硫酸钠溶液超声结晶热力学和动力学研究

硫酸钠溶液超声结晶热力学和动力学研究
硕士研究生：李慧
导
师：曾桂生
申请学位级别：硕 士
学科、专业：环境工程
所在单位：环境与化学工程学院
答辩日期：2013 年 5 月
授予学位单位：南昌航空大学
The study on crystallization thermodynamics and kinetics of sodium sulfate with ultrasound
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induction period were investigated. The crystallization nucleation equation and nucleation orders were determined based on the relationship of ln b or ln N and ln(ΔTmax ) . The graph of two-line was obtained according to the relationship between (ln S)−2 and ln tind . And then, the surface tension and the surface entropy factor are determinated on the basis of the slope of the line. Thus, crystal growth of sodium sulfate is continuous growth mode since f < 3 .
1. Solubility curve and super-solubility curve were measured in blank condition and ultrasonic field by laser measurement system. On the other hand, the effect of ultrasonic time and power on sodium sulfate were researched. According to the experiment results, the solubility of sodium sulfate has an inflection point at 34℃ in our system. Different substances were found around 34℃. When the temperature is higher than that of the inflection point, the solubility curve shows a slow downward trend. Below 34℃, Glauber salt (Na2SO4·10H2O) is separated out from the supersaturated solution. According to the principle of thermal equilibrium, the heat is more likely to move to the endothermic direction with increasing temperature. Thus, with increase of temperature, there is increase of sodium sulfate concentration. When the temperature is above 34 ℃, the dissolution of sodium sulfate crystal becomes exothermic. Thus with temperature rise, there is a decline in the concentration of sodium sulfate. There is heat absorption during the dissolution of Glauber salt. It is explained that the solubility curve is special. The solubility increases with the increasing of ultrasonic time until the balance. And it is increasing firstly with increasing of ultrasonic power but then decreased. In a word, the influence of ultrasound on the solubility of sodium sulfate can not be ignored.
2. Metastable zone width and the induction period were determinated by laser. The metastable zone width is reduced in ultrasound. Factors such as cooling rate, agitating rate, ultrasonic time, power and frequency on the effect of the metastable zone or the
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Abstract
Arsenic-alkali residue is a kind of hazardous solid waste which is formed from antimony smelting enterprises .It is he waste residue generated in the process of antimony smelting. Arsenic and its compounds in arsenic-alkali residue are highly toxic and easily soluble in water. Pollution incident with arsenic is easily happened if it is not kept safe improperly. And sodium sulfate is one of the by-products of arsenic-alkali residue. In industry, sodium sulfate is also widely used in papermaking, textile, medicine, fuel, glass, synthetic fiber and so on. Besides, sodium sulfate with different particle size is very necessary in industry. The study of sodium sulfate on crystallization process is propitious to resource recovery for arsenic-alkali residue. It has important scientific and practical significance to meet the demand of different particle size of sodium sulfate. In this paper, thermodynamics, nuclear dynamics and crystal growth kinetics of crystallization process of sodium sulfate were comprehensively studied.
2.通过激光法测定硫酸钠溶液介稳区及诱导期。测定了降温速率、搅拌强度、 超声时间、功率和频率等因素对介稳区或诱导期的影响。在超声场作用下，介稳 区宽度变窄。介稳区随着降温速率的增加而变宽，随着搅拌转速的增加而变窄。 根据拟合 ln b 与 ln N 和 ln(ΔTmax ) 的关系分别得出受降温速率及搅拌转速影响的成 核方程式和成核级数。受降温速率影响的成核级数随着温度升高持续增加，说明 成核级数受温度的影响较大；受搅拌转速影响的成核级数随着温度升高呈现无规 律变化，说明此成核级数也是受温度影响，但是所受的影响不大。根据不同过饱 和度对硫酸钠诱导期的影响的实验数据看出，过饱和度是促进溶液结晶的推动力。 过饱和度增加，诱导期也随着减小，结晶的时间提前发生。通过对 (ln S)−2 和 ln tind 作图进行拟合得出直线的斜率，得出表面张力及表面熵因子。本实验计算得出表 面熵因子 f < 3 ，因此硫酸钠晶体的生长属于连续生长模式。
1.采用激光测量系统测定了硫酸钠在自然条件及超声场条件下的溶解度曲线 及超溶解度曲线。对超声时间、功率对硫酸钠的溶解度的影响进行了实验研究。 实验得出，在本物系中测得硫酸钠溶解度的转折温度为 34℃，在此温度前后产生 了不同的结晶物相。当低于此转折温度时，物系中所得物相为芒硝，随着温度升 高，溶解度增大；而当高于此转折温度时，物系中所得物相为硫酸钠，随着温度 升高溶解度呈现降低趋势。这种现象也决定了硫酸钠溶解度曲线的特殊性。硫酸 钠溶解度随着超声时间的延长增大直至趋于平衡；超声功率增大则使得硫酸钠溶 解度先增加后呈现下降趋势。这说明超声波对硫酸钠的溶解度产生了不可忽略的 影响。
3.在硫酸钠晶体生长动力学的实验研究中，首先根据一组随机实验得出硫酸钠 粒数密度和粒度关系的曲线，判定出硫酸钠晶体的生长属于粒度相关生长。研究
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了过饱和度、搅拌强度、超声时间、超声功率等影响因素对晶体生长动力学的影 响。通过实验研究表明，过饱和度增大，其成核速率和生长速率均会增加；搅拌 强度越大，晶体的平均粒径越小，粒度分布变窄；超声时间的延长有利于晶体的 成核及生长；晶体平均粒径的大小随着超声功率的的增加不断减小。在实际工业 结晶及实验室研究中，根据研究所得理论数据选择晶体适宜的成核和生长条件， 可得到人们所期望的晶体。 关键词：硫酸钠，超声结晶，晶体热力学，成核动力学，生长动力学
盲审编号
Z133
学校代码 分类号 密级 学号
10406 O644
100430130001
题目 硫酸钠溶液超声结晶热力学和动力
学研究
作者
李慧
学科、专业 指导教师 申请学位日期
环境工程 曾桂生 2013.4
Байду номын сангаас
学校代码：10406 分类号： O644
学号：100430130001
南昌航空大学 硕士学位论文
A Dissertation Submitted for the Degree of Master
On Environment Enginerring by Li hui
Under the Supervision of Prof.
Zeng Guisheng
College of Environmental and Chemical Engineering Nanchang Hangkong University, Nanchang, Jiangxi, China
April, 2013
摘要
砷碱 渣 是 锑 冶 炼 企 业 产 生 的 一 种 危 险 固 体 废 弃 物 ， 是 在 炼 锑 过 程 中 产 生 的废渣叫砷碱渣。砷碱渣中的砷及其化合物有剧毒，且易溶于水，若保管不 善极易引起砷污染事件。其中硫酸钠是处理砷碱渣的副产物砷酸钠复合盐的 主要物质之一。在工业上，硫酸钠在许多领域都有重要的应用，广泛应用于造纸、 玻璃、燃料、纺织、医药、合成纤维中等等。同时工业需求不同粒径的硫酸钠， 因此无论在哪一方面，对硫酸钠体系结晶过程的研究，对砷碱渣中硫酸钠的资源 回收利用、工业上满足不同粒径硫酸钠的需求都有重要的科学意义和现实意义。 本文从硫酸钠结晶的热力学、成核动力学以及晶体生长动力学三方面对硫酸钠的 结晶过程做了全面详细的研究。