聚丙烯酸对自然水体生物膜吸附镉的影响

选择聚丙烯酸(PAA)为水中溶解态高分子天然有机质的代表, 研究了PAA对自然水体生物膜吸附重金属Cd的影响, 包括不同浓度的PAA对吸附的影响, PAA对特定pH下吸附等温线的影响以及不同pH下按不同顺序添加PAA时对吸附的影响. 研究结果表明, PAA的存在一般会降低生物膜对Cd的吸附, 其影响程度与PAA的浓度、 溶液pH、 吸附顺序及生物膜厚度等有关. PAA与Cd的浓度比越高, 其对吸附的影响越显著. 吸附溶液pH越高, PAA的影响越显著. 吸附顺序对吸附的影响在pH较低时不明显, 当pH较高时, 先加PAA后加Cd及两者同时吸附时对吸附的降低作用接近且较大, 先加Cd后加PAA时对吸附的降低作用相对较小. 生物膜较薄时PAA的影响更显著. PAA对生物膜吸附Cd的影响主要由PAA与生物膜之间对Cd的竞争以及三元表面配合物的生成与吸附2种因素共同决定. 高pH会促进PAA与Cd的配合而不利于带负电的配合物在生物膜上的吸附.

Effect of Polyacrylic Acid on the Adsorption of Cd onto Natural Biofilms

Dissolved natural organic matters(DNOM) usually have significant effects on the behavior of trace metals in aquatic environment.As an important solid material existing wildly in natural waters,natural biofilm also affect the behavior of trace metals remarkably,by the action of adsorption.In this study,polyacrylic acid(PAA) was selected as a surrogate for macromolecular DNOM to investigate the effect of DNOM on the adsorption of Cd by natural biofilms.Cd adsorption to natural biofilms without PAA and with different concentrations of PAA was carried out.The influences of solution pH value and component addition sequence on the effect of PAA were also measured.The presence of PAA generally decreased the adsorption of Cd,and the effect was influenced by the concentration of PAA,the solution pH value,the adsorption sequence and the thickness of the biofilms.Higher concentration ratio of PAA to Cd or higher pH value usually resulted in more significant decreasing effect on adsorption.The influence of adsorption sequence on the effect of PAA was insignificant in lower pH range,while in higher pH range,the decreasing effect of PAA on adsorption was more considerable for simultaneous adsorption and PAA first adsorption,than for Cd first adsorption.As to the thickness of biofilms,the effect of PAA was usually significant for thinner biofilms.The role of PAA on adsorption could be attributed to the competition between PAA and the biofilms for available Cd,and to the formation and adsorption of ternary surface complexes.Higher pH value facilitated the complexation between PAA and Cd,and impeded the adsorption of negatively charged complexes on the biofilms.