Tar management is one of the key components to achieve high energy efficiency and low operational costs connected to thermal gasification of biomass. Tars contain a significant amount of energy, and ...unconverted tars result in energy efficiency losses. Also, heavy tars can condense downstream processes, resulting in increased maintenance. Dual fluidized beds for indirect gasification operated with active bed material can be a way to better convert and control the tar generated in the process. Using an active material to transport oxygen in an indirect dual reactor gasification setup is referred to as chemical-looping gasification (CLG). A higher oxidative environment in the gas phase, in addition to possible catalytic sites, could mean lower yields in comparison to normal indirect gasification. This paper investigates the effect of using Steel converter slag (LD slag), a byproduct of steel manufacturing, as an oxygen-carrying bed material on tar species generated in a 10 kWth dual fluidized bed biomass gasifier. The results are compared to the benchmark oxygen carrier ilmenite and conventional silica sand. Three different solid biofuels were used in the reactor system: steam exploded pellets, pine forest residue and straw. Tar was absorbed from the raw syngas using a Solid Phase Adsorption (SPA) column and was analyzed using GC-FID. Bench-scale experiments were also performed to investigate benzene conversion of LD slag and ilmenite at different oxidation levels. The findings of this study suggest that oxygen carriers can be used to decrease the tars generated in a dual fluidized bed system during gasification. Phases in LD slag possess catalytic properties, resulting in a decreased ratio of heavy tar components compared to both ilmenite and sand. Temperature and fuel load showed a significant effect on the tar generation compared to the circulation and steam ratio in this reactor system. Increased temperature generated lower tar yields and lower ratios of heavy tar components for LD slag in contrast to sand.
In this study, four ecotoxicological tests on Vibrio fischeri bacteria, Sinapis alba L. (white mustard), Daphnia magna S. (daphnia's) and earthworms were performed for three types of aqueous slag ...(ladle, blast furnace and converter) leachates with two-grain sizes (<4 mm, <10 mm). Concentrations of toxic elements and concentrations of Cr(VI), Ca, Na, Al, and other ions were determined. The raw slags were analyzed using X-ray fluorescence spectroscopy (XRFS), and major substances were determined by X-ray powder diffraction (XRD). The aqueous slag leachates passed ecotoxicological tests and met the required criteria, showing no toxicity to Vibrio fischeri and complying with white mustard test criteria. According to the results of the ecotoxicity tests with daphnia, the blast furnace slag samples were not ecotoxic, while two other slag samples were found to be entirely compliant. Characterization of the slags showed that the effect of element/ion leachability and slag grain size is essential. Biplot principal component analysis (PCA) showed that grain size does not significantly affect the separation of individuals on the plane. A positive correlation on toxicity was found with pH, conductivity, calcium content, dissolved content, salinity and fluoride concentration, whereas a negative correlation was found with magnesium concentration, dissolved organic carbon and potassium concentration. The effective concentration at 50% inhibition (EC50) value for Vibrio fischeri correlated with the first dimension of bivariate assessment. In summary, it was found that the investigated slags can be effectively reused as they comply with regulations and do not endanger the environment.
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•Ecotests on mustard, daphnia, Vibrio fischeri bacteria were compared with EU norms.•The chemical composition of the leachates affects the results of ecotoxicity tests.•Toxic unit values for Vibrio fischeri bacteria were within norms and non-toxic.•Most of the effective concentration values for the daphnia test were acceptable.•Principal component analysis found grain size effect on two organisms.
Solidification/stabilization technology is one of the most desirable technologies for the remediation of heavy metal contaminated soils due to its convenience and effectiveness. The annual production ...of alkaline industrial wastes in China is in the hundreds of millions of tons. Alkaline industrial wastes have the potential to replace conventional stabilizers because of their cost effectiveness and performance in stabilizing heavy metals in soils. This paper systematically summarizes the use of four alkaline industrial wastes (soda residue, steel slag, carbide slag, and red mud) for the solidification/stabilization of heavy metal contaminated soils and provides a comprehensive analysis of the three mechanisms of action (hydration, precipitation, and adsorption) and factors that influence the process. In addition, the environmental risks associated with the use of alkaline industrial wastes are highlighted. We found that soda residues, steel slag and carbide slag are appropriate for solidification/stabilization of Pb, Cd, Zn and Cu, while red mud is a potential passivation agent for the stabilization of As in soils. However, implementation of remediation methods using alkaline industrial wastes has been limited because the long-term effectiveness, synergistic effects, and usage in soils containing multiple heavy metals have not been thoroughly studied. This review provides the latest knowledge on the mechanisms, risks, and challenges of using alkaline industrial wastes for solidification/stabilization of heavy metal contaminated soils.
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•Alkaline industrial wastes can be used to remediate heavy metals contaminated soil.•Hydration, precipitation, and adsorption are major mechanisms.•Studies on long-term effectiveness and in situ remediation are deficient.•Heavy metal leaching and excessive soil alkalinization are major risks.
By-products from the non-ferrous industry are an environmental problem; however, their economic value is high if utilized elsewhere. For example, by-products that contain alkaline compounds can ...potentially sequestrate CO
2
through the mineral carbonation process. This review discusses the potential of these by-products for CO
2
reduction through mineral carbonation. The main by-products that are discussed are red mud from the alumina/aluminum industry and metallurgical slag from the copper, zinc, lead, and ferronickel industries. This review summarizes the CO
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equivalent emissions generated by non-ferrous industries and various data about by-products from non-ferrous industries, such as their production quantities, mineralogy, and chemical composition. In terms of production quantities, by-products of non-ferrous industries are often more abundant than the main products (metals). In terms of mineralogy, by-products from the non-ferrous industry are silicate minerals. Nevertheless, non-ferrous industrial by-products have a relatively high content of alkaline compounds, which makes them potential feedstock for mineral carbonation. Theoretically, considering their maximum sequestration capacities (based on their oxide compositions and estimated masses), these by-products could be used in mineral carbonation to reduce CO
2
emissions. In addition, this review attempts to identify the difficulties encountered during the use of by-products from non-ferrous industries for mineral carbonation. This review estimated that the total CO
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emissions from the non-ferrous industries could be reduced by up to 9–25%. This study will serve as an important reference, guiding future studies related to the mineral carbonation of by-products from non-ferrous industries.
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A proper and detailed understanding of the thermal stability of Fe-rich fayalite slag-based alkali-activated materials (AAMs) is important due to their potential use in refractory and fire-resistant ...applications. Here, fayalite slag (FS) was used as the main precursor for AAMs. The effects of incorporating ladle slag (LS) or blast furnace slag (BFS) and different temperature exposures up to 1000 °C were investigated through visual observation, compressive strength, ultrasonic pulse velocity (UPV), thermal conductivity, x-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG/DSC), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope coupled with electron probe microanalyzer (SEM-EPMA). The experimental results indicated that the incorporation of LS or BFS as additional calcium and aluminum sources positively affected the high-temperature behavior of blended mortars, which exhibited a reduction in voids, cracks, and thermal shrinkage while having higher residual strength and thermal stability than solely FS-based AAMs. This was mainly due to the differences in mineralogical transformation and the phases formed. Interestingly, the joint effect of elevated temperature exposure and the addition of LS or BFS enhanced the formation of more stable crystalline phases and densified the structure of blended mortars at 1000 °C.
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•Upcycling of Fe-rich fayalite slag as refractory and fire-resistant alkali-activated materials (AAMs) was elucidated.•Ladle slag (LS) or blast furnace slag (BFS) addition improved AAMs properties during ambient and high temperature exposure.•AAMs containing LS or BFS have better mechanical, thermal, and microstructural properties.•Joint effect of elevated temperature and LS or BFS addition favored more stable crystalline phase formation and densification.•The results provided an insight for designing eco-friendly refractory materials for building and construction industry.
► This study presents an investigation into the properties and durability of AASC. ► Strength tests and drying shrinkage measurement were carried out on properties. ► RCPT, high-temperature and ...sulphate attack resistance were performed on durability. ► The performance was discussed and compared with reference concretes produced by OPC. ► Properties and durability of AASC depends on dosage of Na2O and curing conditions.
This study presents an investigation into physical and mechanical properties and durability of alkali-activated slag concrete (AASC). Sodium oxide (Na2O) concentrations of 4%, 5% and 6% of slag weight and liquid sodium silicate with modulus ratio (mass ratio of SiO2 to Na2O) of 0.8 were used as alkaline activators to activate granulated blast furnace slag (GBFS). Specimens with/without phosphoric acid (H3PO4) were cast and cured in the air, under the saturated limewater and in a curing room at relative humidity of 80% RH and temperature of 60°C, respectively. Their performance was discussed and compared with reference concretes produced using ordinary Portland cement concrete (OPC). Test results show that both the dosage of Na2O and H3PO4 of additional mixture are significant factors influencing the properties of the fresh AASC mixtures. In hardened concrete, better properties and durability, such as compressive strength, splitting tensile strength, drying shrinkage, total charge passed, high-temperature resistance and sulphate attack resistance, have been obtained in AASC than comparable OPC. The properties and durability of AASC were significantly dependent on dosage of Na2O and curing conditions. The properties and durability of AASC improved with an increase dosage of Na2O and AASC cured at relative humidity of 80% RH and temperature of 60°C has the superior performance, followed the AASC by air curing and saturated limewater curing based on the presented observations and results.
Electric arc furnace slag (EAFS) and ladle furnace slag (LFS) are by-products of the electric steelmaking sector with suitable properties for use in bituminous mixtures as both coarse and fine ...aggregates, respectively. In this research, the production of a porous asphalt mixture with an aggregate skeleton consisting exclusively of electric steelmaking slags (using neither natural aggregates nor fillers) is explored. The test program examines the asphalt mixtures in terms of their mechanical performance (abrasion loss and indirect tensile strength), durability (cold abrasion loss, aging, and long-term behavior), water sensitivity, skid and rutting resistance, and permeability. The results of the slag-mixes are compared with a standard mix, manufactured with siliceous aggregates and cement as filler. The porous mixes manufactured with the slags provided similar results to the conventional standard mixtures. Some issues were noted in relation to compaction difficulties and the higher void contents of the slag mixtures, which reduced their resistance to raveling. Other features linked to permeability and skid resistance were largely improved, suggesting that these mixtures are especially suitable for permeable pavements in rainy regions. In conclusion, a porous asphalt mixture was produced with 100% slag aggregates that met current standards for long-lasting and environmentally friendly mixtures.
Alkali-activated materials (AAMs) are a kind of hardened slurry produced by an alkali activation reaction between a silicate precursor and an alkali activator that is treated as an environmentally ...friendly cementitious material that can be used in place of ordinary Portland cement (OPC). However, some studies point out that the AAMs with a single precursor had some defects. To realize the high value-added utilization of phosphorus slag (PS), this paper mixed PS with granulated blast furnace slag (GBFS) to prepare alkali-activated composite cementitious materials. The workability, mechanical properties, and hydration of alkali-activated phosphorus slag—granulated blast furnace slag (AAPG) were characterized using fluidity, setting time, compressive strength, flexural strength, hydration heat, XRD, FTIR, TG-DSC, and SEM + EDS. The results show that GBFS can improve the fluidity of AAPG, but the slurry will flash set after exceeding 20% GBFS content. GBFS can rapidly hydrate to generate C-S–H to improve its early strength, but the later stage results in larger pores due to the uneven distribution of matrix products. The hydration generation products of AAPG are C-S–H and C-(N)-A-S–H dominated by the Q
2
unit, with some hydrotalcite by-products generated.
Modern industrialization leads to an increasing demand for steel around the world, the production of one ton of crude steel generates a substantial amount of steel slag (SS11SS: steel slag), ranging ...from 130–200 kg. The accumulation of SS poses economic and environmental challenges, particularly in developing countries with low utilization rates. Therefore, enhancing the utilization ratio of steel slag has become an urgent priority. To address this issue, this paper examines the effect of incorporating steel slag as a supplementary cementitious material (SCM22SCM: supplementary cementitious material) and aggregate in concrete on various properties of concrete, aiming to promote the reuse of steel slag. The analysis results indicate that the incorporation of steel slag powder (SSP33SSP:steel slag powder) may have adverse effects on the initial setting time, volume stability, compressive strength, and durability of concrete. However, these issues can be mitigated through aging processes and high-reactivity SCMs. As for the steel slag aggregate (SSA44SSA:steel slag aggregate), it can effectively enhance the compressive strength of concrete. However, it may negatively impact workability, volume stability, and the residual strength of concrete after exposure to high temperatures. Furthermore, the effect mechanism of SSA on the durability performance of concrete is complex, making it difficult to draw reliable conclusions.
•Two types of SS were analyzed for the chemical composition and physical properties.•Effect of SSP as SCM on various properties of concrete was analyzed.•Effect of SSA on the performance of concrete was analyzed.•Effect of w/b ratio, curing age and replacement ratio on SSA concrete was analyzed.•Suggested research directions for future research on steel slag concrete.
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