Characterization of heavy metals during co-pyrolysis of sludge with PVC

doi:10.16085/j.issn.1000-6613.2022-1862

Abstract

Abstract:

As a major pollutant during sludge pyrolysis, strict emission control of heavy metals is beneficial to ecological environment and human health. To investigate the effects of temperature (500—900℃) and polyvinyl chloride plastic (PVC) blending ratio (5% and 15%) on the migration and transformation behaviors of heavy metals (As, Cr, Cu, Mn, Ni, Pb and Zn), pyrolysis experiments were conducted in a horizontal fixed-bed reactor. It was found that increased temperature and added PVC were beneficial to reduce the residual rate of As, Pb and Zn in biochar, but had almost no effect on the removal of Cr, Cu, Mn and Ni. In addition, the speciation analysis of heavy metals showed that with the increase of pyrolysis temperature, the overall conversions of heavy metals in biochar to more stable forms were observed, except for As. Meanwhile, based on the results of ecological risk assessment of heavy metals in biochar, it was found that the presence of PVC in the feedstock increased the ecological risk of heavy metals in the obtained biochar when the pyrolysis temperature was 500℃ and 600℃. This paper provided a valuable reference for actual industrial thermal treatment of sludge regarding the control of heavy metals emissions.

Key words: sludge, polyvinyl chloride plastic (PVC), co-pyrolysis, heavy metals, ecological risk

摘要：

重金属作为污泥热解处理过程中的主要污染物，对其进行严格的排放控制有益于生态环境和人类身体健康。本文通过在水平固定床反应器内开展城市污泥的快速热解实验，探究了温度（500～900℃）及聚氯乙烯塑料（PVC）掺混比（5%和15%）对重金属元素As、Cr、Cu、Mn、Ni、Pb和Zn在生物炭中迁移转化规律的影响。研究发现，提高热解温度和添加PVC有利于降低As、Pb和Zn在生物炭中的残余率，但对Cr、Cu、Mn和Ni几乎没有移除作用。此外，通过分析重金属赋存形态发现，伴随热解温度的升高，除了As以外，生物炭中的其他重金属元素整体向更稳定的形态转化。与此同时，根据重金属的生态风险评估结果发现，当热解温度为500℃和600℃时，原料中PVC的存在会增大所获取生物炭中重金属的生态风险。本文为实际工业热处理污泥提供了关于重金属排放控制方面有价值的参考。

关键词: 污泥, 聚氯乙烯塑料, 共热解, 重金属, 生态风险

CLC Number:

X705

LI Zhiyuan, HUANG Yaji, ZHAO Jiaqi, YU Mengzhu, ZHU Zhicheng, CHENG Haoqiang, SHI Hao, WANG Sheng. Characterization of heavy metals during co-pyrolysis of sludge with PVC[J]. Chemical Industry and Engineering Progress, 2023, 42(9): 4947-4956.

李志远, 黄亚继, 赵佳琪, 于梦竹, 朱志成, 程好强, 时浩, 王圣. 污泥与聚氯乙烯共热解重金属特性[J]. 化工进展, 2023, 42(9): 4947-4956.

Figures/Tables 7

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样品	工业分析（ad）/%				元素分析（ad）/%
样品	M	V	FC	Ash	C	H	O	N	S	Cl
SS	8.68	44.32	5.06	41.94	18.96	3.645	22.81	2.94	0.885	0.14
PVC	0.25	91.96	7.24	0.55	38.85	5.69	0.39	0.03	0.75	53.49

样品	工业分析（ad）/%				元素分析（ad）/%
样品	M	V	FC	Ash	C	H	O	N	S	Cl
SS	8.68	44.32	5.06	41.94	18.96	3.645	22.81	2.94	0.885	0.14
PVC	0.25	91.96	7.24	0.55	38.85	5.69	0.39	0.03	0.75	53.49

提取形态	样品	提取试剂及条件
酸溶态和可交换态（F1）	0.5g	20mL、0.1mol/L乙酸，振荡16h后离心，取上清液
可还原态（F2）	上一步的固态残渣	20mL、0.1mol/L盐酸羟胺，振荡16h后离心，取上清液
可氧化态（F3）	上一步的固态残渣	首先，5mL、体积分数30%过氧化氢，室温1h；然后，5mL、体积分数30%过氧化氢，水浴(85±5)℃，1h；最后，25mL、1.0mol/L乙酸铵，振荡16h后离心，取上清液
残渣态（F4）	上一步的固态残渣	消解方法如1.3.1节中所述

提取形态	样品	提取试剂及条件
酸溶态和可交换态（F1）	0.5g	20mL、0.1mol/L乙酸，振荡16h后离心，取上清液
可还原态（F2）	上一步的固态残渣	20mL、0.1mol/L盐酸羟胺，振荡16h后离心，取上清液
可氧化态（F3）	上一步的固态残渣	首先，5mL、体积分数30%过氧化氢，室温1h；然后，5mL、体积分数30%过氧化氢，水浴(85±5)℃，1h；最后，25mL、1.0mol/L乙酸铵，振荡16h后离心，取上清液
残渣态（F4）	上一步的固态残渣	消解方法如1.3.1节中所述

样品	重金属含量/mg·kg^-1
样品	产率	As	Cr	Cu	Mn	Ni	Pb	Zn
SS		63.0±2.0	210±8.2	270.0±7.1	1875.0±72.2	92.5±2.4	107.5±8.2	1570.0±39.8
PVC		ND	ND	ND	ND	ND	ND	255.0±11.48
500SS	61.2±0	62.5±2.0	305.0±1.8	393.8±3.8	2679.4±156.3	138.8±2.8	155.6±3.7	2265.0±59.9
500SP1	59.8±0.3	55.0±4.1	293.1±2.7	375.6±2.7	2656.9±9.7	130.6±2.1	145.6±3.2	2197.5±21.1
500SP2	55.5±0.2	45.6±2.1	293.8±2.8	371.3±2.8	2663.8±21.7	128.8±2.8	143.1±3.2	2296.9±22.2
600SS	58.8±0	58.8±3.8	315.6±2.1	401.9±3.7	2848.1±35.9	138.1±2.1	155.6±1.1	2331.3±17.2
600SP1	57.9±0.5	53.8±4.5	325.6±9.1	400.0±8.1	2864.4±104.0	145.0±6.8	156.3±4.5	2331.9±52.0
600SP2	54.5±0.1	47.5±1.8	299.4±3.7	376.3±8.0	2686.9±28.2	135.6±3.7	136.9±3.2	2096.3±35.0
700SS	58.6±0	53.1±5.7	343.1±8.7	426.3±5.4	3018.8±75.3	150.6±2.1	166.9±2.1	2455.6±19.9
700SP1	57.2±0	49.4±4.5	323.8±4.5	412.5±4.0	2963.1±55.2	145.0±1.8	132.5±1.8	1931.9±30.7
700SP2	53.9±0.2	51.9±4.5	316.3±2.2	390.6±6.5	2836.9±64.4	141.3±2.2	88.8±2.8	1071.9±57.0
800SS	56.8±0	41.3±3.8	346.9±6.0	441.9±8.4	2790.0±95.9	154.4±4.5	135.0±1.8	2341.9±90.1
800SP1	55.2±0.1	38.8±6.3	338.1±2.1	424.4±8.5	2825.0±135.3	145.6±2.1	61.9±3.7	907.5±9.5
800SP2	51.9±0	42.5±3.1	327.5±7.9	403.1±7.2	2840.6±93.4	143.1±3.7	38.8±1.3	421.9±20.8
900SS	54.0±0	57.5±4.1	374.4±11.5	464.4±16.9	3291.9±146.2	161.3±7.4	46.9±2.7	1893.1±15.8
900SP1	52.6±0.1	51.3±3.8	332.5±12.5	407.5±17.5	2805.0±75.0	142.5±5.0	23.8±1.3	543.8±8.8
900SP2	50.4±0	48.8±2.8	338.8±5.2	414.4±9.6	3009.4±68.2	144.4±3.2	18.8±2.2	247.5±30.4