High-level arsenite removal from groundwater by zero-valent iron.
The objectives of this study were to conduct batch and column studies to (i) assess the effectiveness of zero-valent iron for arsenic remediation in groundwater, (ii) determine removal mechanisms of arsenic, and (iii) evaluate implications of these processes with regard to the stability of arsenic and long-term remedial performance of the permeable reactive barrier (PRB) technology. A high concentration arsenic solution (50 mg l(-1)) was prepared by using sodium arsenite (arsenic (III)) to simulate groundwater at a heavily contaminated Superfund site in the USA. Batch studies indicate that the removal of arsenic is a two-step reaction with fast initial disappearance of arsenite followed by a slow subsequent removal process. Flow-through columns were conducted at a flow rate of 17 ml h(-1) under reducing conditions for 6.6 mo. Kinetic analysis suggested that arsenic removal behaves as a zero-order reaction at high arsenic concentrations. Arsenic removal rate constants decreased with time and arsenic breakthrough was observed in the column study. Arsenic removal capacity of zero-valent iron was determined to be approximately 7.5 mg As/g Fe. Carbonate green rust was identified from the analysis of surface precipitates; arsenite uptake by green rust may be a major mechanism responsible for arsenic remediation by zero-valent iron. Analysis of HCl-extractable arsenic from iron samples indicated that approximately 28% of arsenic was in the form of arsenate suggesting that a surface oxidation process was involved in the arsenic removal with zero-valent iron.
Lien
Hsing-Lung
HL
Department of Civil and Environmental Engineering, National University of Kaohsiung, 700 Kaohsiung University Rd., Kaohsiung 811, Taiwan, ROC. lien.sam@nuk.edu.tw
Wilkin
Richard T
RT
D018053:Arsenites / Q000737:chemistry*; D019075:Electrophoresis, Capillary; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D014877:Water Pollution, Chemical / Q000517:prevention & control*; D014961:X-Ray Diffraction
D018053:Arsenites; D007501:Iron; C015001:arsenite