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当前,在我国的重金属污染治理行业中,铅蓄电池行业是重点关注行业之一,也是重金属铅离子(Pb2+)的主要污染来源[1],因其隐蔽性、危害性等特点,在土壤中不断富集,最终对人体产生高毒性和致癌性[2],因此,对于铅污染处理极为紧迫. 吸附、反渗透、化学沉淀、离子交换等是处理重金属污染的典型方法[3],与其他方法相比,吸附法因其技术成熟、成本低、沉淀物生成少等优点在重金属污染治理中被广泛应用[4].
在土壤固相物质中,微生物可将土壤有机质(soil organic matter,SOM)同化为自身组分并在其死亡后以微生物残体的形式逐渐积累在土壤中[5],并与土壤矿物相互作用形成各种矿物-有机复合体、配合物或聚集体[6 − 7],成为稳定土壤有机碳库的重要组成部分,其对土壤重金属的治理起到了关键性的作用. 其中,蒙脱石和赤铁矿常作为典型的土壤矿物对重金属吸附进行研究[8],蒙脱石因其较大的比表面积和较高的阳离子交换能力常被作为吸附剂[9],赤铁矿因其含有铁氧化物且边缘表面带正电[10],使得带负电荷的有机质与其相结合,二者皆可与SOM结合形成有机无机复合体[11]. 目前,土壤对Pb2+的吸附主要受到土壤有机质、黏土、铁和锰氧化物等土壤组分的影响[12],且研究了不同物理化学性质的土壤对Pb2+的吸附,如不同质地、不同有机质浓度和不同阳离子交换容量等[13]. 其中,前人就土壤微生物源有机质对Pb2+的吸附主要研究其整体的有机无机复合体[14],而真菌残体较细菌残体更稳定,且在微生物残体碳中占比更高[15],故本文将微生物分为两类菌群(细菌菌群、真菌菌群),取两种典型的矿物(黏土矿物-蒙脱石、铁氧化物-赤铁矿),研究经培养后的微生物残体及有机无机复合体对Pb2+的吸附作用.
本研究旨在探讨微生物残体(细菌、真菌)及其与黏土矿物(蒙脱石、赤铁矿)形成的有机无机复合体的结合机制,进一步解释矿物与微生物相结合后的有机无机复合体对Pb2+的吸附能力,进而表明微生物残体及其与矿物结合形成有机无机复合体对土壤重金属的吸附不可忽视.
微生物残体及其与矿物形成的复合体对Pb2+的吸附解吸
Adsorption and desorption of Pb2+ by microbial necromass and microbial- mineral complexes
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摘要: 土壤有机质是控制土壤重金属吸附行为的重要组分之一,最近微生物源有机质被认为是土壤稳态碳的重要组分,然而,微生物源有机质及其与土壤矿物形成的复合体对重金属的吸附解吸行为关注较少. 以微生物(细菌、真菌)为有机质,黏土矿物(蒙脱石、赤铁矿)为矿物基质,制备细菌残体(BN)、真菌残体(FN)、细菌-蒙脱石复合体(B-M)、真菌-蒙脱石复合体(F-M)、细菌-赤铁矿复合体(B-Fe)、真菌-赤铁矿复合体(F-Fe),研究微生物残体及复合体对铅离子(Pb2+)的吸附解吸过程. 结果表明,真菌残体和细菌残体具有相近的元素组成和有机官能团,其对Pb2+的吸附解吸相一致;但相比于微生物-矿物复合体而言,纯残体对Pb2+的吸附量较大,解吸率也较大,吸附并不稳定. 各个复合体中,尽管赤铁矿-微生物复合体对Pb2+的吸附量较蒙脱石-微生物复合体更小,但经比表面积标准化后,蒙脱石-微生物复合体的吸附明显降低,而赤铁矿-微生物复合体的吸附量前后变化不明显且高于蒙脱石组,表明赤铁矿-微生物复合体在单位面积的吸附能力高于蒙脱石-微生物复合体. 真菌-矿物复合体较细菌-矿物复合体具有更高的吸附,经比表面积标准化后,真菌-矿物复合体仍具有更高的吸附. 同时,各个复合体对Pb2+的解吸率表现为B-M>B-Fe>F-M>F-Fe,表明赤铁矿-微生物复合体通过络合作用对Pb2+的吸附更稳定,真菌-矿物复合体通过更强的阳离子-π作用和络合作用对Pb2+的吸附更稳定. 因此,微生物与矿物形成的复合体对Pb2+的吸附能力在土壤重金属修复治理中需要被关注,这为控制土壤重金属的迁移和生物有效性提供了新的思路.Abstract: Soil organic matter (SOM) is one of the important components controlling the adsorption behavior of heavy metals in soil. However, as an important component of stabilized SOM, little attention has been paid to the adsorption/desorption behavior of heavy metals by microbial-derived organic matter and its complexes formed with soil minerals. In this study, the adsorption/desorption of Pb ions (Pb2+) by microbial (bacteria and fungi) and the complexes with clay mineral (montmorillonite and hematite) were studied, specifically, bacterial necromass (BN), fungal necromass (FN), bacteria-montmorillonite complex (B-M), fungus-montmorillonite complex (F-M), bacteria-hematite complex (B-Fe), and fungus-hematite complex (F-Fe). The results showed that the fungal nacromass and bacterial necromass had similar elemental composition and organic functional groups, and their adsorption and desorption for Pb2+ were consistent. However, compared with the microbial-mineral complex, the microbial necromass has a larger adsorption capacity for Pb2+, the desorption rate is also larger, and the adsorption is not stable. In each complex, although the adsorption amount of Pb2+ by hematite-microbial complex was smaller than that of montmorillonite-microbial complex, after the standardization of specific surface area, the adsorption of montmorillonite-microbial complex obviously decreased, while the adsorption of hematite-microbial complex did not change and was higher than that of montmorillonite group. The results showed that the adsorption capacity of hematite-microbial complex was higher than that of montmorillonite-microbial complex. The adsorption of fungus-mineral complex was higher than that of bacteria-mineral complex, and the adsorption of fungus-mineral complex was still higher after the standardization of specific surface area. Meanwhile, the desorption rate of Pb2+ for each complex was in order of B-M>B-Fe>F-M>F-Fe, indicating that the hematite-microbial complex was more stable for Pb2+ adsorption through complexation, and the fungus-mineral complex was more stable for Pb2+ adsorption through cation-π interaction and complexation compared to bacteria-mineral complex. Overall, our study demonstrated the adsorption capacity of different microbial-mineral complex to Pb2+, which will provide a new idea for controlling the migration and bioavailability of heavy metals in soil.
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Key words:
- microbial necromss /
- clay minerals /
- adsorption and desorption /
- Pb2+.
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表 1 微生物残体及复合体的元素分析
Table 1. Elemental analysis of microbial necromass and complexes
样品
Sample元素质量组成/%
Elemental mass component摩尔原子比
Molar atomic ratioC H O N S H/C O/C (N+O)/C BN 42.1 6.72 31.5 11.1 0.480 1.91 0.561 0.787 B-M 6.72 2.31 11.6 3.24 0.155 4.13 1.29 1.71 B-Fe 9.57 1.03 22.7 2.09 0.239 1.29 1.78 1.97 FN 45.3 6.16 33.6 10.6 0.460 1.63 0.556 0.757 F-M 10.7 1.74 14.6 2.19 0.162 1.96 1.03 1.20 F-Fe 15.6 2.33 24.3 3.92 0.299 1.79 1.17 1.38 注:BN,细菌残体bacterial necromass;FN真菌残体fungal necromass;B-M,细菌残体-蒙脱石bacteria-montmorillonite complex;F-M,真菌残体-蒙脱石fungus -montmorillonite complex;B-Fe,细菌残体-赤铁矿bacteria-hematite complex;F-Fe,真菌残体-赤铁矿fungus -hematite complex. 表 2 微生物残体及复合体的比表面积和孔隙结构
Table 2. Specific surface area and pore structure of microbial necromass and complexes
吸附剂
Adsorbent比表面积/(m2·g−1)
Specific surface area孔容积/(cm3·g−1)
Pore volume平均孔径/nm
Mean pore sizeM 100 0.20 7.76 Fe 5.56 0.03 18.0 BN 4.31 0.01 8.76 B-M 32.6 0.09 10.5 B-Fe 5.83 0.04 25.3 FN 5.32 0.02 11.7 F-M 20.9 0.12 22.6 F-Fe 4.94 0.05 39.4 表 3 微生物残体及复合体的吸附等温线拟合
Table 3. Adsorption isotherm fitting of microbial necromass and complexes
吸附质
Adsorbate吸附剂
AdsorbentLangmuir拟合
Langmuir modelFreundlich拟合
Freundlich modelKL Qm R2 KF n R2 Pb2+ BN 6.21 53.2 0.524 42.7 0.204 0.888 B-M 3.65 56.7 0.765 41.3 0.277 0.887 B-Fe 6.12 0.550 0.725 7.98 0.213 0.828 FN 2.02 63.9 0.902 42.2 0.317 0.935 F-M 7.35 72.2 0.912 83.2 0.306 0.923 F-Fe 7.78 46.5 0.874 42.6 0.216 0.938 M 1.19 10.6 0.445 4.85 0.626 0.957 Fe 1.09 0.823 0.413 0.487 0.210 0.436 -
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