Abstract:

A variety of heavy metals were inevitably produced in the process of sludge pyrolysis. In this study, Co-pyrolysis experiments of municipal sludge with modified sepiolite in several factors including hydrochloric acid impregnation concentration of sepiolite (2—6mol/L), thermal activation temperature of sepiolite (750—950℃), and co-pyrolysis temperature of sludge and sepiolite (400—600℃) were conducted in a horizontal fixed-bed reactor. The effects of these factors on the enrichment characteristics, morphological changes and ecological risks of heavy metal elements Cd, Zn, Pb and Cr in sludge pyrolysis carbon were investigated. The results showed that the addition of modified sepiolite effectively increased the retention rates of Cd, Zn and Pb in the co-pyrolysis temperature range of 400—600℃, but had little effect on Cr enrichment. The modified sepiolite, especially the 950-SEP and 4H-SEP, exhibited a good enrichment effect on Cd, Zn and Pb. In addition, the analysis of the heavy metal fugacity pattern showed that the increase of pyrolysis temperature and modified sepiolite both led conversion of heavy metal in biochar to a more stable form. According to the ecological risk assessment of heavy metals in the pyrolysis biochar, the ecological risk of raw sludge was greatly reduced after pyrolysis. The addition of modified sepiolite effectively reduced the ecological risk of heavy metals in the sludge pyrolysis char below 600℃.

Key words: sludge, sepiolite, heavy metal, pyrolysis, activation, waste treatment

摘要：

污泥热解过程中会不可避免地产生多种重金属，危害人类的健康。通过在水平固定床反应器内开展城市污泥与改性海泡石共热解实验，探究海泡石的盐酸浸渍浓度（2~6mol/L）、海泡石的热活化温度（750~950℃）以及污泥与海泡石共热解温度（400~600℃）对污泥热解炭中重金属元素Cd、Zn、Pb、Cr的富集特征、形态变化及生态风险的影响。研究发现，在400~600℃的温度范围内改性海泡石的添加有效地提高了Cd、Zn、Pb的固留率，但对Cr几乎没有富集作用，其中950℃热活化海泡石（950-SEP）对Cd有良好的富集效果，而4mol/L盐酸浸渍海泡石（4H-SEP）对Zn和Pb展现出了更好的富集性能。此外，通过分析重金属赋存形态发现，提高共热解温度和添加改性海泡石，共热解炭中的重金属元素整体向更稳定的形态转化。根据热解炭中重金属的生态风险评估，原始污泥经热解后其生态风险大大降低，在600℃前，改性海泡石可进一步降低重金属的生态风险。

关键词: 污泥, 海泡石, 重金属, 热解, 活化, 废物处理