Journal of Colloid and Interface Science 328 (2008) 34–40 Contents lists available at ScienceDirect Journal of Colloid and Interface Science www.elsevier.com/locate/jcis Effect of the adsorption of lithium and borate species on the zeta potential of particles of cobalt ferrite, nickel ferrite, and magnetite M. Barale a,b,1 , G. Lefèvre a , F. Carrette b , H. Catalette b , M. Fédoroff a,∗ , G. Cote a a LECA, CNRS, ENSCP, Université Paris 6, 11 rue Pierre et Marie Curie, 75005 Paris, France b EDF R&D, Site des Renardières, 77818 Moret-sur-Loing, France article info abstract Article history: Received 2 July 2008 Accepted 3 September 2008 Available online 1 October 2008 Keywords: Colloids Deposition Sorption Adhesion Lithium Borate Nuclear reactors Zeta potential Magnetite Ferrites Zetametric measurements on suspensions of oxide particles (cobalt ferrite, nickel ferrite, and magnetite) representative of corrosion products from primary circuits of pressurized water reactors were performed at 25 and 70 ◦ C in the presence of lithium and borate species. No effect of lithium ions was observed. Borate species cause a decrease of the isoelectric point (IEP), attributed to the sorption of borate as a negative complex MOB(OH) − 3 . A predictive model based on thermodynamic calculations (2-pK and diffuse layer models) of the surface acidity constants from the data of acid–base titrations combined with an empirical relationship between the surface potential Ψ 0 and the ζ potential determined by zetametry was developed. A whole set of parameters valid at 25 ◦ C, in a range of ionic strength between 10 −4 and 10 −2 mol L −1 and in a range of pH between 4 and 8, was determined for this model. Increase of temperature to 70 ◦ C in the presence of borate results in a decrease of IEP for cobalt ferrite and an increase of the IEP for nickel ferrite.  2008 Elsevier Inc. All rights reserved. 1. Introduction Colloidal particles are present in many natural and industrial solutions. They can be generated by corrosion, due to the solubil- ity limits of corrosion products or detachment of small pieces of material [1]. Their formation and presence can disturb the func- tioning of industrial water circuits, essentially by their deposition in certain parts of the circuit. This is the case in the primary wa- ter circuits of pressurized water reactors (PWR). When colloidal particles pass through the reactor core, their constituents become radioactive by neutron activation [2]. They deposit and accumulate in certain parts of the circuit (zircalloy rods containing the nu- clear fuel, inconel, stainless steel tubes, etc.), leading to “hot” spots, which increase the dosimetry of workers during maintenance op- erations [3]. The deposits can also disturb the heat exchange be- tween the primary and the secondary circuits. In order to understand the behavior of colloidal particles, to predict their transport and deposition, and to lower their nega- tive effects, it is necessary to study their surface reactivity. Indeed, the adhesion reaction between particles and metallic surfaces can * Corresponding author. Fax: +33 (0)156813059. E-mail address: michel-fedoroff@enscp.fr (M. Fédoroff). 1 Present address: AREVA, 1 rue B. Marcet, BP 181, 71205 Le Creusot Cedex, France. be modeled by the DLVO theory [4] where the interaction is the sum of van der Waals and electrostatic forces. In systems involv- ing metallic oxides in water, electrostatic interactions are domi- nant [5], so that the knowledge of the surface potential related to the physico-chemical characteristics of the solutions (tempera- ture, pH, dissolved ions, etc.) is a key point in understanding and predicting their behavior (transport, adhesion of particles on walls, coagulation, etc.) [6,7]. The study of colloidal particles as they are in the primary circuit is a very difficult task due to the conditions of high temperature and pressure (about 320 ◦ C, 150 bars), but the analysis of water removed from the circuit showed that the main part of particles consists of magnetite and nickel or cobalt ferrite [8,9]. The compo- sition of water is another important parameter, since it can alter the surface potential of particles. The main components of pri- mary circuits of PWR are lithium and borate ions (about 1 mg L −1 and up to 1.8 gL −1 , respectively, but varying during the function- ing of the reactor). Although a shift of the isoelectric point (IEP) of hematite toward lower values has been observed in LiCl [10], Li + is generally considered as an inert ion (as K + or Na + ) toward metallic oxides [11]. Its presence at low concentrations should not modify the IEP of particles. An opposite behavior can be predicted for borate ions. Its sorption as a surface complex on metal oxides depends on pH, showing a variation with a maximum centered around pH 9 [12–19]. Infrared spectroscopy measurements have shown that inner-sphere complexes are formed on surfaces of iron 0021-9797/$ – see front matter  2008 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2008.09.007