Higher NaOH Concentrations Research Articles

Zeolite based Geopolymer from Biomass: a Sustainable Adsorbent for Water Softener

Water quality in several areas in Semarang, especially in Tugu sub-district, is still very low and unsuitable for drinking. Ground water contaminated with Ca2+ and Mg2+ ions which is commonly known as hard water. This study aims to examine the potential of zeolite-based geopolymer adsorbents, materials which have a zeolite-like structure but are basically geopolymers. Synthesis of zeolite based geopolymers from rice husk ash, kaolin and NaOH activators has been successfully carried out by the sol gel method. Three-dimensional networks have been formed from Silica (SiO2) and Alumina (Al2O3). Activator solution, NaOH, with variations in concentrations of 4 M (Geopolymer 4), 8 M (Geopolymer 8) and 12M (Geopolymer 12) gives significant differences. As the higher the concentration of activator solution, the more silica and alumina dissolved so that the geopolymer becomes amorphous. These results are consistent with XRD and FTIR data. Geopolymer 12 has an adsorption capacity of 97.4% is the best adsorbent in adsorbing Ca2+ and Mg2+ metal ions with operating conditions at 40°C for 60 minutes. This shows that there is a close relationship between synthesis methods, structural characterization and geopolymer adsorption activities. The higher concentration of NaOH gives amorphous geopolymers. NaOH will activate the silica and alumina surfaces on the geopolymer, making it easier for adsorbents to absorb and interact with the adsorbate molecules, namely Ca2+ ions and Mg2+ ions.

Evolution of the pore and framework structure of NaY zeolite during alkali treatment and its effect on methanol oxidative carbonylation over a CuY catalyst

Alkali treatment is widely used on aluminosilicate zeolites with high Si/Al ratios in order to fabricate mesopores in the framework. However, for zeolites with low Si/Al ratios, the effect of alkali treatment on the pore and framework structure needed further study. In this work, Y zeolite is treated with NaOH solutions of different concentrations and is used as the support for Cu-based catalysts for oxidative carbonylation of methanol to dimethyl carbonate. The physicochemical properties of the supports and corresponding catalysts are characterized by N2 adsorption–desorption, X-ray diffraction, X-ray fluorescence, transmission electron microscopy, inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, and H2-temperature-programmed reduction analyses. The results show that no obvious mesopores are formed under alkali treatment, even at high NaOH concentration. However, amorphous species present in the micropores of Y zeolite are removed, which increases the micropore surface area as well as the crystallinity. Simultaneously, the cage structure is partially destroyed, which also leads to a slight increase of the pore volume and surface area. The altered micropore structure eventually increases the content and accessibility of the exchanged Cu species, which is beneficial to the catalytic activity. When the concentration of NaOH is 0.6 M, the space time yield of dimethyl carbonate for the corresponding catalyst was 151.4 mg g−1 h−1 which is 3.3-fold higher than that of the untreated-Y-zeolite-supported Cu catalyst. However, further increasing the alkali treatment strength can seriously destroy the basic aluminosilicate structure of the Y zeolite and decrease its intrinsic ion-exchange capacity. This results in the formation of agglomerated CuO on the catalyst surface, which was not conducive to catalytic activity.

Cellulose nanofibers from rapidly microwave-delignified energy cane bagasse and their application in drilling fluids as rheology and filtration modifiers

Energy cane bagasse (ECB) is the major residue after the cane is milled to extract juice for sugar, biochemical, and/or biofuel production. The sustainable conversion of ECB into high value-added products can help reduce agricultural waste, and enhance utilization of bioresources. In the present work, we demonstrate that ECB can be converted into cellulose nanofibers (CNFs) that can serve as high value-added additives in bentonite water-based fluids (BT-WDFs). Particularly, cellulose fibers (CFs) were rapidly isolated from ECB by microwave-assisted NaOH / NaClO2 treatments. CFs treated with the higher NaOH concentration and microwave irradiation lost more lignin (96.2 % delignification) and their crystal structure was more completely transformed from cellulose I to II, resulting in smaller diameters (8.5 μm). CNFs suspensions from subsequent wet-grinding and microfluidization of the CFs exhibited typical shear-thinning behaviors and solid-like viscoelastic properties due to the entangled network structure of the CNFs. Formulated fluids with 0.5 wt% of the manufactured CNFs showed good rheological and filtration properties, demonstrating their potential applications in the oil service industry.

Modeling the water absorption and compressive strength of geopolymer paving block: An empirical approach

The use of fly ash as a cement substitute may reduce the increasing cement demand and prevents an increased emission of carbon dioxide (CO2) into the atmosphere. This study aims to produce some compositions of geopolymer paving block (GPB) using different ratios of NaOH/Na2SiO3 combined with fly ash. The empirical models were developed to predict the performance of the GPB samples through the verification of the water absorption and compressive strength. The results showed that an optimum performance of GPB sample is predicted for the NaOH/Na2SiO3 ratio range of 0.4 to 0.67 to be verified at 28 d of the GPB age. The hardness of GPB sample rapidly increases by using a high enough concentration of NaOH in activator leading to significantly increase the compressive strength of paver block. A new approach of predicting the GPB performance has been proposed to support development of pavement construction in civil engineering industry.

EVALUATION OF THE ENGINEERING PROPERTIES OF FLY ASH-BASED GEOPOLYMER BRICKS

This paper is aimed to evaluate the engineering properties of fly ash-based geopolymer bricks. Four geopolymer brick mixtures were designed with a constant solution-to-binder ratio of 0.40 and various concentrations of sodium hydroxide solution. The engineering properties of fly ash-based geopolymer bricks consisting of compressive strength, unit weight, water absorption, water permeability, and ultrasonic pulse velocity were investigated. The microstructure of fly ash-based geopolymer bricks was also investigated by using the scanning electron microscope (SEM). Test results indicated that the compressive strength, unit weight, and ultrasonic pulse velocity (UPV) of geopolymer bricks increased, while the water absorption and water permeability of geopolymer bricks reduced with increasing NaOH concentration. Moreover, brick samples with high NaOH concentration showed a higher geopolymeric reaction of fly ash than brick samples with low NaOH concentration. All geopolymer brick samples produced in this study showed a good quality with compressive strength of above 10.1 MPa, water absorption of below 9.4%, water permeability of below 1.84 L/m2 .h, and UPV of above 2500 m/s.

Improved bioelectricity generation of air-cathode microbial fuel cell using sodium hexahydroxostannate as cathode catalyst

Herein we report the synthesis of tin oxide (SnO2) and sodium hexahydroxostannate (Na2 [Sn(OH)6]) by varying the reaction parameters and established their ORR activity performance in the single chamber microbial fuel cell (sMFC) as cathode catalyst in both pure and mixed culture environments. The electrochemical studies reveal that the Na2 [Sn(OH)6] catalyst synthesized with higher concentration of NaOH has greater ORR catalytic activity than others in terms of onset potential and current density with a four-electron transfer process. The higher power density is also obtained using the same catalyst in the pure and mixed inoculum, which is comparable to the benchmark Pt/C in a sMFC. The developed cathode electrocatalyst can play a cost-effective material for the enriched energy recovery in the sMFC and/or other such electrochemical devices.

Production of modified carboxymethyl cellulose from sawdust and wheat straw

Mines in Zimbabwe are facing a challenge in acquiring modified carboxymethyl cellulose with enhanced depressive properties in flotation pulps because at the moment it is not being produced in the country and this triggered the research on the production of the in demand flotation depressant from wheat straw and sawdust. This involved the extraction of cellulose from wheat straw and sawdust and then modification of the cellulose to carboxymethyl cellulose. A 31.04 % yield of cellulose was successfully extracted from wheat straw and 49.28% from sawdust through alkali treatment process. The cellulose was then converted to Carboxymethyl Cellulose (CMC) by mercerization with various sodium hydroxide (NaOH) concentrations and subsequently etherified with monochloroacetic acid. The CMC yield of cellulose samples from wheat straw and sawdust were 76.80% and 76.40% respectively. The absolute degree of substitution (DSabs) of CMC was found to increase with increasing concentrations of NaOH up to 30% (w/v) of NaOH and decreased at higher NaOH concentration. The molecular weight was determined using intrinsic viscosity and was found to have the same trend as DSabs. Higher DSabs provide a stronger inter-molecular interaction between carboxymethyl and hydroxyl groups which result in higher mechanical properties.

Separation of sodium chromate from high alkaline media based on precipitation transformation using barium hydroxide

Separation and recovery of chromium from a high-concentration NaOH solution by a Ba(OH)2 precipitation process.

Bulk etch rate for PADC CR-39 at extended concentration range of NaOH mixed with ethanol and etchant viscosity study

Bulk etch rate of PADC CR-39 detector in a mixture of NaOH and ethanol alcohol aqueous solution of (8 ml of NaOH + X ml of ethanol: X = 0, 1, 2, 3) at 70 °C was determined using fission track diameter method. Wide range of NaOH concentration, never covered before, from 2 to 30 N was studied. Higher NaOH concentrations and ethanol increase the detector etching rate dramatically leading to a reaction rate far from equilibrium. Arrhenius and multi hit equations are no longer hold and therefore a need for new equations is arise. Viscosity of (NaOH + ethanol) in such wide concentration range was also studied at different temperatures to explain the reaction rate. Many efforts and different fitting equations were used to manipulate the data. Some of these equations are statistically as well as chemically rejected and finally three equations seem to read the data quit well are suggested.

Kraft lignin reaction with paraformaldehyde

Abstract Lignin is the second most abundant biopolymer and will be an important source for carbon-containing compounds in the future. Based on their similar phenolic structures, lignin has great potential to become a valuable substitute for phenol in phenol-formaldehyde resin adhesives. To meet this aim, the sodium hydroxide (NaOH)-catalyzed reaction of kraft lignin with formaldehyde was studied by using paraformaldehyde (PFA) as a formaldehyde source. The advantage of using PFA, the solid polymer of formaldehyde, is the simple composition of the depolymerized solution. According to the results of differential scanning calorimetry (DSC), the lignin reaction was found to require a high NaOH concentration in order for the reaction with PFA to proceed at reasonably low temperatures compared to the curing temperature of phenol-formaldehyde resins (approximately 150°C). On the other hand, high alkalinity conditions are known to favor the disproportionation of formaldehyde to formic acid and methanol. Due to the moderate reactivity of lignin, the Cannizzaro reaction can compete with the methylolation reaction of lignin. Based on the results of 13C, 31P and 1H-13C heteronuclear single quantum correlation nuclear magnetic resonance (HSQC NMR), methylolation was found to be the main reaction occurring in the lignin-formaldehyde reaction.

Arsenic removal from arsenic-containing copper and cobalt slag using alkaline leaching technology and MgNH4AsO4 precipitation

In this study, a novel alkaline cycle leaching and MgNH4AsO4 precipitation technology was used to remove arsenic in arsenic–containing copper and cobalt slag. The phase analysis results indicated the arsenic species mostly existed in the original slag as Cu-As alloy. By adopting NaOH-H2O2 leaching method, the arsenic leaching reached as high as 94.5% under the optimum conditions. The XRD results indicated that copper in the Cu-As alloy was oxidized to be Cu(OH)2 in high concentration NaOH solution. And the optimum conditions were established as: NaOH concentration, 2 mol/L; leaching temperature, 25℃; H2O2 concentration, 5%; and liquid-solid ratio (L/S), 9:1. Thermodynamic analysis showed that it was feasible to selectively precipitate arsenate in alkaline leaching solution in the form of MgNH4AsO4. The XRD results confirmed that the arsenic in the filter residue mainly existed in the form of MgNH4AsO4·6H2O, which has good crystallinity, contributing to a better arsenic and alkali separation. Under the optimum conditions, the content of arsenic in the purified liquid and purified residue were 39 mg/L and 24.15%, respectively. Thus, the purified alkaline solution could be circulated for the leaching process, which is beneficial to the cost reduction and environment protection.

One-step direct fabrication of phase-pure Cu2O films via the spin-spray technique using a mixed alkaline solution

The spin-spray technique was used to fabricate phase-pure Cu2O films at 70 °C with a high deposition rate of 0.3 μm/min. The source solution, containing a mixture of CuSO4･5H2O and l-ascorbic acid, and the reaction solution, containing NH3 and NaOH, were sprayed on the rotating substrates. It was possible to control the grain size, the crystalline orientation of the films, the surface morphology, and the optical band gap by adjusting the concentrations of NH3 and NaOH in the reaction solution. The films fabricated with a low NH3 aq. concentration were composed of nanosized grains and highly [111] oriented. On the other hand, films fabricated with a high NH3 aq. concentration were composed of submicron grains and highly [100] oriented. The surface morphologies of the films varied according to the concentration of NaOH. The surface of the films fabricated with a low NaOH concentration were almost flat and had a {100} orientation on their surface. On the other hand, films fabricated with a high NaOH concentration were composed of pyramidal grains. A smaller grain size in the films corresponded with a higher optical band gap.

A study on initial setting time and the mechanical properties of AASC using the PS ball as fine aggregate

India is the second largest producer of cement in the world with an annual production of 455 Million Tonnes (MT) which is expected to reach up to 550MT by 2020. In India, the increased demand for cement in the construction industry is required to meet the needs of infrastructure development. However, the production of Portland cement releases significant amounts of CO2 to the atmosphere. Therefore, it is necessary to look for sustainable solutions for concrete production by the use of supplementary cementitious materials. The alternative replacement for Ordinary Portland Cement (OPC) can be Ground Granulated Blast Furnace Slag (GGBS), Fly-ash, Silica fume, Rice-husk ash, which is the various industrial by-products. In this present work, an attempt was made to develop Alkali Activated Slag Concrete (AASC) using Precious Slag (PS) ball as fine aggregate. The development of AASC was made with GGBS as the principal binder. Mixes were developed with binder content 443 kg/m3, Sodium Silicate (SS)/Sodium Hydroxide (SH) ratio of 1 and their performance when exposed to ambient temperature were studied. Alkali binder ratio (0.3) with 8, 10, 12 and 14M NaOH was selected for all the AASC mixes. The test results showed that the slump values for the different mixes satisfying the MoRTH guidelines for concrete pavements. The AASC mixes have higher compressive strength ranging between 41–64 MPa. The fatigue life of the AASC mix was has improved by the addition of PS ball, at the higher concentration of NaOH.

Corrosion Behaviour of Type 316L Stainless Steel in Hot Caustic Aqueous Environments

The corrosion behaviour of type 316L stainless steel in aqueous 30–50 wt%. NaOH at temperatures up to 90 °C has been elucidated. Exposure to room temperature environment showed parabolic weight loss behaviour, with corrosion rates of up to 0.4 mm/year. Higher NaOH concentrations and exposure temperatures resulted in a reduced stability of the electrochemical passivity domain, associated with higher corrosion rates. Exposure to de-aerated 50 wt%. NaOH presented corrosion rates of up to 0.5 mm/year at open circuit potential, with maximum corrosion rates under polarisation of up to ≈ 18 mm/year. The formation of a dark iron-oxy-hydroxide and nickel-oxide was observed, with exposure to temperatures in excess of 50 °C. The behaviour of type 316L stainless steel in hot caustic environment is compared to types 204, 304, 2205 stainless steel, and nickel alloy 200.Graphic

Novel process for decontamination and additional valorization of steel making dust processing using two-step correlative leaching

Recycling of steel making dusts often targets Zn removal. Other heavy metals such as Mo, W or Cr do not receive as much attention, and the decontamination of the dusts from these constituents is scarcely addressed in the literature. This study presents a novel approach of the selective separation of Mo from steel making dusts using alkaline solutions with low concentrations, before Zn removal using concentrated alkaline medium. Such an approach has never been reported before and can contribute to more efficient decontamination of the steel making dusts and will increase the value of recovered components since Mo can be significantly preconcentrated. Two samples originating from two steel producers were investigated. One sample contained 2.65% of Mo and 1.87% of Zn, and the second sample had 0.61% of Mo and 35.9% of Zn. Temperature was found to have a low impact on the leaching efficiency of Mo, while increased NaOH concentration promoted leaching of Zn. Excellent pre-concentration of Mo was achieved by using a S:L ratio of 1:3. Almost 5170 mg/L Mo, 1000 mg/L W, no Fe and only 2 mg/L Zn were present in the solution after leaching at 30 °C for 30 min. For the samples containing lower concentrations of Mo and high concentrations of Zn, the selectivity of the process was affected when using higher concentrations of NaOH. A final leachate containing 797 mg/L of Mo and only 11 mg/L Zn was obtained after leaching with 0.05 M NaOH. DFT computations showed that the 2D layered structures of MoO3 and WO3 are decisive factors that account for their high solubilites.

Changes in Fe 2+ /Fe 3+ molar ratio for the formation of spinel CoFe 2 O 4 layered double hydroxide nanoparticles

A facile, fast, and cheap method has been proved for large-scale synthesis of super-paramagnetic CoFe2O4 nanoparticles (CNPs) by the co-precipitation process without surfactant and followed by calcination. In order to fabricate layered double hydroxide nanoparticles, the molar ratio Fe2+/Fe3+ should be changed and confirmed by transmission electron microscopy. Also, all synthesised CNP samples were characterised by X-ray diffraction and vibrating sample magnetometer to investigate the relationship between the crystal size and the saturation magnetisation. The good correlation between the influence of Fe2+/Fe3+ ratio change and the initial pH showed that the slower formation of CNPs was obtained at higher concentration of NaOH and Fe3+. Also, the critical role for the crystal size, morphology, magnetisation characters, and cation distribution in the spinel structure was described well. Furthermore, the maximum saturation magnetisation and crystal size were obtained at the percentage Fe2+/Fe3+ (1:1). The results stated that the synthesised CNPs had the potential to become a promising material in large scale.

Reaction mechanisms of calcined kaolin processing waste-based geopolymers in the presence of low alkali activator solution

The massive amount of kaolin processing waste was daily formed. To reduce the amount of their waste deposited in landfills and to increase the value- adding of recyclable waste, this work interested to use as raw materials in the preparation of geopolymer. This paper studied the reaction mechanisms of calcined kaolin processing waste-based geopolymers in the presence of low alkali activator solution by the pressing method. The reaction mechanisms of geopolymer were measured as a function of NaOH concentration by DSC, XRD, and FTIR analysis. Furthermore, the effects of NaOH concentration and curing time on the mechanical properties and microstructure of calcined kaolin processing waste-based geopolymer were investigated. The DSC, XRD, and FTIR results indicated that the geopolymerization reaction increased with higher NaOH concentrations. Forming the geopolymer by the pressing method led to the particles being close together in a compact matrix. Subsequently, their surfaces were dissolved with NaOH solution, inducing the geopolymerization reaction. This reaction and continuous reaction resulted in the compressive strength and microstructure of the geopolymer. The compressive strengths of the geopolymer synthesized with NaOH concentration of 10 M (curing time of 7 days) and a curing time of 28 days were 26.98 MPa and 28.55 MPa, respectively, which were approximately 22.58% and 52.35% higher compared to the geopolymer synthesized with NaOH concentration of 4 M and a curing time of 1 day. The SEM micrographs of the geopolymer samples displayed more geopolymeric gel and denser matrices with increases in NaOH concentration and curing time. The nitrogen adsorption and pore volume decreased with increases in NaOH concentration and curing time. Synthesis of geopolymers using kaolin processing waste as a raw material is a value- adding and environmentally friendly process.

Fly ash based geopolymer stabilisation of silty clay/blast furnace slag for subgrade applications

The mechanical and microstructural properties of problematic silty clay (SC) stabilised with fly ash (FA) based geopolymer and blast furnace slag (BFS) replacement are presented in this research. The influence factors evaluated included FA:BFS replacement ratio, NaOH concentration, and curing temperature. A series of geotechnical laboratory tests and microstructural analyses were also undertaken. The strength of the stabilised material was found to be governed by interparticle forces, mainly from the contribution of the chemical bonding strength. The results indicated that the unconfined compression strength (UCS) values of FA based geopolymers stabilised with SC/BFS blends increased with increasing NaOH concentration, at the various FA:BFS replacement ratios when cured at various temperatures (25, 50 and 80°C). The high concentration of NaOH could dissolve FA particles to leach silica and alumina which reacted with NaOH to produce a geopolymerization (N-A-S-H gel) process, which resulted in high UCS results. The decrease in FA:BFS ratio however reduced the specific area of particles to be welded by FA geopolymerization products and reduces the geopolymer gel due to the reduction in quantity of FA precursor. As such, the interparticle forces increased as the FA:BFS reduced up to the optimum value and then decreased as the FA:BFS reduced. The optimal FA:BFS ratio was found to be 20:10. An elevated curing temperature accelerated the geopolymerization reaction, leading to the higher UCS at higher temperature. The use of waste by-products BFS and FA to stabilise problematic soil in civil engineering applications will contribute to a significant reduction in construction costs and the sustainable development of the project life cycles.

Ultra-low thermal conductivity via interfacial phonon scattering in PbTe hoppercubes/PbTeO3 microrods for thermoelectric applications

PbTe/PbTeO3 composites were synthesized via hydrothermal method. Sodium hydroxide (NaOH) was used to control the morphology and the formation of PbTe/PbTeO3 composites. The as-prepared samples were extensively studied using various techniques. In the absence of NaOH, PbTeO3 microrods were obtained. The addition of NaOH at varying concentration (7.5 and 12.5 mmol) considerably influenced the phase ratio of PbTe hoppercubes and PbTeO3 microrods. The morphology dependent thermoelectric properties of PbTe/PbTeO3 composites were investigated in the temperature range of 300–660 K by using Spark Plasma Sintered pellet. It revealed that the lower concentration of NaOH (7.5 mmol), which contains the equivalent amount of PbTe hoppercubes and PbTeO3 microrods shows the maximum Seebeck coefficient of 438 μV/K at 420 K and minimum thermal conductivity of 0.44 W/mK at 660 K. Whereas, at higher concentration of NaOH (12.5 mmol) which contains more amount of PbTe hoppercubes and less PbTeO3 microrods shows the maximum Seebeck coefficient of 427 μV/K at 380 K and exhibited ultra-low thermal conductivity about 0.31 W/mK at 620 K. It clearly shows that the more amount of hoppercubes which contains less microrods scattered the phonons more at the grains boundaries of PbTe hoppercubes and PbTeO3 microrods. The possible phonon scattering mechanism of PbTe/PbTeO3 composites was proposed.

Application of the Taguchi method to investigate the effects of experimental parameters in hydrothermal synthesis of Na-P1 zeolite from coal fly ash

The aim of this study is to optimize the hydrothermal parameters to maximize Na-P1 (Na6Al6Si10O32·12H2O) zeolite crystallization from fly ash using the L9 orthogonal Taguchi methodology. The operational parameters considered were the hydrothermal temperature, synthesis duration, NaOH concentration, and liquid/solid (L/S) ratio. Analyses of the mean and variance were applied to investigate the effects of the selected parameters on the crystallization of Na-P1 zeolite. The resulting crystals were characterized by X-ray diffraction analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy, laser granulometry, and cation exchange capacity measurements. The results showed that fly ash undergoes chemical and morphological changes indicating its transformation to zeolite materials. The hydrothermal temperature was found to be the most important parameter contributing to crystallization of Na-P1 zeolite. High NaOH concentration can cause a small decrease in the Na-P1 zeolite content due to the appearance of other zeolites such as hydroxysodalite, Na-X, and chabazite. The content of Na-P1 zeolite was enhanced by increasing the hydrothermal temperature, NaOH concentration, and liquid/solid (L/S) ratio, while variation of the synthesis duration had less effect on Na-P1 zeolite crystallization. The optimum conditions to obtain the maximum content of Na-P1 zeolite were found to be high temperature level (150 °C), NaOH concentration (3 M), and L/S ratio (20), and medium duration (24 h).