Ceramic Sorbents Research Articles

Fabrication of porous Li4SiO4 ceramic sorbent pebbles with high CO2 sorption capacity via the simple freeze-drying method

At present, the Li4SiO4 ceramic sorbents have displayed a great prospect for CO2 gas removal in the atmosphere owing to their high sorption capacity and stable sorption-desorption property. In this paper, a simple method combining the wet method and freeze-drying method is initially employed to fabricate Li4SiO4 sorbent with rich porosity and direction arrangement channels, which overcomes the dense interior structure, barren porosity, inferior adsorption stability, and costly production described in the previous literature. The effects of freeze way and temperature on the interior structure of Li4SiO4 sorbent were studied respectively. In the freeze-drying process, only the freeze-drying Li4SiO4 cylinder (FSC) green sorbents have columnar ice crystals in the interior owing to the temperature gradient, and the unidirectional alignment of pore channels can be obtained after the vacuum drying process due to the sublimation of ice crystals, which will improve CO2 capture capacity. Moreover, it can be seen from the optical image that the sorbent pebbles have a uniform distribution of diameter and sorbent samples of OSF (fabricated without the freezing process), FSP (fabricated with the freezing process), and FSC show excellent mechanical strength of 37.5 N, 22.5 N, and 0.43Mpa, respectively. Compared with OSP and FSP samples, the FSC sorbent performed superior CO2 sorption capacities (0.305 g CO2/g sorbent) and outstanding stability after 40 times cycles due to its optimal pore microstructure. Therefore, the prominent capture capacity and the satisfying crushing load of the FSC sorbents fabricated via the Freeze-drying method in this paper have promising prospects for CO2 removal.

Liquid-phase synthesis of advanced ceramic sorbents with high functionalization and morphological control

Sorption properties, induced by surface reaction such as adsorption, absorption, and ion-exchange reactions, of ceramics are affected by crystallographic properties, including crystallinity, structure, size, and morphology. Through the hydrothermal process, which is a part of the liquid-phase synthesis, crystals with various morphologies can be synthesized in a relatively short time and at low temperatures. Therefore, this process is an effective technique for the enhancement of sorption properties as it facilitates morphology control of ceramics-based purification materials. Herein, morphology-control-based techniques based on the hydrothermal processes for achieving high functionalization of ceramic materials, such as hydroxyapatite (HAp) and sodium titanate (ST) are reviewed, and their applicability for the development of environmental purification materials is verified. An overview of the process design for the morphology control of HAp crystals prepared through the hydrothermal process based on changes in the driving force for crystal growth, i.e., the degree of supersaturation, during the liquid-phase synthesis is presented. Furthermore, the high functionalization (in terms of adsorption and ion-exchange properties) of HAp-based materials prepared through the hydrothermal synthesis is demonstrated. In addition, the effects of unique seaweed-like nanostructures, a higher-order structure composed of ST nanofibers, of ST on its sorption properties are discussed, and the applicability of ST as an inorganic ion exchanger is also investigated.

Wet chemically derived Li4SiO4 nanowires as efficient CO2 sorbents at intermediate temperatures

Lithium silicate based ceramic sorbents are potential materials for CO2 sorption in the temperature range of 500–700 °C. However, its sorption performance at temperatures <500 °C is kinetically limited due to the formation of lithium carbonate as a hard surface layer that limits the CO2 diffusion to the reaction interface. This shortcoming in temperature of application has widely impeded its practical application in industrially important reaction environments such as in petrochemical processes. In the present study, we report compositionally tuned lithium silicate nanowires wherein the formation of hard lithium carbonate layer during the sorption process is addressed through the incorporation of low melting eutectics that softens the carbonate layer and facilitates an easier pathway for the diffusion of CO2. This modification is demonstrated to overcome the kinetic limitations of CO2 sorption in lithium silicate at lower temperatures (<500 °C). The nanowire morphology of lithium silicate also facilitated enhanced CO2 capture as the diffusion path-ways for lithium are considerably shorter compared to the conventional micron sized agglomerates. Further, the compositional tuning of lithium silicate nanowires helped to realize an absorption capacity value of 300 mgg−1 at 450 °C, a value seldom achieved for lithium silicate based materials at such low temperatures. The sorption capacity could also be fully regenerated at the same temperature by a pressure swing operation. The results thus pave the possibility of using modified lithium silicate compositions as CO2 sorbents in industrially significant chemical reaction processes such as high temperature water gas shift reaction where the temperatures are generally in the range of 350–450 °C.

Influence of free and sorbed zinc on cement hydration

Zinc, similarly to many other metals, is known for its negative influence on the rate of hydration in cementitious systems. The present paper deals with a specific form of zinc—Zn2+ ions sorbed on a solid sorbent. The sorbent under study is a waste ceramic powder, exhibiting very good sorption capacity for (not only) zinc. Such ceramic sorbent is intended to be used for removal of Zn2+ from industrial wastewaters. The spent sorbent has to be stabilized in order to prevent leaching of Zn to the environment; the most common stabilization method is incorporation to cement matrix, where the sorbed Zn may harm the hydration course and thus retarded the setting and hardening of stabilizate. Zn is sorbed on the ceramic sorbent in form of insoluble basic zinc sulfate ZnSO4·3Zn(OH)2·4H2O. As a reference system, relatively well-described ordinary Portland cement (OPC) + ZnO (also insoluble Zn form) system was tested. The used Zn contents were 0.08, 0.16 and 0.64% by mass of OPC. Isothermal calorimetry demonstrated large delay in systems with 0.64% Zn, while 0.08% did not have any significant influence on heat evolution, regardless the Zn form. At the medium 0.16% Zn content, the sorbed Zn was less retarding than free ZnO. The influence of Zn on strength, portlandite and C–S–H formation was monitored as well in time. To conclude, the differences between ZnO and sorbed Zn were just moderate; both forms retarded the hydration progress and strength in similar way. Presence of Zn caused formation of C–S–H hydrates with higher Ca/Si ratio than it was detected in OPC control.

Hydration of Ordinary Portland Cement in Presence of Lead Sorbed on Ceramic Sorbent.

Lead, a highly toxic element, is frequently present in various solid wastes as well as in industrial effluents. Sorption with a low cost sorbent is a simple way of Pb removal from liquid streams, but stabilization of spent sorbent has to be ensured in order to prevent Pb leaching out and possible environmental contamination. In previous research, ceramic sorbent, generated as waste product in brick industry, was tested as sorbent and proved high sorption capacity for lead. Lead was sorbed partially as hydrocerussite and partially as adsorbed surface layer. The Pb leaching from sorbent was very high and thus further immobilization of sorbent was necessary. Lead, as well as other heavy metals, is known as retarder of the hydration process of Ordinary Portland Cement (OPC), used for the immobilization. In this paper, influence of sorbed Pb and PbO, as reference compound, on cement hydration was studied by calorimetry, thermogravimetry and Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy (MAS NMR). The sorbed lead was found to be less detrimental to hydration retardation due to the lower solubility of precipitated hydrocerussite in basic environment compared to PbO, which forms plumbate anion.

Contact sorption: a method to reduce the moisture content of coal fines

ABSTRACTThis paper introduces contact sorption with ceramic sorbents as a method to reduce the moisture content of coal fines produced by coal processing plants. The proposed method was tested on laboratory scale where ceramic spheres with diameters of 3 mm and 5 mm were combined with wet coal fines of size fractions between 0.25 mm and 2 mm. The coal had an initial moisture content of 0.25 g(Water)/g(Coal and water), and was dewatered using contact sorption to an average moisture content of 0.13 g(Water)/g(Coal and water) after 2.5 minutes and 0.05 g(Water)/g(Coal and water) after 10 minutes, respectively. This paper focuses on identifying the solid phase conditions essential to improving the contact sorption drying technology, proving that contact between the coal and sorbent material is the main driving force behind this technology. Increasing the sorbent to coal mass ratio and using smaller sorbents with a larger surface area resulted in improved contact and consequently improved moisture mass transfer. The final coal moisture content that could be achieved was independent of coal particle size. Current studies show a reliance on thermal drying technologies to dry the saturated sorbent material, whereas this paper proves that drying with high airflow at low temperatures is sufficient to regenerate the sorbent material. The loaded sorbent material could easily be separated from the dried coal product by dry screening, and could be dried and regenerated afterwards in an air-blown packed bed within 10 minutes. The re-use of sorbent material showed no decrease in its dewatering efficiency, and it was shown to be possible to re-use the sorbents for a large number of cycles. Contact sorption can prove to be a cost-effective and efficient drying method to dewater coal fines in the industry.

Application of heavy metals sorbent as reactive component in cementitious composites

Sorption is technologically simple and cost-effective method for removal of heavy metals from waste waters. Wide range of sorbent can be used; aluminosilicates materials (clay minerals, zeolites) are well known for their ability to sorb ionic species from water solutions. Ceramic materials belong to aluminosilicates as well; the present paper deals with utilization of ceramic powder, generated as waste product in production of hollow bricks, as sorbent for heavy metals. Pozzolanic activity – i.e. ability to replace part of cement in concrete – is another attribute of powdered ceramic materials. The red-clay based ceramic powder was primarily used as sorbent for Cu, Pb and Zn. The sorption experiments revealed that application potential of ceramic sorbent is comparable with other aluminosilicate, low-cost sorbents. The sorption capacity decreased in sequence Cu > Pb > Zn (sorption capacity 91, 186 and 43 mg g−1). Secondly the sorbent with adsorbed metal species was used as cement replacing addition in concrete. This approach has two relevancies; 1) the substitution of cement by ceramic saves natural resources and concrete carbon footprint and 2) the cementitious matrix provides solidification/stabilization of adsorbed species. The unused ceramic powder was found to be very efficient cement substitute (28-days compressive strength 70 MPa was reached); unfortunately the adsorbed metals species influenced negatively the rate of setting and strengthening of concrete. The significant retardation effect was observed in case of Cu, while the influence of Pb and Zn was highly dependent on the sorbent dosage. The studied ceramic powder has not any commercial application yet, but the achieved experimental results indicate its perspective application as low-cost sorbent of ionic species.

Environmental and Technical Possibilities of Marble Waste Recycling in Bricks and Sorbents Production

The article considers the environmental, technological, and economic problems of recycling at application fine marble waste in the production of facing ceramic bricks by the volumetric coloring method. The environmental and economic feasibility of using fine marble waste is proved. Also the problem of obtaining ceramic sorbents is raised.

Surface functionalized nanostructured ceramic sorbents for the effective collection and recovery of uranium from seawater

The ability to collect uranium from seawater offers the potential for a nearly limitless fuel supply for nuclear energy. We evaluated the use of functionalized nanostructured sorbents for the collection and recovery of uranium from seawater. Extraction of trace minerals from seawater and brines is challenging due to the high ionic strength of seawater, low mineral concentrations, and fouling of surfaces over time. We demonstrate that rationally assembled sorbent materials that integrate high affinity surface chemistry and high surface area nanostructures into an application relevant micro/macro structure enables collection performance that far exceeds typical sorbent materials. High surface area nanostructured silica with surface chemistries composed of phosphonic acid, phosphonates, 3,4 hydroxypyridinone, and EDTA showed superior performance for uranium collection. A few phosphorous-based commercial resins, specifically Diphonix and Ln Resin, also performed well. We demonstrate an effective and environmentally benign method of stripping the uranium from the high affinity sorbents using inexpensive nontoxic carbonate solutions. The cyclic use of preferred sorbents and acidic reconditioning of materials was shown to improve performance. Composite thin films composed of the nanostructured sorbents and a porous polymer binder are shown to have excellent kinetics and good capacity while providing an effective processing configuration for trace mineral recovery from solutions. Initial work using the composite thin films shows significant improvements in processing capacity over the previously reported sorbent materials.

Improvements of CaO-based sorbents for cyclic CO2 capture using a wet mixing process

CaO-based sorbents are suitable candidates for CO2 capture at high temperatures. However, the CO2 capture capacity of untreated CaO-based sorbents decreases sharply after a few cycles. In this paper, a wet mixing method was employed to synthesize CaO–molecular sieve–alumina ceramic sorbents for CO2 capture. Cyclic experiments were carried out in a thermogravimetric analyzer (TGA). The sorbent using molecular sieve and alumina ceramic as the calcium precursors showed the best cyclic CO2 uptake capacity, 0.41g CO2/g sorbent after 20 cycles of calcination and carbonation. The synthesized materials were characterized by X-ray diffraction (XRD), nitrogen adsorption and desorption isotherms test, and scanning electron microscopy (SEM)/energy dispersive spectrometer (EDS). The sorbent showed a better sintering-resistant property and a more porous microstructure during multiple calcination and carbonation cycles.

Characterization and modification of porous ceramic sorbent for arsenate removal

Porous ceramic sorbent, synthesized with a mixture of akadama mud, wheat starch, and Fe2O3, has been used for the removal of arsenic, which is an extremely toxic contaminant even at very low concentrations. Acid washing process using dilute HCl solvent and iron impregnation using ferric and ferrous solutions were applied to modify the ceramic for enhancing arsenic removal performance. The batch results indicated that ferric impregnated ceramic (ceramic/FeCl3) exhibited the best arsenic adsorption efficiency at room temperature (25°C) under neutral conditions (pH 6.9). And its maximum adsorption capacity for arsenic removal was 7.12mg/g, estimated by the Langmuir–Freundlich equation with correlation coefficient of 0.984. The equilibrium data also well fitted to Dubinin–Radushkevich adsorption isotherms with a sorption energy E=8.11kJ/mol, indicating that the mechanism for As(V) adsorption on ceramic/FeCl3 was a combination of chemical ion exchange and physical electrostatic attraction, in which chemisorption seemed to be a little stronger. No secondary pollution (toxic sludge and leached iron) caused by the ceramic/FeCl3 was observed.

Fixed-bed performance for production of oxygen-enriched carbon dioxide stream by perovskite-type ceramic sorbent

This paper reports on an experimental study on production of oxygen-enriched carbon dioxide stream by a fixed-bed packed with a perovskite-type ceramic sorbent La 0.1Sr 0.9Co 0.5Fe 0.5O 3− δ , which can adsorb oxygen from air. Oxygen-enriched carbon dioxide stream is produced by passing carbon dioxide into the fixed-bed saturated with oxygen. Fixed-bed experiments were performed to study the oxygen separation performance of this sorbent. The separation process was experimentally confirmed to be a reversible chemical sorption and desorption process. Experimental results are also reported to show the effects of operation conditions, including adsorption time, flow rates of feed gases, and fixed-bed temperatures in the adsorption and desorption steps, on average oxygen concentration of the product stream, oxygen recovery, carbon dioxide recovery and productivity. Experimental results suggest that adsorption and desorption temperatures are the most critical operation parameters. Under the optimum conditions (850 and 900 °C adsorption and desorption temperatures) the fixed-bed adsorber can produce an oxygen-enriched carbon dioxide stream with average oxygen concentration, oxygen recovery, carbon dioxide recovery and productivity, respectively, of 58.8%, 18.7%, 26.6% and 0.272 ml/min. This oxygen-enriched carbon dioxide stream may be used as an oxidant in the oxyfuel combustion process.

High-Temperature Oxygen Sorption in a Fixed Bed Packed with Perovskite-Type Ceramic Sorbents

Oxygen sorption and desorption on two perovskite-type ceramics, La0.1Sr0.9Co0.5Fe0.5O3-δ and La0.1Sr0.9Co0.9Fe0.1O3-δ, were studied in a fixed-bed system. The perovskite-type ceramic packed fixed bed gives very sharp oxygen sorption breakthrough curves with long breakthrough time in the range of 400−900 °C as a result of a favorable oxygen sorption isotherm, high oxygen sorption capacity, and fast oxygen sorption rate for the sorbents. The perovskite-type ceramic sorbents can be reversibly regenerated and exhibit good structural and chemical stability against sorption and regeneration cycles. These results suggest that the perovskite-type ceramic sorbents can be used in fixed-bed processes for effective removal of oxygen from gas streams using a reducing gas sorbent regeneration. The perovskite-type ceramic sorbents can also adsorb a considerable amount of oxygen in 200−300 °C but at a much slower rate. The desorption breakthrough curves are characterized by long tails due to slower desorption rate consta...

Equilibrium of oxygen sorption on perovskite‐type lanthanum cobaltite sorbent

This article reports results of a theoretical and experimental study on oxygen nonstoichiometry, oxygen sorption isotherms, and the heat of sorption of a representative perovskite-type ceramic sorbent La 0.1 Sr 0.9 Co 0.5 O 3-δ .

High-Temperature Sorption Process for Air Separation and Oxygen Removal

This paper describes the concept of a new, efficient high-temperature oxygen sorption process based on a perovskite-type ceramic sorbent for oxygen removal and air separation. The new sorption process takes advantage of the unique properties of certain perovskite-type ceramics that can adsorb a large quantity of oxygen, but not other gases, at high temperatures (300−800 °C). The essential principle of this new sorption process is based on the changing of oxygen nonstoichiometry of the perovskite-type ceramics with temperature and oxygen partial pressure. Two highly oxygen-deficient perovskite oxides, La0.1Sr0.9Co0.5Fe0.5O3-δ, and La0.1Sr0.9Co0.9Fe0.1O3-δ, were examined as candidate materials for the oxygen sorption process. Oxygen sorption equilibrium properties were studied by thermogravimetric analysis (TGA) at 500 and 600 °C and oxygen pressures ranging from 1.3 × 10-4 to 1 atm. The oxygen removal performance at 500 and 600 °C was also investigated in a fixed-bed adsorption column. An infinitely large ...