Reappraisal review on geopolymer: A new era of aluminosilicate binder for metal immobilization

Geopolymers are the inorganic polymers containing aluminosilicate materials in their backbone and are produced from geopolymerization process at ambient or controlled temperature involving alkali activators and balanced proportion of solid silica/aluminium precursor materials. Geopolymeric binders have excellent surface morphology, mechanical strength, and building material properties depending on different origin of sources facilitated by hydrothermal synthesis and solidification/stabilization reactions of inorganic polymers. We present a systematic review of the literature published between 1991 and 2020 to critically analyze the structural chemistry, synthesis and environmental applications of geopolymers and have thoroughly discussed the relevant state-of-the art experimental results to have more insight on the metal immobilization potential of geopolymers. Our aim is also to critically assess the different isotherm and kinetic models to illustrate the different mechanisms for the effective waste management strategies of different geopolymer binders by spontaneous, endothermic and entropy driven thermodynamic metal entrapment process. Therefore, the present review bridges the knowledge gap to throw light on the source of various materials commonly applied to the material/bio based synthesis of geopolymer materials which have direct impact on the geopolymerization process. Such types of approaches trigger the environmentalists and policymakers in the development of a conceptual framework on green sustainable aluminosilicate based adsorbents, which facilitate better waste management by physical entrapment, chemical bonding and/or ligand exchange reactions.