Alkali Metals Ion Exchange on Muscovite Mica

The lithium surface ions of a muscovite, which was partially delaminated with a hot saturated lithium nitrate solution, exchange readily with sodium, potassium, rubidium, and cesium ions. The remaining potassium ions in the interlayers of the muscovite do not exchange at ambient conditions. The surface ion exchange is quite fast but can be followed by measuring the change in conductivity of the reaction mixture. In dilute systems, an initial drop in conductivity due to the exchange of the alkali metal ions with Li+ was observed, which was followed by a slow increase over a long period of time. That increase in conductivity is attributed to the formation of alkali bicarbonates due to the CO2 omnipresent in water. The surface Li+ was exchanged almost quantitatively by K+, Rb+, or Cs+ until a saturation value was nearly reached, while the Li+/Na+ exchange was less quantitative. The equilibrium constants (K) of these reactions as well as the ion exchange capacity were calculated by nonlinear least-squares fits. For the Na+/Li+ exchange K was found to be 4, while those of the K+, Rb+, and Cs+ exchange were too high for an accurate determination. The affinity of the alkali metal ions to muscovite decreased in the order K+, Rb+, Cs+ > Na+ > Li+. Copyright 1999 Academic Press.