Influence Of Alkalinity Research Articles

Influence of pore property and alkalinity on the bio-deposition treatment efficiency of recycled aggregates

Microbial induced calcium carbonate precipitation (MICP) technology has been successfully used to enhance the properties of recycled concrete aggregates. However, the complex source and varied physical and chemical properties of recycled aggregates may have influence on the modification efficiency since microbes are often sensitive to the surroundings. In this study, two representative types of recycled aggregates, recycled concrete aggregates (RCA) and recycled brick aggregates (RBA), were subjected to two kinds of MICP treatments, basic MICP treatment and sodium alginate (SA) aided MICP treatment. The absorption and desorption of bacteria in/on aggregates during MICP treatments were quantified. The physical and chemical properties of aggregates after the bio-treatments were tested, and the influence of alkalinity and pore structure of aggregates under various MICP treatment methods on treatment efficiency were detailed investigated. Results indicated that, when the aggregates were subjected to the basic MICP treatment, the treatment efficiency was more remarkable in RBA, because of its high porosity and moderate pH (around 8–9), which facilitated the absorption of bacteria in/on aggregates and urease activity respectively. While under SA-aided MICP treatment, the influence of pore structure and alkalinity of aggregates on the treatment efficiency was not significant compared with that under the basic MICP treatment, especially the mass of CaCO3 on the aggregates. The biogenic CaCO3 generated by SA-aided MICP treatment not only plugged micropores, but also distributed all over the entire surface of the aggregates, resulting in a sufficient repair of microcracks. Meanwhile, the surface repair may reduce the influence of pore structure and pH of aggregates on the precipitation process, thereby reducing the impact of varied physical and chemical properties of aggregates on the treatment efficiency, which was conducive to the widely unified application of SA-aided MICP treatment in the modification of recycled aggregate based on construction solid waste.

Immobilization mechanism of Mn2+ in electrolytic manganese residue using sintered ceramsites prepared by alkali-mechanical-roasting method

Currently, sufficient information is unavailable on using electrolytic manganese residue (EMR) to prepare sintered ceramsites for immobilization of manganese in EMR. This study used EMR, Na2CO3, and montmorillonite (MMT) as raw materials to prepare ceramsites with the influence of alkalinity, sintering temperature, and sintering time on the investigated ceramsite properties. Under the optimal conditions (i.e., C-2 h= EMR content: 50%, Na2CO3 content: 25%, sintering temperature: 1050℃, sintering time: 2 h), the cylinder compressive strength, porosity, bulk density and apparent density of the ceramsites reached 25.03 MPa, 54.72%, 0.748 g/cm3 and 2.056 g/cm3. The presence of mesoporous pores within the ceramsites made them suitable for adsorption as biocarriers. The leaching concentration of Mn2+ from the ceramsites was 2.26 mg/L, lower than the third grade in standard (GB 8978–1996), suggesting that heavy metals are stabilized within the ceramsite. The main immobilization mechanism in the ceramsites included the formation of a new crystalline phase including jacobsite (Fe2MnO4) and liquid phase encapsulation. The involvement of certain impurities such as Mg2+ in the formation of crystalline phases can influence Mn2+ immobilization. This research not only offers valuable insights into the safe and valuable utilization of EMR but also provides a novel method for preparing ceramsites.

Fly ash-dominated High-Strength Engineered/Strain-Hardening Geopolymer Composites (HS-EGC/SHGC): Influence of alkalinity and environmental assessment

In this study, fly ash (FA)-dominated High-Strength Engineered Geopolymer Composites (HS-EGC) were designed and developed. The influence of alkalinity and the underlying mechanism on the mechanical performance and microstructures were investigated through a systematic study. The developed HS-EGC presented high compressive strengths (over 100 MPa) and high tensile ductility (over 4%). Specifically, results showed that HS-EGC with 6% alkalinity possessed the highest compressive strength of 122.7 MPa, the largest tensile strain capacity of 8.0%, and the highest tensile strength of 12.9 MPa. Tensile over-saturated cracking was observed for HS-EGC with alkalinities of 6% and 8% through crack analysis. Back scattering electron and nanoindentation further confirmed that higher alkalinity resulted in higher reaction degrees, but a strength loss was observed at an alkalinity of 8% due to the deterioration of the reaction product. From the comprehensive review of high-strength Engineered Cementitious Composites (ECC) with similar compressive strength and the existing FA-dominated EGC/ECC, it was found that the developed HS-EGC recorded the lowest embodied carbon, embodied energy, and material cost per MPa compared to all the counterparts. Notably, the HS-EGC with 6% alkalinity in this work pushed the performance envelope of FA-dominated EGC. The findings of this study provided useful knowledge for the design and development of HS-EGC for sustainable and resilient infrastructure.

An environmentally friendly indigo dyeing process using iron (II) gluconate as a reducing agent

This research paper aims to replace the ecologically harmful sodium dithionite traditionally used in the indigo dyeing process with the iron (II) gluconate reducing agent. The density functional theory (DFT) method using B3LYP 6- 311 G basis set was used to determine the optimized structures of iron (II) gluconate and indigo. The highest occupied molecular orbital (HOMO) energy and the lowest unoccupied molecular orbital (LUMO) energy were calculated, and the electronic properties dependent on HOMO-LUMO energies were determined. Furthermore, an ecological dyeing process using this reducing agent was studied. The influences of alkalinity, reduction temperature, and iron (II) gluconate concentration on the fulfilment of the dyeing process were inspected by measuring the obtained redox potential and the color strength of the dyed samples. A full factorial experiment was performed for statistical analysis and optimization of the dyeing process. The results revealed that the developed method is highly effective and capable of generating redox potential and dyeing quality comparable to those obtained with the conventional process employing sodium dithionite. Finally, the substitution of sodium dithionite by iron (II) gluconate reduced the wastewater load generated by the conventional dyeing process.

The role of total Na in the retention of microelements in soils on marine deposits

The influence of alkalinity and other factors on the content of microelements in soils developed on marine deposits is studied. Traditional indicators of exchangeable sodium percentage do not demonstrate the ability to retain microelements, but one can see a close direct correlation between the content of macroelements and the retention of microelements. The efficiency of this group is increased if we take into account the concentration of total Na. The element compositions of soil were determined by neutron activation method. The results show that the Na-related alkalinity of soil can enhance the role of the main macroelements and increase the dispersibility of particles and their aggregating capacity relative to the microelements. The microelement composition was also determined in Gleyic Solonchaks using the Zn concentration due to the anionogenic composition of gley.

Influence of alkalinity on self-treatment process of natural fiber and properties of its geopolymeric composites

The novelty and the aim of this research is to investigate the feasibility of the self-treatment process, which is governed by various levels of alkalinity, i.e., sodium hydroxide (NaOH) solution in the geopolymer system, for natural fibers, and the effect of such treatment on the properties of hemp-geopolymer composites. A digital microscope is used to examine the contact angle (CA). Fourier Transform Infrared (FT-IR) spectrometer, Scanning Electron Microscope (SEM), X-Ray diffractometer (XRD) are used to examine changes in surface functional groups, bonding, micrographs and structural formation of the resulted hemp-based geopolymer products. The results showed that the alkalinity in the geopolymer alternatively acted as an alkaline treatment reagent for the reinforced hemp fibers, which evidently provided effectively self-treatment, indicating by the FT-IR and contact angle analysis. The compressive strength of the composites was slightly dropped as the binder was replaced by the hemp fibers, while the flexural strength and impact resistance were improved by the additional adhesion between the natural fibers and cement matrix. The self-treatment approach could also shorten the preparation process of any natural fibers in geopolymers, allowing both cost-effectiveness in practical usages and in-field applications.

Influence of Alkalinization Over Metal Organic Frameworks MIL-100(Fe) for Enhanced Volatile Organic Compounds (VOCs) Adsorbents

Substantial attempts have been undertaken for the improvement of the air quality over decades; and Volatile Organic Compounds (VOCs) from the chemical and textile industries are truly listed as severe issue to be controlled. To come up with modus operandi for this issue, a novel composite of metal organic frameworks (MOFs) MIL-100(Fe) with salient tuned features of natrite was designed by a green and facile method. Mineralized composite MOFs exhibited enhanced crystallinity than pure MIL-100(Fe) as well showcased a higher surface area of 1300 m² g-1. Through dynamic acetone pressure swing adsorption setup, MIL-0.05Na (MIL-100(Fe) synthesized with 0.05 mM Na₂CO₃ solution) revealed an enhanced acetone adsorption of 210 mg g 1 at room temperature. Gas phase adsorption isotherms confirmed the mono layer adsorption behavior. The kinetics models evaluated that the external mass transfer was the rate limiting step for surface adsorption. The thermodynamic study manifested that the adsorption reaction was spontaneous and exothermic. The proposed mechanism of adsorption was the act of physisorption which enriched the adsorbents reusability. This research work provides a futuristic vista to design mineralized Fe-MOFs composites for an energy saving adsorbents for VOCs removal.

Influence of alkaline and alkali-free accelerators on strength, hydration and microstructure characteristics of ultra-high performance concrete

To broaden the application of ultra-high performance concrete (UHPC) in engineering fields with high-early-strength requirements, accelerators were used to accelerate the setting and hardening of UHPC. This study investigated how alkaline accelerator (NA) and alkali-free accelerator (AS) influence the strength, hydration and microstructure characteristics of UHPC. To achieve the proposed objective, the terms of setting time, strength, released ionic concentration, isothermal calorimetry, X-ray diffraction, scanning electron microscope, energy dispersive X-ray and mercury intrusion porosimetry were performed. The results show that NA and AS significantly increase the setting and hardening rate of UHPC, and their optimal dosages are 2% and 4%, respectively. 2% NA increases the 1 d compressive, splitting tensile and flexural strengths of UHPC by 55.8%, 62.2% and 56.5%, respectively, while 4% AS increases by 10.8%, 21.6% and 21.0%, respectively. However, their later strengths decrease slightly. The first exothermic peak values of NA-2% and AS-4% are about 3 times higher than the reference paste, and their main hydration peaks appear earlier by 38.2 and 23.3 h, respectively. NA and AS contribute to the rapid formation of hydration products and refine the pore structure of pastes.

ЕFFECT OF IRON AND NICKEL DITHIOCARBAMATES ON THE PROPERTIES OF MODIFIED POLYURETHANES

The effect of modifiers - nickel bis(N,N-dimethyldithiocarbamate) (DTC-Ni) and iron tris(N, N-dimethyldithiocarbamate) (DTC-Fe) depending on their content on the structural peculiarities of polyurethane matrix based on polyoxytetramethylene glycol-1000 4,4’-diphenylmethane diisocyanate and 1,4-butanediol has been studied. The method of IR spectroscopy according to the results of NH groups’, C = O- and COC fragments’ association has shown the structuring effect of modifiers due to the PU matrix coordination. The processes of photolysis occurred as a result of exposure of PU under the conditions of the climate chamber have been also studied by IR spectroscopy method. The influence of modifiers and their content on the modified polyurethanes density has been investigated. The planar structure of DTC-Ni has shown to contribute to the density increase of modified PU as the result of polymer chain coordination, while the spherical structure of DTC-Fe - causes a density decrease due to steric hindrances in the implementation of H-bonds. Modification of polyurethanes with both nickel bis (N, N-dimethyldithiocarbamate) and iron tris (N, N-dimethyldithiocarbamate) as well as UV irradiation and moisture under the conditions of the climatic chamber contribute to the increase of water absorption. Studies of the strength properties of modified polyurethanes in comparison with the matrix under the conditions of the climate chamber have established the photosensitizing effect of nickel and iron dithiocarbamates. By studying the mass of samples of PU-DTС-Fe/Ni after extraction with dimethylformamide in the Soxhlet apparatus it has been found an increase in the level of gel fraction (0.29 - 1.58%) with increasing the modifier content, which confirms the presence of a network structure of modified PU due to radical processes taking place during destruction with the modifier participation. The influence of alkaline and acidic media on the destruction level of both modified polyurethanes and their analogues depending on the modifier content under the influence of climatic chamber conditions has been studied. Comparative derivatographic studies in air of weight loss of modified polyurethanes have confirmed the structuring and thermostabilizing effect of DTC-Ni on the PU matrix due to the probable difficulty of oxygen diffusion to the polymer volume, while the spatial structure of PU-DTC-Fe reduces the thermal stability.

The Use of Regression and Neural Network Modelling in Production Monitoring of an Industrial Enterprise

Regression and neural network model for predicting the required dose of coagulant, depending on the quality of river water supplied for water treatment, are considered, their comparative analysis is carried out. For modelling and forecasting, statistical data collected for the period from 2005 to nowadays. Regression models were built on the true values of the factors (water quality indicators) and on their first differences to eliminate the trend in the series. For the models built on the true values, the statistical significance, was confirmed, high values of the coefficient of the determination were obtained, the values of the approximation errors were 22–25 %. In neural network modelling, networks of the multilayer perception were used. Generalization error on the test set when using other type of networks (RBF-networks, Elman networks), was significant above. Computational experiments have shown that, in general, the accuracy of neural network models is higher than regression ones. The average learning error was 7–9 %, the error on the test set increases to 12–16 %. The reliability of the forecast is increased by training the network on more recent data and using a larger set of facts. An increase in the influence of indicators of permanganate oxidability and colour of the initial river water on the dose of reagents with a simultaneous decrease in the degree of influence of alkalinity over the last five-year period was revealed. This confirms the need to periodically update data for building models. Selected models recommended for implementation in industrial monitoring of water treatment technology at the enterprise.

Influence of Alkaline on Generating Aluminum Ammonium Sulfate inside an Air Preheater in a Coal-fired Power Plant

Influence of Alkaline on Generating Aluminum Ammonium Sulfate inside an Air Preheater in a Coal-fired Power Plant

Solvothermal Reaction and Piezoelectric Response of Oriented KNbO3 Polycrystals.

KNbO3 (KN) piezoelectric polycrystals were prepared by a two-step solvothermal reaction process with the managed organic solvents as reaction mediums at a low temperature for a short time. In the solvothermal reaction system, the formation mechanism of polycrystalline KN is mainly the dissolution-deposition mechanism. The influences of alkalinity, viscosity, and the polarity for reaction mediums on the formation of the niobates were investigated. The chemical reaction mechanisms of niobate products and formation mechanism of niobate crystals from the precursor were clarified. The regulating and controlling mechanism of the phase compositions, the morphologies, and the lattice constants for the niobates obtained in varied reaction mediums were revealed. The obtained KN piezoelectric polycrystals are constructed from oriented KN nanocrystals. Piezoelectric hysteresis loops of cuboid KN polycrystals were detected for the first time. A prepared cuboid KN polycrystal shows an average d33* value of 32 pm/V. The study provides a strategy for the development of oriented KN piezoelectric materials to apply the orientation engineering.

Optimization of photosynthetic biogas upgrading in closed photobioreactors combined with algal biomass production

Photosynthetic biogas upgrading in microalgae photobioreactors constitutes a sustainable and environmentally friendly technology for the simultaneous removal of CO2 and H2S from raw biogas. The potential of algal-bacterial symbiosis for biogas purification has been already studied and demonstrated in open photobioreactors. However, few studies have focused on the implementation of this process in closed photobioreactors, which offer higher photosynthetic efficiencies, enhanced biomass productivities, a limited N2 contamination and improved CO2 mass transfer. In this study, the influence of alkalinity (inorganic carbon concentrations from ∼200 to ∼1700 mg L–1), and nitrogen (N) deprivation strategies (24 or 48 h limitation) on both biomethane quality and biomass composition has been evaluated and optimized in a closed tubular photobioreactor (TPBR) interconnected to a mixing chamber and a biogas absorption column (total working volume of 132 L). The increase in the alkalinity of the cultivation broth mediated an increase in the upgrading performance of the TPBR, reaching CO2 removals of 96.3 ± 0.8 %, and a complete H2S abatement, resulting in an enhanced biomethane composition (CH4 = 97.2 ± 0.9 %). Moreover, process operation under N deprivation did not affect the quality of biomethane, which complied with standards required for injection into natural gas grids or use as vehicle fuel. N-deprivation promoted the continuous storage of intracellular carbohydrates (29.0 ± 4.4 % compared with 14.3 ± 2.1 % obtained under N excess). A maximum biomass productivity obtained was of 15.8 ± 4.3 g m–2 d–1 during N excess vs. 11.2 ± 3.3 g m–2 d–1 during N-deprivation at 26.8 d of hydraulic retention time. During the N feast-famine cycles, the cyanobacterial species Pseudanabaena sp. was dominant over green algae.

Influence of alkaline and oxidative pre-treatment of waste corn cobs on biohydrogen generation efficiency via dark fermentation

Stages of waste corn cobs processing leading to the production of biohydrogen via dark fermentation are presented and discussed in this paper. Firstly, the effects of pre-treatment conditions i.e. alkaline, alkaline-oxidizing and Fenton oxidizing pre-treatment of lignocellulosic biomass on the removal of lignin were examined. The solid residue obtained in the first stage was subjected to saccharification by means of enzymatic hydrolysis. The composition of enzymatic hydrolysates and fermentation broths were investigated in order to determine the content of sugars as well as phenolic compounds and fermentation broth composition containing organic acids. The dark fermentation process of the obtained hydrolysates was carried using mixed wastewater sludge from the municipal sewage treatment plant. The highest hydrogen production was obtained for alkaline pre-treated hydrolysates. The effects of investigated chemical pre-treatment methods were discussed in terms of the obtained saccharification efficiency and composition of the gas phase formed during the fermentation, and the composition of fermentation broth.

Effect of self-treatment process on properties of natural fiber-reinforced geopolymer composites

ABSTRACT Natural (hemp) fibers can be used in the cementitious composite as they have superb engineering properties, e.g. environmentally friendly and offer economic advantages. However, alkaline treatment (alkalization) process of natural fiber prior to mixing is required to modify fiber surface, making fibers more adhesive and compatible with cement paste. Geopolymer, one of the green alternative cementitious materials, is fortuitously involved in the alkaline environment, as alkaline solutions are used as its activators. The latent benefit, regarding the influence of alkalinity in geopolymer systems, namely ‘self-treatment process’ was thus investigated. The self-treatment process is a ‘Just-adding’ of as-received hemp fibers into geopolymer mixture without any pre-alkaline treatments. The results showed that the self-treatment process was governed by the alkaline environment in the geopolymer system and alternatively acted as an alkaline treatment condition for natural fibers, indicated by SEM and FT-IR analysis. The pre-alkalization process can be skipped in the self-treatment approach with similar mechanical properties to the ordinary processes. The main findings of this work could be further tailored to partially or fully the conventional alkaline treatment process and provide an opportunity for any other natural fiber geopolymer composites to be easily utilized in massive amount and used in practical applications.

Nanomaterials and nanotechnology for composites: synthesis, structure, properties and new application opportunities

Nanomaterials and nanotechnology for composites: synthesis, structure, properties and new application opportunities

Influence of Alkalinity on the Synthesis of Zeolite A and Hydroxysodalite from Metakaolin

Kaolin is a cheap and abundant source of silica and alumina, which may be used as precursors for the production of zeolites, molecular sieves with pores in the nanometer scale. Brazil, one the largest producers of kaolin, generates tons of kaolin waste in the paper coating process. That waste may be used to synthesize zeolite A and hydroxysodalite, greater added value materials with a wide range of applications. In this work, Zeolite A and hydroxysodalite were synthesized from kaolin waste of processing industries for paper coating. Kaolin was calcined to dehydroxylate kaolinite and obtain metakaolin, an amorphous material with Si/Al ratio equal to 1, being suitable for production of zeolite A and hydroxysodalite. Zeolites were synthesized under static hydrothermal conditions by reacting metakaolin with NaOH solutions of different concentrations. The zeolitic products were characterized by means of X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The results showed that the higher the NaOH concentration in the reaction medium, the higher the proportion of hydroxysodalite in the zeolitic samples.

Influence of alkalinity on the synthesis of hierarchical LTA zeolite by using bridged polysilsesquioxane.

The mechanism of formation of hierarchical LTA zeolite involved the methoxyl groups of bridged polysilsesquioxane hydrolyzing into hydroxyl groups. The covalent Si–O–Si bond between silicon hydroxyl in the above solution and other silica sources forms by dehydration, avoiding phase separation. The influence of alkalinity on the synthesis of hierarchical LTA zeolites was investigated by using bridged polysilsesquioxane. XRD patterns indicate the synthesis of sodalite at the same molar composition of the hierarchical LTA zeolites without bridged polysilsesquioxane. The characterization results from TG and DTG revealed that bridged polysilsesquioxane was successfully incorporated into the as-synthesized hierarchical LTA zeolite. N2-adsorption/desorption results proved that mesopores and the porosities of the hierarchical LTA zeolites are adjustable by a change of alkalinity. SEM images indicated that the morphologies of the hierarchical LTA zeolites changed with increasing alkalinity. The hierarchical LTA zeolites showed faster initial exchange rates of Na+ to Mg2+ compared with conventional LTA.

Direct Synthesis of Sodalite from Kaolin: The Influence of Alkalinity

Alkalinity is one of the most important factors that influence the crystallization process of zeolite and the product properties. The influence of alkalinity on the synthesis of sodalite from kaolin without calcinations was reported in this research. The synthesis of sodalite using molar ratio of Na2O/Al2O3 = x, H2O/Na2O = 128/x and SiO2/Al2O3 = 2/x, where x was the variation of molar ratio of alkalinity: 10, 20, 30, and 40. The synthesis has done by stirring for 6 h, without aging, and the crystallization time was 24 h under hydrothermal method (100 °C). The products were characterized by X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX). The X-ray diffraction pattern and infrared spectroscopy shown that pure sodalite was formed by using molar ratio of alkalinity 10, 20, and 30. The crystallinity and particle size increase along with increasing of alkalinity. Quartz was formed by using molar ratio of alkalinity 40.

Influence of Alkaline and Alkaline Earth Metal Promoters on the Catalytic Performance of Pd–M/SiO2 (M = Na, Ca, or Ba) Catalysts in the Partial Hydrogenation of Soybean Oil-Derived Biodiesel for Oxidative Stability Improvement

Palladium/silica (Pd/SiO2) and Pd–M/SiO2 catalysts, where M stands for sodium (Na), calcium (Ca) or barium (Ba), were studied for their catalytic ability in the partial hydrogenation of soybean oil...