Maithreepala R A, Doong Ruey-An
Department of Atomic Science, National Tsing Hua University, Hsinchu 30013, Taiwan.
Environ Sci Technol. 2004 Jan 1;38(1):260-8. doi: 10.1021/es034428k.
The dechlorination of carbon tetrachloride (CT) by Fe(II) associated with goethite in the presence of transition metal ions was investigated. X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRPD) were used to characterize the chemical states and crystal phases of transition metals on solid phases, respectively. CT was dechlorinated to chloroform (CF) by 3 mM Fe(II) in 10 mM goethite (25.6 m2 L(-1)) suspensions. The dechlorination followed pseudo-first-order kinetics, and a rate constant (k(obs)) of 0.036 h(-1) was observed. Transition metal ions have different effects on CT dechlorination. The addition of Ni(II), Co(II), and Zn(II) lowered the k(obs) for CT dechlorination, whereas the amendment of 0.5 mM Cu(II) into the Fe(II)-Fe(III) system significantly enhanced the efficiency and the rate of CT dechlorination. The k(obs) for CT dechlorination with 0.5 mM Cu(II) was 1.175 h(-1), which was 33 times greater than that without Cu(II). Also, the dechlorination of CT by surface-bound iron species is pH-dependent, and the rate constants increased from 0.008 h(-1) at pH 4.0 to 1.175 h(-1) at pH 7.0. When the solution contained Cu(II) and Fe(II) without goethite, a reddish-yellow precipitate was formed, and the concentration of Fe(ll) decreased with the increase in Cu(II) concentration. XPS and XRPD analyses suggested the possible presence of Cu2O and ferrihydrite in the precipitate. Small amounts of aqueous Cu(I) were also detected, reflecting the fact that Cu(II) was reduced to Cu(I) by Fe(II). A linear relationship between k(obs) for CT dechlorination and the concentration of Cu(II) was observed when the amended Cu(II) concentration was lower than 0.5 mM. Moreover, the k(obs) for CT dechlorination was dependent on the Fe(II) concentration in the 0.5 mM Cu(II)-amended goethite system and followed a Langmuir-Hinshelwood relationship. These results clearly indicate that Fe(II) serves as the bulk reductant to reduce both CT and Cu(II). The resulting Cull) can further act as a catalyst to enhance the dechlorination rate of chlorinated hydrocarbons in iron-reducing environments.
研究了在过渡金属离子存在下，针铁矿负载的Fe(II)对四氯化碳（CT）的脱氯作用。分别采用X射线光电子能谱（XPS）和X射线粉末衍射（XRPD）对固相中过渡金属的化学状态和晶相进行了表征。在10 mM针铁矿（25.6 m2 L(-1)）悬浮液中，3 mM Fe(II)可将CT脱氯为氯仿（CF）。脱氯反应符合准一级动力学，观察到的速率常数（k(obs)）为0.036 h(-1)。过渡金属离子对CT脱氯有不同影响。添加Ni(II)、Co(II)和Zn(II)会降低CT脱氯的k(obs)，而在Fe(II)-Fe(III)体系中加入0.5 mM Cu(II)可显著提高CT脱氯的效率和速率。0.5 mM Cu(II)存在时CT脱氯的k(obs)为1.175 h(-1)，比无Cu(II)时高33倍。此外，表面结合铁物种对CT的脱氯作用与pH有关，速率常数从pH 4.0时的0.008 h(-1)增加到pH 7.0时的1.175 h(-1)。当溶液中含有Cu(II)和Fe(II)但无针铁矿时，会形成红黄色沉淀，且Fe(II)浓度随Cu(II)浓度增加而降低。XPS和XRPD分析表明沉淀中可能存在Cu2O和水铁矿。还检测到少量水相Cu(I)，这反映了Cu(II)被Fe(II)还原为Cu(I)的事实。当添加的Cu(II)浓度低于0.5 mM时，观察到CT脱氯的k(obs)与Cu(II)浓度之间呈线性关系。此外，在0.5 mM Cu(II)改性的针铁矿体系中，CT脱氯的k(obs)取决于Fe(II)浓度，并符合Langmuir-Hinshelwood关系。这些结果清楚地表明，Fe(II)作为主要还原剂还原CT和Cu(II)。生成的Cu(I)可进一步作为催化剂提高铁还原环境中氯代烃的脱氯速率。
