Effects of thermal desorption on the complex contaminated soils of polycyclic aromatic hydrocarbons and heavy metals
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摘要:
热脱附技术被广泛用于污染场地修复，但其对多环芳烃（PAHs）与重金属复合污染土壤的综合影响仍不清楚。选用PAHs和重金属复合污染模拟土壤，探究热脱附温度（220~400 ℃）和停留时间（5~60 min）对土壤中PAHs的影响，分析空气与氮气气氛下热脱附温度（310、340和370 ℃）对土壤中重金属Cu、Pb、As和Cd形态分布的影响。结果表明：随热脱附温度和停留时间的增加，土壤中PAHs去除率显著增加；低环PAHs占比逐渐减少，而高环PAHs占比逐渐增加。在2种气氛热脱附后，Cu、Pb和As弱酸提取态占比略有增加，而Cd弱酸提取态占比显著降低；可还原态和可氧化态的转化趋势具有差异性。随着热脱附温度的升高，Cu、Pb、As和Cd 4种重金属的残渣态占比均逐渐增加，说明热脱附有利于4种重金属的固定。相较于空气，氮气条件下4种重金属可氧化态和残渣态占比均增加；Cu和Pb可还原态占比显著降低，而As可还原态占比有所降低，Cd可还原态占比变化不大。氮气更有利于Cu、Pb和Cd的稳定；相反，空气更有利于As的稳定。
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关键词:
- 热脱附 /
- 多环芳烃（PAHs） /
- 重金属 /
- 形态转化
Abstract:Thermal desorption technology is widely used for the remediation of contaminated sites. However, the combined effects of thermal desorption on the complex contaminated soils of polycyclic aromatic hydrocarbons (PAHs) and heavy metals were still unclear. The complex contaminated simulated soils of PAHs and heavy metals were selected to investigate the effects of thermal desorption temperature (220-400 ℃) and residence time (5-60 min) on PAHs in the soil and to analyze the effects of thermal desorption temperature (310, 340, and 370 ℃) on the morphological distribution of heavy metals (Cu, Pb, As, and Cd) in soil under air and nitrogen atmosphere. The results showed that the removal of PAHs from contaminated soil increased significantly with the increase in thermal desorption temperature and residence time. The proportion of low-ring PAHs gradually decreased while that of high-ring PAHs gradually increased. After thermal desorption treatment in both atmospheres, the proportion of Cu, Pb, and As weakly acid-extracted states increased slightly, while the proportion of Cd weakly acid-extracted states decreased significantly. The conversion trends of the reducible and oxidizable states were different. The proportion of residue states of four heavy metals, Cu, Pb, As, and Cd, increased gradually with the increase of thermal desorption temperature, which indicated that thermal desorption was beneficial to the immobilization of the four heavy metals. Compared with air, the proportions of oxidizable and residual states of four heavy metals increased under nitrogen conditions. The proportions of Cu and Pb reducible states decreased significantly, while the proportions of As reducible states decreased and the proportions of Cd reducible states did not change significantly. These results showed that nitrogen was more favorable for the stabilization of Cu, Pb, and Cd. On the contrary, the air was more beneficial to the stabilization of As.
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Key words:
- thermal desorption /
- polycyclic aromatic hydrocarbons (PAHs) /
- heavy metals /
- speciation
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图 1 热脱附温度和停留时间对土壤中PAHs残留浓度和去除率的影响
注：不同小写字母表示同一温度（停留时间）下不同类型PAHs去除率之间差异显著(P<0.05)。
Figure 1. Effects of thermal desorption temperature and residence time on PAHs removal rate and residual concentration in soil
图 2 热脱附温度和停留时间对土壤中PAHs碳环占比及去除率的影响
Figure 2. Effects of thermal desorption temperature and residence time on the proportion and removal rate of PAHs carbon ring in soil
图 3 空气和氮气气氛下热脱附对Cu、Pb、As、Cd 4种重金属形态的影响
Figure 3. Effects of thermal desorption on the speciation of Cu, Pb, As, and Cd in air and nitrogen atmosphere
表 1 试验土壤重金属各形态占比
Table 1. Proportion of heavy metals in experimental soil
% 重金属 重金属形态 酸可提取态 可还原态 可氧化态 残渣态 Cu 17.243 32.358 33.487 16.912 Pb 20.013 42.169 28.558 9.260 As 22.016 30.124 34.968 12.892 Cd 19.683 25.687 37.485 17.145 
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表 2 试验土壤PAHs浓度
Table 2. PAHs contents in experimental soil
mg/kg Fle Phe Ant Pyr Baa Bap 总PAHs 21.34 18.26 29.87 4.38 46.72 7.21 127.78
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