achieve efficient separation of arsenic acid sodium. It hasan important practical significance and scientific significance.Firstly, the thermodynamics and kinetics of sodium arsenate under thegravitational field were studied, and the solubility curve of sodium arsenate in waterwas also measured by static method with the temperature ranges from283.15to353.15K. Then the formula to calculate solubility is matched by Apelblat empiricalmodel. Based on solubility curve, the thermodynamics data such as supersolubility,metastable zone, induction period, surface tension are measured and analyzed by laserdetection system. Nucleation kinetics and growth kinetics in different supersaturationare studied in a double-walled jacketed crystallizer with the temperature keepconstant.Because of the similarity property to other components, the effect of ultrasound vibrations on the sodium arsenate crystallization process was investigated. Inparticular, the effects of ultrasound vibrations on nucleation kinetics and growthkinetics are studied using a laser-based apparatus with relative supersaturation rangingfrom1.3to1.8. The results show that ultrasound vibrations have a significant effecton reducing induction time and crystal size distribution. Also when ultrasoundimported the gather and broken of sodium arsenate are reduced. The mean size ofsodium arsenate crystals decreased from398.873.27to168.682.07m, as theultrasound power increases from26to130W.Magnetic field is a newly method that used to study the influence of sodiumarsenate cooling crystallization process. The thermodynamics and dynamics duringsodium arsenate cooling crystallization process are studied with the present ofmagnetic field. Based on population balance equations, the sodium arsenate coolingcrystallization was imitated in a double-walled jacketed MSMPR crystallizer and0.6TB magnetic field intensity was introduced. The sodium arsenate crystals weremeasured by Mastersizer3000laser particle analyzer. The kinetic parameters obtainedwere based on population balance and simplified ΔL theory. The results indicate thatboth nucleate and growth rate under are increased with the presents of magnetic field.Also, magnetic field made arsenate crystals size distribution more symmetry.The results indicate that both ultrasound and magnetic field can influence sodiumarsenate cooling crystallization process, the thermodynamics and dynamics arechanged. Sodium arsenate crystal quality obtained in ultrasound and magnetic fieldare more excellent and XRD and IR analyze shows the crystal structure are notchanged.