Mechanism of alkali release from feldspar in alkaline solution

Alkali releasing from two kinds of alkali-bearing feldspars were researched by dealing with alkaline solutions at 150°C. ²⁹Si MAS NMR analyzed the mechanism of alkali release from these feldspars in alkaline solution. The results showed that two kinds of alkaline feldspars obtained the maximum alkali contributions in solution saturated by calcium hydroxide with an excess of solid calcium hydroxide, when increasing the alkali content in this solution, the amount of alkali release from feldspar was reduced largely. The mechanism of alkali release from alkaline feldspar to solution was the result of ion exchange between feldspar and Ca²⁺ ions in solution. These findings lend further emphasis to the likely importance of alkali release in many practical AAR problems and direct the course of further study on this question.