Alkali Fusion Research Articles

The adsorption performance of high crystallinity Na-p zeolites prepared from oil shale ash for the waste water treatment

ABSTRACTS The Na-p type zeolite has been prepared by the alkali fusion hydrothermal synthesis method using the pure oil shale ash (OSA) and mixture of OSA and coal fly ash (CFA) as raw materials, which was used for adsorption of methylene blue (MB). The XRD spectra of zeolite synthesized from pure oil shale residue under different conditions indicated that the optimal experimental conditions were determined as follows: acid leaching concentration of 10%, sodium hydroxide dosage of 7 g, crystallization temperature of 130°C, and crystallization time of 12 h. Under the same conditions, zeolite was synthesized using the mixture of OSA and CFA, and its properties were characterized using XRD, SEM, and BET techniques. The results showed that the specific surface area and crystallinity of the zeolite prepared from the mixture were 59.6 m2/g and 86.32%, respectively, which were higher than that of pure OSA (20.6 m2/g and 64.07%). When 0.05 g of zeolite was added to the 35 mg/L MB solution and adsorbed for 180 min, the removal rates of MB by pure OSA, single-source zeolite and zeolite prepared from the mixture were 27.6%, 83.4%, and 99.2%, respectively. The adjusted R square verified that the pseudo-second-order kinetics and Langmuir isotherm model were the best fitting models. The maximum adsorption capacity (Qmax) of zeolite prepared from the mixture for MB was 55.5 mg/g. The above results proved that the novel material prepared in this study could be a potential effective wastewater treatment material.

Facile Synthesis of Zeolite NaX from Natural Attapulgite Clay for Pb2+ Adsorption

The synthesis of zeolites from natural aluminosilicate minerals has drawn extensive attention due to its significant utility in greening the zeolite manufacturing process. In this study, pure-phase NaX zeolite was synthesized via a low-temperature hydrothermal method, utilizing natural, low-quality attapulgite clay as the raw material. Acidified clay was fully activated through alkali fusion at 200 °C, and the impact of alkali fusion temperature, H2O/Na2O ratio, aging temperature, and crystallization time on the resulting crystalline NaX zeolite was investigated. The optimal conditions for obtaining pure NaX zeolite were determined to be alkali melting at 200 °C for 4 h, an H2O/Na2O ratio of 50, aging at 40 °C, and a crystallization period of 11 h at 90 °C. With a large BET surface area of 328.43 m2/g, the obtained NaX zeolite was used to adsorb Pb2+ from wastewater with a removal rate of 95%. This research provides a valuable method for the extensive and efficient utilization of low-grade natural attapulgite clay. Moreover, this is the first report on the synthesis of pure-phase NaX zeolite using only low-quality natural attapulgite clay as raw material through an atmospheric pressure water bath method.

Evaluation of MgO-rich materials obtained from Ferronickel slag for CO2 sequestration

Because it has a high magnesium content, ferronickel (FeNi) slag is a potential alternative material for CO2 sequestration. The slag can be pretreated by alkali fusion with NaOH to obtain MgO-rich materials. In this study, the potential of this MgO-rich material for CO2 sequestration was investigated using MgO from FeNi slag (MgO-FS) and MgNa2SiO4 from FeNi slag (MNA). A MgO reagent (MgO-R) and FeNi slag were used as reference materials. The carbonation process was carried out using a batch autoclave with various liquid-to-solid (L/S) ratios, initial pressures, times, and CO2 concentrations. The MgO-FS effectively captured CO2 and had a carbonation performance comparable to that of MgO-R. The degrees of carbonation for MgO-R, MgO-FS, and MNA were 68.43 %, 65.53 %, and 39.40 %, respectively, when carbonation was carried out at 423 K and 8 bar with an L/S ratio of 10 mL/g and pure CO2 for 9 h. Combination of the FeNi slag alkali fusion process (1:2 FeNi slag/NaOH mass ratio, 773 K, and 4 h) with water washing and carbonation (4 bar, 423 K, 10 mL/g L/S ratio, 3 h, and pure CO2) gave a CO2 uptake efficiency of 0.119 ± 0.004 g CO2/g FeNi slag. The results of the degree of carbonation (i.e. 65.53 %), X-Ray diffraction spectra (magnesite mineral peak), and scanning electron microscope observations (magnesite crystal appearance) provide evidence that MgO-FS is an effective alternative material for indirect CO2 sequestration.

Efficient extraction of rare earth elements from coal-series kaolin by combining alkali fusion and sulfamic acid leaching

As a solid waste produced by coal mining, the comprehensive utilization of coal-series kaolin is the focus of attention. In this paper, the extraction of rare earth elements (REEs) from coal-series kaolin was carried out by alkali fusion and sulfamic acid leaching. The occurrence modes of REEs in coal-series kaolin was analyzed by means of inductively coupled plasma-mass spectrometry analyse and sequential chemical extraction. The influence of alkali fusion conditions on the leaching of REEs was investigated, and the activation mechanism of alkali fusion was revealed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and field emission scanning electron microscope (FESEM) analysis. In addition, the effect of key operating parameters on the leaching efficiency of REEs from coal-series kaolin was further investigated. The results show that REEs mainly existed in silicate & aluminosilicate state of coal-series kaolin. The mineral structure was destroyed by alkali fusion, and the leaching efficiency of REEs was increased by 59.08 %. At the sulfamic acid concentration of 0.5 mol/L, H2O2 concentration of 0.2 mol/L, solid to liquid ratio of 1/50, the leaching efficiencies of total rare earth elements, light rare earth elements and heavy rare earth elements were 84.91 %, 88.43 % and 71.03 %, respectively.

Synthesis, characterization, and physico-chemical aspects of a new PVC-based quaternary triethanol ammonium chloride anionite for tungsten recovery.

The usability of polyvinyl chloride-based quaternary triethanol ammonium chloride anionite (PVC-TEAC) as a potential extractant for tungstate was investigated to recover tungstate from Gabal Qash Amir, Egypt, assaying 70.91% WO3. Structure elucidation for PVC-TEAC anionite was successfully carried out using several techniques. Experimental measurements, such as pH, agitation time, initial tungsten concentration, anionite dose, co-ions, temperature, and eluting agents, have been optimized. It was found that PVC-TEAC anionite has a maximum capacity of 63 mg per gram. From the distribution isotherm modeling, Langmuir's model fits the experimental results better than Freundlich's, with a theoretical value of 61.728 mg g-1. According to kinetic modeling, the first- and second-order modeling may be regarded as a mixed modeling for a successful adsorption system. Thermodynamic prospects reveal that the adsorption process was predicted as an exothermic, spontaneous, and preferable adsorption at low temperatures. Tungsten ions can be eluted from the loaded anionite, by 1M H2SO4 with a 97% efficiency rate. It was found that PVC-TEAC anionite reveals good separation factor (S.F.) towards most of co-ions. A successful Alkali fusion with NaOH flux followed by tungstate recovery by PVC-TEAC anionite is used to obtain a high-purity tungsten oxide concentrate (WO3), with a tungsten content of 78.3% and a purity of 98.75%.

Structural and optical characterizations of zircon and zirconia nanopowders derived from zircon sands

This study explores the structural and optical properties of zircon (ZrSiO4) and zirconia (ZrO2) nanopowders using two types of natural Indonesian zircon sands. The former powders were synthesized through dissolution and non-dissolution methods, while the latter powders were synthesized using alkali fusion and co-precipitation techniques. x-ray fluorescence (XRF) analysis revealed a reduction in impurities post-synthesis. X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) analyses indicated that the dissolution process yielded pure zircon, whereas the non-dissolution method resulted in the presence of minor additional phases. For zirconia, all samples exhibited a tetragonal phase, albeit with varying structures. Optical properties were investigated using UV–vis spectroscopy, which showed that both materials exhibit high absorption in the ultraviolet region, with slight differences in wavelengths peak. Consequently, zircon and zirconia demonstrated similar band gap energies ranging from 3.76 to 3.95 eV and 3.99 to 4.06 eV, respectively. Photoluminescence testing further revealed identical emission peaks 350 nm for both materials, highlighting their comparable optical characteristics. This study provides valuable understandings into the synthesis and optical properties of zircon and zirconia nanopowders derived from Indonesian zircon sands, emphasizing their potential applications in various optical and electronic fields.

Effect of Temperature on Zirconia Powder Synthesized from Amang Zirconium Oxychloride Precursor

Polymorphic zirconia is economically attractive in various applications due to its low reactivity, high strength, and stability. Zirconia can be synthesized from locally available Amang zircon sand as an inexpensive green alternative as it has a high zirconium content as reported by previous report. Unfortunately, the study was only focused on the formation of zirconium oxychloride despite of high zirconium content from the improved alkali fusion method proposed. Therefore, a further study on zirconia powder calcined in varied temperatures from Amang zirconium oxychloride precursor was done. Amang zirconia powder was then characterized in order to study the effect of temperature on Amang zirconia powder. Elemental analysis showed that zirconium composition was affected by temperature and increased as the temperature increased with the highest zirconium content of 81.28 wt.% with low impurities after calcined at 800 °C for 4 hours. The phase analysis satisfied monoclinic zirconia with minor tetragonal and cubic phase with sharper peaks as calcined temperature increased. Increased tetragonal and cubic phase was observed as the temperature was increased. Morphology analysis showed zirconia powder was angular and pyramidal with large crystal size which led to high tendency of monoclinic phase. Calcination temperature of 800 °C was determined to be the most suitable temperature to calcine high purity zirconia powder using Amang zirconium oxychloride precursor.

Lithium leach residue synthesis process of high crystallinity hydroxysodalite, NaX, NaA zeolites and solidification and migration of potentially toxic elements

Converting lithium leach residue (LLR) into zeolite can reduce environmental impacts while also producing high value-added products. However, the synthesis of zeolites by LLR under alkali fusion may result in the solidification and migration of potentially toxic elements with secondary environmental impacts. Systematic research into this subject is rare in the open literature and the mobility of toxic elements from LLR derived zeolites is yet to be understood. In this paper, we have investigated the highly crystalline synthesis of hydroxy sodalite, X-type zeolite (NaX), and A-type zeolite (NaA) without stencil agent and crystal species, which can be achieved by modulating the alkali fusion temperature, all three zeolites have greater than 90 % conversion of the major elements aluminum and silicon. Meanwhile, the leachability of thallium (Tl), beryllium (Be), and potentially toxic elements (lead (Pb), mercury (Hg), cadmium (Cd), chromium (Cr), arsenic (As), barium (Ba), copper (Cu), nickel (Ni), cobalt (Co), zinc (Zn)) was monitored by pH-dependent leaching test for LLR and three kinds of synthesized zeolites according to the Chinese standard and the emission of toxic elements during the synthesis process was analyzed, to investigate the migration and quantify the distribution of the toxic elements in the LLR to the product zeolites and the cleaning wastewater. The migration efficiency of potentially toxic elements from LLR to the product zeolite and cleaning wastewater was explored. It was found that most of the toxic elements Tl, Be and potentially toxic elements were solidified in the structure of the zeolites by ion exchange (solidification rate > 90 %), and a small portion flowed into the cleaning wastewater. Although there are toxic elements solidified in the structure, there is no significant leaching under various pH conditions, which is in line with the Chinese standard (GB/T 5085.3–2007). Therefore, it is considered that LLR realizes environmentally friendly zeolite production and does not cause secondary pollution to the environment. This work demonstrates great potential for green recycling of LLR from the lithium extraction process and introduces an environmentally friendly slag treatment technology.

The stabilization ability of NaA zeolite derived from fly ash for lead and cadmium in soil: Mechanisms and evaluation of effectiveness

Developing technologies aimed at ecologically restoring is of great significance in addressing the problem of heavy metal pollution. In this study, NaA zeolites (FAZ) originated from fly ash with outstanding performance were prepared by alkali fusion hydrothermal method and used for the solidification and stabilization of heavy metals in soil. After systematic evaluation, it was found that FAZ may lower the leaching concentration of lead (Pb) in soil to <1 mg/kg and increase the stabilization rate of Pb to 80 % in the single Pb-contaminated soil, lower the leaching concentration of cadmium (Cd) in soil to <3 mg/kg and increase the stabilization rate of Cd to 60 % in the single Cd-contaminated soil, and lower the leaching concentration of Pb to 0.15 mg/kg and the leaching concentration of Cd to 0.74 mg/kg in PbCd complex polluted soil. Additionally, Pb stabilization rates reach 60 % and Cd stabilization rates reach 30 %, respectively. Ion exchange is primarily responsible for the adsorption and solidification of Pb and Cd in soil by FAZ. Generally, FAZ has a wide range of applications in the rehabilitation of contaminated soil and significantly lowers the level of heavy metal pollution in soil.

Activation energy and crystal growth coefficient determination of t-ZrO2 using high-temperature synchrotron X-ray diffraction

Abstract Activation energy and crystal growth coefficient of t-ZrO2 (tetragonal zirconia) were determined through an in-situ synchrotron radiation X-ray diffraction (SR-XRD) experiment. The t-ZrO2 precursor was synthesized through (a) purification of zircon sand from Kereng Pangi, Kalimantan to zircon powder, (b) alkali fusion, and (c) co-precipitation. High-temperature SR-XRD experiments were carried out with varying holding times of 1, 2, and 3 hours at 900, 950, and 1000 °C, respectively, where the formation and crystal growth of t-ZrO2 were observed. The diffraction patterns show that t-ZrO2 has formed at 900°C for 1 hour and it grows accordingly. The effect of the heating temperature and holding time on the crystal growth shows that the size of hot crystals increases with increasing temperature and holding time. It is found that the activation energy of t-ZrO2, in general, decreases with holding time, i.e. from 75.3 kJ/mol (3 h) to 57.3 (1h). Meanwhile, Beck’s crystal growth coefficient value is between 0.3 at 900 °C and 0.2 at 1000 °C.

The effects of calcination heating rate on phase formation and structure of zircon sand-derived zirconia

Abstract Phase formation and structure examination has been conducted to study the effects of thermal treatment and heating rates on zircon (ZrSiO4) sand-derived zirconia (ZrO2). A preliminary investigation of the elements present in the sand using XRF revealed that Zr was the major element, corresponding to 92.4% of the sample. The zirconia precursor was synthesized through a three-stage process that involves purifying zircon powder, alkali fusion, and co-precipitation method. The zirconia crystal was obtained by heating the sample to 700, 800 and 900 °C with heating rates of 5 and 10 °C/min, respectively. The formation of tetragonal zirconia (t-ZrO2) with space group P42/nmc is shown in a qualitative study of all sample XRD patterns. Furthermore, Rietveld analysis was used to determine crystal structure parameters including lattice parameters and tetragonality. The calcination temperature and heating rate decide the phase, t-ZrO2 crystallite size, and tetragonality. Furthermore, calcining to 700 and 800 °C created t-ZrO2, however, elevated temperature to 900 °C lead to t→m transformation. The t-ZrO2 size increases with temperature between 700 and 900 °C, range of 9 and 15 nm. Meanwhile, the tetragonality of t-ZrO2 tends to decrease due to m-ZrO2 being present.

Effect of TiO2 on the Phase Transformation and Microstructure Evolution of Ti-Containing Melting Slag in the Alkali Fusion Process

Effect of TiO2 on the Phase Transformation and Microstructure Evolution of Ti-Containing Melting Slag in the Alkali Fusion Process

Extraction of Yttrium from Light-Emitting Diode Waste by Alkali Fusion Followed by Acid Leaching

Extraction of Yttrium from Light-Emitting Diode Waste by Alkali Fusion Followed by Acid Leaching

Synthesis of kaliophilite by alkaline fusion and ultrasonic treatment method from kaolin raw material

Mexico has important kaolin deposits, which must be assessed to obtain products with a high commercial value, such as kaliophilite as raw material for biodiesel production. Two kaolins, A and B, with approximate SiO2:Al2O3 ratios of 1 and 1.2, respectively, were used as raw materials to produce kaliophilite. Both kaolins were obtained from the municipality of Agua Blanca in the State of Hidalgo, Mexico. Kaolins are a source of Al and Si for the synthesis of kaliophilite through an alkali fusion process at 700 °C followed by ultrasonic treatment at 28 kHz to different times and for Kaolin-KOH ratios of 1:1 and 1:1.2 (mass: mass). The kaolins as received and the alkaline mixtures heat and ultrasonically treated were analyzed using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). The most suitable kaolin for synthesizing kaliophilite was kaolin A with the Si/Al mass ratio of approximately 1, which exhibited a higher crystallinity index range from 54 to 79.6%. Higher KOH concentrations promote the amorphous material formation decreasing the kaliophilite amount. The crystallinity index was increased when the time of ultrasonic treatment was increased.

CO2 adsorption by coal fly ash zeolite and modified zeolite-templated carbon

Coal fly ash (CFA), as the main by-product of coal-fired power plants, has a high content of silica-aluminium elements that can be used to prepare zeolite by the alkali fusion method with sound CO2 adsorption capacity. Among the four effect factors of Si/Al, NaOH/CFA, H2O/AFP(alkali fusion product), and crystallisation time, NaOH/CFA had the greatest effect on the CO2 adsorption performance of coal fly ash zeolite (CFAZ), followed by Si/Al and H2O/AFP, and crystallisation time had the least effect. The CO2 adsorption performance of the samples was tested and analysed using the thermal analysis method, the CO2 adsorption amount of CFAZ reached 4.23 mmol g–1 (30 °C, 101 kPa). In addition, the CFAZ and the zeolite-templated carbon (ZTC) adsorption performance is poor at high temperatures. The co-precipitation method modification of CFAZ and ZTC can produce layered double hydroxide derived material, which can adsorb CO2 at high temperatures reached at 3.35 mmol/g (650 °C, 101 kPa). Moreover, ZTC modified with polydivinylbenzene as the hydrophobic material has a sound CO2 adsorption effect in high-humidity environments. Thus, different adsorbents also could be produced using CFA to capture CO2 with a wide temperature range between 25 and 650 °C.

A two-stage process of alkali fusion and organic acid leaching for recovery of critical elements from coal fly ash

Coal fly ash (CFA) is a promising alternative source for critical elements. Most of the critical elements in CFA are associated with the aluminosilicate glassy phase, which hinders their ability to solubilize during acid leaching. In this study, critical elements (Li, Be, Rb, Sr, Zr, Nb, Cs, Hf, Ta, Ga, Ge, Se, Cd, and Tl) were recovered from CFA of Pingwei power plant in China by alkali fusion-organic acid leaching. The results showed that the leaching rate of critical elements after alkali fusion was higher than that of direct organic acid leaching. The leaching rate of total critical elements was 72.56% under the optimal conditions. Among them, the highest leaching rate of Li, Be and Ga was more than 90%, and the highest leaching rate of Ge, Se, Rb, Sr, Zr, Nb, Cd, Cs and Hf was 70%-90%. Characterization analysis revealed that the amorphous aluminosilicate and silica phases in the raw CFA were destroyed by alkali fusion, resulting in nepheline and soluble aluminosilicate phases which were easily dissolved by citric acid. This study provides theoretical basis and technical support for the extraction of critical elements from CFA.

Physicochemical Characterization of Zeolite Materials Produced from Selected Low-Cost Agricultural Wastes

Zeolites play a crucial role in adsorption processes for eliminating pollutants from industrial effluents and are extensively utilized in catalytic activities across diverse syntheses. This study focused on the conversion of three agricultural wastes—corncob, groundnut shell, and sugarcane bagasse—into zeolitic materials through three analytical methods: hydrothermal, microwave sintering, and alkali fusion, respectively. Standard methods were employed to assess the physicochemical parameters of the resulting zeolites. Generally, the produced zeolites had excellent surface areas and porosities. However, zeolites synthesized from sugarcane bagasse via the alkali fusion method exhibited highest porosity (80.9%), whereas that derived from corncob demonstrated highest surface area (1335 m2/g). Point of zero charge for the produced zeolites was within the range of 7.9-9.8, with zeolite produced from groundnut shells via alkali fusion having the highest value (9.8). The elevated porosities and surface areas, and point of zero charge of the synthesized zeolites signify their enhanced adsorptive capacity, implying their suitability for application as adsorbents for the removal of organic and inorganic pollutants. These findings underscore the effectiveness of synthesized zeolites in reducing or completely removing pollutants such as phenols, dyes, pesticides, heavy metals, and inorganic anions from wastewater.

The Study on Alkali Fusion-water Leaching of Silicon From Molybdenum Tailings

Taking the molybdenum tailings produced after beneficiation of the Luanchuan molybdenum mine in Henan Province as the research object, the effects of alkali ore ratio, calcination time and calcination temperature on the activation effect of molybdenum tailings, and the effects of leaching time, leaching temperature and leaching liquid-solid ratio on the silicon leaching rate were investigated by using sodium hydroxide alkali melting-water leaching process. The results show that the optimal conditions for activation are as follows: alkali-ore ratio 1.2:1, calcination time 1 h, calcination temperature 700°C. Under these conditions, the concentration of alkali fusion leaching (Si+Al) of molybdenum tailings is 1.396 mg/L. The optimum conditions for leaching are as follows: leaching time 7 h, leaching temperature 45°C, leaching liquid-solid ratio 6: 1. Under these conditions, the leaching rate of silicon can reach 26.88%. During the calcination process, the crystal structure of quartz is destroyed, and sodium hydroxide reacts with quartz at high temperature to form soluble silicate, which improves the activity of molybdenum tailings and increases the dissolution of silicon

Preparation of one-part geopolymers using coal gasification slag: Effect of alkali fusion product additive and liquid/solid ratio

In this work, one-part geopolymers were synthesized through the alkali fusion and component additive method (AFCAM), utilizing coal gasification slag as the primary raw material. The investigation delved into the influence of varying fusion product contents and liquid/solid (L/S) ratios on the geopolymer properties. The experimental results demonstrated a non-linear correlation between the increase in fusion product content and the compressive strength of geopolymers, revealing an initial ascent followed by a subsequent decline. Additionally, a lower L/S ratio of 0.3 was observed to enhance compressive strength compared to the L/S ratio of 0.4. Notably, the optimal combination of an L/S ratio of 0.3 and a fusion product percentage of 30 % resulted in a remarkable compressive strength of 25.2 MPa. The comprehensive strength analysis suggested that an adequate amount of fusion product enhances the geopolymerization reaction, evidenced by the transformation of aluminum coordination states. Specifically, the conversion of five-coordinated and six-coordinated aluminum in slag to four-coordinated aluminum in geopolymers was observed. Concurrently, increased silicon and aluminum reactivity led to the formation of a robust Q4(4Al) network in the geopolymer gel. The impact of L/S ratios was attributed to the accelerated dissolution and hydrolysis of aluminosilicates at an elevated L/S ratio of 0.4, hindering polycondensation. These outcomes underscore the pivotal role of fusion product content and L/S ratio in governing the strength development of one-part geopolymers.

The Corrosion and Mechanical Behavior of Zirconium Alloy for Alkali Fusion Process at High Temperature

The Corrosion and Mechanical Behavior of Zirconium Alloy for Alkali Fusion Process at High Temperature