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Purpose Adsorbent amendment to contaminated sediments is one in situ remediation method to decrease the bioaccessibility of pollutants from the sediments. In this work, alkali-activated blast furnace slag (BFS) granules were used in a field experiment at Lake Kivijärvi (Finland). The lake was heavily affected by a mining accident in 2012, which released a significant peak load of metals and sulfate. The purpose of this work was to evaluate the performance of the novel amendment material for in situ remediation in real conditions with a preliminary cost estimation. Methods Alkali-activated BFS granules were prepared and characterized for composition, microstructure, and surface properties. Two mesocosms were placed in the lake: one with granule dosing and another without. Sediment and pore water samples were collected after a two-week period. Similar small-scale experiment was performed in laboratory with a three-month duration. Bioaccessibility of metals from sediments was assessed with a three-stage leaching procedure. Results The granules were effective in decreasing the mobility of Fe, Zn, Ni, and Cr in all leaching stages by approximately 50–90% in comparison with unamended sediment in the mesocosm experiment. Laboratory-scale incubation experiments also indicated decreased release of Ba, Co, Ni, Al, Fe, Mg, Mn and S. The estimated material costs were lower than the removal of the contaminated sediments with dredging and off-site treatment. Conclusion The results showed preliminarily the effectiveness of alkaline-activated BFS in the remediation of metal-contaminated sediments in a field experiment. However, topics requiring further study are the leaching of trace elements from the material and impact on the sediment pH.

Nitrogen loss from urea fertiliser due to its high solubility characteristics has led to the invention of controlled release urea (CRU). Majority of existing CRU coatings are produced from a non-biodegradable, toxic and expensive synthetic polymers. This study determines the feasibility of fly ash-based geopolymer as a coating material for urea fertilizer. The effects of fly ash particle size (15.2 μm, 12.0 μm, and 8.6 μm) and solid to liquid (S : L) ratio (3 : 1, 2.8 : 1, 2.6 : 1, 2.4 : 1 and 2.2 : 1) on the geopolymer coating, the characterization such as FTIR analysis, XRD analysis, surface area and pore size analysis, setting time analysis, coating thickness, and crushing strength, and the release kinetics of geopolymer coated urea in water and soil were determined. Lower S : L ratio was beneficial in terms of workability, but it had an adverse impact on geopolymer properties where it increased porosity and decreased mechanical strength to an undesirable level for the CRU application. Geopolymer coated urea prepared from the finest fly ash fraction and lowest S : L ratio demonstrated high mechanical strength and slower urea release profile. Complete urea release was obtained in 132 minutes in water and 15 days in soil from geopolymer-coated urea whereas for uncoated urea it took only 20 minutes in water and 3 days in soil. Thus, geopolymer can potentially be used as a coating material for urea fertilizer to replace commonly used expensive and biodegradable polymer-based coatings.

Alkali-activated materials (AAMs) have been known as an alternative cementitious binder in construction for more than 120 years. Several buildings utilizing AAMs were realized in Europe in the 1950s-1980s. During the last 30 years, the interest towards AAMs has been reinvigorated due to the potentially lower CO

Naturally occurring layered double hydroxide mineral, brucite (BRU), was compared with hydromagnesite (HYD) and a commercial Mg-rich mineral adsorbent (trade name AQM PalPower M10) to remove antimony (Sb) from synthetic and real wastewaters. The BRU and HYD samples were calcined prior to the experiments. The adsorbents were characterized using X-ray diffraction, X-ray fluorescence, and Fourier transform infrared spectroscopy. Batch adsorption experiments were performed to evaluate the effect of initial pH, Sb concentration, adsorbent dosage, and contact time on Sb removal from synthetic wastewater, mine effluent, and textile industry wastewater. Several isotherm models were applied to describe the experimental results. The Sips model provided the best correlation for the BRU and M10. As for the HYD, three models (Langmuir, Sips, and Redlich–Peterson) fit well to the experimental results. The results showed that the adsorption process in all cases followed the pseudo-second-order kinetics. Overall, the most efficient adsorbent was the BRU, which demonstrated slightly higher experimental maximum adsorption capacity (27.6 mg g-1) than the HYD (27.0 mg g-1) or M10 (21.3 mg g-1) in the batch experiments. Furthermore, the BRU demonstrated also an efficient performance in the continuous removal of Sb from mine effluent in the column mode. Regeneration of adsorbents was found to be more effective under acidic conditions than under alkaline conditions.

Peracetic acid (PAA) in combination with transition metals has recently gained increasing attention for organic micropollutant abatement. In this study, aqueous Co(II), Cu(II), and Ag(I) were compared for their capacity to activate PAA. Co(II) outperformed Cu(II) or Ag(I) and the optimum conditions were 0.05 mM of Co(II), 0.4 mM of PAA, and pH 3. However, due to a wider applicability in water treatment, pH 7 (i.e., bicarbonate buffer) was selected for detailed investigations. The abatement of different micropollutant surrogates could be described with a second-order rate equation (observed second-order rate constants, kobs were in the range of 42–132 M⁻¹ s⁻¹). For the para-substituted phenols, there was a correlation between the observed second-order rate constants of the corresponding phenolates and the Hammett constants (R² = 0.949). In all oxidation experiments, the reaction rate decreased significantly after 1–2 min, which coincided with the depletion of PAA but also with the deactivation of the Co(II) catalyst by oxidation to Co(III) and subsequent precipitation. It was demonstrated that Co(II) immobilized on a geopolymer-foam performed approximately similarly as aqueous Co(II) but without deactivation due to Co(III) precipitation. This provides a potential option for the further development of heterogeneous catalytic Co(II)/PAA advanced oxidation processes utilizing geopolymers as a catalyst support material.

In this work, a surface cationized inorganic–organic hybrid foam was produced from porous geopolymer (GP) and cellulose nanocrystals (CNCs). GPs were synthesized from alkali-activated metakaolin using H₂O₂ as a blowing agent and hexadecyltrimethylammonium bromide (CTAB) as a surfactant. These highly porous GPs were combined at pH 7.5 with cationic CNCs that had been synthesized from dissolving pulp through periodate oxidation followed by cationization in a deep eutectic solvent. The GP-CNC hybrid foams were employed as reactive filters in the removal of the anionic dye, methyl orange (MO; 5–10 mg/L, pH 7). The effects of a mild acid wash and thermal treatments on the structure, properties, and adsorption capacity of the GPs with CNCs and MO were investigated. The CNCs aligned as films and filaments on the surfaces of the neutralized GPs and the addition of CNCs improved MO removal by up to 84% compared with the reference sample. In addition, CTAB was found to disrupt the attachment of CNCs on the pores and improve adsorption of MO in the GPs with and without CNCs.

In this work, we compared the main characteristics of highly porous geopolymer components for water treatment applications manufactured by 3D printing, direct foaming, or granulation. Furthermore, different approaches to impregnate the materials with Ag or Cu were evaluated to obtain filters with disinfecting or catalytic properties. The results revealed that all of the investigated manufacturing methods enabled the fabrication of components that possessed mesoporosity, suitable mechanical strength, and water permeability, even though their morphologies were completely different. Total porosity and compressive strength values were 28 vol% and 16 MPa for 3D-printed, 70–79 vol% and 1 MPa for direct-foamed, and 27 vol% and 10 MPa for granule samples. Both the filter preparation and the metal impregnation method affected the amount, oxidation state, and stability of Ag and Cu in the filters. However, it was possible to prepare filters with low metal leaching between a pH of 3–7, so that the released Ag and Cu concentrations were within drinking water standards.

Abstract This paper investigates the effects of reinforcing one-part alkali-activated slag binders (OAASs) with different types of fiber (steel, polyvinyl alcohol [PVA], basalt, and cellulose) and fiber combinations (single and hybrid) on the mechanical and durability properties of OAASs. All OAASs were reinforced by a 1% fiber volume fraction. Compressive and flexural strengths were the mechanical properties, which were addressed. The durability of the reinforced OAASs was examined based on water absorption by immersion and capillary, acid resistance, high temperature resistance, carbonation resistance, and freeze/thaw resistance. The experimental results showed that the fiber type and combination greatly affects the mechanical and durability properties of OAASs. Moreover, the influence of fiber type and combination on high temperature resistance and freeze/thaw resistance is greater than the influence on acid resistance and carbonation resistance. Graphic Abstract

One-part alkali-activated materials prepared with solid-form alkali activator are gaining attention in the construction industry, as they are an easier and safer approach for cast-in-situ applications in comparison with two-part approach (i.e., involving the use of alkali-activator solutions). The present study compares the one-part and conventional two-part mixing methods with two aluminosilicate precursors, metakaolin and ground granulated blast-furnace slag, using identical mix designs (in terms of molar ratios of SiO2, Al2O3, and Na2O) with both preparation methods. The results revealed that using one-part mix delays the setting time, increases the heat of reaction, decreases the shrinkage, and reaches between 80 and 85% of the compressive strength of the two-part mix. In addition, scanning electron microscopy, thermogravimetric analysis, and X-ray diffraction analysis showed no major differences between one- and two-part. However, energy-dispersive X-ray spectroscopy and magic angle spinning nuclear magnetic resonance experiments indicated that the extent of reaction in two-part alkali-activated mixes is higher than for one-part. Graphical Abstract

Glass wool waste remains a challenging waste fraction with relatively little utilization prospects. The present study investigated the development of porous ceramic materials from glass wool waste and spodumene tailings mainly made of quartz feldspar sand (QFS), with 0.05–0.5% silica carbide (SiC) as a pore-forming agent. The formulated compositions were sintered at 950 °C and analyzed in terms of mechanical properties, phase composition, and microstructure using X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray micro-computed tomography. The results showed that a synergetic effect of glass wool and SiC started to be significant from 15 wt% glass wool and 0.05 wt% SiC, the strength reducing and the porosity increasing with the increase of SiC. The porous ceramics were largely amorphous, with compressive strength ranging from 5 to 30 MPa while the water absorption and apparent density ranged from 2 to 10% and 0.7–1.2 g/cm3, respectively. The total porosity varied between 20 and 75%, and the wall thickness between 62 and 68 μm; besides, most of the prepared materials floated in water. These results are of interest for the repurposing of glass wool waste in the development of non-flammable lightweight materials for potential filtering or high-rise building applications.

The synergistic combination of different nanomaterials for improved performance in environmental applications such as the removal of aqueous micropollutants has attracted increasing interest in recent years. This study demonstrates a novel sequential adsorption–aggregation concept that harnesses tubular halloysite nanotubes (HNTs) and flexible cellulose nanofibrils (CNFs) for the removal of a small, anionic dye molecule, chrome azurol S, from water. Hollow HNTs were first allowed to interact with the aqueous dye solution, after which the dye-loaded colloidal nanotubes were aggregated and separated from the water phase with cationized CNFs. The combination of 25 mg CNFs with 1 g HNTs at pH 7 resulted in efficient removal of dye (80%) and turbidity (~100%) and the removal of dye was further promoted in more acidic conditions (within the pH range of 6–8.5) because of the attractive electrostatic interactions. Cationic CNFs not only enabled the separation of dye-loaded clay particles from the water phase through a rapid aggregation but also participated in dye removal through adsorption (~20%). In comparison with nano-sized HNTs, the dye removal performance of micro-sized and chemically similar kaolin was poor (43%). Given the good availability of both HNTs and CNFs and the low consumption of the more expensive component (i.e., CNFs) in the process, the concept is straightforward, readily applicable, environmentally benign, and potentially cost-effective.

Alkali-activation (or geopolymer) technology has gained a great deal of interest for its potential applications in water and wastewater treatment during the last decade. Alkali-activated materials can be prepared via a relatively simple and low-energy process, most commonly by treating aluminosilicate precursors with concentrated alkali hydroxide and/or silicate solutions at (near) ambient conditions. The resulting materials are, in general, amorphous, have good physical and chemical stability, ion-exchange properties, and a porous structure. Several of the precursors are industrial by-products or other readily available low-cost materials, which further enhances the environmental and economic feasibility. The application areas of alkali-activated materials in water and wastewater treatment are adsorbents/ion-exchangers, photocatalysts, high-pressure membranes, filter media, anti-microbial materials, pH buffers, carrier media in bioreactors, and solidification/stabilization of water treatment residues. The purpose of this review is to present a comprehensive evaluation of the rapidly growing prospects of alkali-activation technology in water and wastewater treatment.

In this study, tannin-furanic-based foams enforced with H3BO3 and ZnCl2 are investigated, as well as their properties such as mechanical strength, specific surface area, and pore size distribution. From an industrial point of view, the aforementioned properties of these foams play a key role when used as catalyst, adsorbent, or gas storing materials. Therefore, this study aims to prove that such enforced tannin-furanic foams are promising materials for these types of applications. According to the results, materials that are up to five times stronger can be achieved by carbonizing the foams in comparison to maturing them. With physical activation, it was possible to obtain a specific surface area as high as 845 m2/g with a pore volume of up to 0.35 cm3/g. Chemical activation, using ZnCl2 as the activating agent, produced a specific surface area and pore volume of 737 m2/g and 0.31 cm3/g. However, the pore sizes were mostly microporous, independently of activation procedure used.

Nano/microplastics (NPs/MPs) and organic micropollutants are contaminants exerting serious threats to aquatic ecosystems, which are further aggravated through their interactions. Organic micropollutants can adsorb on the surface of NPs/MPs, enter to the digestive systems of aquatic organisms with NPs/MPs, and desorb from the surface inside the organism. Consequently, the migration behaviour of organic micropollutants is significantly affected increasing their risk to accumulate in the food chain. Therefore, understanding the adsorption interactions between NPs/MPs and organic micropollutants is critical for evaluating the fate and impact of NPs/MPs in the environment. This review article provides an overview about the role of NPs/MPs as (temporary) sinks for organic micropollutants but also as primary sources of organic micropollutants through the leaching of plastic additives. Specifically, the following aspects are discussed: adsorption/desorption mechanisms (e.g., hydrophobic partitioning interaction, surface adsorption by van der Waals forces or hydrogen bonding, and pore filling), influencing environmental factors (e.g., pH, salinity, and dissolved organic matter), leaching of plastic additives from NPs/MPs, and potential ecotoxicological effects arising from the interactions of NPs/MPs and organic micropollutants.

Despite mineral wool waste is only a small fraction of total construction and demolition waste (CDW) by mass, it requires large transportation and landfilling capacities due to its low bulk density, and its utilization remains low compared to other CDW types. It is essential to understand the physical and chemical properties of this waste fraction in order to utilize it, e.g. as fiber reinforcement in composites or as supplementary cementitious material. Here, we provide a chemical and physical characterization of 15 glass wool and 12 stone wool samples of different ages collected from various locations across Europe. In addition, the chemical compositions of 61 glass and stone wool samples obtained from the literature are presented. Glass wool samples show little variation in their chemical composition, which resembles the composition of typical soda-lime silicate glass. Stone wool presents a composition similar to basaltic glass but with variability between samples in terms of calcium, magnesium, and iron content. Potentially toxic elements, such as Cr, Ba, and Ni, are present in mineral wools, but in low concentrations (

This paper focuses on the development of high-strength and eco-friendly one-part (i.e., dry-mix) alkali-activated mortar with ground granulated blast furnace slag as the main precursor. In addition to slag, phyllite dust and silica fume were used as co-binders in binary and ternary blends to improve mechanical properties. Particle packing optimization was employed for the mix proportioning to achieve a compact matrix skeleton. The results revealed that a 10% increase in mortar strength was gained after adjusting the particle packing and an additional 20% increment was observed after blending the slag with other mineral admixtures. Ternary blend with all three binders achieved a mortar compressive strength value of 145 MPa (at 28 d age), which is the highest strength reported in one-part alkali-activated materials. Additionally, ternary blends present potential economic benefits because of their ability to replace slag with lower-cost industrial side streams.

Concrete production is globally a major water consumer, and in general, drinking-quality water is mixed in the binder. In the present study, simulated sea water and reverse osmosis reject water were used as batching water for one-part (dry-mix) alkali-activated blast furnace slag mortar. Alkali-activated materials are low-CO2 alternative binders gaining world-wide acceptance in construction. However, their production requires approximately similar amount of water as regular Portland cement concrete. The results of the present study revealed that the use of saline water did not hinder strength development, increased setting time, and did not affect workability. The salts incorporated in the binder decreased the total porosity of mortar, but they did not form separate phases detectable with X-ray diffraction or scanning electron microscopy. Leaching tests for monolithic materials revealed only minimal leaching. Furthermore, results for crushed mortars (by a standard two-stage leaching test) were within the limits of non-hazardous waste. Thus, the results indicated that high-salinity waters can be used safely in one-part alkali-activated slag to prepare high-strength mortars. Moreover, alkali-activation technology could be used as a novel stabilization/solidification method for reverse osmosis reject waters, which frequently pose disposal problems.

Alkali-activated binders have shown great potential in the reuse of industrial waste materials and have therefore received significant attention. The use of one-part or a “just-add-water” alkali-activated binder aims to avoid the use of alkali-activator solutions which have traditionally been utilized in two-part systems. By using a solid activator, the disadvantages posed by hazardous liquid activators (such as the difficulties of using them on-site) can be minimized. Ceramic materials represent a considerable fraction of construction and demolition wastes, and originate not only from the building process, but also as tiles from industry and rejected bricks. Besides using these waste materials as road sub-base or construction backfill materials, they can also be employed as supplementary cementitious materials or even as raw material for alkali-activated binders. This paper presents the strength development and microstructural results obtained from examining different compositions under various curing conditions (sealing, ambient, and submerged in water). Two different ceramic wastes (with and without firing) were used as a partial replacement (5–10% by mass) of ground granulated blast-furnace slag. Specimens were then cured under three different curing regimes, including: (1) plastic-sealed, (2) unsealed at ambient conditions with an average temperature of 23 °C and 35% RH, and (3) submerged in water until the test date. Mechanical testing (compressive and flexural strengths) and microstructural analysis (SEM/EDX, XRD, MIP, heat of hydration, TGA, and DTA) were used to determine the effects of curing conditions. The results showed that ceramic waste content and type, as well as curing regimes, greatly affect the chemical reaction products, strength development, and structural stability.

Geopolymers have been recently explored as sorbents for wastewater treatment, thanks to their mechanical and chemical stability and to their low-energy manufacturing process. One specific application could be the removal of ammonium (NH4+) through exchange with Na+ ions. Additive manufacturing (AM) represents an especially interesting option for fabrication, as it allows to tailor the size, distribution, shape, and interconnectivity of pores, and therefore the access to charge-bearing sites. The present study provides a proof of concept for NH4+ removal from wastewater using porous geopolymer components fabricated via direct ink writing (DIW) AM approach. A metakaolin-based ink was employed for the fabrication of a log-pile structure with 45° rotation between layers, producing continuous yet tortuous macropores which are responsible for the high permeability of the sorbents. The ink consolidates in an amorphous, mesoporous network, with the mesopores acting as preferential sites for ion exchange. The printed sorbents were characterized for their physicochemical and mechanical properties and the NH4+ removal capacity in continuous-flow column experiments by using a model effluent. The lattices present high permeability and high cation exchange capacity and maintained a high amount of active ions after four cycles, allowing to reuse them multiple times.

The main aim of the work is to study the effect of different fibres (steel, glass and basalt) on resistance of blast furnace slag-based alkali-activated mortar in acidic environment. The alkaliactivated slag mortars were exposed to 5% sulfuric and acetic acid solutions for 30 days. Mass change, compressive strength and microstructural changes were evaluated. In plain mortar, it was observed that 70% of the strength was retained in acetic acid environment whereas only 20% of residual strength remains in sulphuric acid environment. FTIR spectroscopy shows the degradation of the matrix, which implies the alkali-activated mortar was more vulnerable in sulphuric acid environment due to its aggressive nature compared to acetic acid. Decalcification and formation of calcium acetate also hinders the further progress of damage in acetic acid attack. Fibres helped in improving the performance of the mortar by holding the matrix together when the degradation occurred in acidic environment. Compared to plain mortar, incorporation of steel fibres exhibited a maximum strength retention of 19% in acetic acid and 7% in sulphuric acid, followed by glass and basalt fibres. SEM images clearly show the debonding of fibres and disintegration of matrix in acidic environment, which resulted in strength loss.

Geopolymers resemble conventional ceramics but can be manufactured at near-ambient temperatures. In this work, geopolymer–bentonite composite foam with silver nanoparticles was prepared and applied for water disinfection, inspired by point-of-use ceramic water filters. The inactivation efficiency against Escherichia coli and intestinal enterococci bacteria was found to be promising (0.6–2.4 and 0.3–1.4 log₁₀ reductions, respectively) for ∼1 d. However, the inactivation efficiency against somatic coliphage viruses was poor (

Micropollutants escaping conventional wastewater treatment processes pose a threat to biota and the environment. Amongst micropollutants, small and ionizable organic compounds are particularly challenging, since their removal depends significantly on prevailing conditions. In this study, anionic cellulose nanofibrils (CNFs) were shown to perform as promising adsorbents for an ionizable pharmaceutical, salbutamol. The adsorbents were produced from wood cellulose through succinylation pretreatment in urea-LiCl deep eutectic solvent (DES), followed by a nanofibrillation procedure. The impact of pH, contact time, salbutamol concentration, and adsorbent dose on salbutamol uptake were investigated in batch adsorption studies. Based on the results, the chemical modification of cellulose significantly enhanced the adsorption of salbutamol. The adsorption efficiency was mainly dependent on the charge and colloidal stability of the anionic nanofibril suspension rather than the charge of salbutamol, because the adsorption was considerably improved at pH > 7 due to the deprotonation of the cellulose carboxyl groups. The experimental maximum adsorption capacity was 196 mg/g. This study highlights the potential of cellulose nanomaterial adsorbents and the importance of controlling the charge of the adsorbent material when developing solutions for ionizable micropollutant removal.

The aim of this study was the valorization of paper sludge waste from paper industry in designing one-part geopolymer cement using ground granulated blast furnace slag as main precursor. The effects of increasing the amount of paper sludge pretreated with a constant amount of sodium hydroxide (2% of slag) on mechanical strength, heat evolution, setting time and durability were analyzed. The reaction products were characterized using X-ray diffraction and thermogravimetric analysis. The findings showed that paper sludge can successfully be used as a secondary source of calcium carbonate in the one-part (“just add water”) geopolymer. The compressive strength of the cured geopolymer increased with increasing the amount of paper sludge, and the non-reacted sludge acted as a filler. The maximum strength (42 MPa, 28 d) was reached at 18 wt-% paper sludge addition. The main reaction products were calcium aluminate silicate hydrate and hydrotalcite-like cementitious gels. From the perspective of its blast-furnace slag content, strength properties, water absorption and setting time, the one-part geopolymer cement could be classified as a CEM IIIC and Type 32.5N class cement under the European standard EN-197.

In the present experimental/numerical study, a combination of ceramic waste and ground-granulated blast furnace slag were used in the preparation of one-part alkali-activated binders. Moreover, the effect of fiber type and content on hardened-state properties and shrinkage was studied under two different curing conditions. In the first stage of this study water absorption, compressive strength, and flexural strength were assessed. Subsequently, the flexural performance of fiber-reinforced binders was simulated and predicted using finite element models under concentrated and distributed flexural loading, respectively. The experimental results showed that fibers improved mechanical properties, and enhancement was governed by fiber type and curing conditions. Moreover, the numerical results indicated that the developed fiber-reinforced binders offer a flexural load-carrying capacity in the range of 10–40 kN/m2 and permissible service loads were well below the ultimate capacity.

Alkali-activated materials (AAM) are recognized as potential alternatives to ordinary Portland cement (OPC) in order to limit CO2 emissions as well as beneficiate several wastes into useful products. However, the alkali activation process involves concentrated aqueous alkali solutions, which are corrosive, viscous, and, as such, difficult to handle and not user friendly. Consequently, the development of so-called one-part or “just add water” AAM may have greater potential than the conventional two-part AAM, especially in cast-in-situ applications. One-part AAM involves a dry mix that consists of a solid aluminosilicate precursor, a solid alkali source, and possible admixtures to which water is added, similar to the preparation of OPC. The dry mix can be prepared at elevated temperatures to facilitate the reactivity of certain raw materials. This review discusses current studies of one-part AAMs in terms of raw materials, activators, additives, mechanical and physical properties, curing mechanisms, hydration products, and environmental impacts.

Geopolymers are functional materials that can be used in various environmental applications such as adsorbents in pollutant removal from wastewaters. Metakaolin geopolymer (MK-GP) has been proven to be especially suitable for ammonium (NH4 +) removal. In this research, the optimal reagent and raw material ratios in the preparation of MK-GP in terms of NH4 + adsorption capacity were investigated. The response surface methodology based on the face-centered central composite design was used to optimize the levels of three factors: the amounts of hydroxide, silicate, and metakaolin. In addition, the effect of Na or K as the charge-balancing cation was studied. Empirical models were fitted to the experimental data using multiple linear regression. The significance of the models was confirmed by means of analysis of variance. Optimal NH4 + removal efficiency was achieved when the amounts of hydroxide and silicate were maximized, the amount of metakaolin was minimized, and Na-based reagents were used. These trends are most likely a result of optimized conversion of metakaolin into MK-GP.

Alkali-activated binders have received substantial attention due to their excellent potential in enabling the reuse and recycling of industrial solid wastes and by-products. One-part or just-add-water alkali-activated binders are an approach to reduce the negative aspects of using an alkali solution during the preparation of traditional two-part alkali-activated binders. The work aims to utilize the maximum content of ceramic wastes in alkali-activated blast-furnace slag/ceramic binders. The ground granulated blast-furnace slag was partially replaced [10%, 20%, and 30% in weight (wt.)%] by two types of ceramic wastes (porcelain and raw; i.e., fired and unfired). Moreover, the coarse particle size of porcelain ceramic waste was used as recycled aggregate. The specimens were cured under two different curing regimes: (1) sealing with plastic; and (2) using thermal curing conditions for 3 h in 60°C after demolding and then sealing until the test day. Mechanical testing and microstructural analysis were used to characterize the effects of different curing regimes and different ceramic sources. The results showed that replacing ground granulated blast-furnace slag with all types of ceramic wastes reduced the compressive strength; this reduction was mainly caused by reduction of the calcium content. This strength loss was also governed by the ceramic waste type, curing regime type, and curing duration. The microstructural analysis indicated that some cracks formed between the ceramic waste particles and the matrix. Moreover, the microscopic analysis indicated the use of preheating could eliminate cracking.

Soapstone is a soft, magnesium-rich mineral widely used in the production of carved objects and architectural elements, for instance. The processing of soapstone causes the formation of significant amounts of waste powder, which is largely landfilled at the moment. The aim of the present study is to evaluate the suitability of soapstone waste as the main binder for the alkali-activation process using sodium silicate and hydroxide solutions as activators. The results demonstrate that soapstone alone reacts to some extent (compressive strength of 13 MPa at 28 day age), but mechanical properties are improved significantly after replacing 20% of soapstone by metakaolin (compressive strength of 31 MPa at 28 d age). The obtained mechanical properties are closely similar to those of virgin soapstone. Durability properties of the developed alkali-activated binders were similar or better than typical Portland cement-based binders in terms of high temperature, acid, and freeze-thaw resistance, and sorptivity. The material costs alkali-activated soapstone mortar were estimated as approximately 70 €/t. Thus, the results enable utilizing currently underexploited soapstone waste in a sustainable and economically interesting way.

Alkali-activated materials are a low-CO2 alternative for Portland cement in construction. However, one major issue in their use is the poor or varying functionality of the currently available commercial superplasticizers. Especially for one-part (‘just add water’) alkali-activated materials, the number of studies is limited. In this study, one-part alkali-activated mortar was prepared from blast furnace slag by using solid sodium hydroxide as an activator and microsilica as an additional silica source. Comparison of commonly used superplasticizer types revealed that lignosulfonate, melamine, and naphthalene-based superplasticizers are more efficient than the currently most used polyacrylate and polycarboxylate-superplasticizers. Lignosulfonate-based superplasticizer was overall best-performing: it improved significantly the workability (+41% spread, −51% yield stress, −27% viscosity), setting time (+70%), and compressive strength (+19%) at a 0.5 wt% dose. When the amount of water and superplasticizer were optimized, compressive strength of mortar could be doubled (from 19 to 40 MPa at 28 d).

Peracids have gained interest in the water treatment over the last few decades. Peracetic acid (CH3CO3H) has already become an accepted alternative disinfectant in wastewater disinfection whereas p...

Blast-furnace slag and metakaolin were geopolymerised, modified with barium or treated with a combination of these methods in order to obtain an efficient SO4(2-) sorbent for mine water treatment. Of prepared materials, barium-modified blast-furnace slag geopolymer (Ba-BFS-GP) exhibited the highest SO4(2-) maximum sorption capacity (up to 119mgg(-1)) and it compared also favourably to materials reported in the literature. Therefore, Ba-BFS-GP was selected for further studies and the factors affecting to the sorption efficiency were assessed. Several isotherms were applied to describe the experimental results of Ba-BFS-GP and the Sips model showed the best fit. Kinetic studies showed that the sorption process follows the pseudo-second-order kinetics. In the dynamic removal experiments with columns, total SO4(2-) removal was observed initially when treating mine effluent. The novel modification method of geopolymer material proved to be technically suitable in achieving extremely low concentrations of SO4(2-) (