CAS OpenIR
亚熔盐铬盐清洁生产工艺中产品工程应用基础研究
崔雯雯
Subtype博士
Thesis Advisor郑诗礼
2019-07-01
Degree Grantor中国科学院大学
Degree Discipline化学工艺
Keyword铬盐,亚熔盐,结晶铬酸酐,纳米γ-alooh,纳米氧化镁
Abstract

铬是我国最为紧缺的三稀金属,铬铁矿资源高效清洁利用是我国重大战略需求。针对现有铬盐生产工艺铬收率低、能耗高、铬渣量大且污染严重的难题,中国科学院过程工程研究所研发了钾系亚熔盐铬盐清洁生产工艺,可以实现铬资源的高效清洁利用,并实现铬渣的源头削减。但其尚不能生产铬酸酐产品、铝镁副产物附加值较低,产品结构有待升级。本论文重点开展了亚熔盐铬盐清洁生产工艺中重铬酸钾制备铬酸酐产品,伴生铝镁副产物制备纳米材料并用作重金属吸附材料的应用基础研究。本论文主要有以下结论:(1)在测定四元系KHSO4-CrO3-H2SO4-H2O相图和对比分析五元系K2Cr2O7-KNO3-CrO3-HNO3-H2O相图基础上,对硫酸法和硝酸法分解重铬酸钾制备铬酸酐进行了理论分析。理论分析表明,在高浓度硫酸区域,硫酸氢钾和铬酸酐共存,难以获得高纯的铬酸酐产品;而在高浓度硝酸区域,铬酸酐具有单独相区。探索实验研究证实硝酸法可获得高纯度铬酸酐产品,而硫酸法的铬酸酐纯度低,在此基础上建立了硝酸法分解重铬酸钾制备铬酸酐的工艺路线。(2)考察了反应物浓度、搅拌转速、加酸速度和冷却速度等工艺参数对铬收率和CrO3产品性能的影响,获得优化工艺参数。在初始重铬酸钾的浓度为800 g/L 65% HNO3、95% HNO3与65% HNO3体积比(95% HNO3:65% HNO3)为2、搅拌转速为300 rpm、加酸速度为1 mL·min-1、冷却速度为0.1 oC·min-1的条件下,获得一次CrO3晶体经重结晶可获得优于国家标准的高纯度(CrO3含量99.8%以上)的结晶CrO3产品;利用95%浓硝酸对结晶过程进行调控,铬收率可提高至95%以上。(3)硝酸法铬酸酐结晶过程包括反应结晶和冷却结晶两个阶段。查明了铬酸酐反应结晶的结晶动力规律,获得了CrO3成核速率和生长速率方程,成核速率快,生长速率慢,符合反应结晶过程特征;冷却结晶过程中,CrO3晶体由细小的晶核聚集、结合,表面进一步光滑完整。(4)开展了氢氧化铝水热合成法制备纳米γ-AlOOH的研究,考察了水热合成过程中Al(OH)3前驱体浓度、pH值、温度、时间对纳米γ-AlOOH合成过程的影响规律,各工艺参数对纳米γ-AlOOH形貌影响显著。明确了纳米γ-AlOOH的生长机制为Al(OH)3前驱体不断溶解,α-Al(OH)3中间相析出,进而再溶解形成γ-AlOOH的过程。首次将γ-AlOOH纳米片用对碱性溶液中Cr(III)的吸附,发现γ-AlOOH纳米片对Cr(III)的吸附过程符合Langmuir模型,可以用准二级动力学方程进行拟合,其最大吸附容量可达19.85 mg·g-1;并揭示了Cr(III)在纳米γ-AlOOH上的吸附机理为-OH与Cr(OH)4-之间离子交换成键的过程。(5)开展了以液相超声剥离手段制备纳米MgO的研究,在超声仪频率40 kHz、超声功率为150 W、DMF:MgO液固比为600:1、超声时间为2 h的优化条件下,可制备出比表面积为166.44 cm2·g-1的纳米MgO;将所制备的纳米MgO用于对Se的吸附应用研究,发现其吸附热力学符合Langmuir模型拟合,吸附动力学符合准二级动力学方程拟合,纳米MgO对Se(IV)、Se(VI)的最大吸附容量分别可达103.52 mg·g-1和10.28 mg·g-1,查明了Se(IV/VI)在纳米MgO上的吸附过程是由于Se离子(SeO32- and SeO42-)与MgO之间水化形成了较强的内层吸附键。进一步研究表明,MgO纳米片在共存竞争离子存在时仍然对Se(IV/VI)具有较高的吸附容量,同时可以在给定温度下被NaOH溶液有效地脱附。;Chromium is the most scarce critical metal in China, and the comprehensive utilization and clean production of valuable components in chromite have become strategic needs of the nation. To solve the existing problems of the conventional process, such as low recovery of chromium, high energy consumption, a great deal of Cr-containing residue and serious environmental pollution, a cleaner production process of chromate based on potassium hydroxide sub-molten solution has been proposed by the Institute of process engineering, Chinese Academy of Sciences. Clean and efficient utilization of chromium resource and zero emission of Cr-containing residue have been highly fulfilled during this process. However, the products structure of the process needs further improvements due to the lack of chromic anhydride which is the main chromic salt product and the low-value added byproducts of aluminium and magnesium. This thesis focused on the production of chromic anhydride by acid decomposition of potassium dichromate, and the preparation of nano materials using the byproducts of alumumum and magnesium as well as their application in the adsorption of heavy metals in wastwater. The main innovative achievements were summarized as follows:(1) The decomposition of potassium dichromate using sulfuric acid and nitrate acid was analyzed theoretically both by investigating the phase equilibrium of the quaternary system KHSO4-CrO3-H2SO4-H2O and analyzing the phase diagram of the quinary system K2Cr2O7-KNO3-CrO3-HNO3-H2O. The results showed that high-purity chromic anhydride product was difficult to obtain because potassium hydrogen sulfate and chromic anhydride coexisted in the range of high H2SO4 concentration; while chromic anhydride had a separate phase region in the range of high HNO3 concentration. The following experiments confirmed that higher-purity CrO3 product could be obtained by HNO3 method compared to H2SO4 method. The process route for the CrO3 production by decomposing potassium dichromate using nitrate acid was designed based on the experimental results.(2) The effects of reactants concentration, stirring rate, acid feeding rate and cooling rate during the process were explored, and the process parameters were optimized. High-purity and granular CrO3 crystals (CrO3 content is more than 99.8%) were prepared after recrystallization at the original K2Cr2O7 concentration of 800 g/L 65% HNO3, (95% HNO3:65% HNO3) volum ratio of 2, stirring rate of 300 rpm, acid feeding rate of 1 mL·min-1 and cooling rate of 0.1 oC·min-1, which is superior to the product standards. Additionally, the recovery of Cr could achieved to more than 95% by adjusting the acid concentration of the crystallization process using 95% HNO3.(3) The CrO3 cryatallization process by HNO3 decomposition of K2Cr2O7 included reaction cryatallization period and cooling crystallization period. The kinetics of the reaction crystallization was investigated and the nucleation rate and growth rate equations were calculated, respectively. High nucleation rate and low growth rate conformed to the characteristics of reaction crystallization. Complete CrO3 crystals with smooth surface formed by the nucleus aggregation during the cooling crystallization.(4) Nano γ-AlOOH was synthesized with Al(OH)3 precursor by hydrothermal method. Effects of pH values, concentration of Al(OH)3 precursor, temperature and time were investigated, indicating that γ-AlOOH nano particles highly depended on these experimental conditions. The growth mechanism of nano γ-AlOOH was thus explicited as the dissolve of Al(OH)3 precursor, the appearance of transformation phase, the redissolve of transformation phase, and the formation of γ-AlOOH. The as-prepared nano γ-AlOOH was firstly used as adsorbent for tha adsorption of Cr(III) in caustic solution, and the adsorption isotherms and kinetics could be fitted by Langnuir model and pseudo-second order kinetics model, respectively. The maximum adsorption capacity of Cr(III) on nano γ-AlOOH could achieve at 19.85 mg·g-1. The adsorption mechanism was expressed as the exchange of –OH and Cr(OH)4- and formation of complex bonds.(5) Nano MgO was synthesized by ultrasonic exfoliation method. Nano MgO with a BET surface area of 166.44 cm2·g-1 was obtained at ultrasonic frequency of 40 kHz, ultrasonic power of 150 W, DMF:MgO ratio of 600:1 and ultrasonic time of 2 h. The as-prepared nano MgO was used as adsorbent for tha adsorption of Se, and the adsorption isotherms and kinetics could be fitted by Langnuir model and pseudo-second order kinetics model, respectively. The maximum adsorption capacity of Se(IV) and Se(VI) on nano MgO could achieve at 103.52 mg·g-1 and 10.28 mg·g-1, respectively. The adsorption mechanism was expressed as inner-sphere surface complexes(SeO32- and SeO42-) formation on the surface of the nano MgO. Fuether studies showed that high adsorption capacity for Se(IV/VI) in the presence of coexistent anions and efficient regeneratability of adsorbent by NaOH solution at certain temperature were observed.

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/40634
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
崔雯雯. 亚熔盐铬盐清洁生产工艺中产品工程应用基础研究[D]. 中国科学院大学,2019.
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