农田暗管排水系统磷回收的静电负载镧氧化物新材料制备及其选择性吸附机理

The fast development and application of the subsurface drainage system increased the loss of soluble phosphorus in farmland. Hence, to absorb phosphorus fast and selectively under the high-flux condition is vital to control and recover phosphorus from the tile system. Lanthanum oxide and its composite oxides have high adsorption selectivity to dissolved phosphorus, but their powder form has poor stability and loss easily, and hard to apply it independently. Loaded the lanthanum oxide and composite oxides on the ordered Hierarchical porous materials would make the lanthanum oxide highly dispersed, fixed and fully exposed. In this project, potential applicable hierarchical porous materials used were compared and optimized. And the electro-adhesion and post-anchoring condition were redesigned to determine the optimal synthesis procedure，and the electro-adhesion adsorption materials were characterized. Based on the results of the thermodynamic and kinetics analysis，determined the efficiency of selectivity and high-flux adsorption of phosphorus，and evaluated and optimized the synthetic materials. Then, technology based on isothermal calorimetry and high-resolution X-ray photoelectron spectroscopy were used to analyze the micro characteristics and adsorption-desorption mechanism of the composite sorbent during the selective adsorption, high-flux adsorption and the desorption process. Finally, it was to reveal adsorption and recovery mechanism of the composite sorbent on the phosphorus from the subsurface drainage. The implementation of this project could develop an efficiency, high phosphorus adsorption selectivity composite sorbent, and provide theoretical and technical support for the restoration of the non-point source pollution caused by subsurface drainage.

农田暗管排水系统的规模化应用加剧了农田中磷的流失，大流量条件下磷的快速选择性吸附（高通量吸附）是控制磷污染和实现磷回收的有效途径。镧氧化物对磷具有高吸附选择性，但其形态稳定性差、易流失，单独应用效果难以保证。实现镧氧化物有序负载于多级孔材料，将有助于提高其分散性、均匀性、固定效果等，进而强化发挥其活性位点吸附。本项目优选多级孔材料基质，通过优化静电负载条件和后锚定方法，制备并表征静电负载镧氧化物吸附材料（La-EA）；基于吸附静态动态实验的结果并结合热动力学分析，明确其对磷的选择性、高通量吸附效能，优化La-EA吸附饱和后的再生和磷回收途径及参数；采用等温量热技术、高分辨X-射线光电子能谱等微观分析技术，分析吸附脱附过程的微观特征，揭示高通量条件下静电负载镧氧化物吸附材料的选择性吸附机制。本课题开发具有高通量、高选择性的磷吸附材料，为推进农田暗管排水面源污染控制和资源回收提供技术支撑。

由于人类活动导致水质恶化，内源性污染已成为水生态环境的一种“慢性病”。特别是磷等既能引发富营养化的限制元素，又能造成水体毒性的致病元素，容易附着在沉积物上，难以通过相变从水体中去除。本项目提出纳米粒子负载的纳米纤维状的高效磷、砷吸附材料，加速磷砷吸附、回收吸附材料并实现资源回收的目的。利用静电负载方法，以无机、有机及网状金属材料为基质，以不同镧氧化物负载比例合成不同类型的镧吸附核心的纳米纤维材料。考察静电负载技术操作条件（电压、湿度、温度等）、镧金属供给条件（比例、浓度、形态等）对负载效果的影响，优化材料的合成条件。首次制备出具有超高吸附容量的镧纳米颗粒负载纳米纤维膜状吸附材料，利用静电纺方法高效合成吸附容量达到169.5mg P/g的吸附材料，材料孔隙率90%以上，水流阻力小；吸附结果表明，以60 ml/min的流速稳定供应110 ug P/L磷酸盐，以C/C0 = 0.5的流出/流入浓度为指标，以吸附剂总有效容量的73.7%为指标。拓展吸附材料合成技术，在La吸附核心纳米纤维制备方法基础上，采用多巴胺聚合法，合成La-Mn双功能吸附核心的纳米纤维膜状吸附材料，实现对多价态砷的吸附去除。La-Mn氧化物可均匀分布在纳米纤维上。结果表明，材料可将三价砷氧化为五价砷，同时可以对五价砷进行选择性吸附。对其氧化-吸附机制研究发现：首次发现了不溶物La2O3的初始粒子在气溶胶状态下，与水蒸气可以快速反应生产La(OH)3纳米粒子，该过程绿色且转化率可到99.97%。无其他副产物，相较于水热法生成La(OH)3纳米粒子，合成效率是其120倍以上，可实现大量合成。该方法生产效率是水热法合成的100倍， 同时材料的磷吸附容量可达到130mg/g。可回收利用率在80%左右。揭示了LLNM吸附过程与机制，其吸附过程主要为，磷、砷酸根在通过形成配位键的形式与氢氧化镧中的镧元素结合，并在纳米纤维的交错部位结晶，从而实现从水相中脱除。