Aqueous Leachability of Geopolymers Containing Hazardous Species

Geopolymers made from metakaolin by activating using a commercial sodium silicate solution and having Na/Al similar to 1 and Si/Al similar to 2 molar ratios were used to immobilize Ag, Cd, Cr and Ba. The geopolymers were cured at 60(0)C for 24 hours and subjected to the toxicity characterisation leaching procedure (TCLP) after 7 days. The preliminary investigation showed 4.6 mass% Ba added as the hydroxide or nitrate and I mass% Cr3+ added as the nitrate passed the TCLP limit for landfills in the USA. The samples with 1.0 mass% of Cd and Ag (both added as nitrates) and Cr (added as the dichromate) failed the test.