均相硫脲改性PVDF亲和膜的制备及对低浓度金的回收

Affinity membrane is a technique that takes advantages of both membrane separation and affinity chromatography, by which trace amount of gold can be effectively recovered from wastewaters. However, the low utilization rate has become a primary bottleneck of such application. In this work, a PVDF membrane with thio group will be prepared for gold recovery, the utilization rate of the membrane will be elevated by controlling membrane pore size distribution. Detailed implementations are as follows: PVDF resin will be first de-fluorinated with concentrated alkali solution to form double carbon bonds within the chains of the resin; second, Michael addition reaction between the double carbon bonds and thiourea will be performed under N2 atmosphere to obtain theourea modified PVDF; third, affinity membranes will be prepared by nonsolvent-induced phase separation method. Membranes with uniform pore size will be obtained by addition to the casting solution gelation suppression agents for controlled phase separation of the resin from the non-solvent. The dynamic adsorption of gold with the membranes will be studied to quantify the influence of the pore size and its distribution. Based on the existing theory, a mathematical model for improved prediction of breakthrough curves will be established by incorporating the pore size effect. This study will provide better theoretical insight and experimental support for the application of affinity membranes for low concentration precious metal and rare earth recovery from water.

亲和膜兼有膜分离和亲和色谱的优点，可用来有效回收废水中的微量金。然而亲和膜的有效利用率低，已成为制约该项技术推广应用的主要瓶颈。本课题拟结合聚偏氟乙烯（PVDF）与硫脲的特点，制得一种以PVDF为基质，硫基为活性位点的微孔亲和膜；通过调控孔径分布，提高亲和膜的有效利用率。具体实现方法如下，碱性条件下对PVDF树脂进行脱氟处理，在分子链上生成碳碳双键，氮气氛中完成双键与硫脲的迈克尔加成反应，获得硫脲改性PVDF树脂，最后由浸没沉淀相分离法制膜。铸膜液中添加抑制树脂凝聚的相分离控制剂，获得孔径均匀的多孔膜，制成膜色谱后用于对微量金的回收，揭示孔径分布对亲和膜动态吸附性能的影响。以现有的亲和膜平衡扩散模型为基础，考虑膜孔径分布的影响，改进穿透曲线的预测模型。本研究将为亲和膜在微量贵金属甚至稀土从水中回收的应用提供理论与实验依据。

亲和膜兼有膜分离和亲和色谱的优点，可用来有效回收废水中的微量金。然而亲和膜的有效利用率低，已成为制约该项技术推广应用的主要瓶颈。本研究为解决这一难题开展了以下工作。.首先，通过两步法将硫脲接枝在PVDF分子链上，制备出对Au (III) 具有亲和力的改性树脂（Th-PVDF树脂）。仪器表征结果表明Th-PVDF树脂的硫脲接枝率最高为36.3%。通过非溶剂致相分离法制备出具有对称性海绵状网络孔的Th-PVDF膜，其膜厚为310μm，平均孔径为0.81-0.88μm，孔隙率为49-54%。通过两步凝胶浴法，提高了膜的孔径分布均一性。吸附动力学以及吸附等温线均不受膜孔径分布影响，分别符合拟二阶吸附动力学与Langmuir吸附等温式。.其次，制备了Th-PVDF膜色谱并进行吸附过滤实验。Th-PVDF膜色谱可有效截留水中的低浓度Au (III)，穿透位点、膜床利用率δ随膜层数的增加而增多，但膜有效吸附容量qb随膜层增加而轻微下降。在Au (III)与Ni (II)、Co (II)、Fe (III)、Zn (II)、Pb (II)以及Cu (II)这六种金属离子共存时，该膜色谱在模拟废水以及实际废水的吸附过滤中均展现了优异的选择性分离能力。0.15 mol/L硫脲+1.0 mol/L盐酸的混合溶液可对过滤实际废水后的膜色谱进行再生，洗脱效率为92.6%，且其分离性能在四次“过滤—再生”循环内均未出现明显下降。通过XPS研究该膜对Au (III)的吸附机理，结果显示一部分Au (III)是以金的氯化物形式与N、S以及O等原子相结合而被截留；另一部分Au (III)则被还原成Au (0)而被膜截留，并通过SEM观察到了膜上截留的金颗粒。.最后，基于膜色谱分离的特点，构建了兼顾流体传质以及膜孔径分布的新数学模型。该模型中的所有参数均可以通过实验获得，且通过本论文中的实验数据对其进行验证显示，该模型对膜色谱的穿透曲线具有很好的拟合及预测能力。尤其是在穿透点附近，该模型预测结果与实验结果吻合良好。