Alkali Source Research Articles

Synthesis and enhanced adsorption for F− by three novel high entropy LDHs using TEA-assisted hydrothermal technology

Nowadays the design, preparation and application of high entropy LDHs (HE-LDHs) has already become research hotspots. In this paper, three types of high entropy ZnCoCrMgZr-LDHs (HE-LDHs-1, 2 and 3) were successfully prepared for the first time using TEA as alkali source by simple hydrothermal synthesis, and characterized by XRD, TG, SEM, X-ray photoelectron spectroscopy, BET and zeta potential. The effect of triethanolamine (TEA) on the formation of high entropy LDHs and their adsorption behaviour for F− were investigated. Research showed that high content of TEA can maintain and provide more hydroxyl groups required for the formation of LDHs, while the introduction of high valence Zr4+ breaks the regular arrangement of LDHs themselves. Three types of high entropy LDHs have excellent adsorption performance for F− with the maximum adsorption capacities of 113.78 mg/g, 142.12 mg/g and 128.24 mg/g, respectively. They also have strong resistance to anionic interference. The adsorption process is the transition from physical adsorption to chemical adsorption in the F− adsorption process from HE-LDHs-1 to 3. The adsorption isotherm models of LDHs-1 exhibit high R2 values which shown that their F− adsorption behaviour is the result of the combined effect of physical and chemical adsorption. The adsorption behaviour of LDHs-2 and 3 is more in line with the quasi second-order kinetic model and Langmuir model, indicating that the F− adsorption process is a single-layer adsorption based on chemical reaction-controlled kinetics. The lower temperatures are more conducive to the process for all three adsorbents adsorption process generates heat. FLDHs can still re-adsorb the dye CR after four cycles of adsorbing fluoride ions. HE-LDHs exhibit high adsorption, selectivity, and good reuse performance for fluoride ions, making them promising for wastewater treatment applications.

Multiple element approach to P recovery and recycling: A green and sustainable strategy by using fused magnesia waste ash

Recovery of phosphorus through controlling the crystallization of struvite (MgNH4PO4·6H2O), a slow-release fertilizer, is highly attractive, but costly if large amounts of magnesium and alkali have to be added. In this study, a strategy for synchronously recovering phosphorus and nitrogen resources from wastewater and magnesium resources from solid waste was proposed. We demonstrated the fused magnesia waste ash (FMWA), an industrial by-product of magnesia which might serve as a cost-effective source of magnesium and alkali. The results showed that a recovery efficiency of 93.0 % PO43− and 88.8 % NH4+ from synthetic wastewater and 46.6 % Mg2+ from the FMWA was achieved when the ratio of [Mg2+]:[NH4+]:[PO43−] was 1.8:1:1. The magnesium release potential of FMWA was 10 times more than that of other known magnesium-containing solid wastes, due to the process in electric melting furnace damaged the lattice structure of magnesite and converted magnesite to magnesia. XRD analysis showed that crystalline struvite was the major product. The undissolved components of FMWA (MgCO3, MgO and SiO2) acted as crystal seeds, increasing the particle size and accelerating struvite precipitation. The application of FMWA for phosphorus fixation can reduce costs by 98.3 % compared with MgCl2. This research paves the way for employing FMWA in efficient recovery of phosphorus from wastewater, simultaneously achieving the resource utilization of industrial waste.

Synthesis of MgAl-LDH from three alkali sources for boosting flame retardancy of EP with APP

Epoxy resin (EP) is used in construction materials due to its low curing shrinkage, excellent chemical stability, and mechanical properties. However, its flammability limits applications in the field of construction. Co-precipitation method with sodium hydroxide as the alkali source and hydrothermal method with urea as the alkali source are the common ways to prepare MgAl-LDH. In this study, MgAl-LDH1 (abbreviated as LDH1) was prepared by using NaOH as the alkali source at 65 ℃ for 12 h, MgAl-LDH2 (abbreviated as LDH2) by using urea as the alkali source at 120 ℃ for 12 h, and MgAl-LDH3 (abbreviated as LDH3) was prepared by using triethanolamine as the alkali source at 100 ℃ for 2 h. Then, LDH1, LDH2, LDH3 were compounded with ammonium polyphosphate (APP) to synergistically enhance the flame retardant properties of EP (Composite material abbreviated as LDH1-APP-EP, LDH2-APP-EP, LDH3-APP-EP). The results showed that the best flame retardant effect was achieved after compounding APP (5 wt%) with LDH3 (5 wt%) prepared with triethanolamine as the alkali source. Compared with Pure-EP, the peak exothermic rate and peak smoke production rate of LDH3-APP-EP prepared with triethanolamine as the alkali source decreased by 74.54 % and 67.44 %, respectively. Compared with LDH prepared with NaOH and urea as the alkali source, LDH prepared with triethanolamine as the alkali source has a larger layer spacing and a higher weight loss percentage which releases more gases, moisture, and carbon layers formed by triethanolamine during the combustion process to reduce the heat release from the fire. It’s evident that LDH3-APP-EP prepared with triethanolamine as the alkali source has higher residual carbon densities and the lowest residual carbon values based on SEM and Raman test results. This result proves that the LDH3 with triethanolamine as the alkali source has a good effect on EP flame retardation in this paper which provided a new way to design new efficient flame retardants.

Recovery of high-purity hydromagnesite from seawater through carbonation using Ca(OH)2

The economic challenges arising from resource depletion and uneven distribution of Mg in land reserves have spurred interest in technologies for Mg extraction from seawater. Thus, this study introduces a novel method to recover high-purity magnesium carbonate, specifically hydromagnesite, from seawater through carbonation using Ca(OH)₂ as an alkali source. A significant achievement of this method is the production of high-purity hydromagnesite despite the presence of large amounts of Ca, realized only through carbonation without the need for expensive additives such as NaOH. Experimental results reveal that the Ca(OH)₂ content predominantly influences the Mg dissolution efficiency during carbonation and the overall Mg recovery rate. Maximizing the efficiency of this technology relies on using an appropriate amount of Ca(OH)₂. Notably, the appropriate amount of OH− supply enhances CO₂ dissolution, facilitating Mg dissolution. Conversely, an excess of Ca(OH)₂ impedes Mg dissolution. The overall Mg recovery rate reaches a peak of 67 %, enabling the recovery of 3.4 kg of hydromagnesite from one ton of seawater. The findings highlight the effectiveness of the proposed technology as a promising and cost-effective method for extracting high-purity Mg from seawater, utilizing Ca(OH)2, previously considered an impurity, as a cost-effective alkali source.

Low-crystalline urchin-like CuCo2O4/rGO composite for high-performance supercapacitor

Abstract To meet the excellent capacity, power density and long lifespan for supercapacitors, developing advanced transition-metal oxide electrode materials is an important topic. Herein, we explored the effect of alkali source hydrolysis on the structural feature of CuCo2O4 during the growing process. It is found that urea with stronger hydrolysis ability leads to better morphology but larger crystalline grain size. Further, the grain size is decreased by introducing reduced graphene oxide (rGO). Consequently, the urea-derived CuCo2O4/rGO composite with urchin-like hierarchy configuration and small crystalline grain size provides a specific capacity of 1664 C g−1 at current density of 1 A g−1, and remains 65.3% of initial capacity when the current density increases to 30 A g−1. The symmetric supercapacitor achieves a high energy density (16 Wh kg−1 at 7200 W kg−1) and cycle stability (93.2% capacity retention after 10 000 cycles at 10 A g−1). This study highlights the inherent relation between the structural feature and synthesis condition.

Response of partial substitution of MgO for NaOH as the alkali source in hydrogen peroxide bleaching to properties of triploid poplar chemi-thermomechanical pulp

Given the current scarcity of wood fiber resources, it is imperative to investigate the potential of employing weak alkaline hydrogen peroxide for bleaching high-yield pulp (HYP) to meet the increasing demands for paper and paperboard. This work presents an investigation into the characteristics of triploid poplar chemi-thermomechanical pulp (CTMP) hydrogen peroxide bleaching, including the brightness, bleaching yield, bulk, physical strength, and contents of carbohydrates and lignin. The findings show that partial substitution of MgO for NaOH as an alkali source could improve the yield and bulk of the bleached CTMP. When the substitution ratio of MgO for NaOH reached 75 %, the brightness of 74.62 % ISO for the bleached pulp dropped by only 0.47 percent points but the bulk of 2.21 cm3/g increased by 5.74 % compared to those of the control, respectively. Meanwhile, the yield of the bleached CTMP could reach 93.45 %, 5.07 percent points higher than that of the control. The results would be of benefit to the HYP enterprises concerned.

LDH nanocrystal@amorphousness core–shell structure derived from LDH → LDO transformation: Synergistically enhanced energy stored for LIBs anode

With the emergence of advanced electronics and appliances, there is a growing demand for high power/energy density and cyclic stability of Li-ion batteries (LIBs), which stimulates the development of high-performance electrode materials. Herein, we proposed and implemented a novel strategy of employing the LDH → LDO intermediate-transformation amorphization to improve the performance of LDH as LIBs anode. In this work, flower-like NiCo-LDH nanoparticles (LDHRT) are synthesized for the first time by co-precipitation using triethanolamine (TEA) as an alkali source and H2O2 as a size-controlling reagent. Then, the unique LDH nanocrystal@amorphousness core–shell structure was obtained by fine-tuning the heat treatment, which significantly improved the electrochemical properties of the material. The layered structure of LDH and the internal defects of the amorphous phase provide abundant transport channels and a larger accommodation space for Li+, improving the rate capability and capacity of LIBs. In addition, the surface amorphous layer and the reduced size of LDHRT nanocrystals effectively alleviate the volume effect, improving the cycling stability of the electrode material. As a result, superior capacity (1821.3 mAh g−1 at 0.1 A g−1), rate capability, and cyclic stability (∼687.7 mAh g−1 at 0.5 A g−1 after 500 cycles, with the average capacity attrition rate of 0.092 %) were achieved. The Li+ diffusion coefficient and capacity retention rate (after 300 cycles) are higher than nearly 3 orders of magnitude and 50.12 % compared to the LDHRT, respectively. This study has opened a simple, safe, and economical new avenue for developing high-performance electrode materials.

Directly synthesis of H-form ZSM-5 zeolites with n-butylamine in the presence of seed and ethanol

In the research of directly synthesizing H-form ZSM-5, ammonium hydroxide is commonly used as an alkali source instead of NaOH to avoid multiple ion exchange steps. However, the volatile nature and the lack of structure-directing effect of ammonium hydroxide limit its application in practical. In this study, n-butylamine (NBA) was used as the main alkali source to directly prepare HZSM-5 zeolites with SiO2/Al2O3 ratios ranging from 40 to 300 under traditional hydrothermal conditions. The influence of the amount of NBA, ethanol, seed, and pre-crystallization on the synthesis products was investigated under the condition of SiO2/Al2O3 = 80. Theoretical simulation suggested that n-butylamine cations (NBA+) play the most potent directing role in the formation of the MFI structure but could lead to difficulties in removal during calcination. The addition of ethanol as the zeolite growth modifier (ZGM) could decrease the usage of NBA and reduce the difficulties in calcination, and the addition of seed provided the conditions for initiating crystallization in the system that could not spontaneously nucleate. HZSM-5 with different SiO2/Al2O3 ratios were prepared under the optimal crystallization conditions, and the as-synthesized samples exhibited superior textural and acid properties compared to commercial zeolite. Finally, the 1 L scale-up synthesis and MTP reaction were conducted to demonstrate the practicality of this economically and environmentally-friendly synthesis strategy.

Sintesis dan Karakterisasi Nanosilika dari Limbah Silica Scaling PLTP Dieng Melalui Metode Alkali Fusion NaOH

Silica scaling is the main problem that arises in the operation of geothermal power plants (PLTP) in Dieng. Silica scaling can disrupt electricity production and cause a buildup of waste in the environment. Silica scaling has a high silica (SiO2) content so it has the potential to be used as a value-added material, namely nanosilica. One method to obtain nanosilica is alkali fusion. This research aims to obtain nanosilica from silica scaling waste from PLTP Dieng using the alkali fusion method as well as knowing the characteristics of the nanosilica produced. The alkali fusion process is carried out using NaOH as an alkali source. Then mixing silica scaling powder and NaOH at varying temperatures of 600°C, 650°C and 700°C to produce nanosilica. The resulting nanosilica was then characterized to confirm the success of the synthesis process in producing nanosilica particles. The characterization carried out included x-ray diffraction (XRD) to characterize crystallinity, Fourier transform infrared (FTIR) to characterize functional groups, transmission electron microscope (TEM) and particle size analyzer (PSA) to determine particle size. The results of this research showed that amorphous nanosilica was successfully synthesized from silica scaling using the NaOH alkali fusion method. It was found from the results of TEM and PSA characterization that the smallest particle size was produced at a fusion temperature of 650°C. Furthermore, FTIR data also confirms the existence of functional groups at wave numbers identical to silica.

Damage of porous building stone by sodium carbonate crystallization and the effect of crystallization modifiers

Salt crystallization is an aggressive weathering mechanism affecting porous building materials. The extensive use of Portland cement, a source of alkalis, in modern buildings and restoration interventions makes sodium carbonate salts important weathering agents. Herein, we study salt damage to a porous stone commonly used in the Andalusian built heritage (Santa Pudia limestone) due to stress generation associated with the precipitation of natron (Na2CO3·10 H2O). We performed cyclic crystallization tests combined with thermodynamic and poromechanical calculations to determine salt crystallization pressure and effective tensile stress suffered by the material. The outcome reveals that in-pore natron crystallization during cooling/evaporation generates stresses exceeding the tensile strength of the wet substrate, leading to extensive damage by fracturing and material loss. Damage is reduced using aminotris(methylenephosphonic) acid (ATMP), a common phosphonate-based crystallization modifier that induces non-damaging efflorescence growth as opposed to damaging subflorescence growth, which takes place in its absence.

The composition and provenance of Late Bronze Age vitreous materials from Kefalonia, Greece

In this study, we present the results of the analysis of Late Bronze Age (LBA) vitreous materials from three cemeteries on the island of Kefalonia, Greece (Mazarakata, Metaxata, and Kokkolata-Menegata). A multianalytical approach (EPMA, LA-ICP-MS, MC-ICP-MS [Sr-Nd]) was used to determine the composition and provenance of a group of 14 glass beads, a glass fragment, and a faience bead, all dating to the 14th-11th centuries BCE. Most of the beads were produced using a plant ash alkali with one having a mixed alkali composition. Identification of the colorants revealed that the blue glasses were colored using Cu, Co-Cu, or Co. Cobaltiferous alum from the Western Desert of Egypt imparted the blue color to the cobalt containing glasses. Trace element and isotopic analysis showed that all the relief plaques were made using imported Egyptian glass. The isotopic signature of one relief plaque, a triple rosette motif unique to Kefalonia (K13-4), suggests that there may be greater geological variation among the currently identified LBA Egyptian silica and alkali sources or possibly the use of new raw material sources in the region. Silica and plant ashes from different regions were exploited for the manufacture of two beads of Near Eastern origin. One bead (M18-3) was made from an alkali derived from plants likely growing in river valleys in zones MP-1 (northern Iraq) or MP-3 (southern Iraq) and silica from zone MP-2 (deserts in western Iraq/eastern Syria). The other bead was unique in composition characterized by high chromium, silica from northern Iraq (zone MP-1 N), and plant ash from the desert (zone MP-2). Similarities to raw materials used to produce glass at Alalakh may tentatively suggest a similar origin. A Mycenaean Group B faience bead (Co-Cu blue) included in the study was manufactured with an alkali and a source of cobalt that did not come from the Western Desert. Further identification of the alkali type and the source of the raw materials for this faience bead was not possible but similarities were found to Group B beads from Psara and Mesara in Greece.

Artificial coarse aggregate from waste materials, fly ash and Msand dust through geopolymerization

Coarse aggregate is considered the most vital aspect, providing quantity and strength to the concrete. The aggregates are obtained mainly from natural resources by quarrying rocks or riverbeds. Each year, construction industries use large amounts of natural aggregates, resulting in the depletion of raw materials. Different methods, such as sintering, cold bombing, autoclaving, and geopolymerization, can prepare artificial coarse aggregates. Geopolymerization is a chemical reaction between an alkali solution and source materials containing alumina and silicate. The main objective of this study is to develop artificial aggregates with M sand dust and fly ash by geo polymerization. The ratio of Fly ash to M Sand Dust adopted is 40:60 by weight. Different molarities of sodium hydroxide was used for making the artificial aggregates with a solution-to-binder (S/B) ratio of 3.5 and a sodium silicate-to-sodium hydroxide ratio of 2.5. The mechanical properties of the developed lightweight aggregate are determined as per the specification requirement in IS 9142 (1979) for artificial lightweight aggregates for concrete masonry units. By comparison, these geopolymer aggregates are sustainable, and aggregates with 12 molarity NaOH showed better properties than other molarity NaOH aggregates based on its mechanical properties.

Nitrogen buffer gas pressure tuning in a micro-machined vapor cell

We demonstrate a controllable depletion of the nitrogen buffer gas pressure in a micro-machined cesium (Cs) vapor cell from the dynamic heating of an alkali dispenser pill. When the alkali source is laser activated, the gettering compounds within the alkali pill dispenser reduce the nitrogen (N2) content from the vapor for fine-tuning of the alkali to buffer gas pressure ratio, with a demonstrated pressure step size as low as 1 Torr. Additionally, we decrease the buffer gas pressure below 100 mTorr to evaluate the presence of other potential broadening mechanisms. Real-time control of the gas pressure ratio in the vapor cell will have notable benefits for refining atomic sensor performance and provide a routine to achieve various target pressures across a wafer bonded with a uniform back-filled buffer gas pressure.

Alkali-hydrothermal activation of tailings with red mud as a supplementary alkali source to synthesize one-part geopolymer

Alkali-hydrothermal activation of tailings with red mud as a supplementary alkali source to synthesize one-part geopolymer

Evaluation of Thermochemical Treatments for Rice Husk Ash Valorisation as a Source of Silica in Preparing Geopolymers.

The use of geopolymers has revolutionized research in the field of construction. Although their carbon footprint is often lower than that of traditional mortars with Portland cement, activators such as sodium silicate have a high environmental impact in the manufacturing of materials. Employing alternative alkali sources to produce geopolymers is necessary to obtain materials with a lower carbon footprint. The present research explores the use of rice husk ash (RHA) as an alternative source of silica to produce alkaline activators by four methods: reflux; high pressure and temperature reaction; thermal bath at 65 °C; and shaking at room temperature. To evaluate the efficiency of these methods, two types of experiments were performed: (a) analysing silica dissolved by the filtering/gravimetric method; and (b) manufacturing mortars to compare the effectiveness of the treatment in mechanical strength terms. The percentages of dissolved silica measured by the gravimetric method gave silica dissolution values of 70-80%. The mortars with the best mechanical strength results were the mixtures prepared with the thermal bath treatment at 65 °C. Mortar cured for 1 day (at 65 °C), prepared with this activator, yielded 45 MPa versus the mortar with commercial reagents (40.1 MPa). It was generally concluded that utilising original or milled RHA in preparing activators has minimal influence on either the percentage of dissolved silica or the mechanical strength development of the mortars with this alternative activator.

Alternative alkali activator from pulp mill waste – One-part blast furnace slag mortar activated with recovery boiler fly ash

Alternative alkali activators are a growing research area in the field of alkali-activated materials (AAMs) because conventional chemical-based activators, such as sodium hydroxide and sodium silicate, have a large environmental footprint and high costs. Industrial residues are widely studied as substitutional cementitious materials in concrete and precursors in AAMs but not much as activators. In the present study, sodium rich waste from pulp mill was used as an alkali source in AAMs. Recovery boiler fly ash (RBA) is dust-like waste fraction removed from flue gases of recovery boiler by electrostatic precipitators. It consists mainly of alkalis, sulfate, and carbon while sodium sulfate is the main phase. This work utilized RBA as a sole one-part alkali activator for a precursor mixture containing 95 wt% of blast furnace slag and 5 wt% of cement, and the results were compared with two references, one without activator and the other activated with commercial sodium sulfate. The setting properties and strength gain were comparable between the RBA-activated and commercial activator-activated samples. Calorimetry data showed also similar reactivity between them, and X-ray diffractometry, thermogravimetric analysis, and scanning electron microscopy measurements revealed that the same phases were formed. The main issue was the microcracking of the paste samples when using RBA as an activator. Results confirm the earlier findings from the literature, the activator dosage did not greatly impact the properties: in this study, the initial proportion of 1% or 3% Na2O was the most suitable.

Drinking water as a substantial source of toxic alkali, alkaline and heavy metals: Toxicity and their implications on human health

ObjectivesThe objective of the current study was to optimize a highly sensitive method utilizing microwave digestion and iCAP quadrupole inductively coupled plasma mass spectrometry (Q ICP-MS) for the determination of toxic alkali, alkaline and heavy metals in drinking water, and their implications on human health. MethodsA highly sensitive method based on microwave digestion and iCAP Q ICP-MS have been applied for the determination of potential metals alkali (23Na), alkaline (24 Mg) and heavy metals (75As, 208Pb, 111Cd, 59Co, 66Zn and 63Cu) in drinking water of diverse brand and origin. ResultsThe system has provided excellent quality conditions, such as detection limit (DL, 0.007–0.296 µg/L), quantification limit (QL, 0.023–0.893 µg/L) and coefficient of determination (R2, 0.976–0.998) with recovery >99.95%. Amounts of metals in bottled drinking water (BDW) were ranged from not detected to 74847.15 µg/L, whereas, tap water (TW) constitutes 1.12 to 42776.89 µg/L. Average daily dose (ADD, 0.03–516.715 μg/kg/day), hazard quotient (HQ, 0.001–0.08 μg/kg/day) based on heavy metals oral reference dose, and cancer risk (CR, 0.45–244.67 μg/kg/day) based on heavy metals cancer slope factor were achieved for BDW. Nevertheless, ADD (0.03–1028.19 μg/kg/day), HQ (0.01–0.12 μg/kg/day) and CR (0.42–292.80 μg/kg/day) were obtained for TW. As a result, BDW produced lower toxicity values than TW (high risk). Additionally, BDW was found to be brand specific, particularly for international brands that contained zero or very low levels of metals. ConclusionsCurrent investigations have explored the possible impacts of progressively increasing consumption of drinking water, especially in Saudi Arabia. Up to the present time, the levels of potential heavy metal in such water pose predominantly higher toxicity values in TW. Besides, BDW was found to be the brand specific particularly the international brand which contained either zero or low level of metals. As a result, the results highlight the need for strict policies to address the threat of metals in public water.

In-Plane Porous Graphene: A Promising Anode Material with High Ion Mobility and Energy Storage for Rubidium-Ion Batteries.

Rubidium-ion batteries (RIBs) have received a lot of attention in the quantum field because of their fast release and reversible advantages as alkali sources. However, the anode material of RIBs still follows graphite, whose layer spacing can greatly restrict the diffusion and storage capability of Rb-ions, posing a significant barrier to RIB development. Herein, using first-principles calculations, the potential performance of three kinds of in-plane porous graphene with pore sizes of 5.88 Å (HG588), 10.39 Å (HG1039), and 14.20 Å (HG1420) as anode materials for RIBs was explored. The results indicate that HG1039 appears to be an appropriate anode material for RIBs. HG1039 has excellent thermodynamic stability and a volume expansion of <25% during charge and discharge. The theoretical capacity of HG1039 is up to 1810 mA h g-1, which is ∼5 times higher than that of the existing graphite-based lithium-ion batteries. Importantly, not only HG1039 enables the diffusion of Rb-ions at the three-dimensional level but also the electrode-electrolyte interface formed by HG1039 and Rb-β-Al2O3 facilitates the arrangement and transfer of Rb-ions. In addition, HG1039 is metallic, and its outstanding ionic conductivity (diffusion energy barrier of only 0.04 eV) and electronic conductivity indicates superior rate capability. These characteristics make HG1039 an appealing anode material for RIBs.

Phosphate-based geopolymer: Influence of municipal solid waste fly ash introduction on structure and compressive strength

Materials resulting from incorporation of solid waste incineration fly ash into phosphate-based geopolymers, to partially replace metakaolin (up to 50% wt), were studied. X-ray diffraction, scanning electron microscopy, solid-state nuclear magnetic resonance spectroscopy and infrared spectroscopy were adopted to describe the mineralogical changes and the structural modifications of the geopolymer networks which impacted on the mechanical performance (compressive strength) of the materials. The results indicated that fly ash displays a different reactivity compared with metakaolin, behaving preferentially as a source of alkali that compete with the aluminosilicate metakaolin fraction by precipitating crystalline and amorphous phosphates. At 10 wt% of metakaolin substitution with fly ash, the extent and reticulation of the amorphous geopolymer matrix is preserved, and the mechanical properties are retained. At higher waste content (30–50% wt), the fast kinetics of the acid-base reactions involving the fly ash reactive phases prevail over the metakaolin dealumination, and the nature of the material shifts to an alkali-phosphate cement/phosphate-geopolymer composite. This behaviour, together with the development of porosity and presence of low-strength phases in the ash, led to a decline in the mechanical performance with increasing amount of substitution. All in all, this work provides fundamental information in the direction of a sustainable employment of phosphate-based geopolymers, which is limited by the relatively high cost of both metakaolin and phosphoric acid. Moreover, it indicates a recycling opportunity for this type of fly ash.

Recovery of magnesium from flue gas desulfurization wastewater using thermomorphic hydrophilicity amines

The concentrations of hardness ions in saline wastewater from flue gas desulfurization (FGD) are usually very high, which could result in severe membrane fouling in consequent membrane systems. Hence, we investigated the feasibility of recovering Mg2+ from saline wastewater collected from a coal-fired power plant through utilizing thermomorphic hydrophilicity amines. Triethylamine (TEA), diisopropylamine (DIPA) and N,N-dimethylisopropylamine (DMIPA) were chosen as thermomorphic hydrophilicity amines. The effects of temperature change on solubility of amines in aqueous phase were evaluated, and the influences of molar ratio of amine to Mg2+ were also investigated. Results show that the solubility of amines in aqueous phase decreased substantially when temperature was increased from 25 °C to 60 °C. Thermomorphic hydrophilicity amines could be regenerated by mild heating, and regenerated TEA could remove up to 95% of Mg2+ in the actual FGD wastewater. Meanwhile, three amines could effectively increase the pH value of the solutions, and the recovery of Mg2+ was more than 98% as Mg(OH)2 at an amine ratio molar ratio of 2.5. This study demonstrated the great potential of using thermoresponsive amines as alkali sources to recover Mg2+ and the synthesis of reactive MgO in FGD wastewater, providing a reference for the recovery of resources such as Mg2+.