机械力化学反应场中钙系类水滑石(Ca-LDH)固相成矿机理研究

Nitrogen oxides (NOx) is one of the main sources of atmospheric pollution which can be removed by layered double hydroxide (LDH) under the adsorption-photocatalytic oxidation mechanism. Manufacturing LDH with excellent adsorption and photocatalytic performance is the key to the removal of NOx. Calcium-based LDH (Ca-LDH) can exhibit better acid gas adsorption performance than the magnesium-based LDH. However, the conventional solvent ways for the synthesis of Ca-LDH suffered the drawbacks of sewage discharge and severe synthetic conditions. The proposed project intends to synthesize Ca-LDH by a mechanochemical two-step ball milling way with the regulation of structural components. First, the amorphous precursor will be prepared by dry milling, and then a small amount of water will be added and co-ground to achieve LDH crystallization. A series of Ca-LDH (Ca-Zr, Ca-Ti, Ca-Sn, etc.) will be synthesized. The effects of acid-base properties, crystal structure, water content, etc. of the raw materials on the amorphization of the precursor will be explored. The influence of milling time and water addition during the wet milling on the mineralization of the precursor will be discussed. Quantitative Analysis of X-ray diffraction Full Spectrum Fitting will be applied to analyze the yield of Ca-LDH which can be used to establish the reaction kinetic model and then reveal the synergistic effect between dry and wet milling for the ore-forming of LDH in the solid state. The NOx removal performance of the prepared samples will be evaluated and the relationship between the NOx removal performance and the structure of LDH will be explained. The whole work will provide a theoretical basis and technical support for Ca-LDH green solid-state preparation and its environmental application.

氮氧化物（NOx）是大气主要污染源之一，可利用类水滑石（LDH）吸附-光催化氧化协同去除，而制备高吸附和高催化性能的LDH是关键。相比常规镁系LDH，钙系LDH（Ca-LDH）具有更优的酸性气体吸附性能，通常采用液相法合成，但存在污水排放和合成条件苛刻等难题。项目拟采用机械力化学两步球磨实现Ca-LDH结构组分的调控与合成，先通过干磨制备非晶态中间体，再添加少量水湿磨实现LDH晶化成矿，合成系列Ca-Ti、Ca-Zr、Ca-Sn等LDH。探索干磨过程中原料酸碱性质、晶型、含水量等对原料非晶化的影响规律，探讨时间和加水量对Ca-LDH湿磨晶化成矿的影响，利用XRD全谱拟合定量分析Ca-LDH的含量，构建反应动力学模型，揭示干湿磨协同Ca-LDH固相晶化成矿机制，系统评价其去除NOx的性能，建立NOx去除性能与其结构间的关系，为Ca-LDH绿色固相制备和环境应用提供理论依据和技术支撑。

天然水滑石（LDH）在特殊地质环境中才能存在，且含量一般较低，目前LDH主要通过液相共沉淀方法制备。受限于不同金属离子沉淀pH值的差异，目前液相法所得 LDH 主要以二价与三价金属组合为主，四价及以上的金属离子难以形成LDH。钙系LDH（Ca-LDH）隶属于LDH矿物族，Ca元素的存在使Ca-LDH对污染物具有较强的吸附性能，可以有效用于吸附去除环境污染物。本项目系统研究了Ca-Al LDH不同原料组合干磨后样品结晶度、晶型等的变化，并总结出原料干磨获得非晶态中间体是机械力化学高效合成LDH必要条件，强碱性氢氧化钙原料需要添加适当钙盐进行碱度调配才能用于Ca-LDH的合成；采用两步法成功合成Ca-Ti、Ca-Mn水滑石，建立了合成反应动力学及合成反应路径，并用热力学等多种手段详解了合成机理，项目发现原料酸碱度匹配是机械力化学制备Ca-LDH的关键控制因素，通过合理调控原料酸碱度，第一步干式高能球磨获得非晶态中间体，第二步添加少许水湿磨，非晶态中间体晶化成矿，即可获得高结晶度LDH。；系统评价了钙系LDH的吸附性能，通过机械化学方法成功合成Ca-LDH。Ca-LDH和Ca-LDH-Fe复合材料具有优异的五价砷和三价砷去除性能，单次吸附后水中的残余砷浓度低于世界卫生组织的饮用水标准（<10 ppb）。根据合成条件及参数进行Ca-LDH和Ca-LDH-Fe复合材料大规模生产的可行性以及经济成本分析，Ca-LDH的异位处理砷污染水成本为1.17 usd/m3，Ca-LDH-Fe复合材料原位处理砷污染地下水成本为0.22~0.33 usd/m3，与其他处理技术（0.3~20 usd/m3）相比具有一定的成本优势，可用于实际砷污染地下水的修复。