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The emergence of industrial wastes brings with it a series of global environment issues. However, using these wastes including valuable metals as a source of value-added materials will lead to many advantages. The metals can be recovered and transformed for nanomaterial production which offers utility in many applications such as energy conversion and hydrogen evaluation. In this study, recycling techniques were used to synthesize zinc oxide nanofibers from waste brass flue dust. Initially, characterization and experimental analyses were used to confirm the synthesized nanofibers phase purity, morphology, and optical properties. The X-Ray diffraction (XRD) analysis and X-ray photoelectron spectroscopy (XPS) confirmed the nanofibers produced after recycling process were predominantly ZnO and have high purity. It was determined from scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis that the produced samples were in fiber form in nanoscale and high crystallinity. According to the ultraviolet visible spectroscopy (UV-Vis) analysis, the optical band of ZnO nanofibers was found as 3.19 eV. It has been demonstrated with this study that the ZnO nanofibers derived from industrial waste can be used in several energy applications. Also, it was revealed that metal-containing wastes can be disposed of by producing value-added nanomaterials directly from industrial wastes with economical value. [ABSTRACT FROM AUTHOR]

Carbon fly ash (CFA) is the principal industrial waste byproduct from the burning fossil fuel (coal combustion) for the thermal generation of electricity. CFA is a gray or black powdery solid that is constituted mostly metal oxides (Al, Si Fe and Ca), unburned carbon (UC) and other inorganic substance. The management of fly ash has thus been a matter of concern given the requirement of the large area of land for its disposal and potential of causing pollution of air, water, land and effects on human health. Physical and chemical characteristics of fly ash is important, as these characteristics influence its subsequent use and disposal. X-ray diffraction, and fluorescence, scanning microscopy with an energy dispersive spectroscopy, FTIR, BET was the common techniques employed to characterize FA. Characterization by XRD analysis identified the presence of quartz, mullite and sillimanite phases; while the FTIR results allowed the identification of vibrational bands, characteristic of Si-O-Si and Si-O bonds. The EDS analysis coupled to SEM allowed verifying that the composition of the samples is consistent with the results sought and that the morphological characteristics validate the proposed methodology. Surface area analyses (BET) showed that the fly ash possess an active area of 6.02 m² · g-1. [ABSTRACT FROM AUTHOR]

[Display omitted] • The matrix of augmented-simplex-centroid mixture design in a ternary system was adopted to generate the experiments. • The mixture design methodology optimized the development of a geopolymer paste based on three aluminosilicate precursors. • The physicochemical properties of elaborated geopolymers containing different formulations were investigated and discussed. • The combination 75 %FA-25 %MK was recommended for enhancing the compressive strength of the geopolymeric binder. • The formation of N -A S H gel in synthesized geopolymers was confirmed by structural and microstructure analysis. This study focuses on the application of mixture design as a novel approach to developing a geopolymer paste with optimized mechanical properties. It also aims to utilize the abundance of natural or industrial aluminosilicate precursors through their combination for synthesizing high-performance geopolymers. The synthesis factors studied are kaolin (K), metakaolin (MK), and fly ash (FA) as aluminosilicate sources. Different mixture proportions were prepared by adopting an augmented simplex-centroid design. Twelve geopolymer pastes were synthesized by activating the mixtures with an alkaline solution of sodium hydroxide and sodium silicate. After 28 days of solidification under ambient conditions, the compressive strength (MPa) and bulk density (g/cm3) of the geopolymer samples were measured. The structural and microstructural properties of the raw and elaborated materials were analyzed using a range of physicochemical techniques, including X-ray Fluorescence (XRF) spectroscopy, X-ray Diffraction (XRD), Fourier Transform Infra-Red (FTIR) spectroscopy, Scanning Electron Microscopy combined with Energy Dispersive Spectroscopy (SEM/EDS), and Transmission Electron Microscopy (TEM). The results showed that the compressive strength and bulk density of the geopolymeric pastes ranged from 7.59 to 19.48 MPa and from 1.52 to 1.82 g/cm3, respectively. According to the validated special cubic models and optimization results, the optimum mixture of FA (75 %) and MK (25 %) was found to develop the optimized geopolymer (GPO) paste with the best performance. The optimized geopolymer matrix had a non-porous structure mainly formed by a dense amorphous sodium aluminosilicate gel, which gave excellent mechanical properties (1.82 g/cm3 and 20.80 MPa). The practical application of the results of this study includes the development of an efficient geopolymer paste with excellent mechanical properties that can be employed in construction and civil engineering applications. The significance of this work lies in its potential to reduce environmental impacts and minimize waste disposal by utilizing abundant natural resources and industrial waste in the formulation of practical and efficient products. Overall, this study provides valuable insights into the development of an improved geopolymer paste through the application of a mixture design methodology, which can have a significant impact on the construction and civil engineering industries. [ABSTRACT FROM AUTHOR]

The use of more eco-efficient cements in concretes is one of the keys to ensuring construction industry sustainability. Such eco-efficient binders often contain large but variable proportions of industrial waste or by-products in their composition, many of which may be naturally occurring radioactive materials (NORMs). This study explored the application of a new gamma spectrometric method for measuring radionuclide activity in hybrid alkali-activated cements from solid 5 cm cubic specimens rather than powder samples. The research involved assessing the effect of significant variables such as the nature of the alkaline activator, reaction time and curing conditions to relate the microstructures identified to the radiological behavior observed. The findings showed that varying the inputs generated pastes with similar reaction products (C-S-H, C-A-S-H and (N,C)-A-S-H) but different microstructures. The new gamma spectrometric method for measuring radioactivity in solid 5 cm cubic specimens in alkaline pastes was found to be valid. The variables involved in hybrid cement activation were shown to have no impact on specimen radioactive content. The powder samples, however, emanated 222Rn (a descendent of 226Ra), possibly due to the deformation taking place in fly ash structure during alkaline activation. Further research would be required to explain that finding. [ABSTRACT FROM AUTHOR]

Supplementary cementitious materials (SCMs) in industrial waste and by-products are routinely used to mitigate the adverse environmental effects of, and lower the energy consumption associated with, ordinary Portland cement (OPC) manufacture. Many such SCMs, such as type F coal fly ash (FA), are naturally occurring radioactive materials (NORMs). 226Ra, 232Th and 40K radionuclide activity concentration, information needed to determine what is known as the gamma-ray activity concentration index (ACI), is normally collected from ground cement samples. The present study aims to validate a new method for calculating the ACI from measurements made on unground 5 cm cubic specimens. Mechanical, mineralogical and radiological characterisation of 28-day OPC + FA pastes (bearing up to 30 wt % FA) were characterised to determine their mechanical, mineralogical and radiological properties. The activity concentrations found for 226Ra, 212Pb, 232Th and 40K in hardened, intact 5 cm cubic specimens were also statistically equal to the theoretically calculated values and to the same materials when ground to a powder. These findings consequently validated the new method. The possibility of determining the activity concentrations needed to establish the ACI for cement-based materials on unground samples introduces a new field of radiological research on actual cement, mortar and concrete materials. [ABSTRACT FROM AUTHOR]