Novel method for comprehensive utilization of MSWI fly ash through co-reduction with red mud to prepare crude alloy and cleaned slag

Intelligent technologies powering clean incineration of municipal solid waste: A system review

Cleanliness has been paramount for municipal solid waste incineration (MSWI) systems. In recent years, the rapid advancement of intelligent technologies has fostered unprecedented opportunities for enhancing the cleanliness of MSWI systems. This paper offers a review and analysis of cutting-edge intelligent technologies in MSWI, which include process monitoring, intelligent algorithms, combustion control, flue gas treatment, and particulate control. The objective is to summarize current applications of these techniques and to forecast future directions. Regarding process monitoring, intelligent image analysis has facilitated real-time tracking of combustion conditions. For intelligent algorithms, machine learning models have shown advantages in accurately forecasting key process parameters and pollutant concentrations. In terms of combustion control, intelligent systems have achieved consistent prediction and regulation of temperature, oxygen content, and other parameters. Intelligent monitoring and forecasting of carbon monoxide and dioxins for flue gas treatment have exhibited satisfactory performance. Concerning particulate control, multi-objective optimization facilitates the sustainable utilization of fly ash. Despite remarkable progress, challenges remain in improving process stability and monitoring instrumentation of intelligent MSWI technologies. By systematically summarizing current applications, this timely review offers valuable insights into the future upgrade of intelligent MSWI systems.

Towards a low-emission resource circulation of valuable metals from municipal solid waste incineration fly ash

The incineration fly ash (IFA) resulting from municipal solid waste combustion is laden with heavy metals, necessitating proper treatment not only for environmental management but also to reclaim the metal values. The surge in non-traditional metals like cobalt as emerging contaminant within IFA samples further attracts to address this issue. In response, the hydrometallurgical recycling of a cobalt-bearing IFA has been studied. Thereby, approximately 98 % zinc and 96 % cobalt were leached using a 1.0 mol/L H2SO4 solution at 90 °C and 1 h of leaching time. In-depth analysis of the leaching process unveiled metals' dissolution primarily via the ion-exclusion mechanism, as evidenced by lower diffusion coefficients (between 10-9 and 10-11 m2/s) and activation energies (9.6-14.9 kJ/mol). Above 99 % separation of zinc from the cobalt-bearing leach liquor was achieved by extraction with 1.0 mol/L D2EHPA at an equilibrium pH below 3.0, followed by stripping with a 2.0 mol/L H2SO4 solution. Cobalt, remained in the raffinate was efficiently precipitated by adding a 20 % excess dosage of oxalic acid to the stoichiometric ratio of C2O42-:Co2+, resulting in only 5 mg/L cobalt left in the solution when precipitation occurred at a pH of 2.8. Additionally, the conversion of CoC2O4 to high-purity Co3O4 was conducted through heat-treatment at 600 °C. The resulting Co3O4 was mixed with Li2CO3 at a Li/Co molar ratio of 1.1, yielding a LiCoO2 precursor that exhibited good electrochemical properties with a capacity of 128 mAh/g, thus affirming the high quality of the recycled cobalt. A comprehensive life-cycle assessment of the recycling process revealed that cobalt precipitation alone contributes approximately 50 % of the total global warming potential (GWP = 4.2624 kg CO2-eq). Notably, this value is remarkably lower than the GWP reported for primary cobalt production, highlighting the environmentally-friendly approach of this recycling endeavor.

Complementary vitrification of municipal solid waste incineration fly ash from grate furnaces and fluidised bed incinerators via a co-reduction process

The increasing application of municipal solid waste incineration (MSWI) emphasises the need for MSWI fly ash (FA) safe treatment. Based on the compositional complementarity of FA from grate furnaces (G-FA) and fluidised bed incinerators (F-FA), we proposed a co-reduction process to treat G-FA and F-FA together for producing vitrified slag and ferroalloys. The clean vitrified slag and Fe-Cr-Ni-Cu alloy were obtained with the mass ratios of 1:9 ∼ 6:4 (G-FA:F-FA) at 1300℃, which is about 300℃ lower than the conventional G-FA vitrification. The metals Zn, Cd, and Pb were mostly volatilised into the flue gas for potential recovery from the secondary FA. The thermodynamic SiO2-Al2O3-CaO ternary system demonstrated that an optimal mass ratio of the two complementary FA types contributes to the system shifting to the low-temperature melting zone. The co-reduction process of G-FA and F-FA could be a promising option for FA beneficial reutilization with environmental advantages.

Recovery of lead and chlorine via thermal co-treatment of municipal solid waste incineration fly ash and lead-rich waste cathode-ray tubes: Analysis of chlorination volatilization mechanism

In this study, a new lead (Pb) and chlorine (Cl) recovery process via the thermal co-treatment of Municipal solid waste (MSW) incineration fly ash (FA) and waste cathode-ray tubes (CRT) was developed and the synergistic effects under different CRT ratios, temperatures, and residence times were comprehensively investigated. Thermogravimetric experiments revealed that the co-processing of FA and CRT exhibited a remarkable synergistic effect as evidenced by the considerable increase in mass loss and mass-loss rate when compared with the theoretical values. When the mixtures with 50% CRT addition was treated at 1200 °C for 60 min, Pb removal rate reached the maximum value of 98.67%, and the Cl removal rate considerably increased by 37.32% compared to that with FA treatment alone. Additionally, the Cl content in the residue was < 2%. It was mainly attributed to the volatilization of chlorides, such as PbCl2, NaCl, and KCl. CaCl2 generated from the decomposition of CaClOH in FA was conducive to improve Pb removal in CRT through indirect chlorination and destroying the glass structure in CRT. Co-processing of FA and CRT demonstrates promising potential for several benefits, including the reduction in melting temperature, recovery of Pb and Cl from secondary fly ash, and the reutilization of calcium-rich slag.

Fate of Cl and chlorination mechanism during municipal solid waste incineration fly ash reutilization using thermal treatment: a review

Safe and sustainable treatment of municipal solid waste incineration fly ash (MSWI FA) is urgently needed worldwide because of its high heavy metals, dioxin, and chlorine (Cl) contents. Thermal treatment is widely considered as a promising method for treating MSWI FA owing to its high toxic content removal efficiency and resource recovery; however, residual Cl is a concurrent critical problem faced during reutilisation of thermal treatment products. This review summarises the innovative thermal treatment methods of MSWI FA, such as those employed in production of cement, lightweight aggregates, glass slag, and metal alloys. The characteristics of Cl in MSWI FA, removal rate, transformation of water-soluble Cl into water-insoluble Cl, and the effect of different influencing factors such as temperature, composition, superheated steam, and mechanical pressure were analysed. The volatilization and decomposition of NaCl, KCl and CaClOH dominates Cl removal; however, the degradation of organic Cl and heavy metal chlorination volatilization process that generate HCl and heavy metal chlorides, respectively, also contributed to Cl removal. To promote the reutilisation of MSWI FA-based products, the leaching behaviour of residual Cl in products obtained by different thermal treatments was investigated.

Red mud with enhanced dealkalization performance by supercritical water technology for efficient SO2 capture

The total de-alkalization treatment of industrial solid waste red mud (RM) has been a worldwide challenge. Removing the insoluble structural alkali fraction from RM is the key to enhancing the sustainable utilization of RM resources. In this paper, supercritical water (SCW) and leaching agents were used for the first time to de-alkalize the Bayer RM and to remove sulfur dioxide (SO2) from flue gas with the de-alkalized RM slurry. The results showed that the optimum alkali removal and Fe leaching rates of RM-CaO-SW slurry were 97.90 ± 0.88% and 82.70 ± 0.95%, respectively. Results confirmed that the SCW technique accelerated the disruption of (Al-O) and (Si-O) bonds and the structural disintegration of aluminosilicate minerals, facilitating the conversion of insoluble structural alkalis to soluble chemical alkalis. The exchangeable Ca2+ displaced Na+ in the remaining insoluble base, producing soluble sodium salts or alkalis. CaO consumed SiO2, which was tightly bound to Fe2O3 in RM, and released Fe2O3, which promoted Fe leaching. RM-SCW showed the best desulfurization performance, which maintained 88.99 ± 0.0020% at 450 min, followed by RM-CaO-SW (450 min, 60.75 ± 6.00%) and RM (180 min, 88.52% ± 0.00068). The neutralization of alkaline components, the redox of metal oxides, and the liquid-phase catalytic oxidation of Fe contributed to the excellent desulfurization performance of the RM-SCW slurry. A promising approach shown in this study is beneficial to RM waste use, SO2 pollution control, and sustainable growth of the aluminum industry.

Synthesis of metakaolin-based geopolymer foamed materials using municipal solid waste incineration fly ash as a foaming agent

The existence of metallic aluminum in municipal solid waste incineration fly ash (MSWIFA) makes it challenging to recycle MSWIFA into cement materials because expansion occurs in the resultant matrices. Geopolymer-foamed materials (GFMs) are gaining attention in the field of porous materials due to their high-temperature stability, low thermal conductivity and low CO2 emission. This work aimed to utilize MSWIFA as a foaming agent to synthesize GFMs. The physical properties, pore structure, compressive strength and thermal conductivity were analyzed to assess different GFMs which were synthesized with various MSWIFA and stabilizing agent dosages. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis were conducted to characterize the phase transformation of the GFMs. Results showed that when MSWIFA content was increased from 20 to 50%, the porosity of GFMs increased from 63.5 to 73.7%, and bulk density decreased from 890 to 690 kg/m3. The addition of stabilizing agent could trap the foam, refine the cell size, and homogenize the cell size range. With the stabilizing agent increase from 0 to 4%, the porosity increased from 69.9 to 76.8%, and the bulk density decreased from 800 to 620 kg/m3. The thermal conductivity decreased with increasing MSWIFA from 20 to 50%, and stabilizing agent dosage from 0 to 4%. Compared with the collected data from references, a higher compressive strength can be obtained at the same level of thermal conductivity for GFMs synthesized with MSWIFA as a foaming agent. Additionally, the foaming effect of MSWIFA results from the H2 release. The addition of MSWIFA changed both the crystal phase and gel composition, whereas the stabilizing agent dosage had little impact on the phase composition.

Evaluating the recycling potential of ashes discharged from waste incineration facilities and its dependency on pretreatment efficiency in Korea

The amount of incineration ash (IA) is expected to increase in South Korea from the rapidly rising numbers and operation capacities of incineration facilities; therefore, it remains necessary to establish measurements for the enhanced recycling and circularity of IA. This study established a database of hazardous substances in IA by compiling discharge data and survey results from domestic incineration facilities, along with literature survey values. The recycling potential of IA was assessed considering leaching reduction efficiency of various pretreatment methods. In particular, 98.2% of bottom ash and 49.0% of fly ash satisfied the IA recycling criteria after melting. Also, when mixed at a ratio of ∼ 78:22 natural soil to IA, the resulting material was usable for media-contact recycling by meeting the heavy metal content criteria of the Soil Environment Conservation Act.

The physical encapsulation and chemical fixation of Zn during thermal treatment process of municipal solid waste incineration (MSWI) fly ash

Thermal treatment is a promising treatment technology of municipal solid waste incineration (MSWI) fly ash because of its detoxication and volume reduction. However, the relationship between immobilization of heavy metals and mineral transformation during thermal treatment remains unclear. In this study, the immobilization mechanism of Zn during thermal treatment process of MSWI fly ash was investigated by experiment and calculation. The results show that addition of SiO₂ facilitates transition of dominant minerals from melilite to anorthite during sintering, increases liquid content during melting and improves liquid polymerization degree during vitrification. ZnCl₂ tends to be physically encapsulated by liquid phase, and ZnO is mainly chemically fixed into minerals at high temperature. Increase in both liquid content and liquid polymerization degree favors the physical encapsulation of ZnCl₂. The decreasing order of chemical fixation ability of minerals to ZnO is spinel > melilite > liquid > anorthite. To better immobilize Zn during sintering and vitrification process chemical composition of MSWI fly ash should be located in melilite and anorthite primary phases of pseudo-ternary phase diagram, respectively. The results are helpful to understand immobilization mechanism of heavy metals and avoid volatilization of heavy metals during thermal treatment process of MSWI fly ash.

Footprints in compositions, PCDD/Fs and heavy metals in medical waste fly ash: Large-scale evidence from 17 medical waste thermochemical disposal facilities across China

Chemical compositions, polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) profiles and heavy metals (HMs) leachability of medical waste fly ash (MWFA) from 17 thermochemical treatment facilities in eight Chinese provinces were first investigated. Large-scale and extended monitoring revealed high chloride and Zn contents and similar PCDD/Fs congener profiles in MWFA. Particularly, the PCDD/Fs and HMs concentrations implied greater toxicity than that observed for municipal solid waste incinerator fly ash (MSWIFA). The maximum international toxic equivalent value of PCDD/Fs in MWFA was 40 times that of MSWIFA, and the leaching concentrations of Zn and Hg were 15 and 4 times those of MSWIFA, respectively. Notably, MWFA characteristics suggest the possibility of recycling and sustainable disposal solutions owing to the high Cl and Zn content with good recovery instead of landfill disposal. Similarities in chemical composition, PCDD/Fs homolog distribution, and water-solubility of chloride salts allows co-processing of MWFA and MSWIFA via water-washing detoxification and thermal treatment, such as that used in cement kilns. This study supplements existing literature on the characteristics and risk management of MWFA.

Red mud recycling by Fe and Al recovery through the hydrometallurgy method: a collaborative strategy for aluminum and iron industry

In this work, a collaborative strategy for the aluminum and iron industry based on red mud recycling through the hydrometallurgy method was proposed. In this method, Fe³⁺ and Al³⁺ were firstly separated from the red mud by using H₂SO₄ as a leaching agent, which was by-produced from the sintering process of an iron and steel industry. Multiple influence factors on the leaching process were investigated, with the H₂SO₄ addition amount showing the strongest influence on the leaching rates of Al and Fe. The main components of the filter residue were CaSO₄, TiO₂, and SiO₂, which could be reused as additives in the building materials. Subsequently, the final Fe recovery product was obtained through the co-precipitation, Fe/Al separation, and Fe(OH)₃ calcination. In the final product, the content of Fe₂O₃ reached 82.87%, and the iron grade was 58.01%, meeting the requirement being raw materials for sinter production.

Lead-chlorine synergistic immobilization mechanism in municipal solid waste incineration fly ash (MSWIFA)-based magnesium potassium phosphate cement

The high chlorine (Cl) and lead (Pb) content characteristics of municipal solid waste incineration fly ash (MSWIFA) pose environmental risks and hinder resource utilization. Herein, an MSWIFA-based magnesium potassium phosphate cement (MKPC) preparation strategy was developed, which allowed the MSWIFA recycling and the Pb-Cl synergistic immobilization without the washing pretreatment. The compressive strength of the resulting 10 wt% MSWIFA-based MKPC was 28.44 MPa, with over 99.2% reduction in leaching toxicity of Pb and Cl. The high-angle annular dark field scanning transmission electron microscope (HAADF-STEM) and X-ray absorption spectroscopy (XAS) analyzes showed that Pb, phosphate and Cl^- formed Pb₅(PO₄)₃Cl in MKPC. In-situ X-ray diffraction (XRD) tests showed that Pb₃(PO₄)₂ was gradually transformed to Pb₅(PO₄)₃Cl through a dissolution-precipitation process. The formation energy, Bader charge, charge density difference and density of states (DOS) of Pb₅(PO₄)₃Cl were analyzed by first-principles calculations, confirming that Pb₅(PO₄)₃Cl was more thermodynamically stable than Pb₃(PO₄)₂ and PbCl₂ and that electronic interactions between Pb-p, O-p, P-p and Cl-p orbits were the origin of Pb-Cl synergistic immobilization. This work provides a new strategy for the resource utilization of MSWIFA without washing pretreatment, and provides an in-depth understanding of the Pb-Cl synergistic immobilization mechanism.

Basic Research on Co-treatment of Municipal Solid Waste Incineration Fly Ash and Municipal Sludge for Energy-Saving Melting

MSWI fly ash and municipal sludge are solid wastes. Melting vitrification treatment was a resource utilization method. However, the flow temperature of grate furnace MSWI fly ash and municipal sludge was high (>1325 °C), which increased the energy consumption in the melting process. MSWI fly ash contained a large amount of CaO, and municipal sludge contained a large amount of SiO₂, Al₂O₃, and Fe₂O_3. The temperature of melting vitrification can be reduced using these two kinds of CITY garbage as raw materials to change the proportion of ingredients. The eutectic characteristics of MSWI fly ash and municipal sludge and the phase diagrams of CaO-SiO₂-Al₂O₃ (C-S-A) and CaO-SiO₂-Al₂O₃-Fe₂O₃ (C-S-A-F) were analyzed in this paper. It established a low melting point mixing system. The results showed that when the amount of municipal sludge was 50-70%, the flow temperature of the mixtures was <1215 °C, which was significantly lower than that of MSWI fly ash (1490 °C) and municipal sludge (1325 °C). The optimal range of low melting point components was 14.1-36.3% CaO, 21.6-40.4% SiO₂, 6.7-12.6% Al₂O₃, and 6.3-11.4% Fe₂O₃. At 400-1400 °C, the minerals in the mixtures mainly changed as follows: CaCO₃ + SiO₂ + Al₂O₃ → Ca₂SiO₄ + Ca₃SiO₅ + Ca₂Al₂SiO₇ + Ca₃Al₂O₆ + Ca₁₂Al₁₄O₃₃ → CaAl₂Si₂O₈. In the melting experiment, with the increase in temperature, most of the phases in the mixtures might become amorphous. Therefore, the low melting point phase anorthite (CaAl₂Si₂O₈) only accounted for a small part of the final molten product.

The Distribution Pattern and Leaching Toxicity of Heavy Metals in Glass Ceramics from MSWI Fly Ash and Andesite Tailings

The leaching of heavy metals (HMs) is the key factor affecting the resource utilization of municipal solid waste incineration (MSWI) fly ash. A novel fly ash and andesite-tailings-based (FAAT) glass ceramic is prepared with the full-component utilization of MSWI fly ash and andesite tailings. The effects of the content and distribution state of HMs on their leaching toxicity are studied by performing a sequential extraction procedure and leaching toxicity test. The results show that the MSWI fly ash content greatly impacts the HMs' leaching toxicity in glass ceramics. Thus, the addition of MSWI fly ash must be maintained at below 20% so as to meet the class III groundwater standard. Furthermore, the different distribution states of Zn and Cr also affect their leaching toxicity. Zn suits the requirements for leaching toxicity only in a 2080c sample, while Cr fulfills the class III groundwater standard for all the glass ceramics. Since this finding is mismatched with the calculated potential ecological risk index of glass ceramics, the latter can only be used as a reference. Therefore, the results of the present study are of great significance in the vitrification application of MSWI fly ash.

Silica-assisted pyro-hydrolysis of CaCl2 waste for the recovery of hydrochloric acid (HCl): Reaction pathways with the evolution of Ca(OH)Cl intermediate by experimental investigation and DFT modelling

The chlorine evolution mechanism remains unclear during the thermal treatment of CaCl₂/Ca(OH)Cl-containing solid waste. In this paper, we have conducted both experimental investigation and density functional theory (DFT) calculation to elucidate the mechanism of pyro-hydrolysis of CaCl₂ with and without SiO₂ in the temperature ranges of 400-900 °C. It was determined that pyro-hydrolysis of CaCl₂ alone generated a maximum of 12% HCl by decomposition into Ca(OH)Cl, which is a stable intermediate that can be reverted to CaCl₂ at 800 °C. Upon the addition of SiO₂ at an equimolar ratio to CaCl₂, the HCl release extent was accelerated to 50% at 900 °C. Both experiments and DFT calculations prove that the added SiO₂ can promote the dissociation of water molecules which provides hydroxyl ions that enable the conversion of CaCl₂ into Ca(OH)Cl at low temperatures. The resulting Ca(OH)Cl can also quickly react with SiO₂ to form Cl-bearing silicates such as Ca₂SiO₃Cl₂ and Ca₃SiO₄Cl₂ with weakened CaCl bond that are relatively easy to cleave into Cl-free CaSiO₃ and HCl_(g) from 800 °C.

Chemical stabilization of heavy metals in municipal solid waste incineration fly ash: a review

Sufficient attention should be attached to the large amount of fly ash containing high levels of toxic heavy metals generated after municipal solid waste incineration. Because heavy metals could be leached out of the fly ash under specific conditions, it is necessary to stabilize the heavy metals in fly ash before landfill disposal. Processing technologies of incineration fly ash include solidification/stabilization technology, thermal treatments, and separation processes. This study reviewed the current treatment technologies of municipal solid waste incineration (MSWI) fly ash, with the main focus on the treatment of heavy metals in fly ash with chemical stabilization. Chemical stabilization processes involve chemical precipitation of heavy metal and chelation of heavy metals. In multiple studies, chemical stabilization technology has shown practical feasibility in terms of technology, economy, and effect. In addition, the combination of two or more stabilization agents broadens the general applicability of the agents to heavy metals and reduces the cost. The application of joint processing technology realizes the remove of soluble salt from fly ash. To minimize pollutants while increase their usable value, effective use of waste and co-disposal of several kinds of wastes have gradually become the research hotspots. New developments in chemical stabilization are progressively moving towards the sustainable direction of harmlessness and resource utilization of MSWI fly ash.

Stabilization of heavy metals in municipal solid waste incineration fly ash via hydrothermal treatment with coal fly ash

The environmental risk of heavy metals in hazardous municipal solid waste incineration fly ash (FA) is one of the most important concerns for its safely treating and disposing. This study investigated the stabilization behavior of heavy metals in FA using coal fly ash (CFA) as an additive via hydrothermal treatment. The effects of water washing pre-treatment and FA/CFA ratio on leaching behavior, speciation evolution, and risk assessment of heavy metals were studied. The results showed that 96.6-98.0 % of Cl can be effectively removed by water washing pre-treatment and hydrothermal treatment. Most heavy metals (Cr, Cu, Ni, Pb and Zn) (>91.5 %) were stabilized in the hydrothermal product, rather than transferred to liquid phase. Tobermorite can be synthesized by adjusting Ca/Si ratio with the addition of CFA. The heavy metals were transferred into more stable residue fractions with increasing CFA addition, which resulted in the significant reduction of leaching concentrations and risk assessment code (RAC) of heavy metals. Among, the product with 30% CFA exhibited the most superior performance with the lowest leaching concentrations of heavy metals and RAC was at no risk level (<1). In addition, the economic performance of hydrothermal treatment exhibited a potential advantage by comparing with FA-to-cement, FA-to-glass slags and FA-to-chelating agent & cement solidification/stabilization. Therefore, the hydrothermal treatment coupled with water washing pre-treatment would be a promising method for the detoxification of FA, as well as synergistic treatment of FA and CFA.

Red Mud from the Aluminium Industry: Production, Characteristics, and Alternative Applications in Construction Materials—A Review

About 120 million tons of red mud is produced worldwide each year. Due to its high basicity and potential leaching, its storage is a critical environmental problem. This material is typically stored in dams, which demands prior care of the disposal area and includes monitoring and maintenance throughout its useful life. Consequently, it is crucial to figure out an industrial solution able to consumes large volumes of this material. At this moment, there are several studies, the majority in metallurgical procedures, building materials, and in the chemical industry, discussing how to reuse red mud. This paper provides a review of the aluminium process, including metal importance, its global production, and the environmental impact due to its manufacture process. It presents a review of the potential application of red mud showing its overall generation, some relevant characterisation results collected from the literature, and its utilisation in diverse areas of engineering. The study aimed to highlight applications where red mud characteristics may be favourable.

Synthesis of zero-valent iron/biochar by carbothermal reduction from wood waste and iron mud for removing rhodamine B

This study proposes a new process to synthesize zero-valent iron/biochar (Fe⁰-BC) by carbothermal reduction using wood waste and iron mud as raw materials under different temperature. The characterization results showed that the Fe⁰-BC synthesized at 1200 °C (Fe⁰-BC-1200) possessed favorable adsorption capacity with the specific surface area of 103.18 m²/g and that the zero-valent iron (Fe⁰) particles were uniformly dispersed on the biochar surface. The removal efficiency of rhodamine B (RB) was determined to evaluate the performance of the prepared Fe⁰-BC. Fe⁰-BC-1200 presented the best performance on RB removal, which mainly ascribes to that more Fe⁰ particles generated at higher temperature. The equilibrium adsorption capacity reached 49.93 mg/g when the initial RB concentration and the Fe⁰-BC-1200 dosage were 100 mg/L and 2 g/L, respectively, and the pseudo-second-order model was suitable to fit the removal experimental data. LCMC and XRD analyses revealed that the removal mechanism included the physical adsorption of biochar and the redox reaction of Fe⁰. Moreover, copper existing in the iron mud was also reduced to Cu⁰, which was beneficial to catalyze the oxidation of iron; the degradation of RB was promoted at the same time.

Treatment of municipal solid waste incineration fly ash: State-of-the-art technologies and future perspectives

Municipal solid waste incineration (MSWI) fly ash is considered as a hazardous waste that requires specific treatment before disposal. The principal treatments encompass thermal treatment, stabilization/solidification, and resource recovery. To maximize environmental, social, and economic benefits, the development of low-carbon and sustainable treatment technologies for MSWI fly ash has attracted extensive interests in recent years. This paper critically reviewed the state-of-the-art treatment technologies and novel resource utilization approaches for the MSWI fly ash. Innovative technologies and future perspectives of MSWI fly ash management were highlighted. Moreover, the latest understanding of immobilization mechanisms and the use of advanced characterization technologies were elaborated to foster future design of treatment technologies and the actualization of sustainable management for MSWI fly ash.

Utilization of Red Mud as a Source for Metal Ions-A Review

An overview is presented on the prospective use of red mud as a resource in this review. Various scopes are suggested for the utilization of red mud to maintain a sustainable environment. The potential use of red mud covers the valuable metal recovery that could emphasize the use of red mud as a resource. Red mud could act as reduced slag in the metallurgical field for the extraction of minerals and metals for upscale application. Although many studies have revealed the potential utilization of red mud, most of them are only limited to a lab-scale basis. Therefore, a large-scale investigation on recycling of red mud for the extraction in the area of the metal recovery section will draw attention to the extensive use of red mud. Metal ions of major elements Fe (44 wt.%), Al (18.2 wt.%), Si (14.3 wt.%), Ti (9.3 wt.%), Na (6.2 wt.%), Ca (4.4 wt.%) as major elements and of Mg, V, Mn, Cr, K as minor elements and rare earth elements such as Ce (102 mg/kg), La (56 mg/kg), Sc (47 mg/kg), Nd (45 mg/kg), Sm (9 mg/kg). Moreover, an appropriate in-house metal recovery facility with the alumina industry will come out as a cost-benefit analysis.

Co-disposal of municipal solid waste incineration fly ash and bottom slag: A novel method of low temperature melting treatment

Conventional melting for disposing municipal solid waste incineration (MSWI) fly ash or bottom slag needed high temperature and consumed high energy. High calcium content in fly ash and high silicon content in bottom slag brought them high melting point, respectively. Based on the analysis of chemical composition and phase diagram, suitable contents, namely 30%-40% CaO, 45%-60% SiO₂ and 10%-15% Al₂O₃, were proposed to obtain a lower-melting-point mixture system. When the mass ratio of fly ash to bottom slag was 1:5, lowest melting point can be obtained. It was 1,190 ℃, lower than that of fly ash (1,448 ℃) and bottom slag (1,310 ℃). The toxicity characteristic leaching procedure of slags obtained from low melting treatment met the leaching toxicity of Chinese standard GB 5085.3-2007, and the slags containing about 25 wt% CaO, 10 wt% Al₂O₃ and 45 wt% SiO₂ can be used for preparing CaO-Al₂O₃-SiO₂ glass ceramics. The co-process of fly ash and bottom slag realized the low temperature melting treatment with low energy consumption.

Harmless treatment of municipal solid waste incinerator fly ash through shaft furnace

Municipal solid waste incinerator fly ash (MSWI FA) is a type of waste that is harmful to the environment, and the melting treatment methods can treat MSWI FA, removing its potential negative impacts. However, special equipment is required for the FA melting process, which necessitates high costs. Metallurgical shaft furnaces (MSF) can melt MSWI FA efficiently. Therefore, the feasibility of using an MSF for FA treatment was studied herein. First, the fundamental physicochemical properties of the FA were analyzed. Then, the appearance and internal morphology of the FA were examined using a scanning electron microscope. Finally, melting experiments were designed according to the conditions of the MSF. The results show that slag changes into a glassy state under rapid cooling, which is beneficial to the solidification of harmful elements. These harmful elements, including Pb, Zn, and Cu, are thus reduced and volatilized into the flue gas under the MSF's reducing atmosphere. The harmful elements that enter the slag are solidified, causing its leaching toxicity to achieve the national standard requirements. Further, under the simulated MSF smelting conditions, the FA dioxin destroy removal efficiency realized more than 99.99% efficiency. Therefore, the harmless treatment of MAWI FA can be realized through MSF process.

Municipal solid waste incineration fly ash to produce eco-friendly binders for sustainable building construction

Municipal solid waste incinerator (MSWI) fly ash is a residue of municipal solid waste incineration whose recycling is currently a worldwide problem. Therefore, considerable efforts are being made to establish effective recovery techniques so MSWI can be used as a substitute for natural resources in construction, as in masonry blocks, roads and so on, or in the manufacture of new materials. MSWI fly ashes contain elements such as Ca, Si and Al, which make it possible for them to be used as raw material to manufacture cements. This paper presents the results obtained from the physicochemical characterization of two MSWI fly ashes from two Spanish cities. The research aims to explore the feasibility of using MSWI fly ash as raw material for sintering belite cements. The results show that MSWI fly ashes have a suitable composition. However, appropriate pre-treatment will be required to eliminate chloride and possible traces of heavy metals and to improve pozzolanic activity. Furthermore, the addition of vitreous silica in the proper proportions is required. The phases generated after calcination of the blend at 800 °C are not those corresponding to pure belite cements. Nevertheless, the possibility of using these ashes as supplementary cementitious material in the manufacture of eco-cements should be contemplated.

Analysis of the Heat Balance of a Metal Hydride Separator Used for the Separation of Hydrogen from Syngas

The present article discusses the potential for hydrogen separation using a metal hydride separator, which facilitates the generation of hydrogen contained in syngas following the thermal recovery of wastes. The article provides a detailed description of the separator heat balance using analytical calculations and optimised calculations, and by applying numerical methods. The proposed concept of a separator intended for hydrogen separation from syngas offers a solution to a problem associated with the use of metal hydride alloy powders; in particular, their low thermal conductivity. In order to eliminate big temperature differences in the alloy, a heat transfer intensifier was implemented in the metal hydride alloy volume; the intensifier was made of metal and exhibited high thermal conductivity. For the purpose of comparing the thermal fields, the first stage comprised the creation of a numerical simulation of hydrogen absorption without the use of an intensifier. Subsequently, three different geometries were created for an intensifier intended to remove heat from the metal hydride alloy powder towards the separator cover, and the effects of these three geometries were analysed. The implementation of heat transfer intensifiers into the metal hydride alloy powder improved the heat removal by as much as 43.9% and increased the thermal field homogeneity by 77%. A result of the heat removal optimisation was an increase in the hydrogen absorption kinetics and the efficiency of the separator operation.

HCB dechlorination combined with heavy metals immobilization in MSWI fly ash by using n-Al/CaO dispersion mixture

Municipal solid waste incineration fly ash (MSWI-FA) has been strictly controlled as hazardous waste globally because it contains various heavy metals and dioxins. This study prepared a nanometallic Al/CaO (n-Al/CaO) dispersion mixture via ball-milling as a reductive stabilization reagent for the simultaneous immobilization of heavy metals and detoxification of POPs like substance in MSWI-FA. Under optimal conditions, Cu, Zn, Cd, Cr, Ni, and Pb had been significantly immobilized (over 99.9 %) and the leaching concentration of Zn, Cd, Cr, Ni, and Pb were below the detectable limit. Simultaneously, 82.43 % of HCB can be destructed into alkanes and amorphous carbon. The porous structure of the fly ash and alkaline surface of n-Al/CaO promoted the adsorption and cracking of HCB. The highly active n-Al/CaO interacted with water as the hydrogen donor to promote the reductive dechlorination process. Hydrocalumite was a new mineral formed from the adsorption and complexation of heavy metal. Therefore, n-Al/CaO can strengthen the control of heavy metals in the S/S treatment of MSWI-FA, effectively detoxify chlorinated organics, and reduce environmental health risks.