玉米秸秆生物炭对汞、铬复合污染的土壤中重金属钝化作用机制研究

Soil pollution with heavy metals has increasingly become a severe global environmental concern in recent years. In China, more arable lands going to heavy metals pollution which are close to 16.1% of the entire agricultural land. Recently, Chrome (Cr) and Mercury (Hg) contamination in croplands pose a severe health hazardous and environmental concern. Substantial efforts have been made to remediate polluted soils with organic and inorganic materials. In the present studies, the immobilizing effects of biochar derived from maize straw will be investigated in a combination of lab incubation and plot test in which plant growth, metals uptake by plants, concentrations of metals in the soil solution, their distribution among different fractionations, leaching characteristics, bioaccessibility and as well as mobility were determined in Hg/Cr co-contaminated soil. These results could provide scientific basis for exploring fundamental scientific and technological issues relevant to Cr / Hg polluted soil by immobilized amendments application.. Firstly, adsorption experiments will be conducted to assess the adsorption capacity of biochar and biochar treated soil of Cr and Hg to gain insight the underlying mechanism of Cr and Hg on the biochar and biochar treated soil by using fourier transform infrared spectroscopy (FTIR), X-rays diffraction (XRD), scanning electron microscopy (SEM) and adsorption kinetics and isotherms. . Secondly, various techniques such as European Community Bureau of Reference (BCR) sequential extraction, Total Characteristics Leaching Procedure (TCLP), single extraction (CaCl2), etc, were employed to evaluate the simultaneous effectiveness of biochar (BC) amendment to immobilize the Cr and Hg in co-contaminated soil.. At the end, pot experiment will be conducted to simultaneously investigate the effects of biochar on Hg/Cr immobilization and leaching by means of BCR and TCLP. Moreover, biochar amendments effects on metals bioavailability and promoting plant growth were also assessed by Hg/Cr determination in plant, plant enzymatic activities analysis, bioconcentration factor and translocation ratio. Etc.

针对生物炭修复土壤重金属的研究机理，还有待于深入研究。本项目拟采用玉米秸秆制备的生物炭为环境修复材料，以生物炭吸附水中重金属Hg和Cr为切入点，通过吸附动力学和吸附热力学实验研究生物炭不同的物化性质对重金属吸附的影响机理、构效关系和贡献率，同时利用X-射线衍射、红外光谱等现代分析手段，从价态、官能团、结构态等方面来探究生物炭对土壤中重金属Hg和Cr的吸附（稳定化）及其生物有效性的影响机制，并通过土柱淋溶试验、盆栽试验、小区试验研究生物炭吸附重金属的机理对土壤重金属迁移、转化机制的影响。力求从微观角度上阐释生物炭不同的物化性质对土壤重金属复合污染的修复机理。

土壤的重金属污染由于具有累积性、滞后性和不可降解性，已经对生态环境和人类健康带来巨大的挑战。生物炭是一种低成本、环境友好型的吸附剂，近年来被广泛应用于土壤污染的修复中。众多研究表明，生物炭能够钝化重金属的活性，通过控制重金属的形态转化，从而达到固持重金属，降低土壤重金属危害的目的。但是生物炭具有高度的异质性，它主要由无机成分（灰分）和有机炭两部分组成，它们对重金属的钝化都起着非常重要的作用。本项目重点是对生物炭的不同组分修复土壤重金属污染进行定性阐述和定量分析。本项目通过分离提取生物炭的不同组分，通过批量吸附实验、土柱淋洗实验、静态培养实验、盆栽实验等，研究它们对土壤重金属吸附、迁移、钝化的机理和构效关系，并对其进行量化。通过对复杂作用机制的简单量化，更加深入的剖析生物炭对土壤重金属污染的修复机理及作用机制。实验结论表明，虽然无机炭只占生物炭总质量的不到三分之一，但它其中含有的K、Ca等碱金属离子和CO32-、PO43-等离子在修复过程中起了重要作用，作用贡献率要大于有机炭。比如溶液的吸附实验表明，有机炭对Cr(VI)的吸附能力最强，而无机炭的吸附作用很弱，但是土柱实验表明有机炭对Cr(VI)的吸附对于土壤修复不起决定性作用。真正能够降低土壤中Cr(VI)危害的是无机炭，主要原因是无机炭中的这些碱性物质能够降低Cr(VI)弱酸提取态的含量，增加其残渣态的含量。无机炭对Cr(III)的吸附作用要高于有机炭，其中无机炭中的碱金属离子与Cr(III)之间的离子交换起大约60%的贡献率。同样，无机炭也能够大大降低Cr(III)的弱酸提取态含量。对于Hg(II)的吸附，也是由于离子交换而使得无机炭起的作用大于有机炭。因为有机炭中含有丰富的含氧官能团，它能够作为电子供体和穿梭体与重金属发生作用，因此近年来受到极大的关注。但是生物炭中的灰分由于能够使土壤成弱碱性，而起到修复的决定性作用，因此在以后的研究中应该受到更大的关注。