| China's vanadium-titanium magnetite smelting is under rapid development,while the iron ore tailings contains a lot of vanadium resources.For using tailings vanadium resources,the main production process is:vanadium slag sodium salt roasting-water immersion-acid ammonium salt vanadium.This production has mature technology and equipment,and promising long-term economic benefits.After the vanadium extraction,the waste water still contains large amounts of ammonia nitrogen,chromium ions,sodium ions,sulfate ions,chloride ions.In order to achieve resource recycling,environmental protection and economic benefits,this article aimed at Chengde Jianlong Iron and Steel Plant vanadium-titanium magnetite vanadium addition to chromium removal of ammonia in wastewater after the preliminary study.respectively,The sodium salt was recovered from the wastewater in the formation of sodium chloride and sodium sulfate,and the crystallization thermodynamics and kinetics of sodium sulfate were studied.(1)The sodium salt was recovered as sodium chloride.The wastewater was treated by chemical precipitation method.The single factor experimental method was used to determine the best SO42-removal process.The impurity ions in the treated waste water were determined by the chemical method in the national standard.The results showed that the optimum condition of removing SO42-by CaCl2 was that the dosage of precipitant was 7g,pH was 7.87 before reaction,the reaction temperature was 60? and the reaction time was 60min.The coIcentration of SO42-in the wastewater after treatmelt is 2.027g/L,which is lower than the average SO42-concentration of the salt brine in the existing salt water treatment process.The sodium salt can be recovered from the treated wastewater by the existing drying process salt.(2)The sodium salt was recovered as sodium sulfate.Industrial grade sodium sulfate was recovered by evaporation and condensation crystallization.After chemical precipitation,the chemical reagent grade sodium sulfate was reclaimed by recrystallization.The single factor experiment was adopted to determine the optimum technological conditions for recovery of sodium sulfate.The results show that under the premise of reaching the standard and production capacity,the evaporation crystallization can produce the product conforming to the national standard of industrial sodium sulfate class ? at 90%of the evaporation volume;the condensed crystal is considered to produce a thin film crystal in the concentrated raw water to the surface(80%concentration in this experiment),the condensation can be as much as possible in the temperature-5?0? production in line with the national standard industrial grade sodium sulfate class ? products;recrystallization select lgNa2CO3 precipitation Ca2+ exceeded,evaporation and crystallization control at 85%evaporation and below,the crystallization temperature will be controlled at 5?20? chloride can be reduced to 0.005%or less,the product can reach the chemical reagent in the chemical purity.(3)Thermodynamics and Kinetics of Sodium Sulfate Crystallization.The experimental wastewater was mainly Na+-Cl--SO42-system.The complex of the ionic species in the wastewater and the content of Na+-Cl--SO42-in wastewater were studied.The solubility of sodium sulfate in the wastewater was measured by dynamic method.Concentration curve with temperature,and its super-solubility curve was determined by direct method,which provided the basis for the preparation of crystal.The size distribution of sodium sulphate was determined by continuous steady-state method,and the crystal size was larger than 50?m.The growth process of sodium sulphate crystal was independent of particle size.The kinetic model was established and the parameters of the model were analyzed.The nucleation rate and the growth rate of the crystallization process were obtained,which provided the theoretical basis for the crystallization of sodium sulfate. |
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