Solidification Versus Adsorption for Immobilization of Pollutants in Geopolymeric Materials: A Review

Geopolymer (GP) is a class of three-dimensional aluminosilicate binder, which is superior to Portland cement materials in acid, heat and fire resistance. GP is produced by reacting an aluminosilicate source (metakaolin, fly ash or waste) with an alkali metal hydroxide or silicate. The aim of the present work is to review the latest developments in three lines of research that deal with application of GP in treatment of pollutants. The first “intra-solidification” that involves mixing real waste (containing heavy metal pollutants) with the GP precursors to obtain a high mechanical strength material. The second type of solidification is “inter-solidification” that involves incorporation of heavy metals solutions (as simulation of polluted water) during geopolymerization reaction. The third line of research “adsorption” involves agitating GP with heavy metals solutions and studying the ability of GP to remove heavy metals from water. These techniques will be investigated regarding efficiency and mechanism of immobilization, cost and environmental impact. GPs are strong low-cost adsorbents for heavy metals. In intra-solidification, despite the high mechanical strength of the produced GP-containing waste, geopolymerization reduces effectively the leaching of heavy metals. The reverse was observed in the case of inter-solidification which presents a greater challenge than intra-solidification