In a geopolymer matrix prepared by mixing a metakaolinite precursor with a solution of potassium hydroxide and silicate, 1 wt% Ph as the nitrate has been immobilized. Under the United States Environmental Protection Agency test protocol the Ph release was less than 5 ppm, the acceptable limit for landfills in the U.S.A. Electron microscopy showed Ph was present in the major amorphous phase and a minor (similar to 1 vol%) Ca-rich potassium silicate phase. Heating cured samples to several hundred degrees Centigrade was not significantly advantageous for immobilizing Pb.