Advances in Methods for Recovery of Ferrous, Alumina, and Silica Nanoparticles from Fly Ash Waste

A novel and economical approach for the synthesis of short rod-shaped mesoporous silica nanoparticles from coal fly ash waste by Bacillus circulans MTCC 6811

Coal fly ash (CFA) is an industrial byproduct produced during the production of electricity in thermal power plants from the burning of pulverized coal. It is considered hazardous due to the presence of toxic heavy metals while it is also considered valuable due to the presence of value-added minerals like silicates, alumina, and iron oxides. Silica nanoparticles' demands and application have increased drastically in the last decade due to their mesoporous nature, high surface area to volume ratio, etc. Here in the present research work, short rod-shaped, mesoporous silica nanoparticles (MSN) have been synthesized from coal fly ash by using Bacillus circulans MTCC 6811 in two steps. Firstly, CFA was kept with the bacterial culture for bioleaching for 25 days in an incubator shaker at 120 rpm. Secondly, the dissolved silica in the medium was precipitated with the 4 M sodium hydroxide to obtain a short rod-shaped MSN. The purification of the synthesized silica particle was done by treating them with 1 M HCl at 120 °C, for 90 min. The synthesized short rod-shaped MSN were characterized by UV-vis spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Particle size analyzer (PSA), Field emission scanning electron microscopy (FESEM), and transmission electron microscope. The microscopic techniques revealed the short rod-shaped mesoporous silica nanoparticles (MSN) for the final nano-silica, whose size varies from 40 to 80 nm, with an average size of 36 ± 5 nm. The XRD shows the crystalline nature of the synthesized MSN having a crystallite size of 36 nm. The FTIR showed the three characteristic bands in the range of 400-1100 cm-1, indicating the purity of the sample. The energy dispersive X-ray (EDX) showed 53.04 wt% oxygen and 43.42% Si along with 3.54% carbon in the final MSN. The particle size analyzer revealed that the average particle size is 368.7 nm in radius and the polydispersity index (PDI) is 0.667. Such a novel and economical approach could be helpful in the synthesis of silica in high yield with high purity from coal fly ash and other similar waste.

Influence of Waste Glass Particle Size on the Physico-Mechanical Properties and Porosity of Foamed Geopolymer Composites Based on Coal Fly Ash

In order to protect the environment and counteract climate change, it is necessary to take any actions that enable a reduction in CO₂ emissions. One of the key areas is research focused on developing alternative sustainable materials for construction to reduce the global demand for cement. This work presents the properties of foamed geopolymers with the addition of waste glass as well as determined the optimal size and amount of waste glass for improving the mechanical and physical features of the produced composites. Several geopolymer mixtures were fabricated by replacing coal fly ash with 0%, 10%, 20%, and 30% of waste glass by weight. Moreover, the effect of using different particle size ranges of the addition (0.1-1200 µm; 200-1200 µm; 100-250 µm; 63-120 µm; 40-63 µm; 0.1-40 µm) in the geopolymer matrix was examined. Based on the results, it was found that the application of 20-30% of waste glass with a particle size range of 0.1-1200 µm and a mean diameter of 550 µm resulted in approximately 80% higher compressive strength in comparison to unmodified material. Moreover, the samples produced using the smallest fraction (0.1-40 µm) of waste glass in the amount of 30% reached the highest specific surface area (43.711 m²/g), maximum porosity (69%), and density of 0.6 g/cm³.

Rhizobium induced modulation of growth and photosynthetic efficiency of Lens culinaris Medik. grown on fly ash amended soil by antioxidants regulation

Rhizobium leguminosarum is a rhizospheres' nitrogen fixing microbe that improves plant growth and productivity by releasing sufficient nutrient sources from the root, by biological nitrogen fixation, solubilization of phosphorous, acquisition of iron, and enhancement of antioxidant activity in plants. On this account, a greenhouse experiment was carried out to assess the feasibility of growing lentil (Lens culinaris Medik.) on fly ash (FA) amended soil (0%, 10%, 20%, and 30%) in combination with R. leguminosarum inoculation. The data was recorded at 45 day after sowing to evaluate the plant growth characteristics, photosynthetic variables (total chlorophyll and carotenoid pigments, carbonic anhydrase activity, nitrate reductase activity), damage markers (ROS, MDA, and cell viability), and defensive factors (proline and antioxidants). Among the FA-proportions tested, 20% proved most favorable in all the mentioned attributes while 30% concentration had negative repercussions on all the variables. Rhizobium inoculation had synergistic effect on all the concentrations being maximum on 20% FA. Thus, Rhizobium and 20% FA caused a significant increase on growth characteristics, photosynthetic pigments; stomatal behavior (aperture shape, size, and frequency of stomata); and activity of CA and NR, and cell viability. Application of Rhizobium on 20% FA was corroborated with decline in MDA and ROS contents and a coordinated enhancement of the activity of SOD, CAT, and POX. Therefore, 20% FA with fly ash-tolerant strain of Rhizobium in Lens culinaris may be utilized as an integrated approach towards sustainable agriculture and an impulse of management of fly-ash.

Multiple Site Dissimilarities of Herbaceous Species Due to Coal Fly Ash Dumping Based Soil Heavy Metal Toxication

The present study analyzes the determinants and patterns of the regional, local, and differential plant diversity of two different sites with similar climatic but varied edaphic factors. This research was undertaken to study the plant diversity and population structure as a consequence of variation in the soil quality between two biotopes: Guru Ghasidas Vishwavidyalaya in Koni (site-I) and National Thermal Power Corporation in Sipat (site-II). The soil of site-I was found to be fertile and showed rich vegetation. On the other hand, the soil of site II was found to be contaminated with heavy metals, which impacts the flora of the region. The ecology of both sites was studied, and their quantitative and qualitative aspects were compared and contrasted. The abundance, density, and richness of the plants in site II were fairly lower than in site-I, which was confirmed by utilizing Simpson's and Shannon's diversity indices. Many of the species collected from site II were heavy metal accumulators and could also serve as indicators of heavy metal toxicity.

Extraction of silica from fly-ash and fabrication of silica-clay composite for dye removal and kinetic studies

A facile and green approach to extract silica from the coal fly-ash waste is extremely critical for environmental sustainability and economically suitable. In this study, we have used acid-alkali coupled approach to improvised the proficiency of the extraction process. The sodium hydroxide (NaOH) soaking results the formation of the sodium silicate (Na2SiO3) solution then pure silica was obtained by heating at high temperature; this coupled route-way results better yield of silica (SiO2) which is ∼ 40 g. The efficiency of pure silica is not enough to remove toxic effluents from the aqueous media. A highly versatile approach of composite formation was adopted to fabricate silica-clay composite using kaolinite-clay and extracted silica. Both materials, extracted silica and its silica-clay composite were analyzed using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) method, X-ray diffraction technique (XRD) and Fourier transform infra-red spectroscopy (FTIR). The silica-clay composite showed plate-tubular like morphology with enormous binding sites available for the sorption pollutants like organic dyes. It has shown excellent sorption of methylene blue (MB) efficiency of 131.5 mg/g, while silica furnished the sorption of 70.5 mg/g. Results revealed that the synthesized material could probably have better potential for dye removal from industrial effluents.

Behavior of Silica Nanoparticles Synthesized from Rice Husk Ash by the Sol-Gel Method as a Photocatalytic and Antibacterial Agent

Silica nanoparticles (SiO₂ NPs) are one of the most well-studied inorganic nanoparticles for many applications. They offer the advantages of tunable size, biocompatibility, porous structure, and larger surface area. Thus, in this study, a high yield of SiO₂ NPs was produced via the chemical treatment of rice husk ash by the sol-gel method. Characteristics of the prepared SiO₂ NPs were validated using different characterization techniques. Accordingly, the phase, chemical composition, morphological, and spectroscopic properties of the prepared sample were studied. The average particle size of the SiO₂ NPs was found to be approximately 60-80 nm and the surface area was 78.52 m²/g. The prepared SiO₂ NPs were examined as photocatalysts for the degradation of methyl orange (MO) dye under UV irradiation. It was found that the intensity of the characteristic absorption band of MO decreased gradually with exposure time increasing, which means the successful photodegradation of MO by SiO₂ NPs. Moreover, the antibacterial activity of obtained SiO₂ NPs was investigated by counting the coliform bacteria in the surface water using the most probable number (MPN) index method. The results revealed that the MPN of coliform bacteria untreated and treated by SiO₂ NPs was estimated to be 170 CFU/100 mL and 10 CFU/100 mL, respectively, resulting in bacterial growth inhibition of 94.12%.

Analysis of the Possibility of Using Cenospheres in the Production of Cement Mortars for Use in an Elevated Temperature Environment

The topic of research included in this article was the evaluation of the influence of cenospheres on selected parameters of mortar cement. Samples were designed as CEM I 42.5 R Portland cement with the application of different additive amounts. In the experimental work, the consistency, compressive strength, and bending strength were tested after 28 and 56 days of maturation, and after heating temperatures of 20, 300, 500, and 700 °C. The compressive strength was tested on half beams (40 × 40 × 160 mm). Using the obtained results, the properties of the mortars were compared. The research confirmed the possibility of producing cenosphere-modified cement mortars. Cenospheres used in the preparation of cement mortar negatively affected the bending and compressive strength with increasing temperature (20, 300, 500, 700 °C) and increasing content of this additive (10, 20, 30%).

Fluorescence spectroscopy analysis of fly ash removal from aqueous systems: adsorption of alginate to silica and alumina

Fly ash is a toxic industrial waste, mainly consisting of silica and alumina particles, that has been found discharged into the environment. It is proposed that alginate, a naturally occurring biopolymer, can bind to these minerals and thus play a role in water purification. The binding forces involved in this process consist of weak interactions, such as van der Waals forces and electrostatic interactions. Although the attachment of alginate to mineral surfaces is mainly governed by its carboxylate groups, hydroxyl moieties could play a role in the interaction between the polymer and minerals. This work aims to use the SiO₂ and Al₂O₃ particles as models for fly ash and to show the use of alginate biopolymers (fluorescently labelled with an aminonaphthaline sulfonate fluorophore (AmNS)) to coagulate them. The addition of simple electrolytes like NaCl and CaCl₂ encourages the coiling of the polymer chain at high pH values which has an effect on its capability to bind to the inorganic particles. A combination of fluorescence and ICP-MS demonstrated that alginate has a considerable adsorption affinity for Al₂O₃, whereas it attracts SiO₂ weakly. The adsorption process is pH dependent: strong adsorption was observed at low pH values. The dependence of adsorption on the mineral (Al₂O₃ and SiO₂) concentration was also examined under different pH conditions: the adsorption amount was observed to increase by increasing the solid concentration. Adsorption isotherms obtained at low and high mineral concentrations were found to be Henry in type.

A Comprehensive Review on Fly Ash-Based Geopolymer

The discovery of an innovative category of inorganic geopolymer composites has generated extensive scientific attention and the kaleidoscopic development of their applications. The escalating concerns over global warming owing to emissions of carbon dioxide (CO2), a primary greenhouse gas, from the ordinary Portland cement industry, may hopefully be mitigated by the development of geopolymer construction composites with a lower carbon footprint. The current manuscript comprehensively reviews the rheological, strength and durability properties of geopolymer composites, along with shedding light on their recent key advancements viz., micro-structures, state-of-the-art applications such as the immobilization of toxic or radioactive wastes, digital geopolymer concrete, 3D-printed fly ash-based geopolymers, hot-pressed and foam geopolymers, etc. They have a crystal-clear role to play in offering a sustainable prospect to the construction industry, as part of the accessible toolkit of building materials—binders, cements, mortars, concretes, etc. Consequently, the present scientometric review manuscript is grist for the mill and aims to contribute as a single key note document assessing exhaustive research findings for establishing the viability of fly ash-based geopolymer composites as the most promising, durable, sustainable, affordable, user and eco-benevolent building materials for the future.

Conversion of Harmful Fly Ash Residue to Zeolites: Innovative Processes Focusing on Maximum Activation, Extraction, and Utilization of Aluminosilicate

Reuse of the solid residue from coal fly ash alumina extraction (FAAE) by acid leaching is problematic. Conversion of this solid residue into aluminum-rich zeolite (13X) and silicon-rich zeolite (ZSM-5) was investigated in this research. The FAAE residue was activated by alkali roasting with Na₂CO₃ powder (110% mass fraction) at 890 °C for 60 min. Silicon and aluminum were mainly present as two mineral phases, Na₂SiO₃ and NaAlSiO₄, respectively, in the product obtained after roasting. The roasted product was dissolved in water (liquid/solid ratio of 2) after 20 min at 100 °C. The water-leaching liquor was investigated for total conversion to aluminosilicate zeolites without external aluminum or silicon addition. Hydrothermal synthesis of aluminum-rich zeolite 13X was successful after fine tuning of the conditions, although the filtrate had an unusually high SiO₂/Al₂O₃ molar ratio. Production of 13X consumed a large amount of aluminum, which increased the Si/Al ratio to a level suitable for synthesis of ZSM-5. The synthesis of ZSM-5 from the mother liquor of 13X was proved feasible. The FAAE residue was transformed into high-value zeolite products by nearly 100%. Additionally, the tail liquid of this process, mainly containing Na₂CO₃, was completely recycled. This process could be used to realize high-efficiency and high-value utilization of similar aluminosilicate solid wastes.

Remediation of Azure A Dye from Aqueous Solution by Using Surface-Modified Coal Fly Ash Extracted Ferrospheres by Mineral Acids and Toxicity Assessment

The Indian coal fly ash (CFA) is composed of 5-15% ferrous fractions. The variation in percentage depends on the source of coal and the operating conditions of the thermal power plants. The present research work reports the recovery of ferrous particles from CFA by the wet magnetic separation method. The morphological, elemental, and chemical properties of the extracted ferrous fractions were analyzed. In order to achieve surface-modified ferrospheres, the extracted ferrospheres were treated with concentrated HCl followed by sonication. The instrumental analysis reported the ferrous composition is around 16% by weight and belongs to class F. The toxicity of CFA was determined on normal human lung (BEAS-2B) cells using MTS assay. The results showed that CFA’s induced cell toxicity in a dose-dependent manner. The ferrous particles were spherically shaped with various sizes ranging from 200 nm to 7000 nm. It was crystalline in nature and is a mixture of hematite and magnetite. The particles were found to be associated with alumina, silica, oxygen, and traces of Ca, Mg, Ti, and C. The surface-modified ferrospheres were used for the remediation of Azure A dye by batch adsorption study. The removal percentage of dye was 25.03%, within 30 minutes at neutral pH, i.e., 7.2. The surface-modified ferrospheres show potential as an alternate, more economical, and reusable adsorbent for the remediation of Azure A dye in the industries or in common effluent treatment plants. Moreover, the recovery of surface-modified ferrospheres using an external magnet and the reuse of the particles make the material much economical for dye removal at an industrial scale.

Recent Advances in Synthesis and Degradation of Lignin and Lignin Nanoparticles and Their Emerging Applications in Nanotechnology

Lignin is an important commercially produced polymeric material. It is used extensively in both industrial and agricultural activities. Recently, it has drawn much attention from the scientific community. It is abundantly present in nature and has significant application in the production of biodegradable materials. Its wide usage includes drug delivery, polymers and several forms of emerging lignin nanoparticles. The synthesis of lignin nanoparticles is carried out in a controlled manner. The traditional manufacturing techniques are costly and often toxic and hazardous to the environment. This review article highlights simple, safe, climate-friendly and ecological approaches to the synthesis of lignin nanoparticles. The changeable, complex structure and recalcitrant nature of lignin makes it challenging to degrade. Researchers have discovered a small number of microorganisms that have developed enzymatic and non-enzymatic metabolic pathways to use lignin as a carbon source. These microbes show promising potential for the biodegradation of lignin. The degradation pathways of these microbes are also described, which makes the study of biological synthesis much easier. However, surface modification of lignin nanoparticles is something that is yet to be explored. This review elucidates the recent advances in the biodegradation of lignin in the ecological system. It includes the current approaches, methods for modification, new applications and research for the synthesis of lignin and lignin nanoparticles. Additionally, the intricacy of lignin’s structure, along with its chemical nature, is well-described. This article will help increase the understanding of the utilization of lignin as an economical and alternative-resource material. It will also aid in the minimization of solid waste arising from lignin.

Extraction of Value-Added Minerals from Various Agricultural, Industrial and Domestic Wastes

Environmental pollution is one of the major concerns throughout the world. The rise of industrialization has increased the generation of waste materials, causing environmental degradation and threat to the health of living beings. To overcome this problem and effectively handle waste materials, proper management skills are required. Waste as a whole is not only waste, but it also holds various valuable materials that can be used again. Such useful materials or elements need to be segregated and recovered using sustainable recovery methods. Agricultural waste, industrial waste, and household waste have the potential to generate different value-added products. More specifically, the industrial waste like fly ash, gypsum waste, and red mud can be used for the recovery of alumina, silica, and zeolites. While agricultural waste like rice husks, sugarcane bagasse, and coconut shells can be used for recovery of silica, calcium, and carbon materials. In addition, domestic waste like incense stick ash and eggshell waste that is rich in calcium can be used for the recovery of calcium-related products. In agricultural, industrial, and domestic sectors, several raw materials are used; therefore, it is of high economic interest to recover valuable minerals and to process them and convert them into merchandisable products. This will not only decrease environmental pollution, it will also provide an environmentally friendly and cost-effective approach for materials synthesis. These value-added materials can be used for medicine, cosmetics, electronics, catalysis, and environmental cleanup.

Nanobioremediation: A sustainable approach towards the degradation of sodium dodecyl sulfate in the environment and simulated conditions

Nanotechnology has gained huge importance in the field of environmental clean-up today. Due to their remarkable and unique properties, it has shown potential application for the remediation of several pesticides and textile dyes. Recently it has shown positive results for the remediation of sodium dodecyl sulfate (SDS). One of the highly exploited surfactants in detergent preparation is anionic surfactants. The SDS selected for the present study is an example of anionic linear alkyl sulfate. It is utilized extensively in industrial washing, which results in the high effluent level of this contaminant and ubiquitously toxic to the environment. The present review is based on the research depicting the adverse effects of SDS in general and possible strategies to minimizing its effects by bacterial degradation which are capable of exploiting the SDS as an only source of carbon. Moreover, it has also highlighted that how nanotechnology can play a role in the remediation of such recalcitrant pesticides.

Recent Advances in Methods for Recovery of Cenospheres from Fly Ash and Their Emerging Applications in Ceramics, Composites, Polymers and Environmental Cleanup

Coal fly ash (CFA) is a major global pollutant produced by thermal power plants during the generation of electricity. A significant amount of coal fly ash is dumped every year in the near vicinity of the thermal power plants, resulting in the spoilage of agricultural land. CFA has numerous value-added structural elements, such as cenospheres, plerospheres, ferrospheres, and carbon particles. Cenospheres are spherical-shaped solid-filled particles, formed during the combustion of coal in thermal power plants. They are lightweight, have high mechanical strength, and are rich in Al-Si particles. Due to cenospheres’ low weight and high mechanical strength, they are widely used as ceramic/nanoceramics material, fireproofing material, and in nanocomposites. They are also used directly, or after functionalization, as an adsorbent for environmental cleanup—especially for the removal of organic and inorganic contaminants from wastewater. By utilizing this waste material as an adsorbent, the whole process becomes economical and eco-friendly. In this review, we have highlighted the latest advances in the cenospheres recovery from fly ash and their application in ceramics and wastewater treatment.

Recent Advances on Properties and Utility of Nanomaterials Generated from Industrial and Biological Activities

Today is the era of nanoscience and nanotechnology, which find applications in the field of medicine, electronics, and environmental remediation. Even though nanotechnology is in its emerging phase, it continues to provide solutions to numerous challenges. Nanotechnology and nanoparticles are found to be very effective because of their unique chemical and physical properties and high surface area, but their high cost is one of the major hurdles to its wider application. So, the synthesis of nanomaterials, especially 2D nanomaterials from industrial, agricultural, and other biological activities, could provide a cost-effective technique. The nanomaterials synthesized from such waste not only minimize pollution, but also provide an eco-friendly approach towards the utilization of the waste. In the present review work, emphasis has been given to the types of nanomaterials, different methods for the synthesis of 2D nanomaterials from the waste generated from industries, agriculture, and their application in electronics, medicine, and catalysis.

Variations and similarities in structural, chemical, and elemental properties on the ashes derived from the coal due to their combustion in open and controlled manner

Coal fly ash (CFA) and coal-based incense sticks ash (ISA) have several similarities and differences due to the presence of coal as a common component in both of them. CFA are produced from the combustion of pulverized coal during electricity production in the thermal power plants while ISA are produced from the burning of incense sticks at religious places and at houses. A typical black colored Indian, incense sticks are mainly are comprised of coal powder or potassium nitrate, wood chip, fragrance, binder or binding agent, and bamboo sticks. The black colored incense sticks have coal powder or charcoal as a facilitator for smoother burning of incense sticks. The detailed investigation of CFA and ISA by X-ray fluorescence spectroscopy (XRF), electron diffraction spectroscopy (EDS), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), Fourier transform-infrared (FTIR), X-ray diffraction (XRD), particle size analyzer (PSA), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) revealed the morphological, chemical, and elemental properties. Both the coal based ashes comprises minerals like calcites, silicates, ferrous, alumina, and traces of Mg, Na, K, P, Ti, and numerous toxic heavy metals as confirmed by the XRF, ICP-AES, and EDS. While, microscopy revealed the presence of well-organized spherical shaped particles, namely cenospheres, plerospheres, and ferrospheres of size varying from 0.02 μm to 7 microns in CFA. Whereas, ISA particles are irregular, aggregated, calcium to carbon rich whose size varies from 60 nm to 9 microns and absence of well-organized spherical structures. The well developed and crystalline structure in CFA is due to the controlled combustion parameter in thermal power plants during the burning of coal while incense sticks (IS) burning is under uncontrolled manner. So, FTIR and XRD confirmed that the major portion of fly ash constitutes crystalline minerals whereas ISA have mainly amorphous phase minerals. CFA have ferrospheres of both rough and smooth surfaced, which was absent from the ISA and hence ferrous particles of CFA are of high magnetic strength. The detailed investigation of ashes will lead to the applications of ashes in new fields, which will minimize the solid waste pollution in the environment.

Recent Advances in Methods for the Recovery of Carbon Nanominerals and Polyaromatic Hydrocarbons from Coal Fly Ash and Their Emerging Applications

Coal fly ash is found to be one of the key pollutants worldwide due to its toxic heavy metal content. However, due to advancements in technology, coal fly ash has gained importance in various emerging fields. They are rich sources of carbonaceous particles which remain unburnt during burning of various coals in thermal power plants (TPPs). Various carbonaceous nanoparticles in the form of fullerenes, soot, and carbon nanotubes could be recovered from coal fly ash by applying trending techniques. Moreover, coal fly ash is comprised of rich sources of organic carbons such as polycyclic and polyaromatic hydrocarbons that are used in various industries for the development of carbon-derived value-added materials and nanocomposites. Here, we focus on all the types of carbon nanominerals from coal fly ash with the latest techniques applied. Moreover, we also emphasize the recovery of organic carbons in polyaromatic (PAHs) and polycyclic hydrocarbons (PCHs) from coal fly ash (CFA). Finally, we try to elucidate the latest applications of such carbon particle in the industry.