Purpose
This investigation presents a new valorization route of fly ash, based on the synthesis of layered double hydroxide (LDH) used as efficient and cost-effective adsorbent for the stabilization ...of contaminants in sediments.
Methods
LDH were synthesized through an acid leaching method at constant pH followed by precipitation, applied on waste paper fly ash (WPFA) and biomass fly ash (BFA), obtained from industries of the Hauts de France region. The synthesized LDH (LDH
WPFA
and LDH
BFA
) were calcinated at 450 °C, their physico-chemical and adsorption properties were then compared before and after calcination, with a commercial hydrotalcite (HT).
Results
The XRD diffractograms of synthesized LDH showed characteristic bands of hydrocalumite Ca
4
Al
2
(OH)
12
(Cl,CO
3
,OH)
2
·4H
2
O and paraalumohydrocalcite (CaAl
2
(CO
3
)(OH)
4
.6H
2
O) for LDH
WPFA
and LDH
BFA
, respectively. The FTIR spectra showed similar patterns to LDH containing interlamellar anions (CO
3
2−
and OH
−
) in the vicinity of 1360 cm
−1
and 3600 cm
−1
. The LDH morphology presented platelets and hexagonal block shapes with some octahedral forms. The batch and column adsorption results showed that more than 98% of Sb, Zn and SO
4
2−
were stabilized when the sediment matrix was amended with 5% of calcinated LDH
WPFA
, compared to untreated sediment, due to the negative charge of the surface.
Conclusion
Synthesized LDH were able to stabilize both cationic species (by adsorption and electrostatic attraction), and anionic species (by anion exchange) inside the sediment matrix.
Graphical Abstract
The objective of this study was to present a new approach to mineral waste valorization, based on the synthesis of hydroxyapatite (HAP) as an efficient and cost-effective adsorbent for the ...stabilization of fluorides (F-) in soil. Hydroxyapatites were synthesized from the reaction of potassium dihydrogen phosphate (KH2PO4) and waste paper fly ash (WPFA), fine limestone clay (FLC) and limestone filler (LF) rich in calcite. X-ray diffraction characterization results showed that for HAPFLC and HAPFL the main resulting phases were brushite (CaHPO5·2H2O) and for HAPWPFA was hydroxyapatite (Ca5(PO4)3OH). The FTIR spectra showed similar patterns to natural HAP containing orthophosphate groups (PO43-), hydroxylated groups (OH–) and both types A/B of carbonate apatite. SEM-EDS analysis of the individual HAP revealed a morphology consistent with phosphocalcic hydroxyapatite crystals. EDS analysis revealed a Ca/P atomic ratio equal to 1.92, 1.85 and 1.7 for HAPFLC, HAPLF and HAPWPFA respectively, which is similar to the stoichiometry of hydroxyapatites (Ca/P = 1.67). The use of HAP as an amendment to stabilize fluorides (F-) in the soil was demonstrated to be effective, the addition of 1% of the different HAP allowed the decrease of the concentration of F in the raw soil (73.8 mg/kg) to concentrations below the IWSI threshold (10 mg/kg), to 4.68 mg/kg, 5.63 mg/kg, and 0.8 mg/kg for HAPFLC, HAPFL and HAPWPFA respectively. Fluoride (F) sequential extraction results showed that it was extracted from the residual fraction (Fraction 4) after soil treatment, and was generally trapped on the hydroxyapatites (Ca5(PO4)3(OH)) by anion exchange with the hydroxides (OH–) to form the stable and insoluble fluorapatite ((Ca5(PO4)3F).
The increase in energy valorization of paper sludge and biomass waste through incineration results in a rise in waste paper fly ash (WPFA), often perceived as hazardous and requiring specific ...treatment. In this study, natural carbonation technology at a pilot scale was employed to mitigate the hazardous nature of WPFA by enhancing the stabilization of metal and metalloid trace elements (MMTE), particularly barium (Ba) and lead (Pb) leaching. Natural carbonation of WPFA was found to be optimal at a water/solid ratio of 0.3 L/kg under natural temperature and humidity conditions. Batch leaching tests based on thermodynamic equilibrium were used to assess MMTE solubility concerning pH in both non-carbonated and carbonated WPFA at natural pH. After 7 days of natural carbonation, the leaching concentration of Ba and Pb was below the legal limit in France. The concentration of Ba and Pb in carbonated samples decreased by 98.5% and 98%, respectively. Analyses using thermogravimetry, X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy demonstrated the increased formation and quantity of calcite (CaCO3) with longer carbonation times, along with the formation of new minerals as BaCO3 and PbCO3, confirming the immobilization of these elements post-carbonation. The leaching behavior and release potential of carbonated WPFA were further evaluated using the four-stage sequential extraction procedure proposed by the European Commission’s Bureau of Reference (BCR). The speciation of Ba and Pb shifted significantly from the soluble substance (F1) at 17.6% and 14.8%, respectively, to the carbonate fraction (F2) at 0.49% and 0.02% after 90 days of carbonation. The percolation water collected during the carbonation process adheres to discharge standards into the sea.
•Pilot scale natural carbonation of WPFA has been performed.•Ba, Pb and Cl leaching concentration decreased effectively after natural carbonation.•After 7 days of natural carbonation, the WPFA becomes inert.•Percolation water can be eliminated without treatment.•Ba and Pb was precipitated as carbonate BaCO3 and PbCO3.
The combustion of biomass and waste paper sludge in a fluidized bed is ecologically profitable. However, a large amount of by-product with high hydraulic reactivity is produced and is considered as ...wastes. Most of the time the waste paper fly ash (WPFA) goes to landfills, therefore new utilization methods are necessary. In some countries, the high content of metallic and metalloids trace elements (MMTE) in WPFA, more specifically Barium (Ba) and Lead (Pb) makes its valorization difficult. In this paper, the Lightweight Aggregates (LWA) was produced from WPFA by granulating with water in high-intensity granulator. Since WPFA is rich in CaO, the addition of water promotes rapid setting and hydration compared to other types of ash. In this study, different granulation parameters were investigated, such as the rotation modes between the steel pan and the impeller, the rotation speed of the steel pan, the granulation time, in order to improve the mass percentage of the targeted LWA (2–16 mm). In order to evolve the immobilization potential of Ba and Pb, a carbonation process was performed, exposing the manufactured LWA to pure carbon dioxide (CO2) gas at laboratory scale. The physical, morphological, thermal and mechanical characterizations were performed on LWA for use in mortars, concretes or civil engineering constructions.
Results have demonstrated the influence of the rotation mode between the steel pan and the on the distribution of WPFA inside the steel pan and the change in the growth rate of the granules can be observed. Increased density and improved compressive strength with low porosity and water absorption were also found in LWA after carbonation. This was due to the occurrence of both a carbonation reaction and a hydration reaction. Furthermore, the results of thermogravimetry and SEM-EDS confirmed the formation of hydrated phases (ettringite, carboaluminates), also the formation of calcite in the pores and the external surface of the LWA. Regarding environmental aspects, the results have revealed that Ba and Pb were well immobilized in the solid matrix after carbonation.
Display omitted
•LWA was manufactured from WPA without any agglomerating agents.•The physical-chemical properties of LWA were improved after carbonation.•The resulted LWA meet the requirements of NF EN -13,055-1.•The microstructure of LWA was studied before and after carbonation.•Influence of time, mode and rotation speed on the size of the manufactured LWA.
The formulation of an eco-binder only makes sense if the technical and environmental suitability of new waste material have been assessed. This study focuses on the recovery of three sets of waste ...paper fly ash (WPFA): raw, ground, and carbonated, as the main component of an eco-binder. The effect of the partial replacement of ordinary Portland cement (OPC) with WPFAs is studied from a mechanical and environmental point of view. The results show that raw WPFA contributes to the development of compressive strength, especially for low substitution rates (10 and 20%). Grinding results in improved compressive strength, fineness, and stability (at high substitution rates), and also accelerated setting kinetics. Natural carbonation is an effective and low-cost solution that has been proposed to treat WPFA before incorporation into the cementitious matrix. The carbonation contributes to delaying the setting and improving the stability of the matrix. Furthermore, the process of carbonation has been observed to have a beneficial impact on the stabilization of barium through the reduction of its leaching potential, which can contribute to the environmental sustainability of the eco-binder. In conclusion, the replacement of OPC with 20% of carbonated WPFA can save significant amounts of greenhouse gas emissions (27.29%).
