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Alternative TitleCleaner preparation of sodium chromate via pressure oxidative leaching of chromite ore in concentrat
Thesis Advisor张懿 ; 徐红彬
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword铬铁矿   铬酸钠   亚熔盐   加压   碱浸
Abstract铬为重要的战略资源,铬盐系列产品用途广泛。针对我国铬盐生产行业存在的铬铁矿资源利用率低、铬渣环境污染严重等问题,中国科学院过程工程研究所研发了亚熔盐液相氧化法铬盐清洁工艺与集成技术,解除了行业可持续发展的瓶颈问题。铬系产品工程为集成技术的重要组成部分,也是实现行业技术替代的核心研究内容。本论文以铬铁矿分解过程强化为切入点,采用氢氧化钠亚熔盐介质和加压碱浸氧化的方法,研发了铬酸钠的清洁制备工艺,并开展了铬铁矿碱浸过程的热力学、动力学以及铬铁矿伴生组分的浸出行为研究。论文主要取得如下创新性进展: (1) 开展了较高浓度(质量分数约60%)的NaOH水溶液体系中,铬铁矿在纯氧加压状态下的分解热力学研究。结果表明,60% NaOH溶液在高氧压状态下发生氧化分解的热力学趋势较常压状态显著增大。并且,随反应温度的升高,铬铁矿分解趋势变大; (2) 研究了铬铁矿加压碱浸分解过程的宏观动力学,阐明了搅拌转速、铬铁矿粒度、碱矿比、氧分压、碱浓度、反应温度对铬提取率的影响规律。宏观动力学研究结果表明:铬铁矿浸出时,外围包裹未溶解的产物层,其控制步骤即为通过产物层的扩散控制。实验条件下浸出动力学方程为 ,表观活化能为E = 54.5 kJ/mol。工艺研究表明,60%的碱浓度为最优浓度,提高搅拌转速、碱矿比、氧分压、反应温度,降低铬铁矿粒度能明显提高铬铁矿浸出速率。在氧分压3.2 MPa、碱浓度60%、搅拌转速650 min-1、铬铁矿粒度小于50 μm、碱矿比4.0:1、反应温度250 ?C的条件下反应240 min,铬的浸出率可达98%以上; (3) 探索了铬铁矿中主要伴生元素(铁、镁、铝、硅)的浸出行为。在加压碱浸过程中,随着铬铁矿的分解,反应残渣的稳定性增强。反应终渣主要由MgFe2O4和Mg(OH)2组成,渣中部分Fe3+会溶解至液相,并以NaFeO2形式存在。铬铁矿中的铝、硅等伴生组分几乎完全浸出至液相,铝浸出速率快于铬,硅少部分以硅铝酸盐形式沉淀进入渣相; (4) 提出了铬铁矿加压碱浸氧化法铬酸钠清洁制备工艺流程,通过在浸出液中添加CaO脱除液相体系中的铝酸盐、硅酸盐和碳酸盐等杂质,通过蒸发盐析结晶的方法实现氢氧化钠和铬酸钠的高效分离。全流程循环试验研究结果表明,氢氧化钠亚熔盐介质经多次循环,仍然可保持较高的反应活性,其中铝硅碳酸根等杂质组分的浓度可稳定在较低的水平。
Other AbstractAs a strategic resource, chromium is widely used in industries. In order to solve the trouble of low resource utilization rate and severe environmental pollution existing in chrome salt industry, the Institute of Process Engineering, Chinese Academy of Sciences, has proposed clean process and integrated technology based on sub-molten salt liquid-phase oxidation, which removes restrictions on sustainable development of chrome salt industry. Chromium-series product engineering is a part of integrated technology and a core unit to make the technology replacement come ture. In this thesis, intensifying chromite ore decomposition is proposed, with the NaOH sub-molten salt and pressure oxidative leaching method used. The sodium chromate preparation technology based on the investigation of leaching thermodynamics, kinetics and leaching behaviors of accompanying elements is proposed. The following innovative achievements and progresses were exhibited: (1) Thermodynamics of chromite ore decomposition was investigated in relatively high NaOH concentration solution (60% wt) with elevated pure oxygen. Experiment results demonstrate that the trend of decomposition is much larger in 60% NaOH solution with higher oxygen than that of standard state. Meanwhile, the trend will get lager with the increasing reaction temperature; (2) Macro-kinetics of chromite ore decomposition were carried out, and the effects of stirring speed, chromite ore particle size, NaOH-to-ore ratio, oxygen partial pressure, NaOH concentration, reaction temperature on the reaction were also investigated. The apparent kinetics investigation indicates that the insoluble product encompasses the unreacted particle, which leads to the diffusion in product layer being the rate-controlling step. Under the experimental conditions, the leaching process is described by equation of with an apparent activation energy of 54.5 kJ/mol. The experimental results demonstrate that the 60% is the optimal NaOH concentration, and the extraction ratio of chromium increases distinctly with the increase of stirring speed, NaOH-to-ore ratio, oxygen partial pressure, reaction temperature and the decrease of the particle size. The leaching yield reaches above 98% after 240 min at oxygen partial pressure of 3.2 MPa, NaOH concentration of 60%, stirring speed of 650 min-1, particle size below 50 μm, NaOH-to-ore ratio of 4.0:1 and reaction temperature of 250 ?C; (3) The leaching behaviors of main accompanying elements, including Fe, Mg, Al and Si, were studied as well. The stability of process residues is getting higher during the reaction; the COPRs consists of MgFe2O4 and Mg(OH)2; part of Fe3+ is leached into solution in form of NaFeO2; most Al and Si of chromite ore were leached into liquor, and the leaching rate of Al is faster than that of Cr; and part of Si returns to COPRs in form of aluminosilicate; (4) This article introduces the principle flow sheet of whole preparation process. In leaching liquor, CaO is added to remove aluminate, silicate and carbonate, and Cr and NaOH are effectively sperated by evaporative crystallization and salting out; the circulation experiments of whole flow indicate that NaOH still keeps high reactivity after several circulations and that the concentration of impurities, including , and , keeps at relatively low levels. Key words:Chromite ore, Sodium chromate, Sub-molten salt, Elevated pressure, Alkali leaching, Clean process
Document Type学位论文
Recommended Citation
GB/T 7714
张海. 加压液相氧化法铬酸钠清洁制备工艺研究[D]. 中国科学院研究生院,2013.
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