Abstract:

The enrichment of heavy metals Cr, Cd, Pb, and As by phosphate-modified kaolin during the pyrolysis of municipal solid waste (MSW) was investigated. Compared with Na₂HPO₄ and Na₃PO₄ modification, NaH₂PO₄ modified kaolin showed stronger enrichment of heavy metals during the pyrolysis of MSW. The retention rate of heavy metals increased and then decreased with the increase of impregnation ratio, and increased with the increase of addition ratio. The better heavy metal enrichment was reached at 5% impregnation ratio and 5% addition ratio. Without additives, the potential ecological risk index of pyrolysis char decreased with increasing temperature in the range of 400—600℃. The addition of kaolin effectively increased the content of heavy metal residue state, thus reducing the potential ecological risk of pyrolytic carbon. The addition of phosphate-modified kaolin led to an increase in the residue state due to the acid solubility of heavy metal phosphate. The ecological risk of NaH₂PO₄-modified kaolin (H₂P-kaolin) at 5% impregnation ratio increased slightly with increasing temperature mainly due to enhanced physical adsorption of molten sodium metaphosphate and acid solubility of heavy metal phosphates in pyrolysis char, but the ecological risk of pyrolysis char was low. The combined ecological risk was low. From the XPS analysis, it was concluded that the main reason for the adsorption of heavy metals after the addition of H₂P-kaolin was due to the formation of silicate from SiO₂ of kaolin with heavy metals and the reaction of NaPO₃ and Na₃PO₄ with heavy metals to form phosphate, of which phosphate was the main factor.

Key words: municipal solid waste, pyrolysis, heavy metal, kaolin, phosphate

摘要：

研究了磷酸盐改性高岭土在生活垃圾热解过程中对重金属Cr、Cd、Pb、As的富集作用。相较Na₂HPO₄和Na₃PO₄改性，NaH₂PO₄改性高岭土在生活垃圾热解过程中对重金属的富集作用更强。重金属的固留率随浸渍比的升高先增加后减小，随添加比的升高而增加，在浸渍比为5%和添加比为5%时具有较好的重金属富集作用。无添加剂时，在400~600℃范围内随着温度的升高，热解炭的潜在生态风险指数下降。添加高岭土能有效增加重金属残渣态的含量，从而降低热解炭的潜在生态风险。添加5%浸渍比下NaH₂PO₄改性高岭土（H₂P-kaolin）后热解炭的生态风险随温度的升高略有增加，主要原因是熔融的偏磷酸钠增强物理吸附以及热解炭中重金属磷酸盐的可酸溶性，但综合生态风险均为低风险。由XPS分析得出加入H₂P-kaolin之后，吸附重金属的主要原因是由于高岭土与重金属生成硅酸盐以及NaPO₃、Na₃PO₄与重金属反应生成磷酸盐，其中磷酸盐的作用是吸附能力增强的主要因素。

关键词: 生活垃圾, 热解, 重金属, 高岭土, 磷酸盐