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铬铁矿钾系亚熔盐强化浸出新过程应用基础研究
Alternative TitleApplied fundamental research on the process intensification of chromite decompostion in KOH sub-molten solution
陈刚
Subtype博士
Thesis Advisor张懿
2014-05
Degree Grantor中国科学院研究生院
Degree Discipline化学工艺
Keyword铬铁矿 亚熔盐 流场 氧气加压 脱铬
Abstract铬盐是重要的无机化工产品,但现行的铬铁矿高温钠化氧化焙烧工艺铬回收率低,铬渣产生量大,污染极为严重,已严重制约了铬盐行业的可持续发展。中国科学院过程工程研究所针对铬化工行业绿色化提升的急切需求,研发出钾系亚熔盐铬盐清洁工艺,铬回收率提高至98%以上,铬渣源头大幅减量并可用作生产脱硫剂,现已建成万吨级示范装置并实现连续稳定运行。目前示范工程尚存在高浓亚熔盐介质循环能耗较高和钙渣中铬含量超标的问题,影响了工艺的经济性和后期产业化推广。为解决循环碱液高浓蒸发能耗较高的问题,本文以降低铬铁矿分解碱浓度为目标,重点从流场、氧气压力、亚熔盐浓度三个方面进行了低碱亚熔盐条件下铬铁矿强化分解的应用基础研究。对于示范工程钙渣中铬含量超标的问题,开展了离子交换吸附脱铬的应用研究。本论文主要取得了如下创新性进展: (1) 发现搅拌釜内流场对铬铁矿亚熔盐液相氧化反应效果具有重要影响。以相同反应工艺条件下的铬转化率为指标,研究了搅拌桨、通气管等搅拌釜内件等对铬转化率的影响,结果表明相同搅拌功率下径流式桨对系统的混合效果最好,混流式桨的效果次之,而轴流式桨的混合效果最差,其中以六直叶涡轮桨配合管式气体分布器获得了铬转化率最高。 (2) 实验证实氧气压力对铬铁矿亚熔盐液相氧化过程具有显著的强化作用。研究结果表明,增加氧压能有效降低铬铁矿分解的碱浓度及温度,在2.0MPa氧压下,铬铁矿完全分解的钾系亚熔盐浓度可由80wt%降至60wt%,反应温度可由常压分解的320?C降至200?C。实验还发现,活性炭具有氧载体作用,可加速铬铁矿的分解过程。 (3) 比较研究了铬铁矿在70 wt%、60 wt%和50 wt%KOH亚熔盐溶液中氧气加压分解动力学,发现其反应机理与钾系亚熔盐浓度直接相关。随亚熔盐浓度降低,铬铁矿加压分解的速度步骤由扩散控制向表面化学反应控制转移,70 wt%KOH亚熔盐溶液中铬铁矿的加压分解过程受扩散控制,50 wt%亚熔盐溶液如此应过程受表面化学反应控制。另外,氧分压反应级数随亚熔盐浓度降低逐步增加,70 wt%、60 wt%和50 wt%KOH亚熔盐溶液中氧气压力的反应级数分别是0.68、0.74和1.16,氧气对铬铁矿强化分解作用逐渐增强。 (4) 首次发现钾系亚熔盐浓度对铬铁矿分应尾渣的结构和性质有重要影响。当KOH亚熔盐浓度高于60 wt%时,铬铁矿的反应尾渣为无定型氧化铁;而当亚熔盐浓度为50 wt%和60 wt%时,铬铁矿的反应尾渣则分别为氧化铁晶体和多铁酸钾晶体。与无定形氧化铁相比,氧化铁晶体和多铁酸钾晶体的比表面积小,铬吸附量低,经水洗后其铬含量低于国家相关标准要求。 (5) 查明了钙渣中铬离子大部分是以离子交换态存在的酸溶铬,碳酸盐溶液可置换钙渣中的铬离子。比较了硫酸盐、亚硫酸盐、碳酸盐对钙渣的脱铬效果,发现碳酸盐脱铬效果最好,由此开发了二氧化碳结合碳酸盐的钙渣解毒工艺,完成了200L的中试试验,脱铬效果达到了国家相关标准要求。 关键词:铬铁矿,亚熔盐,流场,氧气加压,脱铬
Other AbstractA clean process for chromate salts based on the sub-molten salt technology has been proposed by the Institute of Process Engineering, Chinese Academy of Sciences, and a pilot-plant has been built and run successfully for several years. However, the multi-step evaporation operation and the chromium-containing residues are unfavorable for large-scale commercialization due to the high energy consumption and environmental protection request. In this thesis, the applied fundamental research on the liquid-phase oxidization process is proposed to reduce energy consumption from the angles of the intensification of flow field, pressure field and concentration field. To decrease the chromium content, the applied research on the residues from the angles of surface modification and ion exchange was also carried out. The following achievements and progress were exhibited: (1). The three-phase mixing has an important influence on liquid-phase oxidization process, and the effect of the agitator and vent pipe configuration on the leaching rate was investigated under the same stirring power. The mixing effect of Rushton agitator is the best, and the mixing of the regular propeller is the worst. Compared to the old agitator tank, the chromium extraction increases three times as the flow field of the autoclave has been improved. (2). The active oxygen is the prime cause for sub-molten salt effectively decomposing chromite ore, and increasing oxygen pressure is conducive to generating active oxygen, hence the effect of oxygen pressure on the reaction activity of sub-molten salt was investigated. The chromium extraction reaches 98.4% after 5 h reaction in 60 wt% KOH solution under 200 oC and 2.0 MPa oxygen pressure. This result proved the KOH concentration and reaction temperature of chromite decomposition process can be decreased sharply, and chromium can be effectively leached under mild reaction conditions. (3). The research spectrum of KOH sub-molten salts’ concentration has been broadened from previous 80 wt% to 50 wt%. The leach kinetics of chromite in 50 wt%, 60 wt% and 70 wt% have been investigated with the same devices and chromite samples, respectively. The intensification effect of oxygen pressure in 50 wt% KOH sub-molten salts is the best.The process flow can be greatly simplified by eliminating dilution and evaporation operations, and the energy consumption for recycling KOH is saved. The pilot test with each batch chromite processing capacity of 100 kg has been conducted, and the total energy consumption has been reduced over 50%. (4). The activation carbon is a kind of oxygen vectors, and it plays a role similar to nitrate. The intensification effect of activation carbon on leaching process is very well, and after adding activation carbon chromite can be completely decomposed under 200 oC and ambient pressure in 70 wt% KOH solution. (5). The decomposition production of chromite varies as the function of KOH concentration. The leach residues produced from lower concentration KOH solution contained crystal with lower specific surface area, and the residual chromium content in these residues satisfies the disposal standard for chromium-containing waste. (6). The chromium (Ⅵ) combines with C3AH6 residue by ion exchange adsorption, and carbonate is the best desorbing agent. The chromium (Ⅵ) in the residue can be thoroughly removed by leaching with carbonate solution. The detoxifying process for C3AH6 residue has been designed based on the above conclusion. The pilot test with a daily residue handling capacity of 200 kg has been conducted, and the test specimens has gone through the monitor of environment protection department. Key words: Chromite ore, Sub-molten salt, Flow field, Pressure leaching, Detoxification by removing chromium
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/15540
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
陈刚. 铬铁矿钾系亚熔盐强化浸出新过程应用基础研究[D]. 中国科学院研究生院,2014.
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