铝电解行业废旧阴极炭热处置过程中氟化物转化特性研究

Study on fluoride conversion characteristics during thermal treatment of spent potlining in aluminum electrolysis industry

废旧阴极炭(Spent Potlining,SPL)水溶性氟化物的质量分数较高,被列为危险废物(Hazardous Waste 48,HW48)。热处置具有快速减量化、无害化等优势已成为主流处置方式。利用管式炉模拟SPL与不同质量比污泥焚烧底渣(Textile Dyeing Sludge Combustion Ash,TDSA)、CaO协同热处置,以探索其在750℃、850℃和950℃燃烧过程中氟化物迁移转化行为。定量测试SPL在单烧和掺烧过程中氟化物的挥发率。探究水溶性NaF热处置过程中迁移转化路径、影响因素及固氟机理。利用FactSage 7.1热力学模拟软件模拟SPL与不同添加剂掺烧过程中氟转化规律,以获得F、Na、Ca、S的热交互作用及竞争机制。结果显示:SPL与TDSA和CaO掺烧时,随焚烧温度的升高,F的挥发率也随之增加;当温度高于850℃时,氟化物主要以气态NaF和HF逸出。当添加TDSA时,S与NaF和Ca化合物易结合并生成Na2 SO_(4)和CaSO_(4),促进了NaF转化。SPL单独焚烧时,Na3 AlF6在高温下分解为NaF,当添加CaO和TDSA时,可促使Na3AlF6和NaF转化为稳定、无毒的CaF2。同时,添加CaO可促使NaF转化为更稳定的CaF2和Ca4 Si 2O7F2。研究为SPL无害化焚烧处理过程中氟化物污染控制的添加剂选择及温度的优化提供了理论依据。

Spent potlining(SPL)is classified as hazardous waste(HW48)due to the higher content of water-soluble fluoride.Combustion has the advantages of rapid reduction and harmlessness,which become a promising method of treatment SPL.In this study,a tube furnace was used to investigate the migration and transformation mechanisms of fluoride during SPL combustion with the addition of CaO and textile dyeing sludge combustion ash(TDSA)under air atmosphere with a flow rate of 0.8 L/min at 750℃,850℃and 950℃.The volatilization rates of fluoride during the mono-combustion and co-combustion of SPL with the addition of CaO and TDSA were quantitatively measured.The key factors that influence migration and transformation of NaF and its detoxification mechanism were studied.FactSage 7.1 thermodynamic simulation software was used to simulate the fluorine conversion during the co-combustion of SPL with the addition of different additives.In addition,the competition mechanism of F,Na,Ca,and S was also investigated.The results show that the F volatilization rates increase with increasing temperature during the co-combustion of SPL with the addition of CaO and TDSA.The F-containing compounds mainly release as the formation of NaF and HF when the temperature is above 850℃.In the SPL and TDSA cocombustion process,S compounds are easier to combine with NaF and Ca compounds to generate Na2 SO_(4) and CaSO_(4),which promoted the conversion of water-soluble NaF.With the decomposition of Na3AlF6,a large amount of NaF generates during SPL mono-combustion at high temperatures.Adding CaO and TDSA promotes the conversion of Na3AlF6 and NaF into CaF2.CaO can effectively capture HF and convert NaF into the stable CaF2 and Ca4 Si 2O7F2.The research of the author provides a basic theoretical basis for the selection of additives and the optimization of temperature on the fluoride detoxication in the process of SPL harmless incineration.