Dissolution Of Aluminum Research Articles

Thermophysical Phenomena in Electrochemical Systems

The anodic dissolution of aluminum is studied. A mechanism for the process is proposed and confirmed experimentally. As evidence for this mechanism, it is established that the Nernst–Peters equation can be used to calculate the equilibrium potential of the anodic oxidation of water, which allows determination of the real temperature in the reaction zone.

Phosphorus recovery from sewage sludge - phosphorus leaching behavior from aluminum-containing tertiary and anaerobically digested sludge.

Systematic investigations of the acidic dissolution of phosphorus (P), aluminum (Al), iron (Fe), and calcium (Ca) from Al-containing tertiary sludge were carried out in this work. The results were compared with the dissolution behavior of Al-containing anaerobically digested sludge to evaluate the P recovery potential in the form of struvite from tertiary sludge versus anaerobically digested sludge. Additional investigations of synthetically produced Al sludge served as a comparison for the dissolution behavior of P and Al without the influence of other contaminants (metals, biomass). In addition, the acid consumption was analyzed as a function of the target pH during the dissolution. The dissolution efficiency of ortho-phosphate in tertiary and anaerobically digested sludge after acid treatment at pH 2 was ∼90%. The dissolution efficiency of Al and Ca in tertiary sludge was also ∼90% at pH 2, while the release efficiency of Al and Ca in anaerobically digested sludge was lower, ∼70% at pH 2. In tertiary sludge, about 75% of Fe was found dissolved at pH 2, whereas in anaerobically digested sludge this value was higher, ∼90%. Based on the experimental data, it can be concluded that significant dissolution of phosphorus from Al-containing tertiary sludge can take place at pH < 3. The highest sulfuric acid consumption for P dissolution was observed in the case of tertiary sludge at pH 2.

Fabrication of nanocrystalline supersaturated W–Al alloys with enhanced thermal stability and high sinterability

In this work, nanocrystalline W–Al alloys (up to 20 at.% of Al) were produced by high energy ball milling and powder microstructural evolution was investigated as a function of milling time. It was found that, regardless of the composition, alloys crystallite size progressively decreases and stabilizes around a value of about 10–15 nm after 70–100 h of mechanical treatment. The aluminum dissolution into the bcc W lattice was confirmed by DSC, SEM, and TEM. The formation of intermetallic compounds was detected neither during ball milling nor after thermal treatments up to 1450 °C. Sintering behavior of mechanically alloyed W–Al alloys was tested under pressureless conditions, and a significant improvement in terms of sinterability with respect to pure W was observed. Along with favoring the sintering process, the addition of Al also resulted in a notable enhancement of the coarsening resistance. Indeed, the analysis of ball-milled pure tungsten after thermal treatment at 1450 °C provided an estimated average crystallite size of about 2 μm, while W80Al20 and W90Al10 alloys retained an average crystallite size of about 70 nm and 60 nm, respectively. Although further work is required to optimize sintering conditions for achieving full density samples, the retaining of the nanostructure marks a significant advancement in the field of W-based alloys.

Enhanced bio-recovery of aluminum from low-grade bauxite using adapted fungal strains.

Filamentous fungi have been proved to have a pronounced capability to recover metals from mineral ores. However, the metal recovery yield is reduced due to toxic effects triggered by various heavy metals present in the ore. The current study highlights the fungal adaptations to the toxic effects of metals at higher pulp densities for the enhanced bio-recovery of aluminum from low-grade bauxite. In the previous studies, a drastic decrease in the aluminum dissolution was observed when the bauxite pulp density was increased from 1 to 10% (w/v) due to the high metal toxicity and low tolerance of Aspergillus niger and Penicillium simplicissium to heavy metals. These fungi were adapted in order to increase heavy metal tolerance of these fungal strains and also to get maximum Al dissolution. A novel approach was employed for the adaptation of fungal strains using a liquid growth medium containing 5% bauxite pulp density supplemented with molasses as an energy source. The mycelia of adapted strains were harvested and subsequently cultured in a low-cost oat-agar medium. Batch experiments were performed to compare the aluminum leaching efficiencies in the direct one-step and the direct two-step bioleaching processes. FE-SEM analysis revealed the direct destructive and corrosive action by the bauxite-tolerant strains due to the extension and penetration of the vegetative mycelium filaments into the bauxite matrix. XRD analysis of the bioleached bauxite samples showed a considerable decline in oxide minerals such as corundum and gibbsite. Results showed a high amount of total Al (≥ 98%) was successfully bioleached and solubilized from low-grade bauxite by the adapted fungal strains grown in the presence of 5% pulp density and molasses as a low-cost substrate. Graphical abstract.

A promising process for transformation of hematite to magnetite with simultaneous dissolution of alumina from red mud in alkaline medium

The Bayer bauxite residue (red mud, RM) is environmentally hostile and hazardous to human health. Due to a high content of iron, RM is utilized here by hydrothermal digestion in an original one-stage method of hematite into magnetite conversion during recovery of alumina. The changes in the content of alumina, hematite, and magnetite are confirmed using XRD, SEM, chemical analysis and magnetometry. The yield of alumina reaches 75.4% and more during digestion with addition of lime and FeSO4. The formation of magnetite involves the interaction between ferrous ions generated from FeSO4 and dissolved from hematite of RM in the Bayer liquor and hematite reduction by ions-reductants from initial RM during repeated digestion. The conversion efficiency of hematite reaches 52% through the Bayer digestion at the molar ratio Fe(II)/Fetot in RM 0.17 with following separation of magnetic fraction of RM (MFRM) containing 33% Fe3O4. The saturation magnetization of MFRM grows to 29.5 emu/g compared with 2.90 emu/g for parent RM without noticeable amount of magnetite. The yield of the magnetic fraction increases with increasing iron(II) dosage. The magnetite concentrate isolated from parent RM by the enrichment method with 10.5% Fetot extraction and with mass yield of this concentrate of only 6% has the highest value, 65.5 emu/g, with 34% Fe3O4 content almost similarly to that in MFRM. The particle aggregation is found to be the same in all samples and may not critically affect their magnetic properties. On the whole, we have demonstrated the feasibility of RM digestion for the recovery of alumina and synthesis of magnetite to improve the enrichment procedure, as well as the use of wastes as a technogenic feedstock.

A mechanism knowledge-driven method for identifying the pseudo dissolution hysteresis coefficient in the industrial aluminium electrolysis process

To overcome the difficulties that are associated with the online recognition of the alumina dissolution properties in industrial aluminium electrolysis cells, this paper proposes a method driven by process mechanism knowledge for the identification of a pseudo dissolution hysteresis coefficient (PDHC). The method explicitly represents the process semantemes that are implied in the normalized cell voltage (NCV) and the feed state using the proposed PDHC via process mechanism analysis and process semantic embedding. The PDHC quantifies the online dissolution performance of alumina and, thus, can overcome the inability to express the alumina online dissolution performance in industrial cells. Compared with slope-based methods, the PDHC-based method can not only realize the online recognition of the bath temperature but also detect an abnormal alumina concentration with a lead time of a few integrated feed periods (IFPs), thereby providing a new online basis for the temperature control and feed control of industrial cells. The PDHC identification is an application case of automatic knowledge acquisition in industrial aluminium electrolysis production.

Using Shungite in Water Defluoridation by Galvanocoagulation

Fluorine is a natural component of many sources of drinking water. An excess of fluorine in drinking water leads to metabolic disturbances in bone tissues. In this context, the International Drinking Water Quality Standards recommend adhering to a fluoride content of drinking water of no more than 1.5 mg/dm3. If this value is exceeded, water requires defluoridation. In this work, defluoridation by galvanocoagulation in a drum-type galvanocoagulator was studied. The half-cells of the galvanic couple were aluminum and shungite mined at the Polezhaevskii deposit, Karelia, Russia. The occurring electrochemical processes result in anodic dissolution of aluminum to form the corresponding hydroxides. The fluoride ion forms aluminofluoride complexes with them, which are adsorbed on freshly formed hydroxide flakes. The ratio between the half-cells of the galvanic couple as a significant factor of controlling the process efficiency was studied. It was shown that the fluoride ions were removed most completely at an aluminum : schungite ratio of 1 : 1.5. Experiments on model aqueous solutions of sodium fluoride detected a significant dependence of the process on the initial pH value. The experimental results enabled one to choose a mode of defluoridation of water with various fluoride contents. By the example of treatment of artesian water with a fluoride content of 9.1 mg/dm3 from Mashevka, Poltava oblast, Ukraine, a high efficiency of the studied process was demonstrated: the fluoride ion content of the water treated for 5 min decreased to 0.9 mg/dm3. In addition, when using shungite as a half-cell of the galvanic couple, its disinfecting effect was observed: whereas the initial content of coliform bacteria was 700 in 100 cm3, they were absent in the treated water. The redox potential was also reduced from 340 to 255 mV, which is noteworthy because this parameter has recently received considerable attention as being one of the most important parameters of water in its interaction with the human body.

Impact of Femtosecond Laser Treatment Accompanied with Anodization of Titanium Alloy on Fibroblast Cell Growth

Herein, Ti6Al4V alloy is surface modified by femtosecond laser ablation. The microstructure image obtained by secondary electron microscopy reveals a combination of micrometer spikes or cones superimposed by nanoripples (laser‐induced periodic surface structures). To make the surface hydrophilic, anodization is performed resulting in further smoothness of microstructure and a final thickness of 35 ± 4 nm is estimated for oxide produced after anodization at 10 V (scan rate = 0.1 V s−1) versus standard hydrogen electrode. The obtained electrochemically active surface area (ECSA) is approximately 8 times larger compared with flat mirror polished Ti6Al4V surface. Combined chemical analysis by Pourbaix diagram and X‐ray photoelectron spectroscopy (XPS) analyses reveal that titanium and aluminum are passivating into TiO2 and Al2O3, but the dissolution of aluminum in the form of solvated ion is inevitable. Finally, cell seeding experiments on anodized and laser‐treated titanium alloy samples show that the growth of murine fibroblast cells is significantly suppressed due to unique surface texture of the laser‐treated and anodized titanium alloy sample.

Tussilago Farfara Extract (TFE) as Green Corrosion Inhibitor for Aluminum in Hydrochloric Acid Solution

The dissolution of aluminum in 2 M HCl medium in the absence and presence of Tussilago Farfara Extract (TFE) was examined utilizing Tafel polarization (TP), electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM), gasometry and mass reduction techniques. The outcomes of these procedures illustrated that the inhibiting effect of this inhibitor depends on its concentration and chemical composition. The inhibitive impact of TFE illustrated the blocking of the Al surface by adsorption of its components through the reacted atoms contained in its molecules. The adsorption model was obeyed to Langmuir isotherm. The influence of temperature on the dissolution rate in the non-existence and existence of TFE was observed. Tafel polarization indicated that TFE acts as a mixed kind inhibitor. Impedance outcomes illustrated that the dissolution of Al is monitored by charge transfer mode at all concentrations of the extract. Varied surface examinations like XPS, FTIR, and AFM were checked to affirm the presence of the defensive film on the Al surface. All outcomes measured from all procedures are in perfect conformity.

Effect of acid concentration on the aluminum leaching process

This paper explains a study on microwave-assisted leaching of aluminum from peat clay. Microwave-assisted leaching was undertaken using the Iwaki Pyrex glass reactor in a modified microwave oven. A research was made of the effect of acid concentration, microwave power, temperature, and reaction time on the aluminum leaching recovery. The dominant presence of aluminous minerals determined leaching of aluminum values in hydrochloric acid medium at different concentration and microwave power. The optimum leaching ratio for 4 M hydrochloric acid concentration, 40 °C temperature, and 15 min reaction time was obtained 67% dan 46,6% for 100 W dan 80 W respectively. The microwave assisted leaching is more efficient about overall aluminum dissolution.

Innovative methodology for the utilization of low-grade pyrite cinder containing heavy metals via hydrothermal alkali melting followed by chlorination roasting

Low-grade pyrite cinder (LPyC) is a typical industrial solid waste from sulfuric acid production and is considered an important potential iron resource. This study investigated the utilization of LPyC containing heavy metals through hydrothermal alkali melting followed by chlorination roasting. Results indicated that the hydrothermal alkali melting showed a significant selectivity for the dissolution of silica, alumina and sulfur under optimum conditions (melting at 200 °C for 90 min, 30 wt% NaOH, and a liquid-to-solid ratio of 2:1). Chlorination roasting results indicated that the separation of heavy metals from iron can be realized under optimum conditions (roasting at 1100 °C for 90 min and 4% MgCl2). Moreover, the efficiency of volatilization (EV) of the heavy metals was found in following sequence: EVPb>EVZn>EVCu. After undergoing the entire process, the LPyC containing only 49.34% Fe was purified to about 60.12% with an acceptably low level of heavy metal impurities (0.05% copper, 0.07% lead and 0.11% zinc), and the Fe recovery of concentrate reached 89.65%. To reveal the mechanism of present process, the phase transformation, microstructure and basic thermodynamic evaluation of the process were researched by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy and HSC, respectively.

Effect of triisopropanolamine on chloride binding of cement paste with ground-granulated blast furnace slag

Chloride was one of important factors resulting in steel bar corrosion in reinforced concrete when using sea resources. In this paper, an attempt to promote the chloride binding capacity of the cement-ground-granulated blast furnace slag (GGBS) system was made by adding triisopropanolamine (TIPA). The paste was prepared by 70 wt% cement and 30 wt% GGBS, sodium chloride, TIPA (0.03%, 0.06% and 0.10%, by weight of binder) and water. The paste was cured for 7 d and 60 d, and the chloride binding ratio (CBR) were measured. The hydration heat and compressive strength were examined, then the hydrates and pore structure of the hardened paste were also analyzed; and the effect of TIPA on aluminum and ferric dissolution of GGBS was also studied. The results showed that TIPA could promote CBR at both 7 d and 60 d. The reason was ascribed to three aspects: (1) TIPA facilitate the formation of FS, which contribute to chemical binding; (2) TIPA promoted the formation of C-S(A)-H gel, which would increase the physical binding; (3) TIPA refined the pore structure and increased fractal dimension, which could enhance the migration resistance. Furthermore, TIPA promoted cement hydration and pozzolanic reaction of GGBS by facilitated the dissolution of aluminum and ferric in GGBS. Additionally, the formation of Friedel's salt was promoted due to the transformation of ettringite to AFm-like phase promoted by TIPA. Such results suggested a new way to improve chloride binding capacity of cementitious materials by adding alkanolamine.

Juglans Regia Extract (JRE) as Eco-Friendly Inhibitor for Aluminum Metal in Hydrochloric Acid Medium

The consumption impact of aluminum in the corrosive medium (2 M HCl) in the existence of JRE has been contemplated utilizing, electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM), potentiodynamic polarization (PP), mass loss and gasometry methods. The impact of EIS displayed the expansion in the polarization resistance (Rp) and the decline in the double layer capacitance (Cdl). Polarization demonstrated that JRE goes about as inhibitor of mixed-type. %IE has been seen as various with a concentration of Juglans Regia concentrate and temperature. The adsorption of JRE on the outside of Al from the damaging corrosive medium obeys Langmuir isotherm. All thermodynamic calculations of Al consumption were settled and talked about. The AFM examination of the Al surface indicated that the concentrate avoided consumption by adsorption on its surfaces and diminished the roughness. FTIR outcomes demonstrated the presence of many functional groups by which the adsorption process occurs. The XPS examination affirmed the arrangement of a defensive layer of JRE on the Al surface. Results got demonstrated great harmony which confirms the potential utilization of JRE to inhibit the dissolution of aluminum in the corrosive medium.

Improvement in chloride immobilization of cement-metakaolin system by triisopropanolamine

Metakaolin (MK) is a widely used admixture in chloride immobilization which is conducive to the durability of reinforced concrete. In this study, triisopropanolamine (TIPA) was added into cement-MK system to improve the chloride immobilization by expediting the pozzolanic reaction of MK. The effect of TIPA on hydration of binder composed of 90% Portland cement and 10% MK was investigated, and the hydration behavior was characterized by thermogravimetric analysis, X-ray diffraction, nuclear magnetic resonance spectroscopy, and mercury intrusion porosimetry, based on the evaluation of pozzolanic reaction of MK by ion dissolution. Results indicated that TIPA promoted the hydration of both MK and cement, and chloride immobilization was also improved. The mechanism for the improvement was involved in three aspects: a) TIPA facilitated the dissolution of aluminum from MK to obtain more chloroaluminate salts, strengthening chemical binding; b) TIPA accelerated hydration of cement and MK for more C-S-H gel, conducive to the physical adsorption; c) TIPA increased the amount of hydrates to refine the pore structure, hindering the migration of chloride ion. This investigation provided one new method for improving the pozzolanic reaction of MK to enhance chloride immobilization of cement-MK system.

Processing of Coal Fly Ash for the Extraction of Alumina Values

Coal fly ash is a lightweight incombustible particulate generated during coal combustion. Alumina content in the fly ash is present in the mullite phase, and its high stability calls for alternative processing for conversion to reactive phase before leaching. Mechanical activation with sodium hydroxide was found unsatisfactory for the breakdown of mullite structure, whereas the mullite phase dissociated to sodium silicate and sodium aluminosilicate during the sodium hydroxide thermal treatment. Below 400 °C, hydroxycancrinite is formed, which leads to alumina loss, whereas above 600 °C, it dissociates to sodium aluminate and sodium silicate, facilitating the alumina extraction. Aluminum hydroxide was recovered by acid leaching followed by precipitation and calcination at 1000 °C to obtain gamma-alumina. The aluminum dissolution increased by incorporating thermal treatment from 5 to 80% in muffle and 89.4% in microwave routes. The acid–base precipitation process resulted in the recovery of ~ 98% dissolved aluminum values in the boehmite phase, leaving the solution with less than 50 ppm Al content suitable for leaching application. Microwave processing was found to be a promising and alternative economical route for the alumina extraction from fly ash.

Toward adequate control of internal interfaces utilizing nitrile-based electrolytes.

Methods to control internal interfaces in lithium ion batteries often require sophisticated procedures to deposit coating layers or introduce interphases, which are typically difficult to apply. This particularly holds for protection from parasitic reactions at the current collector, which reflects an internal interface for the electrode composite material and the electrolyte. In this work, electrolyte formulations based on aliphatic cyclic nitriles, cyclopentane-1-carbonitrile and cyclohexane-1-carbonitrile, are introduced that allow for successful suppression of aluminum dissolution and control of internal interfaces under application-relevant conditions. Such nitrile-based electrolytes show higher intrinsic oxidative and thermal stabilities as well as similar capacity retentions in lithium nickel-manganese-cobalt oxide LiNi3/5Mn1/5Co1/5O2 (NMC622)||graphite based full cells compared to the state-of-the-art organic carbonate-based electrolytes, even when bis(trifluoro-methane)sulfonimide lithium salt is utilized. Moreover, the importance of relative permittivity, degree of ion dissociation, and viscosity of the applied electrolyte formulations for the protection of current collector interfaces is emphasized.

(Invited) A Combined Femtosecond Laser Treatment and Anodization Approach to Control Fibroblast Cell Growth on Titanium Alloys

Intra cardiac pace makers are an emerging technology. In case of revisions however they should not be found completely overgrown by fibroblasts. Titanium alloys which are used for their housings can be engineered. For this purpose the titanium alloy is surface treated by femtosecond laser ablation. The microstructure image obtained by secondary electron microscopy reveals a combination of micrometer spikes or cones superimposed by nanoripples or periodic nanoplate-like structure (LIPSS). To make the surface hydrophilic anodization was performed resulting in further smoothness of microstructure and a final thickness of 35±4 nm is estimated for oxide produced after anodization at 10 V vs. standard hydrogen electrode. The obtained electrochemical active surface area (ECSA) is approximately 8-9 times larger as compared to flat mirror polished titanium surface. Combined chemical analysis by Pourbaix diagram and (XPS) analysis reveal that titanium and aluminium are passivating into TiO2 and Al2O3 but the dissolution of aluminium in the form of solvated ion is inevitable. Finally, after exposing the anodized + laser treated titanium alloy sample to murine fibroblast environment, it is found that murine fibroblast cell growth is significantly restricted due to unique surface texture of the laser treated and anodized titanium alloy sample.

Effect of Laser Treatment and Hydrophobization on the Corrosion-Electrochemical Behavior of Aluminum

The effect of laser treatment of aluminum samples on the properties of the surface hydroxide oxide layer is studied. It is shown that treatment in air leads to an increase in the thickness of the oxide layer and the almost complete disappearance of hydroxide forms, which results in deterioration of the protective properties of this layer due to its higher defectiveness and porosity. It is found that the optimal treatment regime for aluminum, the surface of which is covered by an oxide layer with a significant fraction of hydroxides, is laser irradiation in an inert argon gas medium with small (1–2 vol %) oxygen content. Laser treatment leads to the formation of a protective surface layer that effectively inhibits the anodic dissolution of aluminum in a model corrosion medium, borate buffer solution at pH 7.4. It is shown that the initial hydroxide oxide film and the oxide film formed during laser treatment processing are hydrophilic, that is, they are well moistened with water. The surface treatment of aluminum in the initial state and after laser irradiation with a solution of vinyltriethoxysilane (VTES) leads to the formation of a hydrophobic adsorption layer and a significant decrease in the currents of anodic dissolution. Using X-ray photoelectron spectroscopy, it is shown that silane adsorption occurs both with the participation of silicon atoms and carbon atoms of an alkene bond. The hydrophobic layer of adsorbed silane on the laser-treated surface has a greater thickness and has a higher inhibiting effect on the anodic dissolution of aluminum than in the case of the initial aluminum surface.

Anodic dissolution of aluminum and anodic passivation in [EMIm]Cl-based ionic liquids

The anodic dissolution of aluminum in Lewis acidic ionic liquids consisting of AlCl3 and 1-ethyl-3-methylimidazolium chloride was studied using linear sweep and cyclic voltammetry, an electrochemical quartz crystal microbalance (EQCM) and chronopotentiometry at ambient temperature. Anodic passivation of the working electrode was observed in a 2:1 electrolyte while no passivation was found in a 1.5:1 electrolyte. Chronopotentiometry proves the passivation to be caused by local solidification of the electrolyte due to an increase in the aluminum concentration near the anode. EQCM data support these results.

Thermal Behavior of Pyrophyllite Ore during Calcination for Thermal Activation for Aluminum Extraction by Acid Leaching

AbstractIn the production of alumina (Al2O3) from clays by acid leaching, thermal activation by calcination is applied widely as a pre-treatment to improve the dissolution of aluminum. Previous studies have focused only on the thermal behavior of high-purity kaolinite and pyrophyllite, individually. However, thermal activation of complex clay ores containing several silicate minerals and their effect on aluminum extraction have not been studied. The purpose of the present study was to characterize the thermal behavior of a clay ore containing mainly pyrophyllite (Al2Si4O10(OH)2), kaolinite (Al2Si2O5(OH)4), muscovite (KAl2(AlSi3O10)(OH)2), quartz (SiO2), and kyanite (Al2SiO5) from the Pütürge clay deposits (Malatya, Turkey) for possible use in alumina (Al2O3) production by acid leaching. The ore and its calcination products obtained at various temperatures were characterized with respect to their mineral paragenesis, crystal structure, surface morphology, and thermal, calorimetric, and aluminum dissolution properties in order to understand the changes that occurred. Aluminum recovery in the leach solution increased in direct proportion to the dehydroxylation degree (Dtg) of the ore as the calcination temperature increased to 900°C. A maximum aluminum extraction of 90.57% was achieved by leaching of the product from calcination at 900°C. Aluminum extraction decreased sharply above that temperature, even though Dtg increased a little. By increasing the calcination temperature; the structures of pyrophyllite, kaolinite, and muscovite were destroyed by dehydroxylation, resulting in the exfoliation of the mineral layers, thus, a mixture of dehydroxylated phases formed. Depending mainly on the temperature range at which each of the dehydroxylated phases is durable, aluminum could be leached to some extent. The sharp decrease in the extraction of aluminum, iron, and potassium at higher temperatures was attributed to compaction of previously exfoliated layers of the minerals through re-crystallization to form mullite-like structures which seemed insensitive to acid attack during the leaching.