Search Results (17)

In this paper, the enhancement of thermochemical energy storage by alkali metal chloride salts-doped Ca-based sorbents is revealed by experiments and DFT calculations. The results indicate that NaCl and KCl doping increases the reaction rate and cycle stability. Compared to CaO, the conversion of NaCl-CaO and KCl-CaO after one cycle is increased by 59.1% and 61.9%, respectively. This enhancement originates from the oxygen vacancies generated by Na₂O and K₂O and the significantly increased surface area by CaCl₂ as well as the sintering delay. The synergistic effect between Na₂O, K₂O, and CaCl₂ increases the reaction rate of calcium-based materials. Meanwhile, the penetration of low-viscosity molten NaCl and KCl into the calcium-based materials successfully segregates the CaO grains and allows the calcium-based material to maintain the porous structure after 80 cycles, thus exhibiting a high effective conversion rate. In addition, the KCl-CaO composites show the best combined performance in terms of effective conversion and averaged thermal energy density. This work paves the way for the application of chloride salts-doped calcium-based materials. Full article

The influence of raw material factors (component composition of batches, petrographic characteristics, indicators of proximate and plastometric analyses, granulometric composition) and technological factors (coking period, process temperature) on the sorption properties of the carbonized product (coke) was studied. Based on the research results, it is shown that such characteristics of coke as low humidity and ash, minimal yield of volatile matters, developed pore system and low cost make its use as a sorbent promising and economically justified. The obtained equations for predicting the sorption capacity by alkali and acid and adsorption activity by iodine, taking into account the content of vitrinite and the yield of volatile matters coal batch. They are characterized by high approximation coefficients r (0.912 and 0.927 and 0.937, respectively), so they can be recommended for predicting the indicated indicators. Full article

CO₂ uptake by MgO-based sorbents at intermediate temperatures is attractive for pre- and post-combustion CO₂ capture applications. However, besides the high CO₂ uptake potential of these materials (1.1 g CO₂ g⁻¹ sorbent), in practice, the realistic CO₂ capture is far from that of the theorical values. In this work, the sol–gel method was used to synthetize unsupported and supported MgO sorbents (10% Ca⁻ or 10% Ce⁻ support, mol) that were impregnated with different fractions (15, 25, and 35; % mol) of a NaNO₃ single salt or a ternary alkali salt (NaNO₃, LiNO₃ and KNO₃ (18/30/52; % mol)). To understand the role of alkali metal salts (AMSs) in the MgO sorbents’ performance, the working and decomposition temperature ranges of AMS under different atmospheres (CO₂ and air) were evaluated. The findings show that the CO₂ uptake temperature range and maximum uptake (20–500 °C, CO₂ atmosphere) of sorbents are correlated. The cyclic CO₂ uptake of the most promising sorbents was tested along five carbonation–calcination cycles. For the first and fifth cycles, respectively, the 15 (Na, K, Li)-MgO sorbents showed the highest carrying capacity, i.e., 460–330 mg CO₂ g⁻¹ sorbent, while for the 15 (Na, K, Li)-MgO-Ca sorbents, it was 375–275 mg CO₂ g⁻¹. However, after the first cycle, the carbonation occurred faster for the 15 (Na, K, Li)-MgO-Ca sorbents, meaning that it can be a path to overpassing carbonation kinetics limitations of the MgO sorbent, making it viable for industrial applications. Full article

The article presents the distribution coefficient (K_d) values of ¹³⁷Cs and ⁹⁰Sr tracer radionuclides in solutions of sodium and calcium salts for a wide range of commercially available inorganic sorbents: natural and synthetic aluminosilicates, manganese, titanium and zirconium oxyhydrates, titanium and zirconium phosphates, titanosilicates of alkali metals, and ferrocyanides of transition metals. The results were obtained using a standard technique developed by the authors for evaluating the efficiency of various sorption materials towards cesium and strontium radionuclides. It was shown that bentonite clays and natural and synthetic zeolites are the best for decontaminating low-salt natural water from cesium radionuclides, and ferrocyanide sorbents are the choice for decontaminating high-salt-bearing solutions. The manganese (III, IV) oxyhydrate-based MDM sorbent is the most effective for removing strontium from natural water; for seawater, the barium silicate-based SRM-Sr sorbent is the first-in-class. Results of the study provide a possibility of making a reasonable choice of sorbents for the most effective treatment of natural water and technogenic aqueous waste contaminated with cesium and strontium radionuclides. Full article

Although Cs(I) and Sr(II) are not strategic and hazardous metal ions, their recovery from aqueous solutions is of great concern for the nuclear industry. The objective of this work consists of designing a new sorbent for the simultaneous recovery of these metals with selectivity against other metals. The strategy is based on the functionalization of algal/polyethyleneimine hydrogel beads by phosphonation. The materials are characterized by textural, thermo-degradation, FTIR, elemental, titration, and SEM-EDX analyses to confirm the chemical modification. To evaluate the validity of this modification, the sorption of Cs(I) and Sr(II) is compared with pristine support under different operating conditions: the pH effect, kinetics, and isotherms are investigated in mono-component and binary solutions, before investigating the selectivity (against competitor metals) and the possibility to reuse the sorbent. The functionalized sorbent shows a preference for Sr(II), enhanced sorption capacities, a higher stability at recycling, and greater selectivity against alkali, alkaline-earth, and heavy metal ions. Finally, the sorption properties are compared for Cs(I) and Sr(II) removal in a complex solution (seawater sample). The combination of these results confirms the superiority of phosphonated sorbent over pristine support with promising performances to be further evaluated with effluents containing radionuclides. Full article

Global warming and climate changes are among the biggest modern-day environmental problems, the main factor causing these problems is the greenhouse gas effect. The increased concentration of carbon dioxide in the atmosphere resulted in capturing increased amounts of reflected sunlight, causing serious acute and chronic environmental problems. The concentration of carbon dioxide in the atmosphere reached 421 ppm in 2022 as compared to 280 in the 1800s, this increase is attributed to the increased carbon dioxide emissions from the industrial revolution. The release of carbon dioxide into the atmosphere can be minimized by practicing carbon capture utilization and storage methods. Carbon capture utilization and storage (CCUS) has four major methods, namely, pre-combustion, post-combustion, oxyfuel combustion, and direct air capture. It has been reported that applying CCUS can capture up to 95% of the produced carbon dioxide in running power plants. However, a reported cost penalty and efficiency decrease hinder the wide applicability of CCUS. Advancements in the CCSU were made in increasing the efficiency and decreasing the cost of the sorbents. In this review, we highlight the recent developments in utilizing both physical and chemical sorbents to capture carbon. This includes amine-based sorbents, blended absorbents, ionic liquids, metal-organic framework (MOF) adsorbents, zeolites, mesoporous silica materials, alkali-metal adsorbents, carbonaceous materials, and metal oxide/metal oxide-based materials. In addition, a comparison between recently proposed kinetic and thermodynamic models was also introduced. It was concluded from the published studies that amine-based sorbents are considered assuperior carbon-capturing materials, which is attributed to their high stability, multifunctionality, rapid capture, and ability to achieve large sorption capacities. However, more work must be done to reduce their cost as it can be regarded as their main drawback. Full article

With the continuous research on lignin-based sorbents, there are still limitations in the research of spherical sorbents with a high adsorption capacity for Pb²⁺. In order to solve the problem of low adsorption effect, alkali lignin (AL) was modified and assembled to increase the adsorption active sites. In this work, we used dual-modified lignin (DML) as a raw material to assemble a singular lignin-based multilayer microsphere (LMM) with sodium alginate (SA) and dopamine. The prepared adsorbent had various active functional groups and spherical structures; the specific surface area was 2.14 m²/g and the average pore size was 8.32 nm. The adsorption process followed the Freundlich isotherm and the second-order kinetic model. Therefore, the LMM adsorbed Pb²⁺ ascribed by the electrostatic attraction and surface complexation; the adsorption capacity was 250 mg/g. The LMM showed a selective adsorption performance for Pb²⁺ and the adsorption capacity followed the order Pb²⁺ (187.4 mg/g) > Cu²⁺(168.0 mg/g) > Mn²⁺(166.5 mg/g). After three cycles, the removal efficiency of Pb²⁺ by the LMM was 69.34%, indicating the reproducibility of LMM. Full article

Hydrogen is a versatile vector for heat and power, mobility, and stationary applications. Steam methane reforming and coal gasification have been, until now, the main technologies for H₂ production, and in the shorter term may remain due to the current costs of green H₂. To minimize the carbon footprint of these technologies, the capture of CO₂ emitted is a priority. The in situ capture of CO₂ during the reforming and gasification processes, or even during the syngas upgrade by water–gas shift (WGS) reaction, is especially profitable since it contributes to an additional production of H₂. This includes biomass gasification processes, where CO₂ capture can also contribute to negative emissions. In the sorption-enhanced processes, the WGS reaction and the CO₂ capture occur simultaneously, the selection of suitable CO₂ sorbents, i.e., with high activity and stability, being a crucial aspect for their success. This review identifies and describes the solid sorbents with more potential for in situ CO₂ capture at high and medium temperatures, i.e., Ca- or alkali-based sorbents, and Mg-based sorbents, respectively. The effects of temperature, steam and pressure on sorbents’ performance and H₂ production during the sorption-enhanced processes are discussed, as well as the influence of catalyst–sorbent arrangement, i.e., hybrid/mixed or sequential configuration. Full article

The underutilized cement-rich fine fraction of concrete-based demolition waste is a potential sorbent for aqueous metal ion contaminants. In this study, crushed concrete fines (CCF) were found to exclude 33.9 mg g⁻¹ of Cr³⁺, 35.8 mg g⁻¹ of Ni²⁺, and 7.16 mg g⁻¹ of Sr²⁺ from ~1000 ppm single metal nitrate solutions (CCF:solution 25 mg cm⁻³) under static batch conditions at 20 °C after 3 weeks. The removal of Sr²⁺ followed a pseudo-second-order reaction (k₂ = 3.1 × 10⁻⁴ g mg⁻¹ min⁻¹, R² = 0.999), whereas a pseudo-first-order model described the removal of Cr³⁺ (k₁ = 2.3 × 10⁻⁴ min⁻¹, R² = 0.998) and Ni²⁺ (k₁ = 5.7 × 10⁻⁴ min⁻¹, R² = 0.991). In all cases, the principal mechanism of interaction was the alkali-mediated precipitation of solubility-limiting phases on the surface of the CCF. Four consecutive deionized water leaching procedures (CCF:water 0.1 g cm⁻³) liberated 0.53%, 0.88%, and 8.39% of the bound Cr³⁺, Ni²⁺, and Sr²⁺ species, respectively. These findings indicate that CCF are an effective sorbent for the immobilization and retention of aqueous Cr³⁺ and Ni²⁺ ions, although they are comparatively ineffectual in the removal and sustained exclusion of Sr²⁺ ions. As is commonly noted with Portland cement-based sorbents, slow removal kinetics, long equilibrium times, the associated release of Ca²⁺ ions, high pH, and the formation of loose floc may preclude these materials from conventional wastewater treatments. This notwithstanding, they are potentially suitable for incorporation into permeable reactive barriers for the containment of metal species in contaminated groundwaters, sediments, and soils. Full article

Data related to the fabrication of hybrid materials based on the polysaccharide chitosan were systematized and reviewed. The possibility of using chitosan as a “host” matrix for in situ synthesis of inorganic compounds for the preparation of various types of composite materials were investigated. Coprecipitation of metal oxides/hydroxides (Fe, Ni, Al, Zr, Cu and Mn) with chitosan was carried out through the alkalinization of solutions containing metal salts and chitosan, with the addition of ammonia or alkali solutions, homogeneous hydrolysis of urea, or electrophoretic deposition on the cathode. The synthesis of transition metal ferrocyanides and hydroxyapatite was achieved from precursor salts in a chitosan solution with simultaneous alkalinization. The mechanism of composite formation during the coprecipitation process of inorganic compounds with chitosan is discussed. Composite materials are of interest as sorbents, coatings, sensors, and precursors for the production of ceramic and electrode materials. Full article

Currently, slags from secondary steel production, foundries, and blast furnaces represent a major environmental problem since they end up mainly in landfills, and their valorization would bring undeniable advantages both to environment and economy. Moreover, the removal of heavy metal ions from mines wastewater is one of the challenges of the last decades, and adsorption has been proposed as one of the most promising techniques for this purpose. In this context, the use of alkali-activated slags as sorbent can be a good opportunity to develop low cost, environmentally friendly, and sustainable materials. Accordingly, wastewater decontamination by adsorption over a porous monolithic bed made of alkali-activated hydraulic binders is proposed. Alkali-activated materials were prepared using slags from the metallurgical industry and reacted with an alkaline component (high alumina calcium aluminate cement, CAC 80) at ambient conditions. The obtained monolithic foams were tested to evaluate the uptake efficiency towards metal capture. Solutions containing Cu(II), Fe(III), Ni(II), Mn(II), and simulating the metal concentrations of a real mine effluent were tested, both in single- and multi-ion solutions. Promising capture efficiency, values of 80–100% and of 98–100% in the case of the single ion and of the multi-ion solutions were obtained, respectively. Full article

With the target of recovering rare earth elements (REEs) from acidic leachates, a new functionalized hydrogel was designed, based on the phosphorylation of algal/polyethyleneimine beads. The functionalization strongly increased the sorption efficiency of the raw material for Pr(III) and Tm(III). Diverse techniques were used for characterizing this new material and correlating the sorption performances and mechanisms to the physicochemical structure of the sorbent. First, the work characterized the sorption properties from synthetic solutions with the usual procedures (study of pH effect, uptake kinetics, sorption isotherms, metal desorption and sorbent recycling, and selectivity from multi-element solutions). Optimum pH was found close to 5; sorption isotherms were fitted by the Langmuir equation (maximum sorption capacities close to 2.14 mmol Pr g⁻¹ and 1.57 mmol Tm g⁻¹). Fast uptake kinetics were modeled by the pseudo-second order rate equation. The sorbent was highly selective for REEs against alkali-earth and base metals. The sorbent was remarkably stable for sorption and desorption operation (using 0.2 M HCl/0.5 M CaCl₂ solutions). The sorbent was successfully applied to the leachates of Egyptian ore (pug leaching) after a series of pre-treatments (precipitation steps), sorption, and elution. The selective precipitation of REEs using oxalic acid allows for the recovery of a pure REE precipitate. Full article

Activation of natural sepiolite by means of grinding in a planetary mill followed by wet NaOH activation was studied for the purpose of endowing the product with enhanced basicity for potential catalytic/sorptive applications. Synthesized solids were characterized with X-ray powder diffraction (XRD), N₂ adsorption/desorption, scanning electron microscopy (SEM), energy dispersive (EDX), atomic absorption (AAS), Fourier-transform infrared (FTIR) and ²⁹Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies. Surface basicity was determined by titration with benzoic acid. Grinding changed the pathway of sepiolite phase transformation upon NaOH treatment. The as-received sepiolite evolved to Na-sepiolite (loughlinite) with a micropore system blocked by nanocrystalline Mg(OH)₂, while ground samples yielded magnesium silicate hydrate phase (MSH), with well-developed microporous texture. In unmilled sepiolite desilication involved preferential leaching of Si from the center of the structural ribbons, while in ground samples additional loss of Si from ribbon-ribbon corner linkages was observed. In all cases treatment with NaOH led to enhancement of surface basicity. Synthesized materials were tested as catalysts in a base-catalyzed aldol self-condensation of acetone and oxidation of cyclohexanone to ε-caprolactone, as well as CO₂ sorbents. Catalytic trends depended not only on samples’ basicity, but also on texture and phase composition of the catalysts. Grinding combined with alkali activation proved a simple and effective method for boosting CO₂-sorption capacity of sepiolite to the level comparable to amine-functionalized, acid-activated sepiolite sorbents. Full article

Alkali-based CO₂ sorbents were prepared from a novel material (i.e., Laminaria hyperborea). The use of this feedstock, naturally containing alkali metals, enabled a simple, green and low-cost route to be pursued. In particular, raw macroalgae was pyrolyzed at 800 °C. The resulting biochar was activated with either CO₂ or KOH. KOH–activated carbon (AC) had the largest surface area and attained the highest CO₂ uptake at 35 °C and 1 bar. In contrast, despite much lower porosity, the seaweed-derived char and its CO₂-activated counterpart outweighed the CO₂ sorption performance of KOH–AC and commercial carbon under simulated post-combustion conditions (53 °C and 0.15 bar). This was ascribed to the greater basicity of char and CO₂–AC due to the presence of alkali metal-based functionalities (i.e., MgO) within their structure. These were responsible for a sorption of CO₂ at lower partial pressure and higher temperature. In particular, the CO₂–AC exhibited fast sorption kinetics, facile regeneration and good durability over 10 working cycles. Results presented in the current article will be of help for enhancing the design of sustainable alkali metal-containing CO₂ captors. Full article

This work reports and describes a novel alkali-activated metakaolin as a potential binder material for the granulation of zeolites, which are widely used as CO₂ adsorbents. The alkali-activated binders are zeolite-like materials, resulting in good material compatibility with zeolite-based adsorbents. A major problem during the granulation of zeolites is that their adsorption capacities decrease by about 15–20%, because typical binder materials (for example bentonite or kaolin clay) are inactive towards CO₂ adsorption. A possible pathway to solve this problem is to introduce a novel binder that is also able to sorb CO₂. In such a case, a binder plays a dual role, acting both as a binding material and as a sorbent. However, it is important that, alongside the adsorptive properties, a novel binder material must fulfil mechanical and morphological requirements. Thus, in this work, physical and mechanical properties of this novel binder for zeolite granulation for CO₂ adsorption are studied. Alkali-activated metakaolin was found to be efficient and competitive as a binder material, when mechanical and physical properties were concerned. The compressive strengths of most of the obtained binders reported in this work are above the compressive strength threshold of 10 MPa. The future work on this novel binder will be conducted, which includes granulation-related details and the CO₂ adsorptive properties of the novel binder material. Metakaolin was used as a precursor for alkali-activated binders. Binders were synthesized using varying molarity of a NaOH solution and at varying curing conditions. The final products were characterized using density measurements, compressive strength tests, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) analysis, and scanning electron microscopy (SEM). Full article