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

Abstract

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 GPcontaining 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.

Ironmaking and Steelmaking Slags as Sustainable Adsorbents for Industrial Effluents and Wastewater Treatment: A Critical Review of Properties, Performance, Challenges and Opportunities

“…To date, several studies have reported on the benefits of modification and/or activation treatment to increase the specific surface area and density of adsorption sites on the surfaces of the adsorbent particles [42,57,[59][60][61][62][63][64][65][66]. Other studies have also proposed the synthesis of functionalised adsorbents such as geopolymers [74,[118][119][120][121][122][123], permeable reactive barriers or slag filters [124][125][126][127][128][129][130][131][132], zeolites and zeolite precursors [133][134][135] and layered double-hydroxide-based adsorbents [133][134][135][136][137][138]. This section discusses in detail the opportunities to improve the adsorption capacity of slag-based adsorbents.…”

“…Alkali-activated slags, also known as geopolymers, are synthesised from the reaction of a solid aluminosilicate precursor under alkaline conditions to produce a product consisting of hydrous alkali-aluminosilicate and/or alkali-alkali-earth-aluminosilicate phases [74,[117][118][119][120][121][122][123]145]. Geopolymers are amorphous or partly crystalline materials composed of [SiO 4 ] 4− and [AlO 4 ] 5− 3D-tetrahedral structures linked randomly by covalently shared oxygen atoms [74,118,121,123,145]. The negative charge of the [AlO 5 ] 5− tetrahedron is balanced by exchangeable alkali and alkali-earth cations such as Na + , K + , Ba 2+ and Ca 2+ ions.…”

“…Thus, these slags typically contain significant amounts of silica, aluminosilicates and calcium-aluminosilicate phases, which makes them ideal precursors for the synthesis of low-cost, slag-based geopolymer adsorbents. To date, extensive studies have focused on evaluating the performance of geopolymerised slags as novel functionalized adsorbents and photocatalysts in the treatment of industrial effluents and wastewaters [74,117,[119][120][121][122][123]146,147].…”

Solidification of electroplating sludge with alkali-activated fly ash to prepare a non-burnt brick and its risk assessment

“…[15][16][17] In addition, geopolymers usually have lower CO 2 emission, lower-cost raw materials, simpler preparation process, more energy-saving ability, much better chemical corrosion resistance and more effective immobilization of toxic HMs when compared with Ordinary Portland Cement (OPC). 11,[18][19][20][21][22][23] The addition of OPC is benecial for the compressive strength development of y ash geopolymers under ambient conditions, which is supported by some studies. [24][25][26][27][28] According to the literature, several scientists have used geopolymers for the solidication of ES.…”

“…These two aspects had veried that the geopolymer had an excellent immobilization efficiency. 22 Apart from which, the release of these metal ions in the former 8 leaching stages was also responsible for the above phenomenon. 3.5.4 RBCA results and assessment of human health I The HQ analysis.…”