纳米铁生物炭对根表铁膜及土壤-水稻系统Cd、Pb吸附阻控机制

Biotoxicity and mobility of heavy metals in soil depend strongly on their bioavailability rather than on their total contents; and the effects of rice iron plaque on the bioavailability of heavy metals in rhizosphere soil are obviously. Paddy soil complexly polluted with cadmium (Cd) and lead (Pb) is used as the tested soil, and nano-iron supported on biochar is prepared through a coprecipitation method in this project. The hydroponic culture experiment and the pot experiment with rice planting are conducted to study the effects of nano-iron supported on biochar application in soil on the formation of iron plaque and the effects of iron plaque on impedance control mechanisms of Cd and Pb adsorption. The soil culture experiment and the rhizobag experiment with rice planting are carried out to research the effects of nano-iron supported on biochar application in soil on the mobility and transportation of Cd and Pb in soil-rice systems, through analysis of the concentrations of Cd and Pb in soil solutions, iron plaques, and rice tissues, and analysis of the species and bioavailability of Cd and Pb in rhizosphere and non-rhizosphere soils in different rice growth periods. The achievements of this project will offer new techniques and methods for controlling transportation of Cd and Pb in soil to rice plants, and are of great importance for safe utilization of paddy soil polluted with Cd and Pb and for safe food production.

土壤中重金属生物毒性及迁移能力与其生物有效性显著相关，水稻根表铁膜对根际土壤重金属生物有效性影响明显。本项目以Cd、Pb复合污染水稻土为研究对象，利用共沉淀法制备负载纳米铁生物炭，通过添加纳米铁生物炭的水培试验、盆栽试验，研究其对水稻根表铁模形成的影响以及根表铁膜对Cd、Pb吸附阻控机制；运用土壤培养、水稻根袋盆栽试验，取样分析土壤溶液、根表铁膜、水稻各部位中Cd、Pb含量以及水稻不同生育期根际土壤、非根际土壤中Cd、Pb形态与生物有效性，研究负载纳米铁生物炭对土壤-水稻系统中Cd、Pb迁移转运的影响。本项目的开展将为控制Cd、Pb向水稻迁移提供新的手段和方法，对Cd、Pb污染稻田安全利用及粮食安全具有重要意义。

耕地重金属污染是全球关注的环境问题。土壤中重金属的生物有效性直接影响到农作物对重金属的吸收累积。利用生物炭治理修复重金属污染耕地土壤具有很大的潜力。本项目利用共沉淀法在生物炭表面负载纳米Fe3O4颗粒，成功制备出了纳米铁生物炭（BC-Fe），研究了BC-Fe对Cd2+、Pb2+的吸附条件与吸附机制，发现BC-Fe对于Cd2+、Pb2+的吸附效果主要受吸附时间、pH值、添加量、初始温度等因素影响。进一步的研究结果发现，纳米铁生物炭（BC-Fe）对Cd2+、Pb2+的吸附用符合Lagergren准二级动力学方程，吸附反应近似单分子层吸附，且吸附是自发的吸热反应过程，在温度较高时吸附效果更好。通过水培试验，研究了BC-Fe对水稻根表铁膜吸附阻控Cd、Pb的过程与机制。研究发现，BC-Fe能有效诱导水稻根表铁膜的生成，根表铁膜厚度越大，对Cd、Pb的吸附能力也越强；根表铁膜对Cd、Pb的吸附机制以化学吸附控制的离子交换作用。通过水稻种植盆栽试验，研究了BC-Fe对水稻吸收累积Cd、Pb的影响，初步揭示了对土壤Cd、Pb生物有效性的影响机制。研究结果表明，施用BC-Fe能有效降低水稻茎、谷壳、穗节中Cd含量，较低施用量下（0.5-4 g/kg）能显著降低糙米中Cd的吸收累积；初步推断BC-Fe降低土壤Cd有效性的机制在于其较大的比表面积且表面富含C=C、C=O 和-OH等活性基团，通过离子交换、络合作用大量吸附土壤中活性态的Cd，同时BC-Fe增加了土壤 CEC，增强土壤对 Cd2+的吸附固定能力。.本研究的研究结果为利用纳米铁生物炭治理修复重金属污染耕地的实际应用提供了科学依据，为实现中轻度污染耕地安全利用，保障粮食安全生产具有重要意义。