ESTER PHOSPHATE ADSORPTION ON CALCIUM-CAR BONATE

The properties of hexaethoxy esther phosphate undecane (H23C11-(O-CH2- CH2)(6)-O-PO3H2) both in solution and at the solid/liquid interface ha ve been studied. Interactions between calcium and surfactant ions in s olution have been established by using conductivity measurements of aq ueous solutions of calcium chloride, where, depending on conditions, a complex, (ROPO3H)(2)Ca, ora precipitate, ROPO3Ca, can be formed. In o rder to understand the phenomena that occur during the adsorption of h exa ethoxy esther phosphate undecane (H23C11-(O-CH2-CH2)(6)-O-PO3H2) o n calcite, the adsorption isotherm and the electrophoretic mobility ha ve been determined. There are two clear steps on the adsorption isothe rm. The first, due to the direct interaction between the Ca2+ calcite ions and ROPO32- surfactant ions, is a real adsorption phenomenon; the second is due to the precipitation in solution of these ions which al so leads to the abstraction of the surfactant from the solution. The e volution of the electrophoretic mobility of calcite particules with co verage is in agreement with such a mechanism.