Effect of silicate activator pH on the leaching and material characteristics of waste-based inorganic polymers

An increasing demand for utilization of large scale industrial wastes as added-value products is projecting geopolymer technology to the forefront of solidification/ stabilization applications over and above its potential as a ‘green’ alternative to concrete. The present work examines the effect of alkali metal silicate precursor solutions on geopolymerization, in terms of its initial pH-control, on the efficiency of heavy metal (Pb and Cu) containment in geopolymers. The effect of the activator and pH on the source materials was investigated through a variety of dissolution experiments. The immobilization efficiency was assessed through TCLP analyses. By means of compressive strength analyses it was possible to correlate the effects of pH, alkali metal silicate and variable calcium sources with the physical and chemical characteristics of the final product and to postulate reaction mechanisms. The greatest compressive strength was attained utilizing KOH/K-Silicate and the most efficient immobilization of Pb was attained utilizing NaOH/Na-Silicate. Both these maxima occurred at high pH (pH=14).