改性树脂对水中硅酸的选择性去除作用及机理研究

In water treatment process, silicic acid form silica scale attached on the inner wall of the equipment or surface of membranes, blockages the pipelaine or membranes, seriously influence the normal operation of the equipment and its service life. At present, the inhibition study of silica scale formation mainly focus on using inhibitor or precipitating agent, which not only increase the content of organic matter in water, but also produce a large amount of sludge increase the cost of post process. Selective adsorbents have a specific adsorption for the target element without added other reagents. Howerer, the study of the selective removal of silicic acid is still blank, until now. Our previous work showed that the simple adjacent hydroxyl organic matter interact with silicic acid to form stable complexes. Therefore, we propose the idea for the first time to fix some organic matters have adjacent hydroxyl structure on the ion exchange resins by grafting method as a selective adsorbent to remove the silicic acid from water. Molecular grafting technology combined with 29Si and 13C nuclear magnetic resonance spectrum technology (NMR) and the stoichiometric relationship will be used in present study to characterize the surface functional groups and the physical chemical properties of modified resin, and screen the organic matters, which not only interact with silicic acid, but also can graftting on the anion exchange resin. We also analysis the silicic acid selective adsorption coefficient K of modified resin, and analysis the similarities and differences of adsorption capacity, adsorption isotherm, adsorption kinetics models, adsorption thermodynamic parameters and adsorption mechanisms between the different state of silicic acid, to reveal the law of the selective removal of various forms of silicic acid in water by modified resins. This project can provide a new approach and theoretical basis to water treatment technology.

硅酸在水处理过程中形成硅垢附着在设备内壁或膜表面堵塞管道或膜，严重影响设备的正常运行和使用寿命。目前抑制硅垢形成的研究以添加阻垢剂或沉淀剂为主，不仅增加水中有机物含量，还产生大量的污泥，增加后期处理成本。选择性吸附法在不加其它试剂的前提下，针对目标元素具有专一性的优点，但对硅酸的选择性吸附去除研究尚属空白。我们前期工作发现的简单邻羟基有机物可与硅酸形成稳定的配合物，据此本项目首次提出采用接枝法构筑改性树脂作硅酸选择性吸附剂去除硅酸的思路。结合分子接枝技术、29Si和13C的核磁共振波谱技术和化学计量关系表征改性树脂表面官能团及理化性质、筛选既能和硅酸相互作用又能接枝在离子交换树脂上的有机物、分析改性树脂对不同形态硅酸的选择吸附系数K、吸附等温模式、吸附动力模式、吸附热力学参数和吸附机理的异同，揭示改性树脂吸附去除水体中各种形态硅酸的规律，为水处理技术的发展提供新的方法和理论依据。

水体中的硅酸在水利用过程中以硅酸盐沉淀（硅酸水垢）的形式附着在设备内壁或膜表面，减小管道直径或堵塞膜，严重影响水利用设备的正常运行，导致水处理成本的增加。为防治硅垢的形成通常用离子交换树脂吸附去除硅酸。但水体中硅酸主要以分子态存在，树脂对硅酸的去除效果不理想。本项目制备了硅酸特效改性吸附树脂，研究了改性树脂对不同形态硅酸的吸附去除性能，评价了吸附树脂的应用推广前景。本项目共制备了tiron型和GA型两种树脂，研究了对单硅酸、离子态硅酸和聚硅酸的吸附，发现两种树脂对单硅酸的吸附量分别达到8.36 mg/g和8.99 mg/g（用Si表示），是离子交换树脂对硅酸的吸附量的30倍。且其他共存阴离子对两种树脂吸附硅酸的影响不大（除硼酸外），说明两种树脂有一定的选择性。两种树脂不仅能够吸附单硅酸，也能吸附离子态硅酸和聚硅酸，对聚硅酸的吸附量远远大于对单硅酸的吸附量，说明两种树脂可应用于具有较宽的pH范围和浓度范围的硅酸的吸附去除，且有潜力去除所用形态的硅酸。两种树脂通过形成树脂表面1:3配合物的形式吸附单硅酸，而以优先吸附小颗粒聚硅酸的形式吸附聚硅酸。无论是单硅酸还是聚硅酸，都能在树脂表面继续发生聚合反应，在树脂表面形成三维网络结构的硅酸沉淀。静态循环吸附研究表明，两种树脂通过洗脱再生可循环利用，tiron型树脂第四次循环利用率可达80%，GA型树脂的可达50%。动态吸附研究证明在一定的硅酸浓度和流速条件下，突破曲线的突破点随柱高的增加而延长，说明通过调节柱高可完全吸附去除正在运行的水体中硅酸。动态循环吸附研究表明，tiron型树脂和GA型树脂吸附硅酸的生命因子分别为13和5.4，说明tiron型树脂更有利于硅酸的吸附去除。本研究结果为防治水垢技术的发展提供科学依据，在水循环利用领域或水处理领域具有重要的参考价值和应用前景。