Adsorption of copper (II) ions onto sepiolite and electrokinetic properties

We investigated the electrokinetic properties of sepiolite suspensions using the microelectrophoresis technique as a function of pH in the presence of various electrolytes such as, LiCl, NaCl, KCl, Cu(NO3)2, CaCl2, Pb(NO3)2, AlCl3 and Fe(NO3)3 and then, the adsorption of Cu(II) ion onto sepiolite from aqueous solutions as a function of pH, ionic strength and temperature. We found that (1) zeta potential of sepiolite suspensions increased with increasing ionic strength, (2) zeta potential values of sepiolite suspensions in different valence electrolyte solutions in the studied pH ranges increased with increase in electrolyte valence, (3) sepiolite had an isoelectrical point at pH 6.6, (4) the monovalent electrolytes showed similar behavior in the studied pH ranges but di- and trivalence electrolytes different behaviour, (5) Cu(II) ion adsorption increased with increase in pH and temperature, and decrease in ionic strength. Furthermore, experimental data were correlated reasonably well by the Langmuir adsorption isotherm. Adsorption enthalpy was calculated as 24 kJ/mol. The interaction between the sepiolite surface and Cu(II) ions was concluded to be a physical process.