Influence of the Si/Al ratio in geopolymers on the stability against acidic attack and the immobilization of Pb2+ and Zn2+

Abstract

In this research article the influence of the Si/Al ratio in geopolymers was investigated. Samples with a ratio varying between 2.0 and 3.0 were prepared. Furthermore, the lead and zinc inclusion in the geopolymer matrix depending on the Si/Al ratio was analyzed. Therefore, water soluble Pb(NO3)2 and Zn(NO3)2 were added to the geopolymer in a 5% weight percentage. The geopolymers were examined using IR spectroscopy, XRD and SEM. Moreover, leaching experiments in 1M sulfuric acid and 3M hydrochloric acid were carried out in a static leaching method over a period of 28 days. The eluates were analyzed using ICP-OES and the residues of the geopolymers were again examined using the described analytical methods. The effectiveness of geopolymers immobilizing heavy metals is dependent on the Si/Al ratio. Moreover, the structural differences in these geopolymers were proven to influence the stability against acidic attack.