Mine tailings-based geopolymers: A comprehensive review

The mining industry produces a large amount of stone waste and tailings, which poses a threat to the environment. Dumping is the most common means of disposing of this industrial waste, contributing to soil degradation and water pollution with the acquisition of valuable land. Fortunately, it can be recycled in a variety of technologies, including the promising geopolymerization technology, which turns waste into value. This review paper presents recent advances in the production of mine tailings-based geopolymer composites from industrial waste as a potential sustainable building material. This article also provides in-depth studies on the behaviors and characteristics of mine tailings composites utilized in geopolymer production, such as physical properties, mechanical properties, durability properties, microstructural properties, thermal properties, leaching behavior, and potential applications. Besides, study developments are moving towards a comprehensive understanding of the environmental footprints and economic benefits of mine tailings-based geopolymer composites for building applications utilizing mine tailings as suitable concrete material. This review paper also highlights knowledge gaps that must be overcome to progress mine tailings composites for geopolymers, as well as future study opportunities based on prior research and existing challenges.     

Processing,properties and applications of highly porous geopolymers: A review

Geopolymers, possessing a semi-crystalline three-dimensional inorganic network generated by the dissolution and reaction of a solid alumino-silicate source with an activating solution, have attracted increasing attention from both academia and industry because of their unique and favorable characteristics. This review deals with the synthesis, characterization and potential applications of porous geopolymers, realized through different processing routes. Firstly, the processing approaches are divided into five categories: (i) Direct foaming, (ii) Replica method, (iii) Sacrificial filler method, (iv) Additive manufacturing, and (v) Other methods. Their microstructure, porosity and properties are compared and discussed in relation also to the different processing routes. This review highlights the fact that porous geopolymers are promising low-cost candidates for technologically significant applications such as catalyst supports or membranes, filtration of liquid or gases, adsorption and insulation. This review aims at summarizing the main published results and fostering further investigations into developing innovative ways to generate components with improved properties.     

Ceramic-like membranes without sintering via alkali activation of metakaolin,blast furnace slag,or their mixture: Characterization and cation-exchange properties

Alkali-activated (or geopolymer) membranes have emerged recently as an alternative for conventional ceramic membranes. Their main benefit is the simple and low-energy manufacturing not requiring sintering, and thus potential for clearly lower costs, while having largely similar performance as conventional ceramic materials. In this work, metakaolin, blast furnace slag, and their mixture (representing typical low, high, and medium Ca-content raw materials, respectively) were compared as aluminosilicate precursors for the preparation of self-supporting membrane disks (diameter 75 mm, height 3 mm). A thorough material characterization was performed to evaluate mechanical strength, shrinkage, microstructure, chemical composition, pore size distribution, specific surface area, zeta potential, and water flux at different temperatures (20–60 °C) and pressures (200–1000 kPa). Based on this screening, metakaolin-based membrane (i.e., the low-calcium system) indicated overall better performance than the two others based on blast furnace slag or their mixture. As a final part of the study, ammonium-containing model effluent ([NH₄⁺] = 50 mg L^?1) was distributed through the membrane (using 200 kPa pressure at 25 °C) to evaluate the potential for nitrogen removal and recovery. The mass balance examination indicated that ammonium was retained in the membrane matrix (i.e., not concentrated in the retentate fraction), and thus the likely removal mechanism was via ion-exchange. The obtained results provide interesting insights for the further development of alkali-activated membranes for applications requiring ammonium nitrogen removal, such as membrane bioreactors in municipal wastewater treatment.     

The effect of matrix composition and calcium content on the sulfate durability of metakaolin and metakaolin/slag alkali-activated mortars

The work in hand presents the results of an experimental research on the effect of different precursors (binders) used in alkali-activated materials (AMM) and its composition (i.e. SiO₂/Al₂O₃ molar ratio) on their sulfate durability. A reference matrix is formed from the activation of metakaolin (MK); this matrix was modified by the partial replacement of MK with either 20 wt% silica fume (SF) or 20 and 40 wt% blast furnace slag (BFS), so that the SiO₂/Al₂O₃ molar ratio of calcium-free and calcium-rich AAM changed from 3.0 to 3.9. The properties assessed prior to the durability testing were: density (pycnometry), compressive strength, capillary sorption and oxygen permeability. The sulfate durability was investigated by exposing the matrices to a magnesium sulfate solution for 30, 90 and 180 days of attack, after which the residual compressive strength was determined. The reductions in strength after each period of testing were correlated with variations in the pH of the sulfate solutions and with geometry changes (expansion) measured in cylinders exposed to the durability tests. X-Ray diffraction was used to determine the minerals formed onto the surface of the samples after magnesium sulfate attack. The results show that the MK-based AAM present a higher resistance to magnesium sulfate attack. Furthermore, the partial replacement of MK with BFS is responsible for reductions in the mechanical properties after attack to sulfate. This is associated with the formation of ettringite and gypsum in the presence of calcium from BFS, besides the loss of alkalinity from the migration of alkali (Na⁺) to the solution.     

Fly ash-based boroaluminosilicate geopolymers: Experimental and molecular simulations

Geopolymers are cement-free construction materials which are produced by mixing an aluminosilicate source such as fly ash with an alkali activator. Despite their eco-friendly nature, geopolymers suffer the negative impact of the sodium silicate part of the alkali activator on the environment. The use of borax, one of the eco-friendly salts of boric acid, as an activator can potentially lead to the production of more environmentally-friendly geopolymer. However, a better understanding of their theoretical properties could be a milestone to produce new generations of geopolymers with high performance. A growing interest in the prediction of the macroscale properties of geopolymer compounds was the most compelling motivation for this study. Building upon this, the current study focused on both points to apply borax as a potential replacement for silicate-based activators and model all the experiments by molecular dynamics (MD) simulation. Substituting boron with aluminium in the molecular structures of geopolymer was the core idea of the simulation. Compressive strength, density and elastic modulus tests were conducted, and the results were compared with the MD simulation outcomes. Increasing the content of borax in the mixture led to a decrease in all of the properties, although the range of 10–30% of replacement eventuated in acceptable results. A fair agreement between simulation and experimental results was achieved through which the best fitting parameters for atomistic modelling of geopolymers were found.     

Synthesis,microhardness, fracture toughness and microstructural features of chitosan containing alkali activated geopolymers

In this work, geopolymer matrix samples containing different amounts of chitosan, specifically 1, 3, 5 and 10 wt%, were produced to study the effect of a ductile phase within a much more brittle one.The reference geopolymer was produced mixing a commercial metakaolin with sodium silicate solution and sodium hydroxide solution. Geopolymeric slurries were caste into mold and hardened by a thermal treatment at 70 °C and then at ambient temperature for 28 days. Hardened materials, containing different amount of chitosan, were examined by mean of X-ray diffraction, Fourier Transform Infrared Radiation, Scanning Electron Microscope investigation. Microhardness and fracture toughness were measured to study the effects on the samples chemistry and microstructure caused by the introduction of chitosan into the geopolymer. It has been observed that the addition of chitosan lowers materials porosity and microhardness, but slightly improves their fracture toughness.     

(Micro)-structural comparison between geopolymers, alkali-activated slag cement and Portland cement

Concurrently to research conducted on ordinary Portland cement (PC), new types of binders were developed during the last decades. These are formed by alkali-activation of metakaolin or ground-granulated blast furnace slag (GGBFS) and are named, respectively, geopolymers (GP) or alkali-activated slag (AAS). Four different cementitious materials were synthesised: PC, AAS, GP, and a mix GP-AAS and fully compared about their compositions and (micro)-structures.

X-ray diffraction has revealed the presence of semi-crystalline CSH gel binding phase in PC while AAS, GP and GP-AAS are nearly amorphous. Progressive structural changes have been observed between the different samples by means of infrared spectroscopy, ²⁹Si and ²⁷Al magic-angle-spinning nuclear magnetic resonance spectroscopy: there is a polymerisation extent of the (alumino)-silicate framework from PC [SiQ¹ and SiQ² units] to AAS [SiQ² and SiQ²(1Al) units] and finally to GP [SiQ⁴(2Al) and SiQ⁴(3Al) units]. Scanning electron microscopy has shown that GP is a homogeneous matrix while the other materials are composites containing GGBFS grains surrounded by a binding matrix. Energy dispersive X-ray EDX analyses (line scans) have shown the absence of formation of any specific phase at the matrix-grains interfaces.     

工业废料在耐火材料中的应用现状和进展

简单介绍了工业废料的现状,重点阐述了废料在耐火材料中的研究与应用现状,以及废弃料合成耐火原料的方法、再利用途径和发展前景。     

Synthesis,characterization and application of acid and alkaline activated volcanic ash-based geopolymers for adsorptive remotion of cationic and anionic dyes from water

In this work, two geopolymers were prepared by acid activation (GPAc) and alkaline activation (GPAl) approaches using volcanic ash (VA) as the precursor material. The geosorbents were characterized by X-ray diffraction (XRD), Thermogravimetric analysis (TGA), Fourier-transform infrared and Brunauer-Emmett-Teller (BET) surface area analyses and their comparative adsorptive potential for anionic (Eriochrome Black T/EBT) and cationic (methylene blue/MB) dyes from water is herein reported for the first time. GPAl and GPAc had 74.47 and 42.75 m²/g BET surface areas, respectively. Equilibrium adsorption data were described by the isotherm models in the order Freundlich > Sips > Langmuir model. Relative to acid activation (GPAc), alkaline activated geopolymer (GPAl) had the highest adsorption capacity for both MB and EBT, estimated at 952 mg/g and 251 mg/g, respectively, consistent with the BET surface areas. The adsorption rates were best described by the pseudo-second order (PSO) kinetic model. GPAl exhibited faster adsorption kinetics than GPAc as denoted by the adsorption half-life, t_1/2. The thermodynamic functions indicated that the adsorption of both MB and EBT onto the geopolymers was spontaneous, exothermic and feasible. The adsorption was pH-dependent implying electrostatic interactions is the dominant driving mechanism of adsorption. The results show that alkaline activated geopolymers are better sorbents for dye removal than acid activated geopolymers under the examined conditions.     

Catalytic applications of red mud, an aluminium industry waste: A review

Red mud is a by-product of bauxite processing through Bayer process. The amount of red mud generated depends largely on the type of ore used and the processing. Use of red mud as a catalyst can be a good alternative to the existing commercial catalysts. Its properties such as iron content in form of ferric oxide (Fe₂O₃), high surface area, sintering resistance_, resistance to poisoning and low cost make it an attractive potential catalyst for many reactions. Besides red mud, ferric ion sludge from wastewater treatment plant has also been studied for its catalytic properties, mainly due to its ferric oxide constituent. This paper reviews the studies on red mud as a catalyst. The catalyst characteristics, reaction mechanisms involved and performance are examined and compared with iron oxide catalyst and commercial catalysts.     

工业废渣制备硫酸钙晶须及其应用研究进展

通过对硫酸钙晶须生长机理的分析,介绍了目前以工业废渣为原料,采用水热合成技术制备硫酸钙晶须的方法,重点探讨磷石膏制备硫酸钙晶须的研究进展;对硫酸钙晶须在复合材料等领域的应用进行阐述,从而提出硫酸钙晶须在制备、应用等方面的未来发展方向。     

Synthesis and characterization of geopolymers containing blends of unprocessed steel slag and metakaolin: The role of slag particle size

The present research deals with the production and characterization of geopolymers prepared by mixing metakaolin with a steel slag from the production of chromium-manganese steel, a commercial sodium silicate solution and a sodium hydroxide solution. Different specimens were prepared by mixing metakaolin with different proportions of steel slag (20, 40, 60, 80 wt%) characterized by different maximum particle size. Specimens containing just metakaolin and steel slag alone were also prepared for comparison. All specimens have been characterized regarding their compressive strength, specific surface area, water absorption and microstructure. It has been observed that the use of fine steel slag powders leads to increases the performances and that the specimens containing 40 wt% steel slag and 60 wt% metakaolin revealed the best overall behaviour.     

A review on recent applications and future prospects of rare earth oxides in corrosion and thermal barrier coatings,catalysts, tribological,and environmental sectors

Rare earth oxides (REOs) and metals as an important class of materials have generated global interest in modern technology. Here, eight REOs (R₂O₃, R = Yb, Er, Sm, Eu, Y, Gd, Dy, and Ce) are identified those are mostly used in diverse chemical and industrial sectors. In this concise review the applications of these REOs in corrosion protection, thermal barrier coating, hydrophobic coating, catalytic reactions, refrigeration, photoactivity, environmental, and tribological sector are briefly summarized, which are sparsely documented in the existing literature review. In what follows, recently published relevant literature is systematically evaluated and key insights are addressed. The use of REOs as nonstoichiometric compounds or as doping agents to enhance the system performance of specific applications is commendable. Related lab-scale studies, therefore, will invoke the potential exploitation of individual or blended REOs for large-scale commercialization. However, phase transformation and high energy consumption in the thermal coating, multi-step fabrication of hydrophobic coating, the building of aromatic pollutants in catalysis, magnetic entropy shift in refrigeration, and photo corrosion are some of the inherent hindrances of these oxides. These issues warrant prompt actions from the scientific community to deliver cost-effective, efficient, and environmentally sustainable applications. Regardless, this review is expected to provide critical insights into REOs for contrasting industrial applications and encourage interested researchers to dig deeper in finding the best strategic solutions to counter prevalent challenges.     

甲醇制丙烯研究及工业应用最新进展

综述了国内外甲醇转化制丙烯技术的研究进展及相关转化机理;重点阐述了具有代表性的几种甲醇制丙烯(MTP)工艺,并对国内最新工业应用进展进行了详细介绍。新型催化剂的研发和反应器的放大,使MTP技术在煤及天然气化学领域中应用更具优势。     

Recycling of industrial wastes in ceramic manufacturing: State of art and glass case studies

Nowadays, ceramic tile are manufactured at zero emissions permitting to recycle all by-products and part of residues derived from depuration treatments (exhausted lime, glazing sludge and polishing sludge). In addition to this environmentally friendly tendency, in the last years an increasing number of scientific studies demonstrated the feasibility to use alternative raw materials in substitution of different component of the ternary clay-feldspar-quartz system. In the first part of the paper is reported the state of the art of industrial waste recycling in the ceramic sector, with the focus on review studies related to both ceramic tiles and bricks..In the second part of the work are reported two case studies conducted by the authors with the aim to formulate ceramic bodies using alternative raw materials. New tailored compositions were obtained replacing clays, flux and/or inert compounds (higher than 60 wt%) by scraps from packaging waste glass in tiles, and cathode ray tube glasses and packaging waste glass up to 20 wt% in the brick compositions.     

Incorporation of organic liquids into geopolymer materials - A review of processing,properties and applications

Geopolymers, composed of an amorphous three-dimensional inorganic network and synthesized by the activation of a solid alumino-silicate precursor with an alkaline activating solution, have attracted increasing attention because of their environmental benefits and favorable characteristics. This review deals with the development of organic/inorganic composite materials made by adding organic liquids into inorganic geopolymer matrices. Firstly, the incorporation processing approaches are presented and are divided into three categories: (i) Direct incorporation, (ii) Pre-emulsification (iii) Solid impregnation. Their main advantages and drawbacks are discussed in relation to the aimed properties. Secondly, this review highlights that geopolymers are low-cost candidates allowing technologically significant applications, through the incorporation of various organic liquids. Aside from the well-studied immobilization of industrial waste streams commonly known as stabilization/solidification (S/S), the development of highly porous geopolymer foams and the design of reinforced organic/inorganic composite matrices are being notably investigated. This review aims at summarizing the main published results, and fostering further investigations into innovative uses of organic liquids incorporated into geopolymers for a wide range of applications.     

Graphene-DNA hybrid materials: Assembly, applications, and prospects

Among the carbon-based nanomaterials such as carbon nanotubes, fullerenes, graphene and nanodiamonds, graphene received recently widespread attention owing to its exceptional structural, electronic and mechanical properties and potential applications in various domains. However, all currently known forms of graphene materials are not well dispersible or soluble in most common solvents. This limitation deters to explore the chemistry of graphene at the molecular level and its nanobio device applications. One well known solution to this problem is the use of dispersing agents such as polymers, biopolymers, or surfactants in conjunction with the appropriate experimental conditions. Among the various biomolecules, deoxyribonucleic acid (DNA) has emerged as an appealing biomacromolecule for functional materials due to its biocompatibility and renewability in addition to its very interesting double helix structure, which guarantees a range of unique properties that are difficult to detect in other molecules and polymers. Hence, the combination of graphene (a carbon-based nanomaterial), showing exceptional electronic properties, and DNA (a nanostructured biomolecule), having extraordinary recognition properties, demonstrates a new type of nanobio hybrid material. This, in turn, leads to a successful incorporation of the properties of the two different components in new hybrid materials that present important features for potential applications that range from advanced biomedical systems by means of very sensitive electrochemical sensors and biosensors to highly efficient electronics- and optics-based biochips. This article will focus on the recent advancement of the methods available for the chemical functionalization of graphene using DNA by different interactions (covalent or non-covalent and insertion of DNA through graphene nanopore or nanogap), various types of assemblies, and future prospects. Furthermore, the various potential applications of the resulting new nanobio hybrid materials are also highlighted.     

The catalytic effect of the Na and Ca-rich industrial wastes on the thermal ignition of coal combustion

The catalytic effects of four industrial wastes, namely, the soap residue (SR), brine sludge (BS), calcium carbide residue (CCR), and white lime mud (WLM), on coal thermal ignition were investigated. The acidity of palmitate anion associated with Na⁺ in SR was lower than that of chloride anion combined with Na⁺ in BS, which resulted in an improved the combustion of SR. The acidity of OH^- anion combined with Ca²⁺ in CCR was lower than that of CO₃^2- anion combined with Ca²⁺ in WLM, resulting in CCR exhibiting a better catalytic effect on coal ignition. The alkaline metal Na had lower initial ionisation energy than the alkaline earth metal Ca. Therefore, the Na-rich SR exhibited higher catalytic activity on coal ignition than Ca-rich CCR. The ignition temperature of coal with 0.5% SR decreased from 544 to 503℃.     

Polymeric monolithic materials: Syntheses, properties, functionalization and applications

The synthetic particularities for the synthesis of polymer-based monolithic materials are summarized. In this context, monoliths prepared via thermal-, UV- or electron-beam triggered free radical polymerization, controlled TEMPO-mediated radical polymerization, polyaddition, polycondensation as well as living ring-opening metathesis polymerization (ROMP) will be covered. Particular attention is devoted to the aspects of controlling pore sizes, pore volumes and pore size distributions as well as functionalization of these supports. Finally, selected, recent applications in separation science, (bio-) catalysis and chip technology will be summarized.     

工业废渣及改性工业废渣长效氮肥中活性硅、钙、镁的测定

研究建立了测定工业废渣及工业废渣长效氮肥中活性硅、钙、镁的方法，实验表明，方法简单易行、结果准确。