Characteristics and Effects of Modified Attapulgite for Stabilization of Cadmium Contaminated Alkaline Soils
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摘要:
凹凸棒及其改性材料具有较发达的比表面积、丰富的官能团及较强的吸附能力，被作为良好的环境修复材料而成为农田土壤重金属修复领域的研究热点。目前中国农田土壤Cd污染现状仍然严峻，为探究改性凹凸棒的钝化机制及其对碱性土壤Cd污染的钝化效果，本文采用氢氧化钠、氯化铁两种改性剂对凹凸棒改性，利用扫描电镜（SEM）、X射线衍射（XRD）、傅里叶红外光谱（FTIR）及比表面积测定（BET）和孔径分析（BJH）对改性前后凹凸棒的微观结构和表面形态进行表征，结合表征结果分析其钝化机理，开展室内模拟Cd污染碱性土壤培养试验、生菜盆栽试验，采用原子吸收分光光度法测定土壤Cd含量，探究单一施用与复配施用两种改性凹凸棒对碱性土壤Cd的钝化效果差异。结果表明：碱处理后凹凸棒Si—O基团、结构负电荷增多，铁改性后凹凸棒微孔数量增多、比表面积增大，两种改性方法均使凹凸棒的内部结构及表面形态发生明显改变，吸附能力得以提升。碱改性凹凸棒（AM）通过更强的化学吸附能力实现对Cd的钝化，可提高土壤pH和阳离子交换量（CEC），而铁改性凹凸棒（IM）则具有更强的物理吸附能力和较强的化学吸附能力，使得土壤pH降低、CEC升高，两种材料复配施用能够在一定程度上减小了pH升高幅度、提高土壤CEC值，提高钝化效果。碱、铁改性凹凸棒按质量配比3：1、土壤质量的2.00%施用后，土壤Cd有效态含量可降低33.85%，生菜对Cd的富集系数降低24.49%，在各处理组中效果最好。因此，铁改性凹凸棒对碱性土壤重金属Cd具有良好的钝化效果。在实际应用中应避免单独施用碱改性凹凸棒，可考虑与其他钝化材料复配施用，实现在保护土壤质量的同时更好地降低土壤Cd污染。
Abstract:BACKGROUND With the high specific surface area, rich functional groups and strong adsorption capacity, attapulgite (AT) and its modified materials have become a research hotspot in the field of heavy metal remediation of farmland soil.
OBJECTIVES To investigate the stabilization mechanism and effect of different modified AT for Cd-contaminated alkaline soil.
METHODS AT materials were modified by sodium hydroxide and ferric chloride. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and nitrogen adsorption/desorption test (BET-BJH) were used to analyze the microstructure and surface morphology of the modified AT. Combined with the characterization results, the passivation mechanism was analyzed, and the indoor simulated Cd-contaminated alkaline soil cultivation experiment and the lettuce potting experiment were carried out. Soil Cd content was determined by atomic absorption spectrophotometry. The effect differences between single application and compound application of two modified attapulgites in Cd-contaminated alkaline soil were investigated.
RESULTS Alkali treatment made the Si-O groups and structural negative charges increase, and the number of micropores and specific surface area of the iron-modified attapulgite (IM) also increased. The internal pore distribution and surface morphology of attapulgite can be significantly changed in two types of modification, which can also improve their adsorption capacity. Alkali-modified attapulgite (AM) can improve soil pH and cation exchange (CEC) by stronger chemical adsorption capacity, while IM has stronger physical adsorption capacity and strong chemical adsorption capacity, which makes soil pH decrease and CEC rise. To a certain extent, the compound application of the two materials can reduce soil pH and improve CEC, which can improve their stabilization effect. After using the passivation material of AM: IM ratio of 3:1 and 2.00% of the soil mass, the available DTPA-Cd content was reduced by 33.85%, and the BCF of lettuce was reduced by 24.49%. The treatment attained the best stabilization effect.
CONCLUSIONS IM has good stabilization effect on heavy metal Cd in alkaline soil. AM should be avoided for single application, and it can be recombined with other stabilization materials to achieve better reduction of soil Cd pollution while improving the quality of alkali soil.
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表 1 凹凸棒的比表面积和孔体积变化
Table 1. Change in attapulgite properties including BET specific surface area (SBET), and total pore volume (Vpores)
样品材料 孔体积
(cm3/g)平均孔径
(nm)平均粒径
(nm)BET比表面积
(m2/g)凹凸棒原土(AT) 0.08785 4.92 84.02 71.41 碱改性凹凸棒(AM) 0.08573 5.65 98.93 60.65 铁改性凹凸棒(IM) 0.1213 4.65 57.57 104.22 
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