The effects of electrolyte concentration, ion species and pH on the zeta potential and electrokinetic charge density of montmorillonite

Abstract

In this study, the influence of pH, electrolyte concentration and type of ionic species (such as LiCl, NaCl, KCl, RbCl, CsCl, CaCl2, AlCl3) on the electrokinetic properties (zeta potential and electrokinetic charge density) of montmorillonite has been quantified. The zeta potential of montmorillonite particles did not change significantly with change in pH. The valencies of the ions have proven to have a great influence on the electrokinetic behaviour of the suspension. There is a gradual decrease in the zeta potential (from —24 mV to —12 mV) with increase in monovalent electrolyte concentration (from 10-4 M to 10-1 M). At any monovalent electrolyte concentration, the magnitude of the zeta potential increased with the electrolytes in the order Li+ > Na+ > K+ > Rb+ > Cs+. The zeta potential of the montmorillonite minerals in CaCl2 solutions illustrated the same behaviour as the monovalent cations. Less negative values were obtained for the CaCl2 electrolyte (∼–10 mV) due to the greater valence of the ions. A sign reversal was observed at an AlCl3 concentration of 5 x 10-4 M, and, at greater concentrations, zeta potential values had a positive sign (∼20 mV).The electrokinetic charge density of montmorillonite showed similar trends of variation in mono and divalent electrolyte solutions. Up to concentrations of ∼10-3 M, it remained practically constant at ∼0.5 x 10-3Cm-2, while for greater electrolyte concentrations the negative charge produced more negative values (–16 x 10-3Cm-2). The electrokinetic charge density of montmorillonite particles was constant at low AlCl3 concentrations, but at certain concentrations it increased rapidly and changed sign to positive.

Cation exchange interaction between antibiotic ciprofloxacin and montmorillonite

“…4). The surface charge of montmorillonite remains negative over the entire range of pH in this study [31]; thus, the pH influence on the adsorption level is expected to be mainly controlled by the speciation of CIP molecules. In acidic to neutral conditions, although the ratio of zwitterion/cation form increases gradually with pH, the positive charge of the amine group of zwitterionic CIP may still contribute to the adsorption interaction.…”

Effect of total organic carbon content and structure on the electrokinetic behavior of organoclay suspensions

“…Previous work has quantified either the electrophoretic mobility or the zeta potential of montmorillonite in NaCl solutions, with measured values of f ranging from À60 mV to À30 mV [4][5][6][7]. The reported differences may be attributed to variation in parameters such as the degree of isomorphic substitution of the montmorillonite or concentration of the background solutions.…”

“…The reported differences may be attributed to variation in parameters such as the degree of isomorphic substitution of the montmorillonite or concentration of the background solutions. Additionally, when the bulk solution background electrolyte was changed to a different inorganic cation, the measured zeta potential was altered in part according to the affinity of the clay for the inorganic cation [6][7][8][9][10][11][12][13][14][15].…”

Mitigating Fish-Killing Prymnesium parvum Algal Blooms in Aquaculture Ponds with Clay: The Importance of pH and Clay Type

“…Deprotonation of edge sites with increasing pH gives rise to a more negative zeta potential of clays in water [39]. However, the presence of multiple charged cations of alkali earth and/or heavy metals can result in the opposite trend (in pH ranging from 7 to 10), if such cations are present either in the dispersant or on the clay surface [34,35,39]. The reason for this behavior is increased particle aggregation due to the surface coating of clay particles with insoluble carbonates at higher pH.…”

“…Valuable insight into the pH dependence of the adsorption process can be gained through interpretation of zeta potential measurements, an approximation of surface charge that governs the behavior of clay particles in suspension [34][35][36]. Clay particles are inherently negatively charged due to isomorphic substitutions in their crystal lattice and exhibit pH-dependent charges on their edges [37,38].…”