Unravelling the Affinity of Alkali-Activated Fly Ash Cubic Foams towards Heavy Metals Sorption

Caetano, Ana P.F.; Carvalheiras, João; Senff, L.; Seabra, M.P.; Pullar, Robert C.; Labrincha, J.A.; Novais, Rui M.

doi:10.3390/ma15041453

Cited by 12 publications

(7 citation statements)

References 53 publications

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“…It can be noticed that the FTIR pattern of MK had three broad features at approximately 1041 cm −1 , 784 cm −1 , and 439 cm −1 . The densest, asymmetrical, broad feature at 1041 cm −1 indicates the stretching of Si-O bonds in the amorphous MK structure [ 33 , 34 , 35 ]. The vibrations of the AlO 4 tetrahedra in MK were attributed to the broad band located at about 784 cm −1 [ 33 ].…”

Section: Resultsmentioning

confidence: 99%

“…This was most likely caused by the water content of the RM [ 37 ]. The H-O-H stretching vibration in RM was related to the band at 1408 cm −1 [ 34 , 35 ]. For the RM spectrum, the characteristic band at 964 cm −1 corresponding to the asymmetric stretching vibrations of Si-O-Si and Si-O-Al was observed [ 35 ].…”

Section: Resultsmentioning

confidence: 99%

“…The H-O-H stretching vibration in RM was related to the band at 1408 cm −1 [ 34 , 35 ]. For the RM spectrum, the characteristic band at 964 cm −1 corresponding to the asymmetric stretching vibrations of Si-O-Si and Si-O-Al was observed [ 35 ]. Al-O and Fe-O bond groups were contributed by the peak of RM at roughly 406 cm −1 [ 38 ].…”

Section: Resultsmentioning

confidence: 99%

“…The micrographs also show differences in the shape and connectivity of the pores in samples prepared with SDS compared with those produced with Hostapur OSB, the former samples exhibited round-shaped [ 25 ], but mostly closed pores, while in the latter, irregular and open pores were observed. Small and closed pores may contribute to thermal insulation [ 44 ], while open pores will benefit wastewater treatment applications [ 35 ]. The rheology and setting time of the mixture can influence stabilizing of the pores.…”

Section: Resultsmentioning

confidence: 99%

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Evaluation of the Nature and Concentration of the Surfactant on the Properties of Red Mud/Metakaolin Porous Geopolymers Foamed with Aluminium

Bilici

Carvalheiras²,

Labrincha³

et al. 2022

Materials

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The chemical foaming technique is possibly the most common method of producing porous geopolymers. Despite this, to date, the role of the content and type of surfactant on the pore size distribution of porous geopolymers is not fully perceived, as constant surfactant dosages are usually employed. In addition, the comparison of literature studies is challenging since a distinct mixture of designs is employed. This investigation intends to provide additional insights on the topic, focusing on synthesizing red mud/metakaolin geopolymer foams and envisioning their use in thermal insulating applications. Various mixtures were prepared using three commercially available surfactants, namely Hostapur OSB, sodium dodecyl sulfate (SDS), and Triton X114. The content of the surfactant (0.025, 0.05, and 0.075 wt.%) and the amount of the foaming agent (aluminum powder, Al; 0.05, 0.075, and 0.10 wt.%) was modified, keeping the binder composition constant and the physical properties of the produced geopolymers were characterized. Results show that the combination between sodium dodecyl sulfate (0.025 wt.%) and aluminum (0.10 wt.%) leads to the strongest reduction in the foam density, the lowest value here reported being −400 kg/m3. On the other hand, samples produced with Hostapur OSB have much higher open porosity (up to 47.7%) and water absorption (up to 80.4%) values, showing that this surfactant leads to a pore network with higher connectivity. In addition, the microstructure of the foams, particularly pore morphology (size and shape) and connectivity between the produced pores are highly dependent on the type of surfactant, sodium dodecyl sulfate generating coarser pore size distribution with round, but mostly closed pores, while a narrower pore size distribution coupled with smaller size pores is seen with the Hostapur. These results suggest the feasibility of tuning the foams’ properties (porosity and mechanical performance) according to the application by the proper combination of the type of surfactant and their concentration, enabling their use as thermal and acoustic insulators or as filters/membranes in wastewater treatment systems.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Evaluation of the Nature and Concentration of the Surfactant on the Properties of Red Mud/Metakaolin Porous Geopolymers Foamed with Aluminium

Bilici

Carvalheiras²,

Labrincha³

et al. 2022

Materials

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“…Results showed that the removal efficiency is affected by the heavy metals nature and follows the sequence in terms of affinity in a single component system: Pb 2+ > Cd 2+ > Zn 2+ > Cu 2+ . This tendency is related, among others, to the hydrated ionic radius and hydration enthalpy of the different heavy metals (Caetano et al, 2022).…”

Section: Heavy Metalsmentioning

confidence: 92%

Review of recycling alternatives for paper pulp wastes

Vilarinho

Gameiro²,

Capela³

et al. 2022

Front. Mater.

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The demand for products derived from the pulp and paper industry has been increasing over the past years and is projected to further increase over the coming decades. Although being one of Portugal’s most relevant industrial activities, contributing to nearly 2.3% of the GDP, this sector is known to generate a variety of wastes including fly ashes, exhausted bed sands, green liquor dregs, grits, lime muds, biological and pulp and paper mill sludges, which have been mostly disposed of in landfills. This strategy is not aligned with the circular economy vision, and therefore it is imperative to develop new recycling routes for the different waste streams. This scenario has driven a significant research effort in the attempt to design sustainable recycling alternatives for the distinct wastes. This study summarizes the investigations focusing on the valorisation of these wastes in a wide range of applications, including the production of low carbon footprint binders or mortars for the construction sector, but also the production of novel materials for high added-value applications such as wastewater treatment and pH regulation. The present work also highlights the main bottlenecks and future prospects for the studied wastes.

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