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Thesis Advisor李会泉 ; 包炜军
Degree Grantor中国科学院研究生院
Place of Conferral北京
Degree Discipline化学工程
Keyword废scr脱硝催化剂 不可再生 草酸 还原 浸钒

废SCR脱硝催化剂是我国火电厂氮氧化物控制过程中产生的一种危险固体废弃物,其中含有钒、钨等重金属元素,易引起环境污染等问题。本文针对大量不可再生的废SCR脱硝催化剂粉体,系统开展了还原性草酸体系高效浸提钒元素的研究,重点包括酸浸过程工艺优化、酸浸机理、酸浸过程动力学及介质循环过程,研究工作将为废SCR脱硝催化剂回收利用提供技术基础。取得主要进展如下:(1)采用SEM,EMPA以及XPS等分析方法,研究了SCR脱硝催化剂失活前后元素赋存形态变化。分析发现,相比于新催化剂,废催化剂也为锐钛矿型TiO2,但锐钛矿型TiO2载体呈现显著的非均匀分布,且表面V/Ti原子比降低29.53%,V元素中V4+/(V4++V5+)价态比降低25.89%,导致催化剂表面酸性位减少。(2)系统开展了还原性草酸体系高效浸提钒元素的工艺优化,得到最佳浸出工艺条件。在90 °C,20 mL/g,500 rpm,1.5 mol/LH2C2O4条件下浸出,V浸出率高达86.3%,Fe元素完全浸出。通过XPS分析还原性草酸浸钒过程机理,发现浸出液中V元素主要是以V4+为主,废催化剂中V5+和V3+分别被还原和被氧化为V4+。经过还原性草酸浸提后V和Fe元素得到高效浸出,使TiO2载体结晶性更好。(3)基于还原性草酸体系V/W/Fe/Al元素浸出规律,开展了V/W/Fe/Al元素浸出动力学研究,建立了V元素浸出动力学方程。研究发现,V/Al/Fe元素浸出过程为内扩散控制;而W元素的浸出过程为表面反应和内扩散共同控制。对比V元素的Avrami浸出动力学方程计算拟合值和实验值,二者吻合性较好,说明V元素浸出动力学方程准确性较高。(4)针对还原性草酸浸出体系,提出了多次循环-真空蒸发-低温结晶分离的工艺流程,对草酸浸出介质循环过程进行研究。结果表明,在90 °C,5 mL/g,500 rpm,180 min,草酸浓度始终为1.5 mol/L条件下,随着循环浸提次数的增加,V元素浓度逐渐富集到2000 ppm以上。低温结晶分离得到的草酸晶体含有的总杂质含量均小于150 mg/kg,可以再用于浸出过程。

Other Abstract

Spent SCR denitration catalyst, a kind of hazard solid waste produced from the process of denitration on coal-fired power plant in our country, contains poisonous heavy metal elements such as vanadium and tungsten, and easily causes the environmental pollution. In this paper, leaching the large amount of spent SCR denitration catalyst powder by the reducibility oxalic acid was systematically studied. The process emphasizing on the leaching conditions, mechanism, kinetic equation and recycle process by reducibility oxalic acid was carefully clarified. The main achievements are summarized in the following:(1) Scanning electron microscope (SEM), electron microprobe analysis (EMPA) and X-ray photoelectron spectroscopy (XPS) were used to account for the distribution of elements and surface element occurrence change of fresh and spent catalysts. Compared with the fresh catalyst, the spent SCR denitration catalyst existed as an anatase crystal phase. But the titanium element occurrence emerged heterogeneous distribution on the surface of spent SCR denitration catalyst. The atomic ratio of V/Ti reduced by 29.53%. According to the analysis of surface valence and combination, the valent ratio of V4+/ (V5++V4+) decreased by 25.89%, which caused the decreasing of surface acid site.(2) Efficient extraction process of vanadium element by reducibility oxalic acid was studied systematically, and the optimal leaching process conditions were obtained. The leaching rate of V and Fe was respectively 86.3 and 100.0% with the condition of 90 °C, 20 mL/g, 500 rpm and 1.5 mol/L. The mechanism of leaching process was studied by XPS. The process is that V5+ was reduced and V3+ was oxidized to V4+. Leaching liquor was mainly dominated by V4+. After reducibility oxalic acid, V element and Fe impurity were effectively removed, which made the property of crystalline TiO2 carrier better.(3) Based on the leaching behavior of V, W, Fe and Al by reducibility oxalic acid, the kinetic of leaching process and vanadium leaching kinetic equation were studied. It was found that for the Al, Fe and V leaching process, the rate limiting step was internal diffusions control, but for W it was the congenerous control of surface reaction and diffusion. In addition, compared the experimental and simulated data from Avrami equation with various temperature for vanadium leaching process, theoretical and experimental results indicated that they were consistent with each other. It is shown that Avrami model can reflect the vanadium leaching process and the accuracy of it is higher.(4) To achieve the recycling of oxalic acid, the process of cycling–vacuum evaporation-crystallization was used to study the leaching behavior during the cyclic process. The results showed that with the leaching condition of 90 °C, 5 mL/g, 500 rpm, 180 min and the oxalic acid with a constant 1.5 mol/L concentration,. vanadium concentration in leaching liquor increased gradually to more than 2000 ppm as the increasing of cycle leaching process. Oxalate crystal from the crystallization process containing less than 150 mg/kg total amount of impurity elements could be recycled in the leaching process.

Document Type学位论文
Recommended Citation
GB/T 7714
武文粉. 废SCR脱硝催化剂还原酸浸过程基础研究[D]. 北京. 中国科学院研究生院,2016.
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