Water Research 37 (2003) 4135–4142 Sorption kinetics of Fe(II), Zn(II), Co(II), Ni(II), Cd(II), and Fe(II)/Me(II) onto hematite Byong-Hun Jeon*, Brian A. Dempsey, William D. Burgos, Richard A. Royer Department of Civil and Environmental Engineering, The Pennsylvania State University, 212 Sackett Building, University Park, PA 16802-2450, USA Received 5 August 2002; received in revised form 5 June 2003; accepted 12 June 2003 Abstract ThereactionsofFe(II)andotherdivalentmetalionsincludingZn,Co,Ni,andCdonhematitewerestudiedinsingle andcompetitivebinarysystemswithhighsorbate/sorbentratiosin10mMPIPES(pH6.8)solutionunderstrictanoxic conditions.AdsorbedMe(II)wasdefinedasextractableby0.5NHClwithin20h,andfixedMe(II)wasdefinedasthe additionalamountthatwasextractedby3.0NHClwithin7days.BinarysystemscontainedFe(II)plusasecondmetal ion. The extent of uptake of divalent metal ions by hematite was in order of FeXZn>CoXNi>Cd. For all metals tested,therewasaninstantaneousadsorptionfollowedbyarelativelyslowstagethatcontinuedforthenext1–5days. Thissequenceoccurredinbothsingleandbinarysystems,andcouldhavebeenduetoavarietyofsorptionsitetypesor due to slow conversion from outer- to inner-sphere surface complexes due to increasing surface charge. Sorption competitionwasobservedbetweenFe(II)andtheothermetalions.ThedisplacementofFe(II)byMe(II)wasinorder of NiBZn>Cd, and the displacement of Me(II) by Fe(II) was in order of Cd>ZnBNi>Co. Fixed Fe(II) was in order of Fe+Co (20%)>Fe+Cd (6%)>FeBZn (4%)>FeBNi (4%) after 30 days. There was no fixation for the other metals in single or binary systems. r 2003 Elsevier Ltd. All rights reserved. Keywords: Divalent metal ions; Hematite; Slow sorption kinetics; Sorption competition 1. Introduction Fe(III) oxide and Fe(II) are ubiquitous in anoxic environmentsandtheyaffectthedistribution,transport, and biogeochemistry of chemical contaminants by sorptionontoFe(III)oxidesandbycontrolofoxidation and reduction reactions [1–5]. Numerous studies have demonstrated that Fe(II) can be produced by chemical [1] and biological processes [6–8] through reductive dissolution of Fe(III) oxides in various natural and laboratory environments. The released Fe(II) can be precipitated [7,8] and/or can compete with the other contaminants for the solid-phase sorption sites and for dissolved complexing agents [1,9]. Contaminants also affect the reactions of Fe(III) oxides and Fe(II). Cu(II) inhibited the bioreduction ofFe(III)oxide [10].ThesorptionofFe(II)ontoFe(III) oxides adversely affected the bioreduction of Fe(III) oxides [9]. Ni(II) coprecipitated into hydrous Fe(III) oxide (HFO) inhibited HFO bioreduction through an undefined chemical mechanism [6]. Zn(II) can inhibit bioreduction of hematite [11]. The competition among divalent metal ions for sorption on Fe(III) oxides has been studied by means of sorption edge, sorption isotherm or potentiometric titration experiments [12–15]. However, only a few studies investigated the competition between Fe(II) and other divalent metal ions and conflicting observa- tions were reported [16–18]. There are difficulties in interpreting competitive sorption edge experiments due ARTICLE IN PRESS *Corresponding author. Department of Biological Sciences, University of Alabama, A122 Bevill Building, 7th Avenue, Tuscaloosa,AL35487-0206,USA.Tel.:+1-205-348-1803;fax: +1-205-348-1403. E-mail address: bxj114@bama.ua.edu (B.-H. Jeon). 0043-1354/$-see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0043-1354(03)00342-7