地表水的重金属污染是一个全球性的环境问题，多种点源和非点源污染物通过陆地水循环系统汇聚富集到地表水体中，其中包括重金属。本研究聚焦“双碳”背景下的碳捕获、利用与封存技术，汲取生物矿化的灵感，以水合碳酸镁的仿生矿化为基础，探究其对重金属锰铜的吸附固存机制。然而，碳酸盐矿物具有遇酸溶解、粉末易随水流失、结晶周期长和强度稳定性有待提高等缺点。针对上述应用过程中可能存在的问题，本研究以鼠李糖脂为水合碳酸镁仿生矿化的有机基质，以水热碳化的底泥为矿化晶种，同时借鉴仿生矿化中凝胶扩散法的特点，将粉末状的水合碳酸镁优化改进为凝胶颗粒态，以便于实际储存与回收。最后，将水合碳酸镁耦合过碳酸钠制备成原位覆盖材料用于水体修复，采用微宇宙试验，探究黑臭水体缺氧和溶解性有机质组成复杂的情况对重金属（Mn和Cu）迁移转化的影响机制。主要结论如下：

1. 以鼠李糖脂介导水合碳酸镁的仿生矿化，各反应条件的影响分别如下：高温（60-80℃）条件下合成的矿物为纳米片状堆叠的球碳镁石，而低温（20-40℃）条件下合成的则是微纳米棒状的水碳镁石；鼠李糖脂浓度的提高会促使球碳镁石向水碳镁石发生晶相转化，而pH提升的效应则与此相反，强碱性溶液环境有利于促进矿化产物转化为球碳镁石；过高的Mg²⁺/CO^2-₃摩尔比容易导致NH₄Cl等杂质的生成，不利于合成高纯的水合碳酸镁晶体。TG-DSC分析显示水合碳酸镁矿物热解所需的熔融焓随鼠李糖脂浓度的提高而逐渐降低，这表明鼠李糖脂诱导下球碳镁石向水碳镁石的晶相转化是一个放热过程。AFM表明鼠李糖脂介导的仿生矿化过程有利于提高水合碳酸镁矿物晶体的表面粗糙度和异质性。鼠李糖脂与Mg²⁺离子的交互作用延长了仿生矿化的成核诱导期和晶核生长期，XPS和FTIR结果均证实了鼠李糖脂与水合碳酸镁矿物晶体发生了有效复合。鼠李糖脂分子中的羧基和羟基等阴离子官能团可以作为Mg²⁺离子的活性点位，二者稳定结合后即可作为成核位点诱导碳酸根离子的沉淀。随着鼠李糖脂浓度的提升，纳米片状的球碳镁石逐渐附着在水碳镁石的棒状颗粒表面，形成多级结构。

2. 水合碳酸镁矿物材料对溶解态重金属Mn(Ⅱ)和Cu(Ⅱ)的浓度去除率分别可达80.79%和98.86%，而pH<4的酸性环境会严重干扰Mn(Ⅱ)离子的去除效果。在去除机理方面，低浓度条件下，锰的主要去除机理是表面吸附和离子置换，而在高浓度条件下，锰的固存途径以氧化（Mn₃O₄）和共沉淀（Mn[CO₃]）为主。XPS分析表明锰在矿物表面的氧化态随鼠李糖脂浓度的提升而逐渐降低。铜的主要固存形态以碱式碳酸铜的孔雀石和部分氧化铜为主。在酸稳定性方面，水合碳酸镁矿物吸附固存的Mn其酸稳定性临界值在pH=3，而Cu在pH=4及以上可保持较好的酸稳定性。200 mg/L的鼠李糖脂介导合成的水合碳酸镁其酸稳定性最强，其吸附固存的锰铜平均浸出浓度分别为0.11和5.53 mg/L，显著低于其他矿物，这证实本研究成功合成了鼠李糖脂稳定型水合碳酸镁。

3. 以水热碳化的底泥为晶种，以鼠李糖脂诱导仿生矿化，通过蒸发结晶的方法合成水合碳酸镁矿物粉末，将其与凝胶复合进而成功制备水合碳酸镁-底泥凝胶颗粒，用于吸附Mn(Ⅱ)和Cu(Ⅱ)离子。结果表明：底泥为水合碳酸镁的仿生矿化提供了结晶位点，提高了矿化速率。底泥的复合显著提高了凝胶颗粒的压缩模数，优化了凝胶的力学机械性能，增强了颗粒材料的热稳定性，这证明本研究成功合成了强化稳定型的水合碳酸镁凝胶颗粒。吸附动力学显示水碳镁石凝胶对Mn(Ⅱ)的吸附性能更佳，而球碳镁石凝胶则对Cu(Ⅱ)的吸附效果更好。等温吸附特征显示在Mn-Cu共存的混合体系下水合碳酸镁-底泥复合凝胶体现了对Cu(Ⅱ)吸附的高效选择性，且底泥复合后可在一定程度上提升其吸附能力，Cu(Ⅱ)的最大理论吸附量超过100 mg/g。吸附热力学参数表明复合凝胶颗粒对Mn(Ⅱ)和Cu(Ⅱ)的吸附过程均可热力学自发进行，但Cu(Ⅱ)离子的吸附是一个放热过程，而Mn(Ⅱ)离子则是吸热。不同模拟DOM组分对凝胶颗粒吸附性能的干扰主要体现在Cu(Ⅱ)离子上，Mn(Ⅱ)离子的影响规律则不一致，十二烷基苯磺酸钠（SDBS）、富里酸（FA）以及海藻酸钠对Cu(Ⅱ)吸附的抑制效果强于牛血清蛋白（BSA）。在吸附机理方面，FTIR和XPS以及Visual MINTEQ机理模型综合表明碳氧官能团的络合和碳酸盐的矿化沉淀是重金属离子吸附去除的主要机制。

4. 采用混料试验设计将水合碳酸镁、底泥衍生的水热炭以及过碳酸钠进行定量混合，制备了多功能型原位覆盖材料，初步表征分析显示水合碳酸镁矿物材料与重金属Mn/Cu的吸附去除显著相关，为覆盖材料的化学隔离功能提供了保障；底泥的添加对稳定覆盖材料，保证其不被水流侵蚀或随水迁移具有重要贡献；过碳酸钠可以明显改善水体的溶解氧状态，三组分各司其职，其最佳配比条件是水合碳酸镁质量占比约60%，水热底泥占比约25%，过碳酸钠占比约15%。微宇宙试验表明重金属Mn(Ⅱ)和Cu(Ⅱ)对原位覆盖处理的响应规律不一致。不同重金属离子与DOM分子的络合作用存在明显差异，Cu(Ⅱ)离子的络合作用明显强于Mn(Ⅱ)。原位覆盖处理对不同荧光DOM分子与Mn/Cu(Ⅱ)离子发生络合作用的先后顺序具有显著影响：覆盖处理后上覆水体的DOM中微生物代谢产物和类富里酸组分与Cu(Ⅱ)离子优先发生络合作用，而烃类物质和类腐殖酸组分则与Mn(Ⅱ)离子的结合顺序更靠前。原位覆盖材料主要通过影响类腐殖质组分（类腐殖酸和类富里酸）从而干扰DOM与Cu(Ⅱ)离子的结合，而其对类蛋白组分的影响则相对较弱。

本研究对一种基于水合碳酸镁矿物的凝胶颗粒和原位覆盖材料进行了生命周期评估，用于吸附去除水环境中的重金属离子。生命周期的研究重点是复合材料的改性和合成途径，研究结果显示主要的输入能源是电力。这意味着在扩大该工艺规模时，应采取措施提高能源效率，并选择对环境影响较小的能源。

Heavy metal pollution in surface water is a global environmental problem. A variety of point source and non-point source contaminants, including heavy metals, are accumulated in surface water through terrestrial water cycle. Inspired by biomineralization, biomimetic mineralization of hydrated magnesium carbonate (HMC) was improved to strengthen the adsorption and sequestration of dissolved manganese (Mn) and copper (Cu) in the age of carbon capture, utilization and storage (CCUS) technology. However, carbonate minerals lack good chemical stability and mechanical properties. In view of the problems, rhamnolipid and hydrothermally carbonized sediment were used as the organic matrix and crystal seed for biomimetic mineralization of HMC, respectively. In order to facilitate storage and recovery, HMC powder was embedded with alginate polymers to develop HMC hydrogel beads. Finally, HMC was coupled with sodium percarbonate (SPC) to prepare in-situ capping materials for water restoration. The microcosm experiment was conducted to explore the influence mechanism of hypoxia and dissolved organic matter (DOM) on the migration and transformation of heavy metals in malodorous black water. The main conclusions are as follows:

1. High-temperature (60-80℃) mineralization led to nanosheet-stacked dypingite, while nanorod-shaped nesquehonite was obtained at low temperature (20-40℃). Rhamnolipid could promote the transformation of crystalline phase from dypingite to nesquehonite with the increase of concentrations. Strong alkalinity made nesquehonite transformed into dypingite. Excessive molar ratio of Mg²⁺/CO^2- ₃ resulted in the formation of impurities such as NH₄Cl. TG-DSC analysis indicated that the melting enthalpy for the thermolysis of HMC gradually lowered with the increase of rhamnolipid concentrations. AFM showed that the rhamnolipid-mediated mineralization was beneficial for improving the surface roughness and heterogeneity. The interaction between rhamnolipid and Mg²⁺ ions extended the induction period of nucleation and growth of crystal nuclei. Both XPS and FTIR results confirmed the effective incorporation of rhamnolipid with HMC crystals.

2. The removal efficiency of dissolved Mn(II) and Cu(II) by HMC reached 80.79% and 98.86%, respectively. The acidic environment with pH<4 could seriously interfere with the Mn(II) removal. When Mn(II) concentrations were relatively lower, the removal mechanisms mainly involved surface adsorption and ion exchange. As concentration increased, the removal pathway relied on oxidation (Mn₃O₄) and precipitation (Mn[CO₃]). XPS analysis showed that the oxidation state of Mn on HMC surface gradually decreased with the increase of rhamnolipid concentration. The chemical state of Cu included malachite (Cu₂(OH)₂CO₃) and copper oxide (CuO). In terms of acid stability, Mn adsorbed on HMC could maintain at pH≥3, while the similar pH value for Cu was 4. The highest acid stability for sequestration of Mn and Cu was HMC synthesized with 200 mg/L of rhamnolipid. The average leaching concentrations were 0.11 mg/L (Mn) and 5.53 mg/L (Cu), respectively, which were significantly lower than those of other minerals. This confirmed that rhamnolipid-stabilized HMC was successfully synthesized in this study.

3. Using hydrothermal sediment as crystal seeds, rhamnolipid was used to mediate the biomimetic mineralization to prepare hydrated magnesium carbonate (HMC) composites for enhancing the Mn(Ⅱ)/Cu(Ⅱ) adsorption performance of alginate hydrogels. The hydrothermal sediment is beneficial to accelerate the biomimetic mineralization. Sediment could enhance the compressive mechanical property and thermal stability of hydrogels significantly. This indicated that reinforced HMC hydrogel beads have been synthesized successfully in this study. The adsorption performance of nesquehonite and dypingite hydrogels was better for Mn(II) and Cu(II), respectively. Sediment improved the adsorption capability of the hydrogels appropriately with stronger selectivity for Cu(II), with the maximum theoretical adsorption capacity of Cu(II) over 100 mg/g, The adsorption of Mn(II) and Cu(II) on hydrogel beads was thermodynamically spontaneous. Both complexation of functional groups on alginate and mineralization by HMC participated in the adsorption of Mn(II) and Cu(II).

4. Mixture design was used to develop the capping material consisting of hydrothermally carbonized sediment, HMC and SPC. Microcosmic experiment was conducted to investigate the dynamics of Mn and Cu at the sediment-water interface in malodorous black water. Hydrothermal sediment contributed to the mechanical weight, guaranteeing the caps’ stability against water erosion and transport. HMC minerals are associated with the adsorption and sequestration of Mn(Ⅱ)/Cu(Ⅱ). SPC could improve the anoxic condition. The optimal mass proportion is 25% of sediment, 60% of HMC and 15% of SPC based on mixture design. In-situ capping altered the fate and transformation of metals in the sediment-overlying water profile in short term: Mn immobilization while Cu activation. The complexation of Cu(II) ions was significantly stronger than that of Mn(II). In-situ capping treatment had a significant effect on the order of complexation for different fluorescent DOM molecules with Mn(II)/Cu(II) ions: microbial byproduct and fulvic acid-like components were preferentially complexed with Cu(II) ions after capping, while PAH and humic acid-like components were bound to Mn(II) ions in a more preferential order. The humic-like components bound to Cu were primarily interfered with capping treatment, whereas the protein-like components were relatively weakly affected.

In this study, the life cycle assessment of hydrogel beads and in-situ capping materials based on HMC minerals was carried out. The results showed that the main input energy was electricity. This means that when expanding the scale of the process, measures should be taken to improve energy efficiency and select energy sources with less impact on the environment.