Alkaline digestion of glass

A method for the alkaline digestion of soda-lime glass, the method comprising:

• a) forming a mixture of soda lime glass and a hydroxide solution, the mixture having at least 100 grams of glass per litre of H2O, the hydroxide solution having a concentration of 1M or greater to thereby form, by digesting the glass in the mixture at atmospheric pressure:
• an aqueous sodium silicate fraction having a silicate concentration of 50 g/L or greater (calculated as SiO2 equivalent) and a ratio of SiO2:M2O of at least 1, wherein M2O is an alkaline metal oxide;
• and
• a solid material comprising a calcium-silicate-hydrate;
• b) separating the aqueous sodium silicate fraction from the solid material comprising the calcium-silica-hydrate;
• c) treating the solid material comprising the calcium-silicate-hydrate with an acid to dissolve soluble metals from the calcium-silicate-hydrate, thereby producing a liquid phase and a solid phase, wherein the solid phase comprises SiO2;
• d) separating the solid phase comprising SiO2 in step (c) from the liquid phase;
• and
• e) returning at least some of the separated solid phase comprising SiO2 to step (a).