EFFECT OF CO-PYROLYSIS OF SEWAGE SLUDGE AND Ca(H2PO4)2 ON RESIDUE CHARACTERISTIC AND CHROMIUM STABILITY
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摘要: 污泥中不稳定Cr的存在严重威胁环境安全和人体健康。利用正交试验方法优化Ca(H2PO4)2与污泥的混合比、热解终温、升温速率和停留时间,分析其对残渣特性及Cr稳定性的影响。结果表明:热解使污泥中的CH2基团、脂肪族硝基-NO2和硫酸氢盐分解。在添加Ca(H2PO4)2后,残渣中出现了磷酸PO基团、磷酸二氢盐PO2基团和磷酸盐PO4基团。Ca(H2PO4)2在共热解过程中转化为Ca(PO3)2,同时Cr在残渣中会形成Cr2(SO4)3晶型化合物。当Ca(H2PO4)2与污泥的质量比为15%、热解终温为650℃、升温速率为15℃/min、停留时间为90 min时,Cr的残渣态(F4)比例最高。此外,添加15%或30%的Ca(H2PO4)2共热解后,残渣中Cr浸出浓度满足GB/T 14848-2017《地下水质量标准》中Ⅳ类水质要求,表明添加Ca(H2PO4)2共热解可促进污泥中Cr的稳定化。Abstract: Unstable Cr fractions existed in sludge seriously threatens environmental safety and human health. Conditions including the blend ratio of sludge and Ca(H2PO4)2, final temperature, heating rate, and retention time, were optimized using an orthogonal experiment. And its effects on residue characteristic and Cr stability were further investigated. Results indicated that pyrolysis could lead to the decomposition of functional groups in sludge, such as CH2, aliphatic nitro-NO2, and bisulfate. In co-pyrolysis with Ca(H2PO4)2, phosphorous functional group was generated in co-pyrolysis residue. Ca(H2PO4)2 was decomposed and Ca(PO3)2 was formed. Meanwhile, Cr in sludge could be transformed into a crystalline compound of Cr2 (SO4)3 during co-pyrolysis. When the condition was blend ratio of 15%, final temperature of 650℃, heating rate of 15℃/min, and retention time of 90 min, the proportion of F4 fraction was the highest. In addition, the leaching concentration of Cr met the IV standard stipulated by the groundwater quality standard (GB/T 14848-2017), indicating that Cr in sludge could be more stable in co-pyrolysis with Ca(H2PO4)2.
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Key words:
- sewage sludge /
- co-pyrolysis /
- chromium /
- morphological change /
- toxic leaching
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