酸性有机材料调控赤泥有机矿质复合体形成机制与成土趋势研究

Bauxite residue is a highly alkaline waste generated during the production of alumina, and its accumulation threatens the surrounding ecological environment and restricts the sustainable development of the alumina industry. Soil pedogenesis through substrate improvement can solve the environmental problems caused by bauxite residue, and it is the most promising way for large-scale bauxite residue disposal. However, the strengthening mechanism of the occurrence and evolution of bauxite residue pedogenesis, and the long-term effect and stability of alkali reduction during soil-forming are still unclear. The purpose of this project is to study the organo-mineral complex formation mechanism and pedogenesis tendency driven by acid organic materials during the bauxite residue pedogenesis. To clarify the mechanism of organic matter and alkaline components by measuring the composition of bauxite residue mineral phase and its elemental distribution. The relationship and extent of organic matter and bauxite residue minerals, and the key factors for the formation and stability of organo-mineral complexes are explored, by means of determination of TG-TDA, differential thermal chromatography, FT-IR and NMR, and organic carbon, iron-aluminum oxide and electrolyte content of different grain grades in bauxite residue. The morphology, element distribution, and humic acid functional groups composition and distribution characteristics of organo-mineral complexes were analyzed and characterized. Combined with the physicochemical indexes such as surface chemistry and the spatio-temporal variation of microbial biomass and community structure, the bauxite residue pedogenesis tendency and its long-term pedogenesis evolution were elucidated. The research findings have important guiding significance for understanding and accelerating the bauxite residue pedogenesis.

赤泥是氧化铝生产过程中产生的高碱性废弃物，其堆存威胁周边生态环境，制约氧化铝工业的可持续发展。通过基质改良实现土壤化可解决赤泥引起的环境问题，是目前最具前景的规模化赤泥处置方式。但赤泥土壤发生与演变过程的强化机制和降碱、成土的长效性与稳定性尚不明确。本项目拟开展酸性有机材料调控赤泥有机矿质复合体形成机制与成土趋势研究，通过测定调控后赤泥矿物相组成及其元素微区分布，阐明有机质与碱性组分的作用机制；借助差热-色谱、FTIR和NMR等手段及不同粒级颗粒有机碳、铁铝氧化物和有机矿质复合度的测定，分析表征有机矿质复合体的结构、形貌及胡敏酸官能团组成和分布特征，探究有机质与赤泥无机矿物的结合关系和程度，阐明赤泥有机矿质复合体的形成机制和稳定性；结合表面化学性质等理化指标及微生物量和群落结构的时空变化规律，阐明赤泥成土趋势及其土壤化演变的长效性机制。研究成果对理解和加速赤泥土壤结构形成具有重要指导意义。

赤泥的露天堆放对堆场及周边土壤、水体和大气造成一定的环境风险，其处置已成为限制氧化铝工业发展的瓶颈问题。本研究采用酸性有机材料将赤泥转变为一种可支持植物生长的基质，系统研究了赤泥碱性转变过程中酸性有机材料与赤泥碱性组分的响应关系，以及酸性有机材料促进赤泥土壤化演变的作用机制；通过酸性有机材料降低赤泥碱性，从长远改进赤泥物理结构、提高赤泥化学稳定性、加速赤泥植被恢复，为实现赤泥规模化处置及堆场自然生态重建有重要的学术价值和现实意义。主要研究结果如下：硝基腐殖酸调控下赤泥中碱组分和矿物组分不断参与中和反应，低于3%的添加量导致可溶性Al(OH)4−、Na2CO3和NaOH的中和，而高于3%的添加量则使钙霞石、方解石和钙铁榴石的溶解，这导致赤泥中无定形氧化铁和有机结合态氧化铁含量的显著增加；硝基腐殖酸破坏了K与赤泥中含Mg、Fe和Ti矿物的结合，导致游离钾增加。硝基腐殖酸中和后的赤泥具有较高的富里酸和腐殖化物质；赤泥等电点显著降低，Zeta电位的降低使赤泥颗粒分散状态趋于聚集，表面电荷性质更接近土壤；硝基腐殖酸中和后赤泥中大团聚体数量显著增加，团聚体中的钙和铁作为无机胶结剂与有机质相结合从而促进微团聚体的形成。硝基腐殖酸和醋渣的对于赤泥ESP和养分的调节优于柠檬酸，柠檬酸更多的参与了赤泥有机矿质复合体基本结构单元的形成中，而硝基腐殖酸和醋渣在小颗粒的聚集中起重要作用。发芽率试验和盆栽试验表明，耐性植物披碱草和柠条在绿矾、硝基腐殖酸及醋渣处理赤泥基质中的发芽率均高于50%，在柠檬酸处理基质中的发芽率最差，且低于未处理赤泥中的发芽率；耐性植物定殖进一步促进了赤泥碱性矿物的溶解，增加了大团聚体含量，激活了酶活性，促进养分循环，微生物群落多样性和丰富度显著提高；具有复杂根系网络的披碱草促进了赤泥团聚体的形成和稳定性。