Cooperative Effects of Dodecylpoly(oxyethylene) Sulfate Ion and Divalent Metal Ion on ζ Potentials of Inorganic Solid Particles in Electrolyte Solutions

Abstract

Relation between C potentials iron 010 oxide (Fe2O^2-) or titanium oxide (TiO₂) and calcium ion or magnesium ion concentration in the solutions, containing sodium dodecylpoly(oxyethylene) sulfate (R120(E0)SO₃Na, where n is 1 or 3), sodium hydroxide, sodium chloride and calcium chloride or magnesium chloride was studied, in order to examine the previously predicted dependence of the Stern charge densities (a) on calcium ion concentration. These experiments were conducted under the same conditions as the previous one as follows; in the presence of definite concentration of R, 20(E0)O^2-1a and 0.3mmolg sodium hydroxide at ionic strength of O.01 and 25°
C. With the increase in the ratio of divalent metal ion concentration to total cation concentration (Cmo. /(Cm++ C. ), where Me- indicates CO+ or Mg2+), C potentials of Fe2O^2- or TiO₂ increased sharply up to a maximum value and then decreased, in the presence of sufficient amounts of R12O(E0)O₃Na. On the other hand, C potentials decreased exponentially in the absence of R120(E0)O₃Na. The cooperative effect of R120(E0), SO^2-la and divalent metal ion on C potential of solid particles in miscellaneous electrolyte solutions was shown in Figs.1 to 4. The double layer charge density (id) was calculated by the equation 3 in which C potential was used instead of the Stern potential (To). Some of the dependences of d on calcium ion concentrations were shown as the solid lines in Figs.5 and 6, together with the dotted lines which were referred to a. The ad depended on (Coo++ C. ) in the same manner as a did. These facts support the previous prediction that the mutual charge cancellation of R120. (E0)SO^2-1a and divalent metal ion on solid particle might cause the characteristic dependence of surface charge density on divalent metal ion concentration in the presence of definite concentration of R120(E0)O₃Na.