Review The limitations of applying zero-valent iron technology in contaminants sequestration and the corresponding countermeasures: The development in zero-valent iron technology in the last two decades (1994e2014) Xiaohong Guan a , Yuankui Sun a , Hejie Qin a , Jinxiang Li a , Irene M.C. Lo b , Di He c , Haoran Dong d,* a State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China b Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China c School of Civil and Environmental Engineering, University of New South Wales, Sydney 2052, Australia d College of Environmental Science and Engineering, Key Laboratory of Environmental Biology and Pollution Control, Hunan University, Changsha, Hunan 410082, China article info Article history: Received 19 November 2014 Received in revised form 17 February 2015 Accepted 18 February 2015 Available online 28 February 2015 Keywords: Mass transfer Passive layer pH Iron oxides Corrosion products abstract Over the past 20 years, zero-valent iron (ZVI) has been extensively applied for the remediation/treatment of groundwater and wastewater contaminated with various organic and inorganic pollutants. Based on the intrinsic properties of ZVI and the re- actions that occur in the process of contaminants sequestration by ZVI, this review summarizes the limitations of ZVI technology and the countermeasures developed in the past two decades (1994e2014). The major limitations of ZVI include low reactivity due to its intrinsic passive layer, narrow working pH, reactivity loss with time due to the pre- cipitation of metal hydroxides and metal carbonates, low selectivity for the target contaminant especially under oxic conditions, limited efficacy for treatment of some refractory contaminants and passivity of ZVI arising from certain contaminants. The countermeasures can be divided into seven categories: pretreatment of pristine ZVI to remove passive layer, fabrication of nano-sized ZVI to increase the surface area, syn- thesis of ZVI-based bimetals taking advantage of the catalytic ability of the noble metal, employing physical methods to enhance the performance of ZVI, coupling ZVI with other adsorptive materials and chemically enhanced ZVI technology, as well as methods to recover the reactivity of aged ZVI. The key to improving the rate of contaminants removal by ZVI and broadening the applicable pH range is to enhance ZVI corrosion and to * Corresponding author. Tel.: þ86 0731 88822778. E-mail address: dongh@hnu.edu.cn (H. Dong). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/watres water research 75 (2015) 224 e248 http://dx.doi.org/10.1016/j.watres.2015.02.034 0043-1354/© 2015 Elsevier Ltd. All rights reserved.