Aluminum Precipitation Research Articles

Alumina coating of polyvinylidene fluoride (PVDF) surface in liquid phase

A two-step procedure is developed for preparing alumina coated polyvinylidene fluoride particles (diameter, ∼100 μm) whose chemically inert and non-adhesive surface is initially grafted with polystyrene. The first coating step involves deposition of alumina precipitation centres into the polystyrene layer using the reaction of trimethylaluminium with a small residual amount of water retained within the porous brushy polystyrene structure after incomplete drying of the particles. The second coating step is performed through gentle precipitation of aluminium hydroxide from an aqueous aluminium chloride solution, with the alumina deposition being directed by the precipitation centres implanted during the first step. As a result of this process, the particles are covered uniformly with inorganic material. The quality and thickness of the final coating layer are controlled by the precipitation rate and stirring conditions.

Studies on separation and purification of fission 99Mo from neutron activated uranium aluminum alloy

A new method has been developed for separation and purification of fission 99Mo from neutron activated uranium–aluminum alloy. Alkali dissolution of the irradiated target (100mg) results in aluminum along with 99Mo and a few fission products passing into solution, while most of the fission products, activation products and uranium remain undissolved. Subsequent purification steps involve precipitation of aluminum as Al(OH)3, iodine as AgI/AgIO3 and molybdenum as Mo-α-benzoin oxime. Ruthenium is separated by volatilization as RuO4 and final purification of 99Mo was carried out using anion exchange method. The radiochemical yield of fission 99Mo was found to be >80% and the purity of the product was in conformity with the international pharmacopoeia standards.

Aluminum elution and precipitation in glass vials: effect of pH and buffer species

Inorganic extractables from glass vials may cause particle formation in the drug solution. In this study, the ability of eluting Al ion from borosilicate glass vials, and tendencies of precipitation containing Al were investigated using various pHs of phosphate, citrate, acetate and histidine buffer. Through heating, all of the buffers showed that Si and Al were eluted from glass vials in ratios almost the same as the composition of borosilicate glass, and the amounts of Al and Si from various buffer solutions at pH 7 were in the following order: citrate > phosphate > acetate > histidine. In addition, during storage after heating, the Al concentration at certain pHs of phosphate and acetate buffer solution decreased, suggesting the formation of particles containing Al. In citrate buffer, Al did not decrease in spite of the high elution amount. Considering that the solubility profile of aluminum oxide and the Al eluting profile of borosilicate glass were different, it is speculated that Al ion may be forced to leach into the buffer solution according to Si elution on the surface of glass vials. When Al ions were added to the buffer solutions, phosphate, acetate and histidine buffer showed a decrease of Al concentration during storage at a neutral range of pHs, indicating the formation of particles containing Al. In conclusion, it is suggested that phosphate buffer solution has higher possibility of forming particles containing Al than other buffer solutions.

Effect of iron/aluminum hydrolyzed precipitate layer on ultrafiltration membrane

In order to fully understand the effect of iron/aluminum hydrolyzed precipitate layer on ultrafiltration (UF) membrane, both hydrolyzed precipitate layers on a flat sheet UF membrane surface were investigated. The results showed that the aluminum hydrolyzed precipitate layer was much better than that of the iron hydrolyzed precipitate layer on protecting the UF membrane. X-ray diffraction (XRD) demonstrated that the structure of the aluminum precipitate layer was amorphous. Although the precipitate layer of aluminum sulfate hydrate could cause a slight flux decline, it improved the protection of the UF membrane to some extent. The rejection of different pollutants with Al precipitate layer was much higher than that without Al precipitate layer and many humic acid (HA)/bovine serum albumin (BSA) with different molecular weights could be adsorbed by the Al precipitate layer, especially for those with larger molecular weight. The rejection of 1:1 (by weight) HA/BSA mixture was higher than that of only HA or BSA in the presence of the precipitate layer of aluminum sulfate hydrate.

Enhanced settling of fine silica by direct AC electrocoagulation

Ground silica (d50, 20 μm) was treated as an aqueous suspension of 5·0 wt-% solids by alternating current electrocoagulation (AC/EC) in the direct mode. The initial settling rate increased linearly by 0·054 m h−1 per minute of AC/EC, with the maximum (>7·32 m h−1) occurring at t>120 min of AC/EC. Up to 75 min, floc size controlled the initial settling rate; at longer times, floc morphology took control.Aluminium released from the electrodes was adsorbed as it entered the pulp, and could be viewed as having been metered in continuously. Aluminium precipitation became prominent after ∼75 min of AC/EC time and was not deleterious to the enhancement of settling behaviour.Two years after its preparation, electrocoagulated silica was demonstrated to be an effective coagulant for as-received silica and oil sands fluid fine tailings.

Formation of the nanostructure in amorphous alloys of the Al-Ni-Y system

The formation of the amorphous-nanocrystalline structure during the crystallization of metallic glasses of the Al-Ni-Y system has been investigated by X-ray diffractometry, differential scanning calorimetry, and transmission electron microscopy. It has been shown that the crystallization onset temperature depends on the chemical composition of the alloy, and the crystallization is accompanied by changes in the structure of the amorphous phase, such as the phase separation and the formation of amorphous regions of various compositions with different short-range orders. The nanocrystals nucleate in the amorphous phase by the heterogeneous mechanism. It has been found that the size of precipitated aluminum nanocrystals depends on the alloy composition. The amorphous-nanocrystalline structure formed during the thermal treatment is stable and remains unchanged during the isothermal annealing at 150°C for 500 h.

Evaluation of trace metals bioavailability in Japanese river waters using DGT and a chemical equilibrium model

To develop efficient and effective methods of assessing and managing the risk posed by metals to aquatic life, it is important to determine the effects of water chemistry on the bioavailability of metals in surface water. In this study, we employed the diffusive gradients in thin-films (DGT) to determine the bioavailability of metals (Ni, Cu, Zn, and Pb) in Japanese water systems. The DGT results were compared with a chemical equilibrium model (WHAM 7.0) calculation to examine its robustness and utility to predict dynamic metal speciation. The DGT measurements showed that biologically available fractions of metals in the rivers impacted by mine drainage and metal industries were relatively high compared with those in urban rivers. Comparison between the DGT results and the model calculation indicated good agreement for Zn. The model calculation concentrations for Ni and Cu were higher than the DGT concentrations at most sites. As for Pb, the model calculation depended on whether the precipitated iron(III) hydroxide or precipitated aluminum(III) hydroxide was assumed to have an active surface. Our results suggest that the use of WHAM 7.0 combined with the DGT method can predict bioavailable concentrations of most metals (except for Pb) with reasonable accuracy.

Friction stir welded joints of Al–Li Alloys for aeronautical applications: butt-joints and tailor welded blanks

Structural design for safety critical components, as airframes, requires comprehensive characterization of the materials and joints properties. This characterization must take into account a large amount of variables required for accurate design to ensure structural integrity during the different phases of the product life cycle of an aircraft. One of the most important variables in this characterization is fatigue behavior due to the cyclic loads during the life of an airframe.The application of welding processes to replace riveted joints in aeronautical structures is an attractive option, since it allows joints with less stress concentration points and might be applied efficiently without overlapping the two joining parts (with a butt-joint configuration), reducing the joint weight. This weight reduction can have a small impact in production costs, but has a huge impact in the life cycle costs. Friction stir is the most appealing welding process in aeronautical structures since it has been shown to produce joints with excellent properties when applied to aluminum alloys and can deal with hardened precipitated aluminum alloys, since it is a semi-solid state process. Furthermore, this joining process allows to join dissimilar materials and plates with different thicknesses, creating in this way tailor welded blanks, which support the manufacturing of optimized panels by tailoring their strength in function of their needs.This article presents a mechanical characterization of friction stir welds of last generation aluminum–lithium alloys, including tailor welded blanks with different thicknesses, with potential applications in aeronautical and aerospace components. Mechanical characterization with crack initiation and fatigue crack growth tests were included in this study for an enhanced assessment of these alloys behavior, and was preceded by welding parameter calibration.

Rapid Alkalization in Lake Inawashiro, Fukushima, Japan: Implications for Future Changes in the Carbonate System of Terrestrial Waters

The global carbon cycle, one of the important biogeochemical cycles controlling the surface environment of the Earth, has been greatly affected by human activity. Anthropogenic nutrient loading from urban sewage and agricultural runoff has caused eutrophication of aquatic systems. The impact of this eutrophication and consequent photosynthetic activity on CO2 exchange between freshwater systems and the atmosphere is unclear. In this study, we focused on how nutrient loading to lakes affects their carbonate system. Here, we report results of surveys of lakes in Japan at different stages of eutrophication. Alkalization due to photosynthetic activity and decreases in PCO2 had occurred in eutrophic lakes (e.g., Lake Kasumigaura), whereas in an acidotrophic lake (Lake Inawashiro) that was impacted by volcanic hot springs, nutrient loading was changing the pH and carbon cycling. When the influence of volcanic activity was stronger in the past in Lake Inawashiro, precipitation of volcanic-derived iron and aluminum had removed nutrients by co-precipitation. During the last three decades, volcanic activity has weakened and the lake water has become alkalized. We inferred that this rapid alkalization did not result just from the reduction in acid inputs but was also strongly affected by increased photosynthetic activity during this period. Human activities affect many lakes in the world. These lakes may play an important part in the global carbon cycle through their influence on CO2 exchange between freshwater and the atmosphere. Biogeochemical changes and processes in these systems have important implications for future changes in aquatic carbonate systems on land.

Coagulant mixing revisited: theory and practice

Are rapid-mixing tanks with intense mixing necessary? Intense mixing applies to the coagulation mechanism of charge-neutralization of negatively-charged particles, but this is not a common coagulation method. More common is precipitation of aluminum or iron for coagulation of particles and natural organic matter, which is often called sweep-floc coagulation. Coagulation by precipitation is indifferent to mixing intensity. Energy and cost savings are realized by designing mixing systems for coagulation that do not use tanks with mechanical mixers. Systems examined are hydraulic methods (weirs, Venturi meters, others) including the non-mechanical systems of pipe and open-channel static mixers. These systems provide sufficient mixing intensity for sweep-floc coagulation and for certain conditions provide sufficient mixing intensity for charge-neutralization coagulation with much less energy input. Mixing systems designed specifically for coagulant addition, such as rapid-mixing tanks and pipe and open-channel static mixers, should be sized based on the average daily flow not on the plant capacity flow. This produces sustainable designs with lower capital costs for all systems and lower operating costs for rapid-mixing tanks.

Aluminum Removal from Leach Liquor of Nitric Acid Pressure Leaching Laterite Ores

In this paper, the removal of aluminum in leach liquor of nitric acid pressure leaching laterite was investigated, and a new method of aluminum removal by precipitation with calcium sulphide was presented. The effect of reaction temperature, pH value before ageing and ageing time on the removal of aluminum were examined in details. The optimum conditions were determined as follows: reaction temperature 40 °C, pH 3.9~4.1 (before aging) and aging time 30 min. Compared with the traditional precipitation method, the loss of nickel and cobalt was less than 1% in the obtained aluminum precipitate slag, which is 3% lower than that by the traditional method; the filtration rate of aluminum precipitate slurry was faster than the traditional method, when the filtration press was controlled at -0.04 MPa, the filtration rate of aluminum precipitate slurry could reach 0.109 m3/(h•m2), which is 6.5 times higher than that obtained by the traditional method.

Effects of Er and Zr additions on precipitation and recrystallization of pure aluminum

The effects of Er and Zr on the precipitation and recrystallization of pure aluminum were investigated using hardness testing, optical microscopy and transmission electron microscopy. The results show that the recrystallization temperature of the Al–0.2Er–0.2Zr (wt.%) alloy is about 450 °C, which is significantly higher than that of Al–0.2Er (wt.%) alloy (350 °C), owing to the presence of nanosized and coherent Al3 (Er, Zr) precipitates. The synergetic effects of Er and Zr on the precipitates and recrystallization resistance of Al–Er–Zr alloys are discussed.

Treatment of Spent Pot-lining with Aluminum Anodizing Wastewaters: Selective Precipitation of Aluminum and Fluoride as an Aluminum Hydroxyfluoride Hydrate Product

Wastewaters generated by the aluminum anodizing industry have been identified as a source of acid, Al3+, and caustic values that could be used for the treatment of spent pot-lining (SPL) generated in primary aluminum smelting. In this paper, recovery of aluminum and fluoride values as an aluminum fluoride product that could be converted into smelter grade (SG) AlF3 for recycling in aluminum smelting is reported. Experimental observations were contrasted with a thermodynamic model of the solution equilibria and new values for the solubility product of AlF2OH·1.4H2O, 10–15 at 30 °C and 10–23.8 at 50 °C, are reported. Neutralization of leachates obtained from SPL treatment with aluminum anodizing acid wastewaters was performed using 2 M NaOH and, alternatively, waste caustic solutions from the aluminum anodizing industry. pH-static precipitation with 2 M NaOH successfully recovered 92 wt % of the solubilized fluoride as AlF2OH·1.4H2O at pH 4.0 and 70 °C, although a hydrolyzed Na5Al3F14-like product (3–5 wt % Na) coprecipitated. Seeded heterogeneous nucleation of AlF2OH·1.4H2O on SG Al(OH)3 yielded a product that could be acceptable to AlF3 manufacturers, meeting specifications for particle size and phosphorus and silicon content. Caustic wastewaters from the aluminum anodizing industry were identified as suitable to provide the caustic values required for precipitation, providing that Al concentration is decreased by aging the solutions under seeded conditions. The use of caustic waste from the aluminum anodizing industry to treat the SPL leachates obtained with acidic anodizing waste totally removes the need of chemical reagents for SPL treatment and fluoride recovery.

Electrochemical dosing of iron and aluminum in continuous processes: A key step to explain electro-coagulation processes

The aim of this work is to study the main differences between aluminum and iron production during electrochemical coagulation processes, attending not only to the coagulant dosage, but also to the characteristics of the coagulants produced. To do this, the influence of both pH and current density have been studied. It has been observed that there is a super-faradaic production of aluminum because of a promoted corrosion at the alkaline pHs produced on the cathode surface. This efficiency decreases for high values of current density because of cathodic protection processes. On the contrary, for iron electrodes, it does not exist a super-faradaic dissolution within the range of current densities studied but simply a decrease in the efficiency for alkaline pH values and high current densities, because of the formation of Fe3+ instead of Fe2+ during the electro-dissolution process. With respect to speciation, it has been observed the formation of monomeric species at acidic pHs and precipitate species for pHs above 5. In addition, for aluminum, monomeric species are also the primary species for pHs above 9 and some polymeric species are formed at pHs between 4 and 6. The superficial charge of both metal precipitates is very similar. For pHs below 9, both aluminum and iron precipitates have a positive charge due to the adsorption of monomeric soluble hydroxometals positively charged or protons on the precipitate surface. For pHs above 9 the aluminum precipitate is negatively charged due to the adsorption of soluble hydroxometal species negatively charged or hydroxyl ions on the precipitate surface. On the contrary, iron precipitate does not have a superficial charge for alkaline pH, because there is almost no formation of soluble negatively-charged species.

Application of physical–chemical and biological–chemical methods for heavy metals removal from acid mine drainage

Acid mine drainage (AMD) represents a serious environmental problem related to sulfide minerals and coal mining. High content of toxic metals and high acidity in AMD adversely affects surface water, groundwater and soil. The abandoned mine of the Smolník deposit in Slovakia is a typical example in this respect. The quality of AMD needs to be monitored and suitable treatment methods need to be developed.The aim of this paper was to demonstrate the technical feasibility of heavy metals removal from AMD using physical–chemical and biological–chemical methods. The base of the physical–chemical method was electrowinning. The principle of the biological–chemical method was the selective sequential precipitation (SSP) of metals with the application of hydrogen sulfide produced by sulfate-reducing bacteria and sodium hydroxide solution. Both the electrowinning and SSP processes decrease the content of heavy metals in AMD. The pre-treatment of AMD by chemical iron–aluminum precipitation (in the case of electrowinning tests) and chemical iron precipitation (in the case of SSP tests) improved the selectivity of the processes. A further aim of the work was the improvement of the SSP.During the electrochemical experiments, 99% Zn removal – under metallic form – and 94% Mn removal – under MnO2 form – both with a high degree of purity, were achieved. The SSP process reached the selective precipitation of chosen metals with 99% efficiency – Fe, Al and Mn in the form of metal hydroxides, Cu and Zn as metal sulfides. The results achieved may be used for designing a process appropriate for the selective recovery of metals from the AMD discharged from the Smolník deposit.

Monodispersity and stability: case of ultrafine aluminium nanoparticles (<5 nm) synthesized by the solvated metal atom dispersion approach

The synthesis of THF coordinated aluminium nanoparticles by the solvated metal atom dispersion (SMAD) method is described. These colloids are not stable with respect to precipitation of aluminium nanoparticles. The precipitated aluminium nanopowder is highly pyrophoric. Highly monodisperse colloidal aluminium nanoparticles (3.1 ± 0.6 nm) stabilized by a capping agent, hexadecyl amine (HDA), have also been prepared by the SMAD method. They are stable towards precipitation of particles for more than a week. The Al–HDA nanoparticles are not as pyrophoric as the Al–THF samples. Particles synthesized in this manner were characterized by high-resolution electron microscopy and powder X-ray diffraction. Annealing of the Al–HDA nanoparticles resulted in carbonization of the capping agent on the surface of the particles which imparts air stability to them. Carbonization of the capping agent was established using Raman spectroscopy and TEM. The annealed aluminium nanoparticles were found to be stable even upon their exposure to air for over a month which was evident from the powder XRD, TGA/DSC, and TEM studies. The successful passivation was further confirmed with the determination of high active aluminium content (95 wt%) upon exposure and storage under air.

A method for Ca, Fe, Ga, Na, Si and Zn determination in alumina by inductively coupled plasma optical emission spectrometry after aluminum precipitation

In this present work a method for the determination of Ca, Fe, Ga, Na, Si and Zn in alumina (Al 2O 3) by inductively coupled plasma optical emission spectrometry (ICP OES) with axial viewing is presented. Preliminary studies revealed intense aluminum spectral interference over the majority of elements and reaction between aluminum and quartz to form aluminosilicate, reducing drastically the lifetime of the torch. To overcome these problems alumina samples (250 mg) were dissolved with 5 mL HCl + 1.5 mL H 2SO 4 + 1.5 mL H 2O in a microwave oven. After complete dissolution the volume was completed to 20 mL and aluminum was precipitated as Al(OH) 3 with NH 3 (by bubbling NH 3 into the solution up to a pH ~ 8, for 10 min). The use of internal standards (Fe/Be, Ga/Dy, Zn/In and Na/Sc) was essential to obtain precise and accurate results. The reliability of the proposed method was checked by analysis of alumina certified reference material (Alumina Reduction Grade-699, NIST). The found concentrations (0.037% w w −1 CaO, 0.013% w w −1 Fe 2O 3, 0.012% w w −1 Ga 2O 3, 0.49% w w −1 Na 2O, 0.014% w w −1 SiO 2 and 0.013% w w −1 ZnO) presented no statistical differences compared to the certified values at a 95% confidence level.

Control of thickness and morphology of thin alumina films deposited via Pulsed Chemical Vapor Deposition (Pulsed CVD) through variation of purge times

Thin alumina films were deposited onto graphitic carbon fibers at 77 °C by gas phase exposure to sequential pulses of trimethylaluminum and water vapor, each pulse being separated from the subsequent one by a purging pulse of nitrogen gas. By varying the duration of the purging pulse, one can tune the morphology of the deposited film from a gas phase precipitation reaction to deposition controlled by surface saturation. A purge time of 15 s leads to non-uniform and non-conformal films, the fibers at the perimeter of the bundle were coated with a thicker film compared to the fibers inside the bundle. The film deposition rate inside the bundle was about 0.83 nm/cycle, which is much higher than a single alumina monolayer per cycle. This indicates a significant precipitation of alumina from gas phase reactions onto the carbon fibers. With increasing purge time, homogeneity and conformality of the film improved and the variation of thickness from perimeter to inside the bundle decreased significantly. At 30 s purge time, the films were already smooth and conformal, as expected for a deposition controlled by surface saturation, and the deposition rate was 0.34 nm/cycle. Further increase of purge time up to 100 s, did not change the morphology significantly, and led to a deposition rate of 0.27 nm/cycle which is less than expected for a monolayer. Experiments conducted at increased pumping speed gave essentially the same results. The deposition rate observed here in the mode of deposition controlled by surface saturation is higher than commonly reported for Atomic Layer Deposition (which usually is conducted at higher temperatures). Increasing the deposition temperature led to deposition rates in accordance with the values reported for Atomic Layer Deposition.

Recycling of aluminum and caustic soda solution from waste effluents generated during the cleaning of the extruder matrixes of the aluminum industry

Anodising industries use a concentrated caustic soda solution to remove aluminum from extruder matrixes. This procedure produces very alkaline effluents containing high amounts of aluminum. The work reported here was focussed on recycling aluminum, as aluminum hydroxide, from these effluents and regenerating an alkaline sodium hydroxide solution. Briefly, the method comprises a dilution step (necessary for reducing the viscosity of the effluent and allowing the subsequent filtration) followed by a filtration to eliminate a substantial amount of the insoluble iron. Then, sulphuric acid was added to neutralize the waste solution down to pH 12 and induce aluminum precipitation. The purity of the aluminum salt was improved after washing the precipitate with deionised water. The characterization of the solid recovered, performed by thermogravimetric analysis, Fourier transform infrared spectroscopy and X-ray diffraction, indicated characteristics typical of bayerite. The proposal method allowed recovering 82% of the aluminum present in the wastewater with high purity (99.5%). Additionally, a sufficiently concentrated caustic soda solution was also recovered, which can be reused in the anodising industries. This procedure can be easily implemented and ensures economy by recycling reagents (concentrated caustic soda solution) and by recovering commercial by-products (aluminum hydroxide), while avoiding environmental pollution.

Porous Alumina Ceramics Prepared by the Hydrolysis-Assisted Solidification Method

We used the hydrolysis-assisted solidification (HAS) process to form the alumina green bodies from the suspensions. A total of 2.5 wt% of AlN powder, with respect to the solids content, was added to an aqueous alumina suspension containing 53.5 vol% of solids. During the hydrolysis of the AlN powder, the aluminum hydroxide reaction product precipitated on the surface of the alumina particles. The effect of the precipitated aluminum hydroxide on the density and the bending strength, after sintering the alumina samples prepared by the HAS process at temperatures up to 1300°C, was investigated. In comparison with conventionally formed samples, a similar strength was measured at a lower sintered density for the partially sintered alumina prepared by the HAS process. These improved properties could be ascribed to the formation of aluminum hydroxide in the form of boehmite lamellas on the surface of the particles during the HAS consolidation process. Boehmite lamellas topotactically transform with temperature into various transition aluminas; however, the change in the crystal structure did not affect the morphology, which remained the same up to 1100°C. These lamellas hindered the densification of the samples up to 1100°C, but at higher temperatures, the lamellas transformed into nanosized α-alumina particles, which enhanced the neck growth, resulting in a very high measured flexural strength at sintered densities up to 70%.