Microstructure and Pb2+ Adsorption Properties of Blast Furnace Slag and Fly Ash based Geopolymers

Abstract

In this study, a blast furnace slag (BFS) and fly ash (FA) based adsorbent geopolymer to be used for removing Pb2+ from aqueous solutions were synthesized using the hydrothermal method at 60 °C for 24 h, and then cured at 25 °C for another six days. The alkali activator applied in this work was a combination of sodium hydroxide and sodium silicate solutions at a mass ratio of 2. The geopolymer slurry was adjusted to a Si/Al molar ratio of 3. A BFS-based geopolymer (GS) having a specific area of 23.56 m2/g and pore size and volume of 7.8 nm and 73 cm3/kg, respectively, surpassed the raw material surface by approximately 13-fold. An FA-based geopolymer (GA) having a specific area of 35.97 m2/g and a size and porous volume of 9 nm and 124 nm, respectively, surpassed the raw material surface by approximately 23-fold. In addition, GS and GA showed a cation exchange capacity (CEC) of 241.30 and 286.96 Meq/100 g, respectively. X-ray diffraction (XRD) determined sample crystallinity and it was proven by scanning electron microscopy (SEM), showing that both geopolymers were constituted of unreacted particles surrounded by amorphous and semi-amorphous products. Through Fourier transform infrared spectroscopy (FTIR), a band that was assigned to the asymmetric stretching vibration of Si-O-M (M = Na+ and/or Ca2+) non-bridging oxygen type was observed, which suggested that Na and Ca could serve as exchangeable ions in the ionic exchange process. Adsorption test data indicated that good adsorption was obtained when a neutral pH was used at room temperature, and the adsorption isotherm showed that GA had more adsorption sites than GS, which meant greater maximum adsorption capacity.

Mixed-Phase Ion-Exchangers from Waste Amber Container Glass

“…In general, the batch uptakes of Pb 2+ and Cd 2+ by AN-150, AF-150 and AH-150 and their associated equilibrium times fall within the ranges reported for other low-cost and waste-derived inorganic materials [3,[30][31][32][33][34][35][36][37][38][39][40]. The batch uptakes of Pb 2+ and Cd 2+ by AN-150, AF-150 and AH-150 are compared with those of other low-cost and waste-derived inorganic sorbents in Table 5 [3,[30][31][32][33][34][35][36][37][38][39][40].…”

“…In general, the batch uptakes of Pb 2+ and Cd 2+ by AN-150, AF-150 and AH-150 and their associated equilibrium times fall within the ranges reported for other low-cost and waste-derived inorganic materials [3,[30][31][32][33][34][35][36][37][38][39][40]. The batch uptakes of Pb 2+ and Cd 2+ by AN-150, AF-150 and AH-150 are compared with those of other low-cost and waste-derived inorganic sorbents in Table 5 [3,[30][31][32][33][34][35][36][37][38][39][40]. The Pb 2+ removal capacities and equilibrium times of the amber glass-derived mixed-phase sorbents were superior to those reported for waste concretes [31,32] and inferior to those of fly ash-derived zeolite Na-X [33] and hydrated calcium silicate gel [35].…”

“…Increases in supernatant Cd 2+ solution pH from an initial value of 5.4 to 7.3 for AH-150, and to 8.6 for both AN-150 and AF-150 were noted, although the trends did not correlate directly with the observed extents of Cd 2+ -removal. The batch uptakes of Pb 2+ and Cd 2+ by AN-150, AF-150 and AH-150 are compared with those of other low-cost and waste-derived inorganic sorbents in Table 5 [3,[30][31][32][33][34][35][36][37][38][39][40]. The Pb 2+ removal capacities and equilibrium times of the amber glass-derived mixedphase sorbents were superior to those reported for waste concretes [31,32] and inferior to those of fly ash-derived zeolite Na-X [33] and hydrated calcium silicate gel [35].…”

Self-Immobilizing Metals Binder for Construction Made of Activated Metallurgical Slag, Slag from Lignite Coal Combustion and Ash from Biomass Combustion

“…It has also been proven that in the matrix made of fly ash a very insoluble compound of lead Pb 3 SiO 5 formed [ 82 ]. According to Medina et al [ 83 ], who synthetized alkali-activated GGBFS- and FA-based geopolymers for use as an adsorbent of Pb 2+ , Na and Ca content generated active sites for ion exchange process and the lead was better absorbed then, this was also very well confirmed in the case of the ZK1z10nc mix. Ariffin et al [ 84 ] presented many examples of research proving the heavy metals absorbing properties of fly ash based geopolymers and other geopolymer based adsorbents, but they usually involved less complex blends compared to present research.…”

Geopolymers and Alkali-Activated Materials for Wastewater Treatment Applications and Valorization of Industrial Side Streams

“…Ground granulated BFS has a high specific area due to the small particle size distribution, which makes it an excellent candidate as adsorptive material [13,30]. However, in order to avoid the leaching of heavy metals from BFS during deployment of these materials in water remediation techniques, alkaline activation were suggested for entrapment/binding impurities within the GPs' matrix [31][32][33][34]. The presence of significant amounts of silica, aluminosilicates, and calcium-alumina-silicates in a pristine material makes the geopolymerization process rapid and effective resulting in rigid and enduring compositions.…”