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在分析聚乙烯热解特性的基础上,研究热解时间、热解温度及聚乙烯与铬渣质量比对Cr(VI)还原的影响,并运用XANES和EXAFS光谱研究铬元素的形态变化,并对反应机制进行分析.结果表明,(1)聚乙烯在热解过程中可以有效将Cr(VI)还原,还原率随着温度的升高而升高,当热解温度达到550℃,还原率为99.93%;随着PE投加量增大,Cr(VI)还原率逐渐上升,当质量比超过0.05时趋于稳定;Cr(VI)还原伴随塑料热解反应进行,6min后趋于稳定;最优反应条件为热解温度550℃、热解时间6min、PE/铬渣质量比0.05.(2)使用XAS铬形态分析过程中以Cr2O3作为Cr(Ⅲ)的参考物较CrCl_3更为合理,铬渣中Cr(VI)还原产物为无定型Cr_2O_3;(3)由于PE主要由C、H两种元素组成,不含O元素,相比生物质还原剂,可以更高效还原Cr(VI);(4)Cr(VI)与挥发份充分接触反应条件下,Cr(VI)可持续还原.
Based on the analysis of pyrolysis characteristics of polyethylene, the effects of pyrolysis time, pyrolysis temperature and the mass ratio of polyethylene to chromium slag on Cr (VI) reduction were studied. The morphological changes of chromium (Cr) were studied by XANES and EXAFS The reaction mechanism was analyzed.The results showed that: (1) Cr (VI) could be effectively reduced during the pyrolysis of polyethylene and the reduction rate increased with the increase of temperature. When the pyrolysis temperature reached 550 ℃, the reduction rate (99.93%). With the increase of PE dosage, the reduction rate of Cr (VI) gradually increased and stabilized when the mass ratio exceeded 0.05. The reduction of Cr (VI) followed the plastic pyrolysis reaction and stabilized after 6 minutes. The optimal reaction conditions were pyrolysis temperature of 550 ℃, pyrolysis time of 6 min, mass ratio of PE to chromium slag of 0.05. (2) It is more reasonable to use Cr2O3 as Cr (Ⅲ) reference material in XAS chromium form analysis, The Cr (VI) reduction product in chromium slag is amorphous Cr_2O_3. (3) Since PE is mainly composed of C and H elements and contains no O element, Cr (VI) can be reduced more efficiently than biomass reducing agent. (4) Cr (VI) can be continuously reduced under full contact with Cr (VI) and volatiles.