The Effect of Si/Al Ratios on the Properties of Geopolymers Prepared from Water Treatment Residue (WTR) Containing Heavy Metals

The aim of this research was to develop a geopolymer cementing material using water treatment residue (WTR )as the aluminosilicate source, with the addition of rice husk ash (BHA) as a source of crystalline silica, and a heavy metal added to the binders (WTR and NaOH )at 30, 50 and 70% by weight. The geopolymers were prepared by NaOH activation of WTR and BHA mixtures of eight different compositions, followed by curing at ambient temperature. The compressive strengths of the geopolymers were determined up to 60 days. The samples cured for 28 days were examined by microstructure. The samples prepared with a Si/Al ratio of 2.00 without heavy metal and with 30% heavy metal were found to produce the greatest strength at all curing times. After 28 days, all samples had gained 30% greater strength than the 7 day-samples. XRD revealed the presence of sodium aluminum silicate hydrate, and sodium zinc silicate, sodium iron silicate oxide and sodium aluminum hydroxide chromium oxide in geopolymer matrices, while an FTIR vibration band related to the geopolymer product shifted to 1002 cm-1. WTR and BHA are useful waste materials for geopolymer synthesis and produce useful products for applications such as heavy metal immobilization.