Process Optimization for Chromic Oxide Preparation through Hydrogen Reduction of Chromates at Low Temperature

氧化铬(Cr2O3)是铬盐工业重要产品之一, 工业应用广泛。中国科学院过程工程研究所开发的铬酸钾低温氢还原法氧化铬生产工艺是以氢气作为洁净介质，低温还原铬酸钾中间体，短流程清洁生产氧化铬，反应介质实现了再生循环，具有重大的经济与环保效益。本论文针对铬酸钾低温氢还原法氧化铬生产工艺存在产品杂质含量高、单程收率低的问题，对生产工艺流程进行了优化，并以铬酸钠为原料，对铬酸盐低温氢还原过程的动力学和反应机理进行了研究。 本文主要取得了以下创新性进展： （1）针对铬酸钾晶体中以高铁酸钾形式存在的水溶性铁，提出了强化高铁盐水解沉淀的分离提纯方法，可将铬酸钾晶体中的铁含量由0.74 %和1.04 %降至检测限以下；根据生产过程中碳钢设备引入的铁多为铁磁性三氧化二铁的特点，提出了磁分离的除铁方法，工业生产线采用磁分离设备除铁实验研究结果表明，氧化铬产品中的铁含量可降至0.1 %以下，满足产品质量要求。 （2）提出并优化了示范工程氢还原产物酸洗脱钾工艺。在选定的四种酸—硫酸、硝酸、草酸、铬酸中，以硝酸的脱钾效果最好。针对示范工程氢还原中间产物，硝酸洗涤脱钾的最佳工艺条件为：搅拌速率400 r•min-1，温度80 ℃，液固比5:1，搅拌时间60 min，硝酸浓度0.3 mol•L-1。在此优化条件下，钾脱除率可达到70.4 %，氧化铬直收率由73.9 %提高至86.9 %。 （3）在分析Cr(NO3)3-KNO3-HNO3-H2O体系溶解度数据与相图的基础上，提出采用真空蒸发结晶方法分离硝酸铬副产品、采用冷却结晶方法分离硝酸钾副产品的方法，从而实现了酸洗脱钾液的再生循环。 （4）以铬酸钠为原料，采用TGA/DSC法进行了氢还原动力学研究，研究结果表明：在430 ~ 500 ℃之间，铬酸钠氢还原过程发生的主要反应为Na2CrO4•4H2O + 1.5H2  NaCrO2 + NaOH + 5H2O。用Doyle-Ozawa法和Kissinger法确定了反应的动力学参数，求得反应活化能E为342.47 kJ•mol-1，反应级数n为0.87

盐析结晶法分离铬酸钾

关联了不同温度下K2CrO4在K2CrO4-KOH-H2O体系中的溶解度数据，分析了从K2CrO4-KOH-H2O体系中通过盐析结晶方式分离KzCrO4的可能性；通过K2CrO4-KOH-H2O体系中K2CrO4的盐析结晶实验，得出了初级成核现象发生时，体系的最大过饱和度与过饱和速率之间的动力学关系式及结晶过程中盐析剂浓度、盐析结晶终点KzCrO4收率、溶液体积等工艺参数间的关系，探讨了以KOH作为盐析剂，采用盐析结晶方法从K2CrO4-KOH-H2O体系中分离提纯K2CrO4的可行性，为K2CrO4的高效分离提供了一种新思路

盐析结晶法分离铬酸钾

关联了不同温度下K2CrO4在K2CrO4-KOH-H2O体系中的溶解度数据,分析了从K2CrO4-KOH-H2O体系中通过盐析结晶方式分离K2CrO4的可能性;通过K2CrO4-KOH-H2O体系中K2CrO4的盐析结晶实验,得出了初级成核现象发生时,体系的最大过饱和度与过饱和速率之间的动力学关系式及结晶过程中盐析剂浓度、盐析结晶终点K2CrO4收率、溶液体积等工艺参数间的关系,探讨了以KOH作为盐析剂,采用盐析结晶方法从K2CrO4-KOH-H2O体系中分离提纯K2CrO4的可行性,为K2CrO4的高效分离提供了一种新思路

盐析结晶法分离铬酸钾

关联了不同温度下K2CrO4在K2CrO4-KOH-H2O体系中的溶解度数据，分析了从K2CrO4-KOH-H2O体系中通过盐析结晶方式分离KzCrO4的可能性；通过K2CrO4-KOH-H2O体系中K2CrO4的盐析结晶实验，得出了初级成核现象发生时，体系的最大过饱和度与过饱和速率之间的动力学关系式及结晶过程中盐析剂浓度、盐析结晶终点KzCrO4收率、溶液体积等工艺参数间的关系，探讨了以KOH作为盐析剂，采用盐析结晶方法从K2CrO4-KOH-H2O体系中分离提纯K2CrO4的可行性，为K2CrO4的高效分离提供了一种新思路

含锂矿物机械化学强化提锂工艺

采用机械化学活化方法,在机械活化过程中用K2SO4为活化添加剂,强化锂云母中惰性Li-O配位结构活化转型,通过温和稀酸浸出高效分离锂,考察了活化过程添加剂用量、球磨时间和球料比及浸出条件如酸浓度、液固比、搅拌速度、温度和时间等对锂回收率的影响,确定了最佳工艺条件,讨论了反应过程机理。结果表明,机械化学活化强化破坏云母片层结构中的Si-O-K结构,降低了Si-O配位结构对Li-O配位结构的牵制力,导致Li-O键强减弱,反应活性增加。在最优条件下(精矿与K2SO4质量比5:1、球磨机转速500 r/min、球料质量比20:1、球磨时间3 h、硫酸浓度15vol%、液固比4 L/g、反应温度80℃、浸出搅拌速率200 r/min),锂浸出率可达99.1%

铬酸钠氢还原反应动力学

The environmental problem resulting from the traditional production process of chromic oxide has spawned public concerns all over the world. Integrated in the clean production technology of chromium compounds with sub-molten salt media, the preparation process of chromic oxide through hydrogen reduction of alkali metal chromate salt enables the clean and short-route preparation of chromic oxide. Moreover, the alkali metal hydroxide byproducts can be recycled as reaction media inside the process. To explore the reaction kinetics and mechanisms of the hydrogen reduction process, the reduction of sodium chromate in H2 atmosphere was investigated by using TGA and DSC techniques. The isothermal TGA measurement results showed that in the temperature range from 703 K to 773 K, the hydrogen reduction had only one step of mass loss and the mass loss rate was from 5.91% to 6.36~. The main products of the reaction were NaCrO2 and NaOH, as confirmed by XRD patterns of the reduction products. The non-isothermal TGA measurements of hydrogen reduction was investigated at six different temperature rising rates of 1, 5, 10, 15, 20 and 30 K · min^-1 .According to the Doyle-Ozawa and Kissinger methods, the activation energy was 342.47 kJ · mol^-1 and the order of reduction reaction was 0.87. The results in this work will help to enhance the reaction efficiency and optimize the process flow

铬酸钠氢还原反应动力学

The environmental problem resulting from the traditional production process of chromic oxide has spawned public concerns all over the world. Integrated in the clean production technology of chromium compounds with sub-molten salt media, the preparation process of chromic oxide through hydrogen reduction of alkali metal chromate salt enables the clean and short-route preparation of chromic oxide. Moreover, the alkali metal hydroxide byproducts can be recycled as reaction media inside the process. To explore the reaction kinetics and mechanisms of the hydrogen reduction process, the reduction of sodium chromate in H2 atmosphere was investigated by using TGA and DSC techniques. The isothermal TGA measurement results showed that in the temperature range from 703 K to 773 K, the hydrogen reduction had only one step of mass loss and the mass loss rate was from 5.91% to 6.36~. The main products of the reaction were NaCrO2 and NaOH, as confirmed by XRD patterns of the reduction products. The non-isothermal TGA measurements of hydrogen reduction was investigated at six different temperature rising rates of 1, 5, 10, 15, 20 and 30 K · min^-1 .According to the Doyle-Ozawa and Kissinger methods, the activation energy was 342.47 kJ · mol^-1 and the order of reduction reaction was 0.87. The results in this work will help to enhance the reaction efficiency and optimize the process flow

含锂矿物机械化学强化提锂工艺

采用机械化学活化方法,在机械活化过程中用K2SO4为活化添加剂,强化锂云母中惰性Li-O配位结构活化转型,通过温和稀酸浸出高效分离锂,考察了活化过程添加剂用量、球磨时间和球料比及浸出条件如酸浓度、液固比、搅拌速度、温度和时间等对锂回收率的影响,确定了最佳工艺条件,讨论了反应过程机理。结果表明,机械化学活化强化破坏云母片层结构中的Si-O-K结构,降低了Si-O配位结构对Li-O配位结构的牵制力,导致Li-O键强减弱,反应活性增加。在最优条件下(精矿与K2SO4质量比5:1、球磨机转速500 r/min、球料质量比20:1、球磨时间3 h、硫酸浓度15vol%、液固比4 L/g、反应温度80℃、浸出搅拌速率200 r/min),锂浸出率可达99.1%