Abstract:

The transfer process of polychlorinated biphenyls (PCBs) to the surface of iron-based materials (i.e., mass transfer process) is a key step in the degradation of PCBs by iron-based materials. Humic acid (HA) and surfactant Tween-80 have been widely concerned for their ability to affect the degradation of PCBs by changing the mass transfer process, while there are few reports on the differential mechanisms of these two factors. In this study, the micro-scale Ni-Fe particles were employed to explore the effects of HA (10, 50 and 100 mg∙L^-1) and Tween-80 [1, 25 and 500 critical micelle concentration (CMC)] on the degradation of 2, 2′, 4, 4′, 5-pentachlorobiphenyl (PCB-99) by Ni/Fe in aqueous solution. The solid-liquid distributions of HA, Tween-80 and PCB-99 were analyzed to understand the differential mechanisms regulating the mass transfer process. The results showed that both HA and Tween-80 inhibited the degradation of PCB-99 by Ni/Fe, and both of the degradation processes conformed to the pseudo-second-order kinetic model. The higher concentration of HA or Tween-80 resulted in more significant inhibition and lower degradation rate of PCB-99. The HA layer on the Ni/Fe surface covered the reactive sites and prevented the contact of PCB-99 with Ni/Fe, resulting in 49.48% of PCB-99 remaining on the solid phase without being degraded. Tween-80 mainly affected the mass transfer process via enhancing the mobility and solubilization of PCB-99. The Tween-80 adsorbed on the Ni/Fe surface reduced the interfacial tension, increased the mobility of PCB-99, and led to a decrease in mass transfer efficiency. When the concentration of Tween-80 in the liquid phase exceeds the CMC value, the formed micelles trapped 56.01% of PCB-99 in the hydrophobic core, making it difficult to contact with Ni/Fe. This study provides a scientific basis for the degradation of persistent organohalogenated hydrocarbons.

Key words: nickel-iron particles (Ni/Fe), polychlorinated biphenyls (PCBs), surfactant (Tween-80), humic acid (HA), mass transfer process

摘要：

多氯联苯（PCBs）向铁基材料表面传输的过程（即传质过程）是铁基材料降解PCBs的关键途径。腐殖酸（HA）和表面活性剂吐温-80（Tween-80）能够通过改变传质过程来影响PCBs的降解而被广泛关注,但关于两者改变传质过程差异性及其机制的报道较少。通过制备微米镍铁（Ni/Fe）颗粒,探究不同质量浓度HA（10、50、100 mg∙L^-1）和Tween-80[1、25、500倍临界胶束浓度 (CMC)]对Ni/Fe降解水溶液中2, 2′, 4′, 4′, 5-五氯联苯（PCB-99）的影响,通过体系中PCB-99、HA和Tween-80的固液分配来解析两者改变传质过程的机制与差异。结果表明,HA和Tween-80均抑制Ni/Fe降解PCB-99,降解过程符合准二级动力学模型,HA或Tween-80的质量浓度越高,抑制作用越显著,PCB-99的降解率越低。其中,HA吸附在Ni/Fe表面形成HA层,覆盖反应位点,阻碍PCB-99和水与Ni/Fe接触,导致留在固相上而未被降解的PCB-99占初始加入量的49.48%。相反,Tween-80主要通过增流和增溶作用影响传质过程,Tween-80吸附在Ni/Fe表面,能够降低界面张力,增加PCB-99的流动性,导致传质效率下降;当液相中的Tween-80质量浓度超过CMC时,PCB-99被困在胶束形成的疏水核中,占PCB-99初始加入量的56.01%,难以接触Ni/Fe。该研究可为持久性有机卤代烃的降解提供科学依据。

关键词: 镍铁颗粒, 多氯联苯, 表面活性剂, 腐殖酸, 传质过程