Metallurgical Solid Waste Research Articles

Efficient and stable hydrogen evolution and antibiotic degradation in all-pH-scale water/alkaline seawater using Fe-Co phosphide hollow nanocages fabricated from metallurgical solid waste

The utilization of seawater, a plentiful and cost-effective resource, instead of freshwater for H2 production through electrolysis has garnered significant attention. Herein, we present the synthesis of open-structured Fe-Co phosphide (FCP) nanocages for the overall seawater electrolysis, employing metallurgical solid waste (steel rolling sludge, SRS) as the precursor material. The FCP nanocages demonstrate exceptional catalytic activity for the hydrogen evolution reaction (HER) in all pH scales, achieving performance comparable to that of Pt/C catalysts at high current densities. The electrolyzer assembled with FCP||FCP requires 1.57 and 1.68 V to achieve current densities of 10 and 100 mA cm−2, respectively. Furthermore, the assembled FCP electrolyzer showcases over 100 h of cycling stability and nearly 100% Faradaic efficiency. Crucially, it can be powered by commercially available silicon solar panels, operating under an intensity of 100 mW cm−2, and by wind-driven sources, rendering it highly promising for real-world applications. The seawater hydrogen evolution system coupled with levofloxacin (LEV) degradation was constructed for the first time. The oxidation potential of LEV oxidation reaction (LEVOR) was significantly lower than that of oxygen evolution reaction (OER), indicating that the LEV degradation reaction occurred preferentially and achieved a removal efficiency of 98.57% within 60 min. This study provides effective strategies for valorizing SRS and offers insights into the fabrication of high-performance catalysts.

Flame‐retardant rigid polyurethane foam composites with the incorporation of steel slag and DMMP: A novel strategy for utilizing metallurgical solid waste

AbstractSteel slag (SS) as solid waste, has low resource utilization efficiency and seriously endangers environmental safety and human health. To explore the potential utilization value of SS and address the flammability challenge of rigid polyurethane foam (RPUF), with a novel flame‐retardant system composed by SS and dimethyl methyl phosphonate (DMMP) was explored. The DMMP/SS system effectively improved the high temperature stability of the RPUF composites. When the mass ratio of SS and DMMP was 1:1, the limiting oxygen index of RPUF/DMMP/SS reached 23.1 vol% and UL‐94 vertical combustion tests passed V‐2 level. Upon incorporation of 15 wt% DMMP, the initial decomposition temperature (T−5 wt%) reduced to 165.3°C, a decrease of 32.2%, while the Tmax2 and residue yield at 700°C exhibited negligible alteration. The peak heat release rate of RPUF/DMMP/SS composite (118.20 W g−1) was 11.02% lower than that of pure RPUF, indicating the significant enhancement of fire safety of the composites. Results confirmed that a synergistic flame‐retardant mechanism was existed between DMMP and SS in enhancing the fire safety of RPUF composite. Introducing a 20 wt% SS content reduces the ID/IG ratio to 1.85, thereby markedly enhancing its heat resistance. This work provides a new application field of SS and paves a novel approach to enhance fire safety of polymers.

Polyurethane reinforced with micro/nano waste slag as a shielding panel for photons (experimental and theoretical study)

This study not only provides an innovative technique for producing rigid polyurethane foam (RPUF) composites, but it also offers a way to reuse metallurgical solid waste. Rigid polyurethane (RPUF) composite samples have been prepared with different proportions of iron slag as additives, with a range of 0–25% mass by weight. The process of grinding iron slag microparticles into iron slag nanoparticles powder was accomplished with the use of a high-energy ball mill. The synthesized samples have been characterized using Fourier Transform Infrared Spectroscopy, and Scanning Electron Microscope. Then, their radiation shielding properties were measured by using A hyper-pure germanium detector using point sources 241Am, 133 BA, 152 EU, 137Cs, and 60Co, with an energy range of 0.059–1.408 MeV. Then using Fluka simulation code to validate the results in the energy range of photon energies of 0.0001–100 MeV. The linear attenuation coefficient, mass attenuation coefficient, mean free path, half-value layer and tenth-value layer, were calculated to determine the radiation shielding characteristics of the composite samples. The calculated values are in good agreement with the calculated values. The results of this study showed that the gamma-ray and neutron attenuation parameters of the studied polyurethane composite samples have improved. Moreover, the effect of iron slag not only increases the gamma-ray attenuation shielding properties but also enhances compressive strength and the thermal stability. Which encourages us to use polyurethane iron-slag composite foam in sandwich panel manufacturing as walls to provide protection from radiation and also heat insulation.

Metallurgical slag used for efficient growth of Chlorella pyrenoidosa to achieve CO2 conversion to biodiesel

AbstractMetallurgical slag such as solid waste generated in the steel industry carries environmental pollution risks, but it is rich in nutrients required by microalgae. Metallurgical slag used for carbon capture and biomass energy conversion has multiple benefits: (i) reduction and harmless treatment of metallurgical solid waste, (ii) assisting in carbon neutrality by efficient carbon fixation, and (iii) production of biodiesel from CO2. In this study, AOD, BOF, BFS, HVS, and VTS slag were applied to culture Chlorella pyrenoidosa (C. pyrenoidosa) with the regulation of growth, carbon fixation, and lipid synthesis. An excellent fixed amount of CO2 with 94.59 mg is obtained from C. pyrenoidosa biomass at BOF slag added (mass ratio of CO2 captured/microalgae/slag with 1.99/1.00/10.53) since high Ca/Mg mass ratio of 419 (8.38 mg/L Ca and 0.02 mg/L Mg), no Cr and low concentration of Al (0.04 mg/L) contribute to regulating antioxidant enzyme activity (SOD and POD) to resist ROS and improving PEPC activity to reduce carbon flux toward lipid to promote biomass synthesis. Both metal concentrations from Ca (5.86 mg/L), Mg (0.05 mg/L), Al (0.42 mg/L), and Cr (0.006 mg/L) and suitable pH (10.53) in AOD leaching solution at solid/liquid ratio of 0.5 g/L change carbon flow toward efficient lipid synthesis (47.07 wt%) by continuously providing raw materials and energy by regulating ACC, ME, and PEPC activities. High value‐added biodiesel with high concentrations of C16 and C18 methyl esters from lipid of C. pyrenoidosa is achieved, following other ecological and economic benefits including 197 mg CO2 captured and 2198 mg AOD applied with harmless. In this study, C. pyrenoidosa is cultured with elements from metallurgical slag solid waste, which promotes C. pyrenoidosa efficient carbon fixation to assist in carbon neutrality, and provides guidance for CO2 conversion to high‐value‐added products with low cost.

Optimization of Ratio and Hydration Mechanism of Titanium-Extracted Residual Slag-Based Filling Cementitious Materials

Using metallurgical solid waste Titanium-extracted Residual Slag (TRS) as mine-filling cementitious material is crucial to reduce the filling cost and promote the utilization of solid waste resources. In this paper, taking the strength of the backfill at different curing ages as the response target, the Design-expert mixing design was used to optimize the proportioning experiment of titanium-extracted residual slag, titanium gypsum, silicate cement, and total tailings, to analyze the interactions and influences of the materials on the strength of the backfill, and to analyze the hydration mechanism of the titanium-extracted residual slag-based filling cementitious materials under the optimal proportioning. The results show that: (1) the order of the sensitivity of each component to the strength of backfill is: composite activator > cement > titanium gypsum > titanium-extracted residual slag, and there are different degrees of interaction between them; (2) the optimal ratio of titanium-extracted residual slag-based filling cementitious materials is TRS:titanium gypsum:cement:composite activator = 55:25:17:3; (3) early strength formation of backfill is mainly related to its hydration products ettringite and C-S-H, the rapid nucleation and cross-growth of ettringite in the early stage forms an effective physical filling effect, which is the main reason for the formation of high early strength, and the later strength of backfill benefited from the continuous accumulation of C-S-H encapsulation and bonding, which further densified its internal structure; (4) the use of titanium-extracted residual slag-based filling cementitious materials contributes to safe, green, and economic mining.

Mechanism Analysis and Experimental Research on Leaching Zn from Zinc Oxide Dust with an Ultrasound-Enhanced NH3-NH4Cl-H2O System

Zinc oxide dust (ZOD) is an industrial solid waste produced in the production process of wet smelting Zn, with large output and great pollution to the environment. The recycling of metallurgical solid waste such as zinc oxide dust is very important to achieve the sustainable development of the circular economy. An experimental study of zinc (Zn) leaching from zinc oxide dust using an ultrasound-enhanced ammonia–ammonium chloride system was performed. The effects of ultrasonic power, leaching time, total ammonia concentration, and other factors on the leaching rate of zinc from zinc oxide dust were investigated. The results revealed that the leaching rate of Zn reached up to 80.70% under the condition of ultrasound power of 1000 W, reaction time of 15 min, total ammonia concentration of 6 mol/L, [NH3]:[NH4+] of 1:1, L/S of 5:1, temperature of 45 °C, and stirring speed of 100 r/min. The conventional leaching was conducted under similar conditions, except that the time was controlled to 40 min and the zinc leaching rate was 71.15%. The leaching rate of Zn in the ultrasound condition was improved by 9.55% compared with that in the conventional leaching process. XRD, laser particle size, and SEM-EDS analyses were conducted to study the leaching residues of ZOD. The analysis results showed that in the ultrasound condition, the largest leaching rate of soluble ZnO phases was achieved after 15 min of leaching. Under the ammoniacal system, it was difficult to leach ZnFe2O4, Zn2SiO4, and ZnS phases, which partly accounted for the low zinc leaching rate. Additionally, through ultrasound-enhanced treatment, the ZnO particles encapsulated in ZOD particles were broken into smaller sizes and exposed to the leaching solution. Thus, the leaching rate of Zn was improved. The experimental results show that ultrasound can tremendously improve the effect of Zn extraction from ZOD, shorten reaction time, and help reduce energy consumption and environmental pollution, making it a promising application in the treatment of secondary Zn resources.

Fabrication of 2D TiO2/α-Fe2O3/Fe-g-C3N4 heterogeneous from metallurgical solid waste for Photo-Fenton catalysis of levofloxacin/Cr(VI): Electron transfer pathway and DFT calculation

Herein, the 2D Nano α-Fe2O3 were prepared by solvent-free method from rolling iron scale (RIS) - a by-product of metallurgical industry. 2D TiO2/α-Fe2O3 nanostructures were prepared using the obtained nanocrystals. Fe-doped g-C3N4 (Fe-g-C3N4) was synthesized using RIS as the raw material. A Composite of TiO2/α-Fe2O3 and Fe-g-C3N4 was combined to prepare a TiO2/α-Fe2O3/Fe-g-C3N4 heterojunction with high catalytic performance. This heterojunction was employed as a photo-Fenton catalyst to synergistically remove Cr(VI) and levofloxacin (LEV). The TiO2/α-Fe2O3/Fe-g-C3N4 heterojunction enhanced the intensity of the visible light response and suppressed the recombination of photogenerated electrons and holes. The N-Fe-O bridge, formed by synergistic coordination effects, enhanced the charge lifetime by decreasing the impedance of the catalyst and increasing the electron transfer rate. Additionally, the Fermi level and work function of the sample were calculated, providing further evidence for the electron transfer. Direct electron transfer between TiO2/α-Fe2O3/Fe-g-C3N4 and LEV/Cr(VI) was observed, indicating its importance in the removal of pollutants. To determine the potential degradation pathways, the energy orbitals of LEV derived from DFT calculations were analyzed. Overall, the study presents an excellent strategy for the sustainable use of RIS and the preparation of highly active catalysts. In conclusion, TiO2/α-Fe2O3/Fe-g-C3N4 is predicted to considerably contribute to studies on treating heavy metal and organic pollutant-contaminated wastewater.

Mechanism and property optimization of stainless steel slag for preparation of cementitious materials

The effective utilization of stainless steel slag on a large scale has posed a persistent challenge. To address this problem, this study used the orthogonal test method to investigate the optimisation of the ratio of stainless steel slag preparation cementitious materials while exploring the curing mechanism of metallurgical solid waste materials and its stability and the leaching of heavy metals. The experimental results revealed that the optimal combination consisted of 59% granulated blast furnace slag(GBFS), 35% stainless steel slag(AODS), and 6% desulfurization gypsum(DG). This composition yielded impressive compressive strength values of 11.40 MPa at 3 days and 28.36 MPa at 28 days. The stainless steel slag(AODS) contains a large amount of highly reactive calcium-containing material, accelerating the hydration reaction for 7–28 days. Moreover, the 3CaO·2SiO2·3 H2O(C-S-H) dense layered structure and related products produced by the hydration reaction can effectively encapsulate the Cr2O3 particles. As a result, the strength, stability and safety of the cementitious materials were significantly improved.

Fabrication of iron doped titanium dioxide photocatalytic nanocomposite supported by water-quenched blast furnace slag and photocatalytic degradation of wastewater

Metallurgical solid waste blast furnace water quenched slag (WBFS) was employed as carrier materials to prepare Fe–TiO2/WBFS composite photocatalyst using a sol-gel method for improving both the photocatalytic activity and the high-value utilization of metallurgical solid waste. The Fe3+ doping technology was adopted to increase the utilization of solar energy. The influencing factors and photocatalytic activity were systematically evaluated by thermogravimetry/differential thermal analyser (TG-DSC), X-Ray Diffraction (XRD), Brunauer-Emmett-Teller (BET) method, scanning electron microscopy-energy spectrometer (SEM-EDS), X-ray photoelectric spectroscopy (XPS), UV–Vis absorption spectrum and photoluminescence spectra technology through the degradation rate of methylene blue (MB) solution. The results showed that the Fe3+ ions were successfully incorporated into the TiO2 lattice, which had no effect on the crystalline phase of TiO2 and expanded the spectral response range of TiO2 from the ultraviolet region to the visible light region. When the calcination temperature was at 450 °C and the number of Fe–TiO2 sol loading cycles was two times, the photocatalytic activity of Fe–TiO2/WBFS presented the strongest, and the degradation ratio of MB reach the maximum value of 98.9 %. A uniform and dense anatase TiO2 thin film was wrapped on the surface of WBFS. The photocatalytic activity first improved and then weakened with an increase of calcination temperature, Fe3+ doping amounts and the loading cycles of sol. The TiO2 film changed from thin to thick and uneven to uniform, until cracking and spalling phenomenon finally occurred with an increase of Fe–TiO2 sol loading cycle from 1 to 3 times. When the Fe–TiO2/WBFS was reused for four times, the degradation rate of MB could still show 67.4 %, being far higher than that of TiO2/WBFS of 25.4 %.

Synthesis of ZnO nanoparticle from Electric Arc Furnace (EAF) dust prepared by hydrothermal method via hydroxide precipitation

Electric Arc Furnace (EAF) dust is a type of metallurgical solid waste that is produced as a by-product of steel manufacturing and contains important metals such as zinc (Zn). Processing Zn from EAF dust into metal oxides such as zinc oxide (ZnO) is critical for a variety of applications. The hydrothermal technique of extracting Zn from EAF dust uses hydrochloric acid (HCl) as a leaching agent and sodium oxide (NaOH) as a precipitating reagent. In this study, the process begins with leaching using HCl 3 M at a temperature of 80 °C for 5 hours. The product is then filtered to separate the Zn and other components in the EAF dust. The method is then continuing for precipitation using NaOH 10% as a precipitating agent. Then, initiating the hydrothermal process with time variations of 1, 3, and 6 hours and temperatures of 120 °C, 150 °C, and 200 °C. The UV-Vis characterization result showed that the absorbance value was around 365 nm, which is typical of ZnO. The XRF analysis demonstrated an increase in the presence of ZnO compound. The XRD results showed that as the hydrothermal temperature and duration increased, so did the crystallinity in ZnO. The results shown that ZnO nanoparticles can be prepared from EAF dust as a raw material using the hydrothermal technique via hydroxide precipitation.

A novel approach to treating nickel-containing electroplating sludge by solidification with basic metallurgical solid waste

Nickel-containing electroplating sludge is a solid waste generated during the treatment of electroplating wastewater, often managed through solidification with materials such as cement and lime. This paper presents a novel approach for solidifying nickel-containing electroplating sludge using basic metallurgical solid waste. A mathematical model was employed to determine the kinetics of Ni2+ leaching, yielding the kinetic equation α(t) = 0.97∗(1-exp (-0.19∗t)). Rapid leaching occurred in the initial 10 min, reaching a concentration of 86.78 mg/L, followed by a slower release, peaking at 104.54 mg/L within 40 min. Through the solidification of electroplating sludge with basic waste materials, it was found that the inclusion of 2.0 % lime, 12.2 % sintering dust, and 2.5 % steel slag resulted in Ni2+ leaching concentrations of 0.28, 0.41, and 0.61 mg/L, respectively, all meeting the discharge standard of <1.00 mg/L. Phase analysis indicated that the main constituents of the solidified products were C–S–H and CaSO4, with no detectable change in the crystallinity of Ni2+ before and after solidification. Thermodynamic calculations further demonstrated that under basic solidification conditions, Ni2+ transforms from NiSO4 to Ni(OH)2. Microscopic morphology analysis revealed that the encapsulation of Ni2+ by C–S–H and CaSO4 led to the densification of the porous microstructure of the electroplating sludge, achieving effective solidification.

Valuable Recovery Technology and Resource Utilization of Chromium-Containing Metallurgical Dust and Slag: A Review

As a type of metallurgical solid waste with a significant output, chromium-containing metallurgical dust and slag are gaining increasing attention. They mainly include stainless steel dust, stainless steel slag, ferrochrome dust, and ferrochrome slag, which contain significant amounts of valuable elements, such as chromium, iron, and zinc, as well as large amounts of toxic substances, such as hexavalent chromium. Achieving the harmless and resourceful comprehensive utilization of chromium-containing metallurgical dust and slag is of great significance to ensuring environmental safety and the sustainable development of resources. This paper outlines the physicochemical properties of stainless steel dust, stainless steel slag, ferrochrome dust, and ferrochrome slag. The current treatment technologies of chromium-containing metallurgical dust and slag by hydrometallurgy, the pyrometallurgical process, and the stabilization/solidification process are introduced. Moreover, the comprehensive utilization of resources of chromium-containing metallurgical dust and slag in the preparation processes of construction materials, glass ceramics, and refractories is elaborated. The aim of this paper is to provide guidance for exploring effective technology to solve the problem of chromium-containing metallurgical dust and slag.

Silica Fume Enhances the Mechanical Strength of Alkali-Activated Slag/Fly Ash Pastes Subjected to Elevated Temperatures

The fireproof design of geopolymers through adjusting multi-component metallurgical solid wastes has attracted increasing attention, due to their potential low carbon emission, cost effectiveness, and role in environmental conservation. Herein, the effects of silica fume (SF) on the microstructure and mechanical properties of alkali-activated slag/FA (fly ash) pastes subjected to elevated temperatures (150, 500, 850, and 1200 °C) are investigated to clarify whether or not SF has a positive role in the mechanical strength of the slag/FA (slag/FA = 30:70, wt.%) geopolymer during building fires. The results show that the replacement of FA with 10 wt.% SF (silica fume) promotes the increasing pore volume with a diameter of 0.2~3 μm, leading to an increase in the compressive or flexural strength below 850 °C, “right shifts” of the endothermic peak, and uniform and compact fracture surfaces. Meanwhile, gehlenite and labradorite are generated after exposure above 850 °C. The bloating effect of the SF-containing sample occurs at 1200 °C, leading to a greater deformation due to the further restructuring of the amorphous geopolymer chain N–A–S–H or N–(Ca)–A–S–H composed of [SiO4]4− and [AlO4]5−. This paper explores an effective approach to improving geopolymers’ fireproof performance by adjusting the formulation of solid waste.

Agglomeration and bonding mechanism of typical metallurgical solid wastes

Agglomeration and bonding mechanism of typical metallurgical solid wastes

Efficient lipid synthesis of Chlorella pyrenoidosa promoted under heavy metals from electric arc furnace slag

Electric furnace slag was highly productive and rich in elements, which can be used as a nutrient source for microalgae growth. The regulation of growth and lipid synthesis of Chlorella pyrenoidosa (C. pyrenoidosa) in electric arc furnace slag leaching solution with or without citric acid was investigated to develop efficient lipid production method with low cost. High lipid content of 45.89 wt% from C. pyrenoidosa with adding electric arc furnace slag leaching solution ≤40% into BG11 was obtained due to C. pyrenoidosa increasing lipid accumulation to resist oxidative stress caused by heavy metals in electric arc furnace slag (Ca of 5.13 mg/L, Fe of 0.05 mg/L, Mn of 0.12 mg/L and Cr of 0.01 mg/L). Exogenous citric acid can improve the ability of C. pyrenoidosa to resist heavy metal toxicity with high biomass content (0.44 g/L) achieved. The cooperation of multiple metal ions in electric arc furnace slag shortened the biomass accumulation stage and prolonged and speeded up the lipid synthesis stage of C. pyrenoidosa by modulating PEPC, ACC and ME activities. This study provided guidance for the industrialization of low-cost lipid-rich microalgae and metallurgical solid waste treatment.

Properties and microstructure of total tailings cemented paste backfill material containing mining and metallurgical solid waste

Introduction: In order to improve the utilization efficiency of industrial waste discharged in the process of iron and steel metallurgy, a kind of material that can replace cement for mine filling is sought. In the test, steel slag (SS) and vanadium-titanium slag (VTS) were used as the primary raw materials to prepare cementing agents (CA). Then, combine it with vanadium-titanium iron ore tailings (VTIOTs) to make mine cemented paste backfill material (CPBM).Methods: The composition, properties and hydration mechanism of CPBM are studied through various tests, in-cluding mechanical property test, hydration heat test, X-ray diffraction (XRD), scanning electronic mi-croscopy (SEM), and fourier transform-infrared spectroscopy (FT-IR).Results: The results show that when the following conditions are met, the slump is 216 mm, and the 28-day flexural strength and compressive strength of CPBM reach 4.25 and 9.41 MPa, respectively, which meets the requirements of Chinese National Standard GB/T 39489-2020 Technical specification for the total tailings paste backfill: the mass percentage SS: VTS: phosphogypsum (PG): dicyandiamide waste slag (DWS) = 31:59:6:4; the content of compound phosphoric acid (CPA) accounts for 4% of the dry material; the cement sand ratio of CPBM is 1:4; the paste mass concentration (PMC) is 80%; and the content of water reducing agent (WRA) is 0.18%.Discussion: Mechanism studies show that the hydration product of the CA is mainly ettringite (AFt) and C-S-H gel. The addition of CPA promotes the hydration of active minerals in SS and VTS. The existence of PG pro-motes the formation of AFt, and the formation of AFt further promotes the fracture of [AlO4]5− and [SiO4]4− along the bridge oxygen in VTS and SS.

High-efficiency recycling of copper-cadmium slag by ozonation with ultrasonic catalysis

Copper-cadmium slag, a kind of hazardous metallurgical solid waste, has attracted attention in the fields of environmental protection and resource recovery because of its high output and richness of valuable metals. However, it is difficult to separate and recycle efficiently due to its oxidation resistance and strong wrapping property. To address this challenge, the ozonation with ultrasonic catalysis method is proposed for leaching of copper-cadmium slag in this work. Mechanical and cavitation effects of ultrasound can break wrapping layer and renew reaction interfaces. The active free radicals produced by ultrasonic/ozone can enhance the oxidation of reaction system and cause the inert metal copper to oxidize more easily. The leaching percentage of copper is 99.3%, which is 45.7% higher than that of conventional condition. Diffusion is proved to be the restrictive link in the copper dissolution process via kinetic experiment with a low activation energy of 3.71 kJ/mol under ultrasonic/ozone condition. The hydroxyl radical is detected by electron paramagnetic resonance and confirmed that it is beneficial to increase the recovery rate of metal in slag by quenching experiment. This study illustrates the value of ozonation with ultrasonic catalysis technology in efficient and green economy separation and recovery of various metals from hazardous waste.

Preparation and properties of anorthite‐based ceramics by using metallurgical solid waste and fly ash

AbstractA large amount of metallurgical solid waste accumulation poses a serious threat to the environment. Study on synergistic reinforcement of synthetic process of metallurgical solid waste‐based ceramics with fly ash is of great significance in reducing environmental pollution and resource utilization. A metallurgical solid waste‐based ceramic used as building ceramic was developed with the erosion part of used MgO–C bricks and fly ash as main raw materials, and the amount of solid waste added to the prepared ceramics was at least 60 wt% and up to 90 wt%. The effects of fly ash content and sintering temperature on the crystalline phase transitions, morphologies, and the main physical and mechanical properties of ceramics were investigated by X‐ray diffraction, scanning electron microscopy, and mechanical testing. The results show that the obtained ceramics presented maximum bending strength and minimum water absorption, 80.14 MPa and 5.04%, respectively, when the raw material proportions were the erosion part of used refractories accounted for 60 wt%, fly ash 20 wt%, pyrophyllite 10 wt%, and quartz sands 10 wt%, and the process parameters were the sintering temperature 1150°C, sintering time 120 min, and molding pressure 15 MPa.

Novel halogen‐free Si‐C‐P flame‐retarding coatings constructed by DOPO/flake graphite co‐doping silica fume‐based geopolymer

AbstractA facile design for value‐added recycling of metallurgical solid waste is urgent for developing safe and sustainable human settlements. Therefore, novel DOPO/flake graphite (FG) co‐doped silica fume‐based geopolymer coatings for flame‐retarding plywood were prepared to seek a halogen‐free and low‐carbon Si‐C‐P fireproof method. The results show that appropriate DOPO (1 wt%) constitutes an enhanced flame retardancy, evidenced by the reduced peak of heat release rate (decreases from 153.48 to 96.94 kW m−2) and the rising flame retardancy index (climbs from 1.00 to 2.32). Meanwhile, its pyrolysis is identified as the three‐level chemical reaction model (F3), the hydrogen bond crosslinking between the POC and HOSiO results in a rising Eα at 1000–731°C (increases from 163.60 to 198.83 kJ mol−1). Finally, the synergistically flame‐retardant mechanism consists of water volatilization at 100°C, the as‐formed porous carbonaceous layer at about 200°C, transformations of DOPO at 300–500°C, the formed DOPO derivatives at 500–700°C, and the decomposition of DOPO derivatives (condensed phase barrier) above 700°C, respectively. The yielded residues generate a 56% formaldehyde adsorption rate. It proposes a halogen‐free and low‐carbon strategy for designing Si‐C‐P hybrid flame‐retarding coatings, indicating an ecological direction for the value‐added utilization of metallurgical solid waste.

Flame-Retarded Rigid Polyurethane Foam Composites with the Incorporation of Steel Slag/Dimelamine Pyrophosphate System: A New Strategy for Utilizing Metallurgical Solid Waste.

Rigid polyurethane (RPUF) was widely used in external wall insulation materials due to its good thermal insulation performance. In this study, a series of RPUF and RPUF-R composites were prepared using steel slag (SS) and dimelamine pyrophosphate (DMPY) as flame retardants. The RPUF composites were characterized by thermogravimetric (TG), limiting oxygen index (LOI), cone calorimetry (CCT), and thermogravimetric infrared coupling (TG-FTIR). The results showed that the LOI of the RPUF-R composites with DMPY/SS loading all reached the combustible material level (22.0 vol%~27.0 vol%) and passed UL-94 V0. RPUF-3 with DMPY/SS system loading exhibited the lowest pHRR and THR values of 134.9 kW/m2 and 16.16 MJ/m2, which were 54.5% and 42.7% lower than those of unmodified RPUF, respectively. Additionally, PO· and PO2· free radicals produced by pyrolysis of DMPY could capture high energy free radicals, such as H·, O·, and OH·, produced by degradation of RPUF matrix, effectively blocking the free radical chain reaction of composite materials. The metal oxides in SS reacted with the polymetaphosphoric acid produced by the pyrolysis of DMPY in combustion. It covered the surface of the carbon layer, significantly insulating heat and mass transport in the combustion area, endowing RPUF composites with excellent fire performance. This work not only provides a novel strategy for the fabrication of high-performance RPUF composites, but also elucidates a method of utilizing metallurgical solid waste.