Colloids and Surfaces A: Physicochem. Eng. Aspects 339 (2009) 192–198 Contents lists available at ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa Improved coagulation performance using preformed polymeric iron chloride (PICl) Ta-Kang Liu a,∗ , Ching-Ju Monica Chin b a Institute of Ocean Technology and Marine Affairs, National Cheng Kung University, 1 University Road, Tainan City 70101, Taiwan b Graduate Institute of Environmental Engineering, National Central University, 300 Jhongda Rd., Jhongli City 32001, Taiwan article info Article history: Received 1 August 2008 Received in revised form 21 January 2009 Accepted 16 February 2009 Available online 25 February 2009 Keywords: Coagulation Polymeric iron chloride (PICl) Restabilization Charge reversal abstract Jar tests were conducted using synthetic waters containing model colloids and organics to evaluate the coagulation performance of simple FeCl 3 and polymeric iron chloride (PICl) having various polymer yield. Coagulation of synthetic model waters with PICls of different hydrolysis ratios was compared to simple ferric chloride under varying conditions of pH and model water concentrations. The use of PICls seemed to produce similar reduction in turbidity and TOC when compared with using FeCl 3 as a coagulant under typical range for coagulation; however, treatable region was broadened to lower pHs for coagulation of both model waters. By eliminating the region of restabilization of turbidity at lower pHs, an additional region for coagulation using PICls at pH 5–6 was observed. A conceptual surface charge distribution when using different coagulants was established to explain the restablization observed in this study. The different coagulation behaviors of PICls when compared to simple FeCl 3 are probably due to their larger sizes and bearing lower charge density. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Aluminum and iron salts are commonly used as coagulants in the treatment of water for public supply. Inexpensive compared to organic polymeric coagulants, these metal salts are used in large quantity as the primary coagulants in drinking water treatment processes. Coagulation includes all the reactions such as in situ coagulant formation, chemical particle destabilization and physical interparticle contacts while flocculation is a transport phenomenon that involves particle collisions [1]. Both physical transport and chemical destabilization are important in coagulation and floccula- tion processes; however, physics controls particle aggregation only when the chemistry is favorable [2]. A major drawback of using these metal-based coagulants directly is that the actual coagulant species are formed in situ by dilution under the prevailing raw water conditions and in competition with other reaction [3]. There- fore, it is crucial to control the chemistry of the coagulant in order to improve their effectiveness and optimize the coagulation and flocculation. Partial neutralization of metal salts prior to their application is a technique that can ensure optimum solution conditions and avoid the interference of competitive conditions. By partially neutraliz- ing the metal salts, the desirable highly charged cationic coagulant species can be obtained prior to their application. Polyaluminum ∗ Corresponding author. Tel.: +886 6 2757575x31146; fax: +886 6 2753364. E-mail address: tkliu@mail.ncku.edu.tw (T.-K. Liu). chloride (PACl) has been developed by partially neutralizing AlCl 3 and its use in practice has been continuously spreading [4,5]. It is believed that most of these commercial PACl coagulants contain substantial amount of tridecamer Al 13 [6]. Coagulant species pre- pared by partially neutralizing the metal salts can be more effective due to their larger size and bearing higher positive charges, which makes them more strongly adsorbed on negatively charged sur- face of natural colloids. In connection with interests in improving the coagulation processes, numerous researchers have applied PACl for water and wastewater treatment and a considerable amount of literatures have been generated since the 1980s. PACl coagulants were found to be superior to simple alum in their wider operat- ing pH range, lower dose required and less sludge produced, better performance in colder conditions, more effectively precipitating organic substances, and lower residual aluminum in treated water [7–11]. However, Shi et al. [12] found that PACl was less effective than conventional aluminum salt in removing humic acid with large molecular and hydrophobic properties, possibly due to the decomposition of Al 13 during the coagulation processes. In recent years, public concerns about the potential connection between the residual aluminum in drinking water and the sus- pected adverse health effects, e.g., Alzheimer’s disease, have been brought to intense discussion [13,14]. As a result, the use of iron- based coagulants has gradually gained in popularity. The polymeric iron chloride (PICl), however, is still in a developing stage and its application is limited in contrast to the successful commercializa- tion of PACl coagulants to improve coagulation processes [15]. One of the main problems seems to be the low polymer yield in the pre- 0927-7757/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2009.02.029