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•An approach for separating Ga/Fe and Al from CG/CFA HNO3 leach liquor was proposed.•Ga/Fe and Al can be separated with cupferron as a Ga-Fe synchronous chelation agent.•The oxygen of ...cupferron acted as the coordination atom chelated with Ga and Fe.•Cupferron was able to regenerate in the presence of NH4OH.
Coal gangue and fly ash are typical coal-based solid waste and can be considered as Al and Ga resources. The HNO3 leaching technology was proposed by our team for the economical and efficient co-extraction of Al and Ga, whereas the separation and recovery of metal elements became a challenge due to the variety of co-existing ions in the leach liquor. In this work, a Ga-Fe iso precipitation strategy with cupferron (C6H9N3O2) as a selective precipitant followed by regeneration and circulation of cupferron was proposed. The feasibility of the technique was assessed by thermodynamic analysis. The systematic precipitation experiments showed that 99.05 % of Ga, 99.89 % of Fe, and 4.74 % of Al were transferred into the complex precipitation product at optimal conditions. And the separation factor of Ga vs. Al and Fe vs. Al were as high as 2101.74 and 17713.93, respectively. The precipitation mechanism was revealed via a suite of characterization methods to be the chelation of metal ions and cupferron, with the terminal oxygen (N = O) and hydroxyl oxygen (O–H) as ligating atoms. The regeneration rate of cupferron reached 81.28 % with an ammonium hydroxide (NH3·H2O) concentration of 8 mol/L. And the circulation experiment demonstrated the excellent performance of the regenerated cupferron. This work provides a new insight into the deep removal of Fe and the enrichment of Ga from the acidic solution.
Alkali activated binders (geopolymer) is an emerging technology to produce concrete without the use of any Ordinary Portland Cement (OPC) by alkali activation of alumino-silicate source materials ...such as fly ash and/or slag. Limited knowledge on durability issues like corrosion behaviour of reinforced geopolymer concrete impedes the usage of this technology in structural applications.
This study explored the chloride permeability and initiation of chloride induced corrosion of geopolymer concrete in accelerated chloride environment using longer test period. Corrosion initiation was also monitored in embedded rebar in 2% chloride contaminated concrete. Corrosion state of the rebar was monitored using non-destructive test method using Cu/CuSO4 reference electrode.
The results showed that the apparent chloride diffusion coefficient of blended fly ash and slag geopolymer concrete is lower than that of OPC concrete. The diffusion coefficient also decreased with the increase of slag content in the binder. Blended fly ash and slag geopolymer concrete also exhibited higher aging factor than OPC concrete indicating improved resistance to chloride ingress with time. The study also showed that the embedded rebar in fly ash and slag based geopolymer concrete has higher protection against corrosion than a rebar in OPC concrete even when the concrete is contaminated with significant levels of chloride.
•Chloride ingress rate in geopolymers containing slag is low.•Age factor of geopolymer is significantly higher than OPC.•Geopolymer can hinder corrosion in steel rebar.
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•Detoxification effects of RKS and NS ceramsites process are monitored and analyzed.•Environmental impacts of RKS and NS ceramsites technology are evaluated by LCA.•Key materials and energy ...consumption are recognized and recommendations are proposed.
Harmless treatment and reuse of municipal solid waste incinerator fly ash are challenging. Two reuse technologies of converting incinerator fly ash to ceramsites via rotary kiln sintering and non-sintering have been demonstrated in China. Field monitoring results reveal that the destruction efficiency of PCDD/Fs are both higher than 99% in two processes. The leaching rate of heavy metals in both ceramsite products, their pollutant emissions in production process meet the standards. Environmental impacts of two ceramsite products were compared using life cycle assessment approach. Rotary kiln sintering ceramsite has lower environmental impacts in most categories and delivers a smaller integrated impacts index than non-sintering ceramsite. For rotary kiln sintering ceramsite, transportation, electricity and curing agent in dust disposal are the most significant contributors to most of environmental impacts categories results, accounting for 33.7%, 29.0% and 24.6% to the integrated impacts index, respectively. For non-sintering ceramsite, curing agent and electricity contribute 69.6% and 15.8% to the integrated impacts index, respectively. Based on these life cycle assessment results, recommendations for current plant operation and new plants planning are proposed.
Supplementary cementitious materials (SCMs) are commonly used in concrete mixtures as a replacement of a portion of clinker in cement or as a replacement of a portion of cement in concrete. This ...practice is favorable to the industry, generally resulting in concrete with lower cost, lower environmental impact, higher long-term strength, and improved long-term durability. SCMs have been used in Portland cement concrete for decades and many of their effects are well-understood. Most recent research on SCMs has focused on a few areas: exploring new materials, increasing replacement amounts, developing better test methods, treating or modifying materials, and using additives (e.g. limestone or nanosilica) to improve performance. The advances in knowledge provided by research in these areas are reviewed in this paper, emphasizing the impact of the research on the field.
Phase pure zeolite-A and zeolite-X were synthesized using coal fly ash (CFA) obtained from Indian thermal power plants by employing alkali fusion method followed by hydrothermal technique. The fusion ...of fly ash with Na2CO3 was accomplished by heating at 800 °C/2 h by maintaining fly ash to Na2CO3 ratio at 1.2. The fused mass was found to be nepheline (Na4Al4Si4O16); and on subsequent treatment of the fused mass with 3 M NaOH under hydrothermal condition transformed to zeolite-A (Na12Al12Si12O48.27H2O) and zeolite-X (Na88Al88Si104O384.194H2O). The effluent solution from zeolite-A synthesis was utilized to prepare cancrinite. The zeolites were characterized by XRD, FTIR, TG-DTA, SEM and surface area of the powders were measured by BET technique. The specific surface area of the zeolite-A and zeolite-X were found to be 58.29 ± 0.20 and 164.34 ± 5.4 m2g−1 respectively. The TG-DTA studies showed the conversion of nano-crystalline to micro-crystalline zeolites with loss of adsorbed water. The ion exchange capacities of these nano-crystalline zeolites were evaluated by using simulated nuclear waste solutions containing Cs+or Sr2+ ions. The adsorption capacity of zeolite-A was found to be 95.74 mg/g and 54.12 mg/g respectively for Sr2+ and Cs+ions. Similarly, zeolite-X shows the adsorption capacity of 93.14 mg/g and 53.14 mg/g respectively for Sr2+ and Cs+ ions.
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•Zeolite-A & zeolite-X were synthesized from fly using Na2CO3 fusion method followed by hydrothermal reaction at 100 °C/6 h.•The fly ash was converted to zeolite-A and zeolite-X through nepheline as the intermediate phase.•Specific surface area of zeolite-A & zeolite-X measured by BET technique was 58.29 ± 0.20 and 164.34 ± 5.4 m2g−1 respectively.•The adsorption capacity of zeolite-A for Sr2+ (95.74 mg/g)is higher than Cs+ ions (54.12 mg/g).•The adsorption capacity of zeolite–X for Sr2+ (93.14 mg/g)is higher than Cs+ ions (53.14 mg/g).
Zeolite was synthesized from coal fly ash by a fusion method and was used for the removal of heavy metal ions (Pb²⁺, Cd²⁺, Cu²⁺, Ni²⁺, and Mn²⁺) in aqueous solutions. Batch method was employed to ...study the influential parameters such as adsorbent dosage, pH, and coexisting cations. Adsorption isotherms and kinetics studies were carried out in single-heavy and multiheavy metal systems, respectively. The Langmuir isotherm model fitted to the equilibrium data better than the Freundlich model did, and the kinetics of the adsorption were well described by the pseudo-second-order model, except for Cd²⁺ and Ni²⁺ ions which were fitted for the pseudo-first-order model in the multiheavy metal system. The maximum adsorption capacity and the distribution coefficients exhibited the same sequence for Pb²⁺ > Cu²⁺ > Cd²⁺ > Ni²⁺ > Mn²⁺ in both single- and multiheavy metal systems. In the end, the adsorption capacity of zeolite was tested using industrial wastewaters and the results demonstrated that zeolite could be used as an alternative adsorbent for the removal of heavy metal ions from industrial wastewater.
Magnetic polyaniline nanofibers were synthesized by oxidative polymerization using protonic acid and fly ash magnetic beads as dopants and ammonium persulfate as oxidant. The synthesized magnetic ...polyaniline was characterized by FT‐IR, UV, XRD and SEM, and its morphology and structure were revealed. Polyaniline magnetic electrodes were prepared by pressing method, and their electrochemical properties were analyzed by cyclic voltammetry and constant current charge–discharge methods. The capacities of polyaniline powders doped with optimal concentration of hydrochloric acid and p‐toluene sulfonic acid at current density of 1 A/g were 250.75 and 410.5 F/g, respectively. The magnetic polyaniline doped with optimal acid concentration has good conductivity through impedance measurement analysis. A smooth and uniform film was prepared by pressing magnetic polyaniline powder and its photosensitivity was observed under different monochromatic illumination. The results show that the current and voltage have a linear relationship and that different monochromatic light energies can be distinguished significantly with the increase of voltage.
Preparation and properties of fly ash magnetic beads/polyaniline composites.
•Baking-electrolysis method was designed to recover alumina from coal fly ash.•Product hydrogen can be treated as a clean energy to realize efficient process.•Product sulfuric acid, sulfur trioxide ...can be returned to the baking-electrolysis process to promote zero pollution discharge.
Clean and efficient extraction of aluminum hydroxide from coal fly ash has environmental and economic benefits. The current study mainly aimed to develop an efficient and nonhazardous baking-electrolysis process to extract aluminum hydroxide from coal fly ash. During acid baking, the important parameters that affect aluminum, iron, and calcium leaching efficiency were studied. The maximum leaching efficiency of aluminum reached 86.8% (iron leaching efficiency was 61.0% and calcium leaching efficiency was 83.0%) under the optimal conditions of T = 200 °C, t (acid baking) = 90 min, and t (ball milling) = 5 min. X-ray diffraction, scanning electron microscopy and laser granulometry were used to investigate the mineralogy phases, microstructures, particle size distributions, and the mechanism of the acid baking process. X-ray diffractometry and scanning electron microscopy results revealed that aluminum hydroxide with porous plate-like structures was the main electrolytic product. The electrolysis mechanism was analyzed by cyclic voltammetry. This method offers the advantages of reusing the effluent after electrolysis, and the hydrogen product is a clean form of energy. Thus, the proposed baking-electrolysis process provides a promising technique as an efficient and potential zero-waste integrated process for sustainable valorization of coal fly ash.
Due to their good performance and environmental friendliness, fly ash-based construction materials have great potential as alternatives to ordinary Portland cement. To realize sustainable development ...and beneficial use of fly ash in the construction industry, this paper presents a comprehensive review of relevant literature to evaluate the properties and performance of fly ash, with a particular focus on recent advances in characterization, compositional understanding, hydration mechanism, activation approaches, durability and sustainability of fly ash as a construction material. Several key aspects governing the performance of fly ash, including chemical composition, activator type and hydrates evolution in concrete, are highlighted. Finally, the important needs, pertinent to the optimal and broad utilization of fly ash as an integral part of sustainable construction materials, are identified for further research and development, where large-scale application studies, further classification of fly ash, advanced characterization tools and technology transfer to biomass fly ash are recommended.
To address the environmental problems caused by solid waste while promoting the sustainable development of mines, gangue and fly ash can be used as underground backfill materials to achieve the ...comprehensive utilisation of solid waste mining resources. We measured the compressive deformation characteristics of samples with different ratios of gangue to fly ash and analysed their stress-strain relationship and associated changes in their porosities using a YAS-5000 servo testing machine and a homemade compression apparatus. Moreover, we revealed the mechanisms of deformation resistance of gangue and fly ash from both a macro and meso perspective and determined that the optimal ratio of gangue to fly ash is 0.35. In addition, taking the backfill face in Coal Mine as an example, mixed materials of gangue and fly ash at a ratio of 1:0.35 were backfilled into a goaf. After mining of the working face, the surface only sank by 170 mm approximately. This method not only effectively disposes of solid wastes, i.e., gangue and fly ash, on a large scale but also controls surface subsidence to protect adjacent buildings and structures. Therefore, the coordinated development of coal resource mining and environmental protection are realised.
