【作者】 方瑶瑶；

【导师】 曾光明；

【作者基本信息】 湖南大学 ， 环境工程， 2009， 博士

【摘要】 胶团强化超滤是一种表面活性剂和超滤相结合的技术,在处理低浓度金属离子废水方面有很好的前景。本论文系统研究了阴离子表面活性剂胶团强化超滤去除水溶液中镉离子的各项控制参数。首先利用动态光散射法测定十二烷基硫酸钠胶团的直径大小、zeta电势等信息,研究不同情况下的胶团性质。在此基础上,研究了阴离子表面活性剂胶团强化超滤法对重金属离子的去除效率和渗透通量,考察了溶液浓度、pH值、跨膜压力、非离子表面活性剂、超滤膜种类、电解质等的影响,并采用核磁共振法对胶团强化超滤技术的机理进行了初步研究。动态光散射法研究发现表面活性剂浓度未达到临界胶团浓度CMC时就已经发现了大直径预胶团的存在。胶团的形成可能是一个多步骤过程,胶团直径随SDS浓度的增加而减小,小胶团可能比大胶团更容易排列整齐,使烷基链不易接触到水分子。胶团zeta电势随着Cd2+浓度的增加而增大,更多的Cd2+进入胶团stern层。非离子表面活性剂的加入使混合胶团直径减小,胶团表面电荷密度降低。当SDS浓度未达到其CMC 8 mmol/L就得到了较高的Cd2+截留率,这是由于浓差极化作用以及Cd2+的存在导致了CMC的降低。Cd2+浓度不变时,进料液SDS浓度增加使Cd2+截留率先快速增加后逐渐稳定。SDS浓度不变时,进料液Cd2+浓度增加使Cd2+截留率先轻微增加然后快速下降。当溶液pH值小于3时,大量H+与Cd2+在胶团表面竞争吸附使Cd2+截留率下降。渗透通量随跨膜压力的增加先直线增加后保持不变。非离子表面活性剂浓度的增加使Cd2+截留率先增大后减小,因为非离子表面活性剂的加入既生成了更多的胶团,又降低了混合胶团的反离子结合度。5种超滤膜的渗透通量从高到低依次为:P30 > P10 > C30 > P8 > C10。纤维素膜的标准通量比聚醚砜膜的标准通量要高得多。单位压力渗透通量随着跨膜压力的增大而减小。当S/M为10不变时,P8膜的Cd2+截留率随着跨膜压力和进料液浓度的增加而增大;但P10和P30膜的Cd2+截留率随跨膜压力的增加先增大后降低,进料液浓度越大,降低幅度越大。这是因为跨膜压力和进料液浓度的增加使得浓差极化作用增强,但各超滤膜对胶团的截留率不同。纤维素膜的Cd2+截留率不受跨膜压力增大的影响,而且C10和C30膜的Cd2+截留率比P10和P30膜低得多。这是因为,相同截留分子量的纤维素膜的纯水通量要小得多,浓差极化作用很弱。影响金属离子截留率的主要因素是价态,金属离子种类是次要因素。相同价态的金属离子与SDS胶团之间的静电吸附能力非常相近,Cd2+、Cu2+、Ni2+三种金属离子的截留率没有明显的区别。当NaCl浓度较高时,Na+和Cd2+之间存在着与胶团表面吸附的竞争,导致Cd2+截留率显著降低。Cd2+与溶液中的阴离子越容易形成络合物,则能与胶团结合的Cd2+越少。Cl-与Cd2+形成的络合物最稳定,SO42-次之,NO3-和CO32-最弱。核磁共振实验结果中的23Na+化学位移观测值随着Cd2+浓度的增加而增大,意味着越来越多Na+的从胶团结合态转变为自由态,Cd2+在胶团上的吸附能力更强。更多还原

【Abstract】 Micellar-enhanced ultrafiltration, a surfactant-based separation process, is promising in removing multivalent metal ions from aqueous solutions. The micellar-enhanced ultrafiltration (MEUF) of cadmium from aqueous solution using anionic surfactants sodium dodecylsulfate (SDS) was investigated systematically in this paper. The micelle size and zeta potential of SDS micelles were determined by dynamic light scattering measurements (DLS). The effects of feed concentration, pH, transmembrane pressure, nonionic surfactants, membranes and salts were studied. The preliminary investigation on the mechanism of micellar-enhanced ultrafiltration was also studied by nuclear magnetic resonance mensuration.According to the results of dynamic light scattering measurements, large premicelle was found in solution with SDS concentration lower than cmc. The formation process of micelle is thought to be a stepwise process. The micelle size decreased with the increasing surfactant concentration. The monomer molecules in the small micelle may be arranged more orderly than those in the large micelle. The zeta potential increased with cadmium concentration, more Cd2+ ions were bound with micelle. The micelle size also decreased with the increasing nonionic surfactant concentration, the surface charge density of micelles was reduced rapidly. The high Cd2+ rejection were obtained when the SDS concentration lower than the CMC of SDS (8 mmol/L). This may attribute to the concentration polarization and the decrease of cmc because of the addition of Cd2+. When the feed Cd2+ concentration were fixed, the Cd2+ retention increased with feed SDS concentration first, then attained a plateau at higher SDS concentration. The Cd2+ retention increased slightly with feed Cd2+ concentration first then decreased rapidly with the fixed feed SDS concentration. Large numbers of H+ compete with Cd2+ to bind with micelles. The Cd2+ retention would decline if the solution pH lowers than 3. The permeate flux increased with the transmembrane pressure then keep constant. The Cd2+ retention increased with the nonionic surfactants concentration then decreased. The addition of nonionic surfactants increased the number of micelles and also decreased the counter-ion binding degree of mixed micelle.The specific flux values of various membranes decreased in the order as follows: P30 > P10 > C30 > P8 > C10. The specific flux gradually decreased with the increase of transmembrane pressure. When the ratio of surfactant to metal concentration was fixed at 10, the Cd2+ retention of P8 membrane decreased with the increase of transmembrane pressure and feed concentration. However, the Cd2+ retentions of P10 and P30 membranes increased with transmembrane pressure firstly then decreased. The higher the feed solution, the more the Cd2+ retention decreased. The reason for this is the different effects of concentration polarization which enhanced by the increase of TMP and feed concentration. No significant influence of pressure on the rejection of Cd2+ was observed during the experiments with two cellulose membranes. The rejections of Cd2+ of cellulose membranes were much lower than those of polyethersulfone membranes. This can be attributed to the lower concentration polarization because of the much smaller water permeate flux of cellulose membranes.The rejections of metal ions strongly depend on the valence of metal ion. The electrostatic attraction of micelle and metal ions with the same valence were much closed. The rejection of Cd2+、Cu2+、Ni2+ were almost the same. The rejections of Cd2+ decreased rapidly with the NaCl concentration. This can be attributed to the competition of Na+ and Cd2+ for the binding with micelles. The stronger the complexation of Cd2+ and the anion in solution, the more the rejection of Cd2+ decreased. The complexation ability of anions decreased in the order as follows: Cl- > SO42- > NO3-≈CO32-.23Na+ magnetic resonance mensuration chemical shift increased with the Cd2+ concentration. It means that more Na+ change from the binding state to free state. The electrostatic attraction of Cd2+ and micelle were stronger.更多还原