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This study investigates the pozzolanic reactivity of ferronickel slag (FNS), the fourth most discharged smelting by-product in China. Cumulative heat of hydration (R3) tests were conducted on FNS with varying fineness levels (111.27 to 4.5 m) to compare its performance with conventional supplementary cementitious materials (SCMs). The R3 results ranged from 34 to 132 J/g, increasing with finer particle size. Notably, the coarsest FNS showed reactivity similar to quartz filler (34 J/g), while the finest sample exhibited a 3.9-fold increase, though still only half that of fly ash (222 J/g). Similar trends were observed in bound water content and portlandite consumption. Calcium silicate hydrate (C-S-H) was the sole reaction product detected, indicating a pozzolanic reaction. Finer FNS particles enhanced the initial dissolution of Si and Mg, with dissolved silicon playing a key role in C-S-H formation. Despite magnesium being a major component of FNS, its dissolution remained limited (< 2.1 mg/L). A mortar strength test further validated the limited reactivity of FNS, showing a modest reduction in strength when 25% FNS was incorporated. These findings highlight that while grinding improves FNS reactivity, it remains less effective than conventional SCMs, suggesting the need for additional activation methods to enhance its performance.

The electrical behavior of the electric smelting furnace (ESF) in ferronickel production is primarily governed by slag conductivity, which is closely linked to ionic mobility. This study examines the relationship between slag viscosity and electrical conductivity through experimental measurements and thermodynamic modeling. The viscosity and conductivity of actual ferronickel slags were measured, and synthetic slags with similar compositions were analyzed to isolate the effects of individual oxides. Results show that viscosity decreases with increasing basicity and FeO content, while solid-phase formation at lower temperatures sharply increases viscosity. Electrical conductivity rises with temperature due to reduced viscosity and enhanced ionic transport, and increases markedly up to 17 wt.% FeO owing to higher Fe ion concentrations and partial electronic conduction. Actual ferronickel slags exhibited slightly higher conductivity than synthetic ones, likely due to minor oxides such as NiO. These findings provide insight into the coupled thermophysical and electrical behavior of ferronickel slags, offering guidance for optimizing ESF efficiency and operation.

A novel process for the synthesis of hydrated silica derived from ferronickel slag (FNS)-leaching residue was proposed in this study. The products of the purification of hydrated silica with 99.68% grade and 95.11% recovery can be obtained through ammonium fluoride (NH4F) roasting, followed by the process of water leaching, ammonia precipitating, and acid cleaning under the optimized conditions. The effects of NH4F mass ratio, roasting temperature, and roasting time on the water-leaching efficiency were investigated in detail. The thermodynamic and X-ray diffraction analyses indicated that the amorphous silica in FNS-leaching residue was converted to water-soluble fluoride salts ((NH4)2SiF6) during the roasting process, which are also supported by the scanning electron microscopy and thermogravimetry analyses. The Si–O bonds in amorphous silica could be effectively broken through the ammonium fluoride activation during a low-temperature roasting process. This work provides a meaningful reference for further studies on the facile synthesis of hydrated silica with similar mineral compositions.

The use of electric furnace ferronickel slag (FNS) as a supplementary cementitious material is the current focus of research. This study investigates the effect of mechanical grinding and chemical additives on the activity excition of FNS, as well as the associated synergistic mechanisms. This study shows that the addition of triethanolamine (TEA) increases the fine-grained content in FNS powder, which facilitates the depolymerization of FNS and the early hydration of aluminum tricalcium. Furthermore, the addition of Ca(OH)2 raises the alkalinity of the cementitious system, which promotes the availability of Ca2+ ions and accelerates the hydration process, resulting in the generation of additional hydration products. The enhancement of late hydration of C3S by TEA and its combination with the secondary hydration of Ca2+ at high alkalinity are the pivotal factors to improve the strength of cementitious composite. A mixture of FNS and 0.03% TEA is subjected to grinding for 90 min, using the obtained micropowder which replaces 20% of the cement, and subsequently, after being excited with 3% Ca(OH)2, the FNS micropowder reaches the quality standards of S95 slag powder. It is worth remarking that the micropowder prepared by mixing FNS with 3% Ca(OH)2 and 0.03% TEA and grinding it for 81 min also meets the S95 standard for slag powder. The larger dosage of FNS in cement is supported by the observed synergy between TEA and Ca(OH)2. This research will provide valuable insights for the expanded application of FNS in construction materials.

Knowledge of the phase equilibria in the MgO–CaO–SiO[sub.2]–Al[sub.2]O[sub.3] slag system is crucial for the nickel laterite smelting process. The phase equilibria of this slag system were experimentally investigated, focusing on the olivine and tridymite/cristobalite primary phase fields, using high-temperature equilibration and quenching methods, followed by Scanning Electron Microscopy–Energy Dispersive X-Ray analysis. The phase equilibria of the MgO–CaO–SiO[sub.2] slag system at 1400 °C and 1500 °C were first determined in the absence of ferronickel alloy. The phase equilibria between 1400 °C, 1450 °C, and 1500 °C were then determined under a reducing condition, i.e., at equilibrium with ferronickel alloy and solid carbon. Finally, the effect of Al[sub.2]O[sub.3] addition on the liquidus and solidus compositions in the slag system under the reducing condition was investigated at 1400 °C and 1450 °C. Comparisons between the experimentally constructed diagram, previous data, and FactSage-predicted phase diagrams have been provided and discussed. The present study identified the liquid slag both in the absence and presence of ferronickel alloy and solid carbon, as well as in the presence of Al[sub.2]O[sub.3] impurity, within the formation boundaries of olivine and tridymite/cristobalite solids. Identifying the liquid slag area is essential to ensure that the nickel laterite smelting slag can be tapped from the furnace.

This paper presents a study on the combined use of two by-products, namely quarry dust (QD) and ferronickel slag (FNS), as a full substitute for natural sand to improve the greenness of concrete production. Quarry dust was used in increments of 25% to a maximum of 75% substitution, where nickel slag was used as the remaining proportion of fine aggregate. All the combinations of quarry dust and nickel slag were found to be compliant with AS 2758.1 and they showed notably better grading than 100% sand. In this research, standard concrete tests, such as the slump test for fresh concrete, and compression, tensile and shrinkage tests for hardened concrete, were conducted. Scanning electron microscopy and X-ray diffraction analysis were also conducted for microstructural investigation. The results concluded that the combinations of quarry dust and nickel slag in concrete as a whole substitution of sand provide similar results for these properties. Specifically, 25% quarry dust with 75% nickel slag proved to be the most promising alternative to sand, with compressive and splitting tensile strengths of 62 and 4.29 MPa, respectively, which were 16% and 20% higher than those of the control mix. Also, lower drying shrinkage was observed for this combination compared to the control mix. The higher strength is attributed to the rough texture and angular shape of both quarry dust and nickel slag providing a better mechanical interlocking. The validity of this result has also been confirmed through image analysis of micrographs from various specimens. In microstructural investigations, specimens with QD and FNS exhibited fewer voids and a more compact surface compared to the control specimen. This shows the potential for further research into the use of quarry dust and nickel slag in the production of green concrete.

Ferronickel slag (FNS) is a byproduct produced during ferronickel alloy manufacturing, primarily used in the manufacturing of stainless steel and iron alloys. This material is produced by cooling molten slag with water or air, posing significant disposal challenges, as improper storage in industrial yards can lead to environmental contamination. This study investigates the chemical and mineralogical characteristics of reduction ferronickel slag (RFNS) and its potential use as an alternative aggregate in hot mix asphalt (HMA). The research is based on the practical application of HMA containing RFNS in an experimental area, specifically the parking lot used by buses transporting employees of Anglo American, located at the Codemin Industrial Unit in Niquelândia, Goiás, Central Brazil. Chemical analysis revealed that RFNS primarily consists of MgO, Fe2O3, and SiO2, which are elements with minimal environmental impact. The lack of significant calcium content minimizes concerns about expansion issues commonly associated with calcium-rich slags. The X-ray diffractogram indicates a predominantly crystalline structure with minerals like Laihunite and Magnetite, which enhances wear and abrasion resistance. HMA containing 40% RFNS was tested using the Marshall methodology, and a small experimental area was subsequently constructed. The HMA containing RFNS met regulatory specifications and technological controls, achieving an average resilient modulus value of 6323 MPa. Visual inspections conducted four years later confirmed that the pavement remained in excellent condition, validating RFNS as a durable and effective alternative aggregate for asphalt mixtures. The successful application of RFNS not only demonstrates its potential for local road paving near industrial areas but also underscores the importance of sustainable waste management solutions. This research highlights the value of academia–industry collaboration in advancing environmentally responsible practices and reinforces the contribution of RFNS to enhancing local infrastructure and promoting a more sustainable future.

This study investigated the air aging converter (Basic Oxygen Furnace, BOF) slag aggregate mortar with pulverized fly ash (PFA) and ferronickel slag (FNS). The chemical composition and mineralogical constituents of BOF incorporated mortar were analyzed. Setting time, flowability, compressive strength, and length change were measured to evaluate the fundamental properties of BOF mortar. The X-ray CT analysis was employed to observe the effect of converter slag in the cement matrix visually. The results showed that the hydration of BOF generated a pore at the vicinity of the aggregate, which decreased the compressive strength and increased the length change of mortar. However, the PFA or FNS incorporation of PFA or FNS can decrease the alkalinity of pore solution and subsequently reduce the reactivity of BOF aggregate. Thus, the incorporation of PFA and FNS can be a way to eliminate the disadvantage of BOF, such as volume expansion.

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 2 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 2 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. Graphical abstract

Blast furnace ferronickel slag (BFFS) has the potential to serve as a supplementary cementitious material (SCM) in the production of cement and concrete. While the composite binder containing BFFS presents varying heat release kinetics under different curing temperatures, the effect of BFFS content on the apparent activation energy ( E a ) and temperature sensitivity of the composite cementitious binder has rarely been systematically explored. In this study, the modified ASTM C1074 method with hyperbolic and exponential functions is adopted to calculate the E a values of the composite binders incorporating different amounts of BFFS via isothermal calorimetry. The results indicate that the calculated E a values are influenced by different kinetic functions, and increasing the BFFS content from 0 to 50% has significantly elevated the E a value and enhanced the temperature dependence of BFFS blended cement paste. Moreover, the temperature sensitivity of the composite binder containing BFFS is compared to those containing traditional SCMs, including ground granulated blast furnace slag (GGBFS) and low-calcium fly ash (FA). The study reveals that the E a value of 50% BFFS blended cement paste is close to that of 50% GGBFS blended cement paste, and higher than that of 50% low-calcium FA blended cement paste. The high temperature sensitivity of BFFS blended cement can be leveraged to promote the early-age strength gain under different curing temperatures.