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Mesoporous silica is emerging as a nanomaterial with potentially huge applications in the industrial sector, particularly in the fields of chemical catalysis, host-guest encapsulation, and adsorbents. These materials possess well-defined honeycomb-shaped pores that can be fine-tuned to suit adsorbing moieties of different molecular sizes, with adjustable release rates. The most significant drawback that hampers the commerciality of mesoporous silica-based processes is that the inorganic precursors used in the synthesis of these materials are quite expensive. These costs can be offset somewhat by using low-cost, renewable precursors from natural sources and recycling industrial wastes. In this review, we have collected some of the more recent laboratory attempts to prepare mesoporous silica material from low-cost precursors. Scientometric analysis was performed to find the potential of mesoporous silica manufacturing from ash sources. Various sources of mesoporous silica preparation and works related to them were explained in detail. This article also explores various techniques used for the development and gives a brief insight into the possible applications for mesoporous silica. Graphical abstract Highlights Industrial waste ash and natural materials are promising sources for silica. An overall analysis of waste utilization was provided using Scientometric studies. Sustainable silica sources are used in the preparation of mesoporous materials. The use of low-cost and eco-friendly silica sources is of environmental importance. Current and future expectations were addressed on utilizing waste ash.

Concrete production utilizes cement as its major ingredient. Cement production is an important consumer of natural resources and energy. Furthermore, the cement industry is a significant CO2 producer. To reduce the environmental impact of concrete production, supplementary cementitious materials such as fly ash, blast furnace slag, and silica fume are commonly used as (partial) cement replacement materials. However, these materials are industrial by-products and their availability is expected to decrease in the future due to, e.g., closing of coal power plants. In addition, these materials are not available everywhere, for example, in developing countries. In these countries, industrial and agricultural wastes with pozzolanic behavior offer opportunities for use in concrete production. This paper summarizes the engineering properties of concrete produced using widespread agricultural wastes such as palm oil fuel ash, rice husk ash, sugarcane bagasse ash, and bamboo leaf ash. Research on cement replacement containing agricultural wastes has shown that there is great potential for their utilization as partial replacement for cement and aggregates in concrete production. When properly designed, concretes containing these wastes have similar or slightly better mechanical and durability properties compared to ordinary Portland cement (OPC) concrete. Thus, successful use of these wastes in concrete offers novel sustainable materials and contributes to greener construction as it reduces the amount of waste, while also minimizing the use of virgin raw materials for cement production. This paper will help the concrete industry choose relevant waste products and their optimum content for concrete production. Furthermore, this study identifies research gaps which may help researchers in further studying concrete based on agricultural waste materials.

Pervious concrete (PC) provides multiple benefits, including reducing stormwater runoff, purifying water, recharging groundwater, and reducing the heat island effect. This study aims to determine an effective way to reuse municipal solid waste incinerator (MSWI) fly ash (FA), MSWI bottom ash (BA), and rice husk ash (RHA) as single or binary partial replacements for ordinary Portland cement (OPC) in PC. The ashes and PC specimens were characterized via X-ray fluorescence spectroscopy, X-ray powder diffraction, field emission-scanning electron microscopy, and Fourier transform infrared spectroscopy. The compressive strength, water permeability, and toxicity characteristic leaching procedure (TCLP)-released metals were investigated to evaluate the PC quality. The main components of the ashes were similar to those of OPC, suggesting that the ashes could be reused as cement materials; however, the cementitious activity of the ashes, especially MSWI FA, was relatively low. All ashes except 1100 °C MSWI FA met the standard requirements and can be applied as pozzolanic materials. The three PC specimens with binary replacements containing RHA (550, 700, and 900 °C) and MSWI BA (1100 °C) showed a synergistic effect and exhibited a higher 90-day compressive strength than the other specimens with single and binary ash replacements containing RHA (550 and 900 °C). The water permeability ranged between 0.106 and 0.391 cm/s, and the TCLP-released metal concentrations from all specimens met the regulatory standards of Taiwan. The results indicated that replacement with MSWI BA and RHA in cement materials provides an acceptable compressive strength and water permeability.

A sustainable solution for the global construction industry can be partial substitution of Ordinary Portland Cement (OPC) by use of supplementary cementitious materials (SCMs) sourced from industrial end-of-life (EOL) products that contain calcareous, siliceous and aluminous materials. Candidate EOL materials include fly ash (FA), silica fume (SF), natural pozzolanic materials like sugarcane bagasse ash (SBA), palm oil fuel ash (POFA), rice husk ash (RHA), mine tailings, marble dust, construction and demolition debris (CDD). Studies have revealed these materials to be cementitious and/or pozzolanic in nature. Their use as SCMs would decrease the amount of cement used in the production of concrete, decreasing carbon emissions associated with cement production. In addition to cement substitution, EOL products as SCMs have also served as coarse and also fine aggregates in the production of eco-friendly concretes.

The rapidly increasing generation of municipal solid waste (MSW) threatens the environmental integrity and well-being of humans at a global level. Incineration is regarded as a technically sound technology for the management of MSW. However, the effective management of the municipal solid waste incineration (MSWI) ashes remains a challenge. This article presents the global dynamics of MSWI ashes research from 1994 to 2018 based on a bibliometric analysis of 1810 publications (research articles and conference proceedings) extracted from the Web of Science database, followed by a comprehensive summary on the research developments in the field. The results indicate the rapid growth of annual publications on MSWI ashes research, with China observed as the most productive country within the study period. Waste Management, Journal of Hazardous Materials, Chemosphere and Waste Management & Research, which accounted for 35.42% of documents on MSWI research, are the most prominent journals in the field. The most critical thematic areas on this topic are MSWI ashes characterisation, dioxin emissions from fly ash, valorisation of bottom ash and heavy metal removal. The evolution of MSWI ashes treatment technologies is also discussed, together with the challenges and future research directions. This is the first bibliometric analysis on global MSWI ashes research based on a sufficiently large dataset, which could provide new insights for researchers to initiate further research with leading institutions/authors and ultimately advance this research field.

Rare earth elements (REE) have been recognised as critical raw materials, crucial for many clean technologies. As the gap between their global demand and supply increases, the search for their alternative resources becomes more and more important, especially for the countries which depend highly on their import. Coal fly ash (CFA), which when not utilised is considered waste, has been regarded as the possible source of many elements, including REE. Due to the increase in the energy demand, CFA production is expected to grow, making research into the use of this material a necessity. As Poland is the second biggest coal consumer in the European Union, the authors have studied different coal fly ashes from ten Polish power plants for their rare earth element content. All the fly ashes have a broadly similar distribution of rear earth elements, with light REE being dominant. Most of the samples have REE content relatively high and according to Seredin and Dai (Int J Coal Geol 94: 67–93, 2012 ) classification can be considered promising REE raw materials.

Over the past decades, extensive studies on municipal solid waste incineration (MSWI) ashes have been performed to develop more effective recycling and waste management programs. Despite the large amount of research activities and the resulting improvements to MSWI ashes, the recycling programs for MSWI ashes are limited. For instance, although the U.S. generates more MSWI ashes than any other country in the world, its reuse/recycle programs are limited; bottom ash and fly ash are combined and disposed of in landfills. Reuse of MSWI ashes in the construction sectors (i.e., geomaterials, asphalt paving, and concrete products) as replacements for raw materials is one of most promising options because of the large consumption and relatively lenient environmental criteria. The main objective of this study was to comprehensively review MSWI ashes with regard to specific engineering properties and their performance as construction materials. The focus was on (1) the current practices of MSWI ash management (in particular, a comparison between European countries and the U.S.), (2) the engineering properties and performance of ashes when they are used as substitutes of construction materials and for field applications, and (3) the environmental properties and criteria for the use of MSWI ashes. Overall, the asphalt and concrete applications are the most promising, from both the mechanical and leachate viewpoints. However, cons were also observed: high absorption of MSWI ash requires a high asphalt binder content in hot-mix asphalt, and metallic elements in the ash may generate H2 gas in the high-pH environment of the concrete. These side effects can be predicted via material characterization (i.e., chemical and physical), and accordingly, proper treatment and/or modified mix proportioning can be performed prior to use.

In recent years, the research direction is shifted toward introducing new supplementary cementitious materials (SCM) in lieu of in place of Portland cement (PC) in concrete as its production emits a lot of toxic gases in the atmosphere which causes environmental pollution and greenhouse gases. SCM such as sugarcane bagasse ash (SCBA), metakaolin (MK), and millet husk ash (MHA) are available in abundant quantities and considered as waste products. The primary aim of this experimental study is to investigate the effect of SCBA, MK, and MHA on the fresh and mechanical properties of concrete mixed which contributes to sustainable development. A total of 228 concrete specimens were prepared with targeted strength of 25MPa at 0.52 water-cement ratio and cured at 28 days. It is found that the compressive strength and split tensile strength were enhanced by 17% and 14.28%, respectively, at SCBA4MK4MHA4 (88% PC, 4% SCBA, 4% MK, and 4% MHA) as ternary cementitious material (TCM) in concrete after 28 days. Moreover, the permeability and density of concrete are found to be reduced when SCBA, MK, and MHA are used separately and combined as TCM increases in concrete at 28 days, respectively. The results showed that the workability of the fresh concrete was decreased with the increase of the percentage of SCBA, MK, and MHA separately and together as TCM in concrete.

Biomass combustion generates considerable amounts of ash that are related to slagging/fouling problems in combustors. Numerous indices have been proposed in the literature for the evaluation of slagging/fouling tendencies. This paper is focused on the characterization of various biomass ashes in terms of their slagging/fouling tendency. For this purpose, the chemical composition of ash samples from fourteen solid biofuels (and a lignite sample as a reference) was analyzed by scanning electron microscope, energy-dispersive spectroscopy, ion chromatography and elemental analysis. Modification/normalization of the available ash indices was performed by taking into account not only the chemical composition of the ash but also the Gross Calorific Value of the fuels and the amount of the produced ash. Two versatile tools were developed, a total Ash Quality Index (tAQI) and an Ash Quality Label (AQL), in order to express the information derived from various indices with a single number or letter. The modified indices result in different characterization from the unmodified ones and lead to a more objective/fair evaluation of the slagging/fouling tendency. The comparison of large number of indices of large number of samples is enabled via the tAQI and the AQL. Samples with a tAQL ≤ 1 belong to class ‘A’ (low slagging/fouling problems) while samples with a tAQL > 6 belong to class ‘G’ (extremely high tendency to slagging/fouling problems). The tAQI and AQL are a novel concept for the categorization and labeling of solid biofuels regarding their slagging/fouling tendency and could contribute to the waste/biomass residue market for energy proposes.

Globally, concrete is widely implemented as a construction material and is progressively being utilized because of growth in urbanization. However, limited resources and gradual depravity of the environment are forcing the research community to obtain alternative materials from large amounts of agro-industrial wastes as a partial replacement for ordinary cement. Cement is a main binding resource in concrete production. To reduce environmental problems associated with waste, this study considered the recycling of agro-industrial wastes, such as sugarcane bagasse ash (SCBA), rice husk ash (RHA), and others, into cement, and to finally bring sustainable and environmental-friendly concrete. This study considered 5%, 10%, and 15% of SBCA and RHA individually to replace ordinary Portland cement (OPC) by weight method then combined both ashes as 10%, 20%, and 30% to replace OPC to produce sustainable concrete. It was experimentally declared that the strength performance of concrete was reduced while utilizing SCBA and RHA individually and combined as supplementary cementitious material (SCM) at 7, 28, 56, and 90 days, respectively. Moreover, the initial and final setting time is increased as the quantity of replacement level of OPC with SCBA and RHA separates and together as SCM in the mixture. Based on experimental findings, it was concluded that the use of 5% of SCBA and 5% of RHA as cement replacement material individually or combined in concrete could provide appropriate results for structural applications in concrete.