NaOH System Research Articles

The effects of pH regulators on the flotation separation of sphalerite and dolomite and their interaction mechanism

pH regulators play a key role in mineral flotation. In the study, the effects of CaO, Na2CO3 and NaOH on the flotation separation of sphalerite and dolomite were investigated, and the interaction mechanisms were analyzed by flotation tests of mixed minerals, scanning electron microscope (SEM) and energy dispersion spectrum (EDS), turbidity, Zeta potential and the extended Derjaguin-Landau-Verwey-Overbeek (EDLVO) theory. The results indicated that Na2CO3 was favorable for flotation separation of sphalerite and dolomite, but NaOH had a negligible effect. CaO improved the flotation recovery of MgO to a maximum value of 9.29%, but it was unfavorable to the enriched sphalerite. SEM-EDS results revealed that dolomite was adsorbed on the sphalerite surface in the three systems, but the amounts of dolomite attached in the CaO system was higher than those of the other two systems. Turbidity tests indicated that the turbidity in the CaO system was less than that in Na2CO3 and NaOH systems. The sphalerite surface was negatively charged regardless of the pH regulators. Na2CO3 and NaOH hardly affected the surface potentials of dolomite. However, CaO changed the surface potential of dolomite from negative value to positive value under high alkaline condition. EDLVO theoretical calculations revealed that the electrostatic forces in CaO system were stronger than that in Na2CO3 and NaOH systems, leading to the slime coating.

Anti-corrosion investigation of silver coated starch-chitosan nanocomposite on Al in NaOH wash solution

This work focuses on the effectiveness of a Starch-Chitosan nanocomposite containing embedded silver nanoparticles in preventing the Al corrosion in a 3 M NaOH system. Using Fourier Transform Infrared spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), and X-Ray Powder Diffraction (X-RD) methods, the produced polymer nanocomposite was studied. Gravimetric, impedance, potentiodynamic polarization and SEM//EDAX techniques were used to test the efficiency of Starch-Chitosan nanocomposite embedded with silver nanoparticles (Ag@Starch-CS polymer nanocomposite) as an eco-friendly inhibitor. Activation parameters and adsorption isotherm support both physical and chemical adsorption mechanisms with robust protection efficiency. The Tafel curves validated that, Ag@Starch-CS polymer nanocomposite performs as an anodic type of corrosion inhibitor. The presence of OH, NH2, etc., groups in Ag@Starch-CS polymer nanocomposite was found to have contributed significantly to the inhibition process by interacting with the Al surface.

How Thick Aqueous Alkali Should be Better for Aluminum-Air Batteries at Sub-Zero Temperatures: A Critical Anti-Freezing Concentration.

The application of portable aluminum-air batteries (AABs) in extreme environments is an inevitable demand for future development. Aqueous electrolytefreezing is a major challenge for low-temperature operations. Conventionally, enlightened by the organic system in metal ion batteries, blindly increasing the concentration is regarded as an efficient technique to reduce the freezing point (FP). However, the underlying contradiction between the adjusting mechanism of the FP and OH- transportation is ignored. Herein, the aqueous alkali solution of CsOH is researched as a prototype to disclose the intrinsic conductive behavior and related solvent structure evolution. Different from these inorganic electrolyte systems, the concept of a critical anti-freezing concentration (CFC) is proposed based on a specific temperature. The relationship between hydrogen bond reconstruction and de-solvation behavior is analyzed. A high conductivity is obtained at -30°C, which is also a recorded value in an intrinsic aqueous AAB. The homogenous dissolution of the Al anode is also observed. As a general rule, the CFC concept is also applied in both the KOH and NaOH systems.

Mechanism of catalyst on morphological evolution of Al(OH)3 during Al–H2O reaction

The morphologies of Al(OH)3 crystals prepared via the Al–H2O reactions with various catalysts and the growth mechanisms of these crystals were investigated. The reaction was carried out with NaOH, KOH, tetramethylguanidine (TMG), and tetramethylammonium hydroxide (TMAH) as catalysts. The evolution of the obtained product was observed in situ, and the products obtained after 120 min of reaction have the shapes of the hexagonal prism, long-hexagonal prism, long rod, and irregular rod, respectively. In the NaOH and KOH systems, the products are gibbsite, and the gibbsite crystals grow along the (110), (001), and (100) faces in the NaOH system, and the (100), (102), and (110) faces in the KOH system. However, in the TMG and TMAH systems, the products are bayerite, and the bayerite crystals grow along the (110), (111), and (001) faces. It is worth mentioning that gibbsite has more Al—O bonds than bayerite, giving rise to the formation of columnar crystals.

Ultrasonic-enhanced selective arsenic removal and sulfide conversion from iron slag

There are numerous valuable metals and the hazardous element arsenic in the iron slag produced in the zinc hydrometallurgy. The arsenic must be removed for comprehensive recovery of valuable elements. Generally, the alkaline arsenic removal produces large amounts of iron hydroxide colloids and iron slag agglomeration. Here, ultrasonic enhancement of NaOH–Na2S system is proposed to selectively remove arsenic from iron slag. Ultrasound destroys the agglomeration and encapsulation of zinc-containing iron slag and promotes the liquid-solid interfacial reaction. The arsenic removal percentage is 92.24% under ultrasonic power of 400 W, which is 12.14% higher than the conventional alkaline arsenic removal. The apparent activation energy of ultrasonic-enhanced alkali leaching for arsenic removal is calculated to be only 8.84 kJ/mol by kinetic experiments. Diffusion is proved to be the limiting link in the ultrasonic-enhanced leaching process for arsenic removal. This study proves that ultrasonic-enhanced Na2S–NaOH system has a good prospect for selective removal of arsenic from iron slag.

Stepwise extraction and utilization of silica and alumina from coal fly ash by mild hydrothermal process

Coal fly ash (CFA) is a potential secondary resource. In this study, silica and alumina from CFA were leached and utilized through a gentle alkali hydrothermal process. The results of CFA desilication with a single NaOH solution showed that amorphous silica was dissolved at a relatively low temperatures. Under optimized conditions, the leaching rate of SiO2 reached 33.81 %, while that of Al2O3 only was 1.37 %. Amorphous honeycomb calcium silicate hydrate was then well prepared by using silicon-rich liquid with CaO. The new aluminosilicate structures (sodalite) were detected in desilicated coal fly ash (DSCFA), which hinder the silica dissolution. After the optimal hydrothermal leaching in Ca(OH)2+NaOH system, the leaching rate of Al2O3 in DSCFA reached 39.84 %. The dealuminated CFA were mainly composed of friendly nano-flake tobermorite. With the increase of temperature, time, alkali concentration and Ca/Si, the tobermorite phase gradually changed to hibschite. The obtained alumina lixivium was well transformed into valuable porous boehmite via a carbonation process. Finally, the pilot tests excellent results, leaching about 41 % of SiO2 and 42 % of Al2O3, further demonstrating the feasibility of the whole hydrothermal process of desilication with a single alkali followed by aluminum extraction with mixed alkali.

The influence of additive MgO and its content on the carbonation resistance of alkali-activated slag concrete with different activators

The influence of additive MgO and its content on both the compressive strength and carbonation depth of alkali-activated slag concrete (AASC) was investigated under an accelerated carbonation environment. Furthermore, the modification mechanism of MgO on the carbonation resistance of AASC was explored by multiple analytical techniques. Results showed that the incorporation of MgO effectively enhanced the post-carbonation compressive strength and diminished the carbonation depth of concrete. As the MgO content increased, there was a gradual reduction in carbonation depth. The incorporation of MgO promotes the hydration of slag, altering the Al environment, and promoting the formation of C-S-H and Mg-Al hydrotalcite phases. Moreover, the addition of MgO resulted in the emergence of magnesium carbonate and calcium magnesium carbonate in the carbonation products, which filled the pores and prevented the further diffusion of CO2 into the interior. In addition, the improvement effects are more pronounced in the water glass system compared to the NaOH system.

Supercritical hydrothermal synthesis of nano-ZnO: Effects of key parameters and reaction mechanism

In this paper, ZnO particles with the particle size as low as 23 nm were successfully prepared by supercritical hydrothermal synthesis technique. The particle size of nano-ZnO decreased with the increase of temperature and pressure. Nano-ZnO particles in ZnSO4 system were spherical with smaller particle size. The discrepancy in nano-ZnO produced by different precursor of Zn(NO3)2, Zn(CH3COO)2 or ZnSO4 is attributed to the anion effects and supersaturation. The particles in the KOH system (29 nm) were smaller than those in the NaOH system (44 nm). For precursor concentration, intermediate Zn(OH)2 was generated at lower concentration, while Zn4SO4(OH)6·4H2O was produced at higher concentration. For alkali concentration, as the gradual increase of KOH concentration, Zn(OH)2 began to decrease and gradually transformed into Zn(OH)3– and [Zn(OH)4]2−. When the KOH concentration reached a certain value, [Zn(OH)4]2− occupied the dominance in the mixed solution.

Preparation of TiO2 pigment from ilmenite ore concentrate by molten alkaline process

TiO2 pigment production from an ilmenite concentrate via a molten alkaline process was investigated. The ilmenite concentrate (54.19% TiO2) was first roasted in the molten NaOH system at various temperatures ranging from 600 to 800°C while the mass ratio of NaOH/ilmenite was varied within the range of 0.8-1.2 for 1 hour. The achieved roasted efficiency was up to 93.93% at a temperature of 700°C and NaOH/ilmenite ratio of 1:1. The roasted product was first leached in water and then in a solution of HCl 20% at 50ºC for 2 hours. The TiOCl2 solution was hydrolysed at 95oC for 2 hours. Precipitation of the hydrolysis process was then calcinated at 800oC. The final obtained product contained up to 96.37% of TiO2. Ilmenite can be used as a raw material in a molten alkaline process. It is obvious that not only high purities of TiO2 could be achieved, but also the reduction of waste materials, raw materials, energy, and time.

Analysis of the Influencing Factors of the Efficient Degradation of Waste Polyurethane and Its Scheme Optimization.

This work proposes an efficient catalytic recovery and utilization method for waste polyurethane foam. This method uses ethylene glycol (EG) and propylene glycol (PPG) as two-component alcohololytic agents for the alcoholysis of waste polyurethane foams. For the preparation of recycled polyethers, the conditions of different catalytic degradation systems were catalyzed by duplex metal catalysts (DMC) and alkali metal catalysts, and a synergy with both was also used. The experimental method was adopted with the blank control group and was set up for comparative analysis. The effect of the catalysts on the recycling of waste polyurethane foam was investigated. The catalytic degradation of DMC and the alkali metal catalysts alone, as well as the synergistic effect of the two catalysts, was explored. The findings revealed that the NaOH and DMC synergistic catalytic system was the best, and that the system activity was high under a two-component catalyst synergistic degradation. When the amount of NaOH added in the degradation system was 0.25%, the amount of DMC added was 0.04%, the reaction time was 2.5 h, and the reaction temperature was 160 °C, the waste polyurethane foam was completely alcoholized, and the prepared regenerated polyurethane foam had high compressive strength and good thermal stability. The efficient catalytic recycling method of waste polyurethane foam proposed in this paper has certain guiding and reference values for the practical production of solid-waste-recycled polyurethane.

Carbon nanotubes doped with nitrogen, modified with platinum or platinum-free for alkaline H2-O2 fuel cell

A series of cathodic and anodic catalysts for alkaline H 2 -O 2 fuel cells (FC) deposited on the surface of functionalized and nitrogen-doped carbon nanotubes (CNT) was synthesized and studied by various structural and electrochemical methods. It was established that, due to the minor defect structure, CNT NaOH (functionalized in alkali) exhibit high corrosion stability. A further increase in the activity in the oxygen reduction reaction (ORR) and the stability of CNTs is observed following their doping with nitrogen. The high activity of CNT NaOH+N is attributed to pyridine groups and the increased electrical conductivity of this catalyst. It was shown that CNT NaOH comprise effective substrates for hydrogen oxidation reaction catalysts. The PtMo/CNT NaOH system containing 12 wt.% Pt at a molar ratio of PtMo=1:1 is characterized by the highest catalytic activity among investigated anode platinum and non-platinum catalysts. The use of this catalyst made it possible to reduce the content of platinum to 0.1-0.2 mg/cm 2 , while preserving the characteristics that significantly exceed those of the active layer containing 60Pt/C (HiSPEC 9100) catalyst (0.6 mgPt/cm 2 ).

Extraction of Copper from Chalcopyrite Using Alkaline Glycine–Ammonia Solutions

Chalcopyrite is well known as being refractory to conventional leaching approaches at atmospheric pressure. The current study investigated a hybrid approach using aqueous ammonia as a pH modifier for glycine-based lixiviant systems to leach copper from chalcopyrite while maintaining surface refreshment using ceramic media at room temperature. The glycine–ammonia system exhibited significantly better copper extraction than the traditional glycine–NaOH system. A copper extraction of 91.5% was achieved after 72 h of leaching by using 0.71 M ammonia, at a Gly:Cu molar ratio of 4:1, by using a solid content of 1%, with a ceramic media: solid ratio of 3:5 and at ambient temperature. Adding ceramic beads during leaching led to a breakup of particles and a refreshment of particles’ surfaces that significantly improved the copper extraction. At a solid content of 10%, oxygen is essential for leaching; a copper extraction of 95.4% was achieved with oxygen injection, while only 33.4% copper extraction was obtained without introducing oxygen. A kinetic analysis indicates that the leaching rate is limited by combined liquid film diffusion and diffusion through the product layer. A conceptual flowsheet is proposed, where chalcopyrite concentrate can be extracted by a leaching–grinding process and copper can be recovered by a solvent extraction–electrowinning circuit.

Interesterification Process of Palm Oil Using Base Catalyst: The Effect of Stirring Speed and Type of Catalyst on Kinetic Energy and Dipole Moment

Making biodiesel which has so far been carried out, is a transesterification process with glycerol by-products. Glycerol has a low economic value and is usually only disposed of as waste. An alternative process for producing biodiesel with more valuable by-products is interesterification. The by-product of the interesterification reaction is triacetin which is widely used in the chemical, food, and pharmaceutical industries. The operating conditions of the interesterification reaction were the reaction temperature of 60⁰C, the molar ratio of palm oil: methyl acetate = 1: 6, the reaction time of 1 hour, catalyst type (KOH, NaOH), stirring speed (200, 300, 400, 500, 600 rpm) and catalyst mass (0.25, 0.5, 0.75% wt. oil). From the analysis and calculation, the highest FAME yield was 57.30% at reaction temperature 60⁰C, the molar ratio of palm oil: methyl acetate = 1: 6, reaction time 1 hour, KOH catalyst, stirring speed of 300 rpm, and catalyst mass 0.75% wt oil. From the calculation of ChemDraw software for the triglyceride + methyl acetate + KOH system had a kinetic energy of 3,670 kJ/kmol and a dipole moment of 20,330 debyes, whereas the triglyceride + methyl acetate + NaOH system had a kinetic energy of 2,977 kJ/kmol and a dipole moment of 11,457 debyes so that the KOH catalyst was superior in terms of reactivity and solubility. Biodiesel produced had an acid value of 0.3927 mg KOH/gr and met ASTM D664 for a maximum acid value of 0.5 mg KOH/gr.

Mechanisms of dispersion of metakaolin particles via adsorption of sodium naphthalene sulfonate formaldehyde polymer

The influence of different alkali and alkaline earth cations (Na+, K+, Ca2+, and Mg2+), and of solution pH, on surface interactions of metakaolin particles with a sodium naphthalene sulfonate formaldehyde polymer (SNSFP) (a commercial superplasticizer for concretes) was investigated in aqueous systems relevant to alkali-activated and blended Portland cements. This study used zeta potential measurements, adsorption experiments, and both in situ and ex situ Fourier transform infrared spectroscopy measurements of the suspensions to gain a fundamental understanding of colloidal interactions and physicochemical mechanisms governing dispersion in this system. SNSFP was most effective in dispersing metakaolin suspensions in Ca2+-modified aqueous NaOH systems (CaCl2-NaOH) at dosages of 5 wt.%. Additionally, Ca2+ was the most effective alkaline earth cation mediator in providing a dispersion effect in metakaolin dispersed in aqueous NaOH and SNSFP mixtures, while Mg2+ was the most effective in aqueous KOH and SNSFP mixtures. The colloidal dispersion remained stable in the highly alkaline environment, and therefore SNSFP could be utilized to improve dispersion of metakaolin-based alkali-activated systems. The suggested mechanism for colloidal stability and fluidity of metakaolin-based cements (e.g. Portland cement blends and alkali-activated cements) is explained by changes in the distribution and structure of the electric double-layer, as well as structural forces, due to alteration in surface charge density and hydrated shell, facilitating competitive adsorption of the polymer.

Dissolution Behavior of Sodium Phosphate in a Na3PO4–Na2WO4–NaOH Solution System

Sodium hydroxide autoclaving is the main method for smelting scheelite in China. In this method, sodium phosphate is added as an additive to realize the highly efficient decomposition of scheelite, and a crude sodium tungstate solution containing sodium phosphate and sodium hydroxide is obtained. In the subsequent process of ion exchange, phosphorus ions in the solution compete with the resin adsorption of tungstate, which reduces the adsorption capacity of the resin and endangers the purity of the subsequent sodium tungstate solution. To remove the phosphorus from crude sodium tungstate solution, a chemical purification method is usually adopted. The principle of the chemical purification method is to use chemical reagents to react with impurities to form precipitates to achieve the purpose of impurity removal. Because of the advantages of simple industrial implementation and high impurity removal efficiency, it has been widely used in phosphorus removal from crude sodium tungstate solution. However, in the process of phosphate removal in a crude sodium phosphate solution, the chemical purification method has some disadvantages. First, the additional cost of chemical reagents is required, and other metal impurities from chemical reagents would be introduced to crude sodium tungstate solution. Second, phosphate impurity removed by the chemical precipitation method is usually sedimented in other forms but sodium phosphate, which makes the phosphate resource unable to be recycled for tungsten smelting. Therefore, a novel phosphorus removal method needs to be developed. The dissolution behavior of sodium phosphate in a Na3PO4–Na2WO4–NaOH system was investigated in this paper. The results showed that in binary or ternary solution systems of sodium phosphate, sodium tungstate, and sodium hydroxide, the common-ion effect and salt effect exist simultaneously. The common-ion effect decreases the solubility of sodium phosphate, while the salt effect increases the solubility of sodium phosphate. Increasing the concentration of sodium hydroxide or sodium tungstate and lowering the temperature of the solution can greatly reduce the phosphorus concentration in crude sodium tungstate solution, making the crude sodium tungstate solution meet industrial requirements of ion exchange. The results of the study lay a theoretical foundation for the development of new phosphorus removal methods.

Chemiluminescence of Aldehydes in Pyrogallol–NaOH System Using Polyaniline/Cu(I) as Catalyst

Chemiluminescence of Aldehydes in Pyrogallol–NaOH System Using Polyaniline/Cu(I) as Catalyst

TEMPO-Mediated Oxidation Promotes Cellulose Dissolution in a Zincate–NaOH System at Suprazero Temperatures

TEMPO-Mediated Oxidation Promotes Cellulose Dissolution in a Zincate–NaOH System at Suprazero Temperatures

Modeling and Experimental Studies on Carbon Dioxide Absorption with Sodium Hydroxide Solution in a Rotating Zigzag Bed

The enhancement of mass transfer is very important in CO2 absorption, and a rotating zigzag bed (RZB) is a promising device to intensify the gas–liquid mass transfer efficiency. In this study, the mass transfer characteristics in an RZB in relation to the overall gas-phase volumetric mass-transfer coefficient (KGa) were investigated with a CO2–NaOH system. A mathematical model was established to illustrate the mechanism of the gas–liquid mass transfer with irreversible pseudo-first-order reaction in the RZB. The effects of various operating conditions on KGa were examined. Experimental results show that a rise in the liquid flow rate, inlet gas flow rate, rotational speed, absorbent temperature, and absorbent concentration was conducive to the mass transfer between gas and liquid in the RZB. It was found that the rotational speed had the largest impact on KGa in the RZB. The KGa predicted by the model agreed well with that by the experiments, with deviations generally within 10%. Therefore, this model can be employed to depict the mass transfer process between gas and liquid in an RZB and provide guidance for the application of RZBs in CO2 absorption.

Experimental study on CO2 mass transfer in blade unit of tridimensional rotational flow sieve tray

• Mass transfer processes of rotational-perforated flows in a blade unit were separated. • Mass transfer of rotational-perforated flows in a blade unit was investigated with the liquid phase rotational flow ratio. • Variations of overall volumetric mass transfer coefficients of rotational–perforated flows with gas-phase artificial rotational flow ratio were investigated. • Relationships between mass transfer processes of total and rotational–perforated flows were investigated. The mass transfer performance of CO 2 is an index for the design of CO 2 capture equipment. In this study, the mass transfer characteristics of CO 2 in the blade unit of a tridimensional rotational flow sieve tray (TRST) were investigated using a CO 2 –NaOH system. The rotational and perforated flow modes were separated experimentally, and the rotational flow ratio of the gas phase at the outlets was controlled such that the flow characteristics of the blade unit were similar to those of the TRST. The effects of the gas-phase artificial rotational flow ratio ( R ctrl ), gas-phase F -factor ( F s ), and liquid spray density ( L W ) on the overall volumetric mass transfer coefficients of the rotational and perforated flows ([ K G a V ] rot , [ K G a V ] per ), as well as the overall volumetric mass transfer coefficient of the total process ([ K G a V ] tot ), were investigated. The results showed that under the experimental conditions, [ K G a V ] rot increased with R ctrl and L W . F s did not significantly affect [ K G a V ] per , whereas [ K G a V ] per increased with L W , reaching a maximum value of 0.00194 kmol/(m 3 ∙s∙kPa). The mass transfer processes of the two flow modes are complementary. When R ctrl is 0.5, [ K G a V ] tot is optimal at 0.0023 kmol/(m 3 ∙s∙kPa). This study lays a theoretical foundation for the optimal design of TRSTs.

Chemical composition and monolignin in alkali and acid treated corncob affect sugar release

In order to understand how do chemical composition and monolignin in corncob material affect biomass digestion, the effect of alkali(NaOH), acid(H2SO4) pretreatment condition and the combined severity factors (CSF) on the chemical composition and monolignin content in corncob, and the effect of chemical composition and lignin monomers content in the pretreated corncob on sugar release were comparably investigated. In NaOH and H2SO4 system, lignin and hemicellulose content decreased to almost zero at combined severity factor (CSF) 9.5 and 10.5, respectively. 5 mol/L NaOH followed by enzymatic hydrolysis for 72 h could give rise to 84.62% reducing sugar yield, which was 2.02 times higher than that treated by H2SO4. A negative correlation was found between lignin, hemicellulose and sugar release upon alkali and acid pretreatment, respectively. Evaluation of monolignin in corncob samples suggested that higher S/G ratio or removal of H-monomer was favorable to sugar release in both alkali and acid system. Thus, corncob substrates with lower lignin and hemicellulose content and higher S/G ratio may be conducive to enzymatic digestibility of biomass.