Chemical stability of Laponite in aqueous media

In this work the stability of Laponite against dissolution in its aqueous dispersions is investigated as a function of initial pH of water before mixing Laponite, and concentration of Laponite. Dissolution of Laponite is quantified in terms of the concentration of leached magnesium in the dispersions. Interestingly the solvent pH is observed to play no role in the dissolution of Laponite in dispersion over the explored range of 3 to 10. Furthermore, contrary to the usual belief that Laponite dissolves when the pH of aqueous dispersion decreases below 9, the dissolution of the same is observed even though dispersion pH is above 10 for low concentrations of Laponite (1 and 1.7 mass%). On the other hand, for dispersions having a high concentration of Laponite (2.8 mass%) and pH in the similar range (> 10) no dissolution is observed. Measurement of ionic conductivity of dispersion shows that the concentration of sodium ions in dispersion increases with the concentration of Laponite, which appears to have a role in preventing the dissolution of Laponite.