Electrokinetic properties of kaolinite in mono- and multivalent electrolyte solutions

Zeta potential, known as the electrical potential at the shear plane, ζ, is one of the important electrokinetic properties of clay minerals. For many applications, the sign and the magnitude of the ζ potential is necessary to be known. For clay soils, it is usually negative. In this study, the electrokinetic properties of kaolinite have been investigated using the microelectrophoresis technique as a function of solid-liquid ratio, pH and type and concentration of electrolyte. The electrokinetic properties of kaolinite suspensions have been determined in aqueous solutions of mono-, di-, and trivalent salts such as NaCl, KCl, LiCl, NaNO3, NaCH3COO, MgCl2, CaCl2, BaCl2, Na2CO3, Na2SO4, AlCl3, FeCl3, Na3PO4 and divalent heavy metal salts such as CoCl2, CuCl2 and Pb(NO3)2. Furthermore, systematic zeta potential experiments have been performed to determine the isoelectric point (iep) and potential determining ions (pdi). From the experimental results, (i) the zeta potential of kaolinite is not significantly affected by the solid concentration; (ii) pH strongly altered the zeta potential of kaolinite; (iii) kaolinite has an isoelectric point at about pH 2.35; (iv) monovalent cations and anions, and di- and trivalent anions were indifferent electrolytes for kaolinite whereas MgCl2, CaCl2, BaCl2, CoCl2, CuCl2, Pb(NO3)2, AlCl3 and FeCl3 changed the interface charge from negative to positive.