Residual Aluminum Research Articles

Residual Aluminium in Water Intended for Human Consumption

Aluminium is one of the environmental factors that may have an impact on Alzheimer’s and Parkinson’s disease. Some epidemiological studies show a relationship between the concentration of aluminium in drinking water and the incidence of Alzheimer’s disease. The article presents and discusses the results of research on the effect of the type and dose of non-prehydrolyzed aluminium coagulants on the concentration of residual aluminium in water intended for human consumption. Aluminium sulphate (VI) and sodium aluminate were tested as coagulants. Analysis of the obtained test results showed that lower concentrations of residual aluminium were found after coagulation with aluminium sulphate (VI), which is hydrolyzed acidally, lowering the pH of the water in the range of 7.47 to 7.12 providing good conditions for the formation of Al(OH)<sub>3</sub>. A less useful coagulant due to the concentration of residual aluminium was sodium aluminate, which undergoes basic hydrolysis creating conditions for the transition of Al(OH)<sub>3</sub> into soluble Al(OH)<sub>4</sub><sup>−</sup>.

Treatment of aluminum and fluoride during hydrochloric acid leaching of lepidolite

A two stage hydrochloric acid leaching process is proposed for the treatment of lepidolite and recovery of alkali metals. The separation characteristics of aluminum and fluoride in the leachate were also determined. The transformation of lepidolite into silica-like residue was tentatively identified through X-ray diffraction measurements. The leach liquor was heated and concentrated and by evaporation to drive off to remove some of the hydrogen chloride and hydrogen fluoride from the acidic leachate, followed by cooling to deposit crystals. This yielded an overall hydrogen chloride and hydrogen fluoride removal of 25.4% and 2.52%, respectively. The main components of the crystals were aluminum and potassium chlorides, with small amounts of fluoroaluminate, polyaluminum chloride, and aluminum hydroxyfluoride. The crystals were calcined at 623 K, with a further 43.9% of hydrogen chloride and 4.33% of hydrogen fluoride being driven off and captured by adsorption equipment, which was beneficial for the subsequent separation of impurities. Investigation of the major mineral phases revealed that lower temperature calcination of the crystals tended to produce less-soluble polyaluminum chloride, aluminum hydroxyfluoride, fluoaluminate, and alumina. Water leaching of crystals after calcination at 623 K gave a leach liquor with 7.74 g/L of lithium, 0.15 g/L of aluminum and 0.25 g/L of fluoride. The fluoaluminate in the leach liquor led to the production of secondary precipitates after neutralization. The [AlFn]3-n species were partially dissociated to F− and Al(OH)4− at a strongly basic pH. The residual aluminum and fluoride concentrations were 0.01 g/L and 0.05 g/L, respectively, at the pH of 9. Since alkali chlorides such as lithium chloride are very soluble, there was less lithium loss during neutralization than in the corresponding sulfate system.

Removal of natural organic matter and ammonia from dam water by enhanced coagulation combined with adsorption on powdered composite nano-adsorbent

Abstract Enhanced coagulation and adsorption were investigated in separate and combined processes to alleviate problems created by high levels of NOM (15 mg L−1) and ammonia (2.5 mg L−1 NH4-N) in dam water. Raw water acidification to pH 6.2 with optimised enhanced coagulation in jar tests achieved effective (68%) DOC reduction and satisfactory residual turbidity, aluminium, and colour, however removed only 5% ammonia. Adsorption on the nano-adsorbent (termed ACZ) led to 45% DOC reduction and excellent 58% ammonia removal in 30 min. Concurrent enhanced coagulation and complementary adsorption using only 80 mg L−1 alum and 150 mg L−1 ACZ doses showed high performance with 76% ammonia, 90% DOC, and 95% trihalomethanes formation potential (THMFP) reduction in 20 min time. Concurrent treatment can be simply implemented utilising readily available rapid mixers and flocculators, and operated on demand. Pre-adsorption and consecutive enhanced coagulation using the same alum and ACZ doses resulted in slightly better DOC but reduced (61%) ammonia removal. The results showed that concurrent treatment could safely resolve a challenging operational problem. ACZ combines the distinct advantages of zeolite and activated carbon in a single product, and may find additional uses in removing taste and odour, heavy metals, and synthetic organic matter from ground and surface waters.

Comparison and optimization of the performance of natural-based non-conventional coagulants in a water treatment plant

Abstract This study aims to assess the efficiency of two natural-based coagulants, namely calcium lactate and tannic acid, and compare them with conventional coagulants, including polyaluminium chloride (PACl) and ferric chloride. Jar test experiments were performed on the raw inlet water of the Isfahan water treatment plant (IWTP) in Iran. Response surface methodology was implemented to design and optimize the experiments. The factors considered in the design were coagulant dose, pH, initial turbidity, and temperature. Results showed the acceptable efficiency of natural coagulants in turbidity reduction, so that they meet the potable standard levels. The final water turbidity in the optimum condition for calcium lactate, tannic acid, PACl, and ferric chloride were 0.58, 0.63, 0.56, and 0.76 NTU, respectively. The comparison between the performances of the coagulants showed no significant difference in turbidity removal. However, the sludge volume produced as well as the impact on pH alteration after coagulation–flocculation were lower when using natural coagulants than with conventional coagulants. Also, the residual aluminum for PACl measured was higher than the desired limit according to Iran's drinking water standard. Finally, the simple additive weighting method was used to rank the four coagulants based on the selected criteria. The results showed that the natural coagulants could be preferable to the conventional coagulants if the concerns regarding disinfection by-product formation due to their residual organics were resolved. Since this issue was fixed in the IWTP due to the ozonation process, calcium lactate was proposed as an efficient alternative to PACl.

Optimization of ceramic foam fabrication for removal of aluminium ion from aqueous solutions

Residual aluminium ion in water after the coagulation step in water and wastewater treatment units is a health issue that requires an effective solution. A kind of ceramic foam is developed that can be utilized to remove aluminium ions from water. Ceramic material was coated in slurry form over polyurethane sponge that is used as a structure. Full factorial experiments were performed to study the effects of polymeric sponge number, number of immersions in the slurry, sintering temperature, and soaking time on ceramic foam properties. Fabrication conditions are modeled and adjusted such that the optimum ceramic foam attained good adsorption capacity while having necessary compression strength to be used as packing. The optimum ceramic foam was obtained to be a 20 sponge number with four times immersions in slurry and the sintering occurred at 860 °C in 135 min. Characterizations of optimum ceramic foam were performed by SEM imaging and measuring specific surface area, porosity, density, and determining adsorption isotherm. The maximum measured adsorption capacity of ceramic foam at 25 °C was 3.0639 mgg−1. Regeneration tests were performed using a 0.001 M HCl solution. It is observed that 76 % of adsorption capacity can be maintained by the first cycle, and after ten times of the adsorption/desorption cycles, this value reaches to 19.7 %.

Solvent refining of silicon for solar cells – some practical aspects

Solvent refinement has been suggested as an energy- and cost-efficient process to produce high purity silicon for photovoltaic solar cells. In this process, metallurgical grade silicon is dissolved in a liquid metal e.g. Al at high temperature. High purity silicon crystals can then be precipitated by decreasing the temperature and extracted from the melt. Residual aluminium is then removed by leaching, and after remelting and directional solidification, the purified silicon can be used as silicon for solar cells.Metallurgical grade silicon (99 wt%Si) with iron as the main impurity has been dissolved to 40 wt% in liquid aluminium at 1000 °C. Silicon crystals have been extracted slightly above the eutectic temperature. The crystals have then been leached in 10% hydrochloric acid at room temperature. Silicon crystal have been sorted into three size fraction which have been melted separately and thereafter analyzed by light optical- and electron microscopy with EDS analysis. After leaching, extracted material has been remelted together with silicon oxide in order to oxidize residual aluminium.The extracted material contains significant amounts of residual Al-Si eutectic. The aluminium has not been removed completely by the leaching and insoluble metal rich intermetallic compounds have been found in the smallest size fraction. The residual aluminium can be further reduced by oxidation by silicon oxide and sedimentation of the aluminium oxide.

Effect of Organic Fluoride on Combustion Performance of HTPB Propellants with Different Aluminum Content

ABSTRACT Aluminum is an important contributor to energy of solid propellants. Completeness of aluminum combustion has key effect on the release of energy. In this paper, hydroxyl-terminated polybutadiene (HTPB) based propellants with aluminum content from 16% to 24% were prepared with a kind of organic fluoride (OF). Meanwhile, propellants without OF were also prepared as a comparison. The theoretical specific impulse and the heat of explosion of these propellants were calculated and measured, respectively. The particle size, morphology and elemental composition of the condensed combustion products for these propellants were characterized by laser measurement of particle size, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The burning rates of propellants were tested by CCD line-scanning camera and a high-pressure chamber measurement system. The high-speed photographic system was used to study the agglomeration process of the melting aluminum particles on the propellant burning surface. The results indicate that with increasing aluminum content, both the theoretical specific impulse and the measured heat of explosion show a trend of increasing until an aluminum content of 20%. The large particle size and residual active aluminum in the condensed combustion products increase with increasing aluminum content in the propellants, but decrease significantly after addition of OF. Under the same pressure, the burning rates of the blank and OF propellants decrease with increasing aluminum content, but the burning rates of OF propellants are slightly higher than those of the blank propellants. For the propellants with OF, the melting aluminum particle on the burning surface is less agglomerated and brighter, meaning more complete aluminum combustion.

Effects of aluminum on the expansion and microstructure of alkali-activated MSWI fly ash-based pastes

Alkaline activation is of great potential in the solidification of municipal solid waste incineration (MSWI) fly ash, but the metallic aluminum in the ash inhibits its application. This work studies the effects of residual metallic aluminum on the expansion and microstructure of alkali-activated MSWI fly ash-based pastes. Based on the results obtained, an optimized preparation process is suggested. Characterizations of the pastes include expansion ratio, morphology (SEM), mechanical strength and microstructure (XRD and FTIR). It is confirmed that MSWI fly ash could be solidified through alkaline activation when using a small amount of coal fly ash to adjust the reactive silica and aluminum ratios. In the optimized preparation, sodium hydroxide was added separately, so that expansion in the pastes was significantly mitigated, the formation of geopolymer gel was improved and the compressive strength of the pastes increased.

The effects of photodynamically activated curcumin on the preservation of low alum treated ready-to-eat jellyfish

Residual aluminum in jellyfish is largely due to the use of alum as a firming agent. Simply lowering the usage of alum during jellyfish dehydration may not only affect its texture, but also increase its susceptibility to foodborne pathogens and spoilage bacteria. In this study, the antibacterial effects of curcumin-mediated photodynamic treatment on jellyfish were investigated. The ready-to-eat flame jellyfish was dehydrated by brine prepared by a NaCl salt containing 3.5% alum followed by curcumin-mediated photodynamic treatment. The jellyfish samples were analysed for total bacterial count; aluminum residuals; total volatile basic nitrogen content; proximate composition (water, lipid, protein, carbohydrates, and ash contents); texture (hardness, cohesiveness, springiness, chewiness) and sensory quality (texture, colour, odour and overall acceptability). The data showed that decreasing alum usage significantly lowered the residual aluminum compared to jellyfish dehydrated by brine prepared by salt mix containing 10% alum. In addition, photo-irradiating the jellyfish with curcumin at 50 μM by blue LED light (16 mW/cm2) for 15 min presented desirable preserving effects. Moreover, jellyfish after this antimicrobial photodynamic treatment also showed acceptable sensory scores. Together, these findings suggest that photodynamic treatment is a promising method suitable to be used for the preservation of low-alum treated ready-to-eat jellyfish.

Fluoride removal from water by composite Al/Fe/Si/Mg pre-polymerized coagulants: Characterization and application

Fluoride, an anionic pollutant, is possibly to be found in excessive concentrations especially in groundwaters and can show detrimental effects on human health, in concentrations higher than the commonly applied legislation limit of 1.5 mg/L The most commonly applied method for water de-fluoridation is performed by Al-based coagulants, which however presents some important limitations, such as the applied relatively high dosage, producing rather excessive amounts of chemical sludge. In this study, the use of novel pre-polymerized Al-based coagulants was examined, regarding their efficiency towards fluoride removal, as compared with the conventionally applied AlCl3. The novel coagulants were characterized by measuring the main physico-chemical properties, the aluminum species distribution, the zeta potential, the particles' size distribution and the produced flocs’ sizes. The results showed that the Mg-containing coagulant (PSiFAC-Mg30-10-15) was the most efficient, when applied in pH values relevant to fluoride-containing groundwaters; it was also the only coagulant, which increases its efficiency at pH values > 7. The uptake capacity of coagulants, regarding fluoride, to reach the residual/equilibrium concentration limit of 1.5 mg F/L (Q1.5-value) at the pH value 7.0 ± 0.1 were found 170, 134 and 94 mg F/g Al for the cases of PSiFAC-Mg30-10-15, AlCl3·6H2O and PSiFAC-Na1.5-10-15, respectively. Accordingly, at the pH value 7.8 ± 0.2 the Q1.5-values were found 189, 118 and 41 mg F/g Al for the same coagulants; whereas considering the residual aluminum concentration this was ranged at 15 ± 5, 25 ± 5 and 30 ± 5 μg Al/L, respectively. In addition, (beneficial) increase of residual magnesium concentration, when applying the coagulant PSiFAC-Mg30-10-15 was 15 ± 5 mg/L.

Effectiveness of chitosan as a natural coagulant in treating turbid waters

Aluminum, Lime and iron coagulants are commonly used in most industries for many decades to coagulate particles in surface water also removing turbidity from the water prior to flocculation, sedimentation or filtration. Although effective, inorganic coagulants have several disadvantages, there has been a concern about the relation between aluminum residuals in treated water and Alzheimer disease and toxic effects of metallic coagulants on the aquatic environment. Hence nowadays, there has been great attention in the improvement of natural coagulants in treated water such as chitosan; chitosan is a natural linear cellulose-like copolymer of glucosamine and N-acetyl-glucosamine widely distributed in nature. The present study was aimed to investigate the effects of chitosan on the removal of suspended solids (bentonite clay) from water. A series of batch flocculation tests with chitosan under different conditions was conducted. The results indicate that chitosan is a potent coagulant for bentonite suspension. Coagulation of chitosan showed efficiency of 96.9%. The coagulant performed well at concentration of 1g chitosan/100 ml water at PH=6.

Separation of Refined Silicon from Al-Si Alloys by Air Pressure Filtration

The separation of refined silicon from Al-Si alloys through a solvent refining process was studied. Purified silicon particles were separated by air pressure filtration using stainless steel sieves as the filtration media. After the efficient removal of impurities in the refining process, the effects of the mesh number (N), separation temperature (T), silicon content in the alloy (ω(a)), and pressure differential (p) on the separation efficiency were evaluated. At N = 80, T = 873 K (600 °C), ω(a) = 45 wt pct and p = 0.25 MPa, the recovery rate of refined silicon was 98.2 pct, and the residual aluminum in the separated silicon was less than 8 wt pct. The separation process was efficient when N = 60 to 150. It was advisable for the separation temperature to approach the eutectic temperature. Efficient filtration could be achieved when ω(a) = 35 to 55 wt pct. The filtration efficiency was improved with a higher pressure differential, and the separation was efficient at p ≥ 0.10 MPa. The results show that air pressure filtration is a promising method to separate refined silicon.

A novel process for the selective precipitation of valuable metals from lepidolite

The treatment of lepidolite by a multistage leaching process was studied for the extraction of alkali metals as alkali alums and brines. The precipitation characteristics of the aluminum and fluorine in the solution were also investigated. The transformation of the mineralogical species in lepidolite into albite and silicon dioxide was tentatively identified by X-ray diffraction measurements. The crystallization was aimed at the separation of rubidium and cesium from an acidic solution containing potassium as the main contaminant. The alum mixture contained on average 7.5% potassium, 1.3% rubidium and 0.30% cesium. The main crystalline components were aluminum sulfate and AlF(SO4)·5H2O after concentration. The aluminum in the solution was removed by adding potassium sulfate with a K/Al mole ratio of 2 at various pHs to yield an overall aluminum precipitation of 62.1–66.6%. Under weakly acidic and neutral conditions, soluble aluminum may transform into insoluble aluminum, such as Al(OH)3. Additionally, soluble AlFx(3−x)+ species tended to precipitate directly with OH−, thereby achieving the formation of Al-OH-F complexes. The AlFx(3−x)+ species at high pH were partially dissociated into F− and AlOH2+, Al(OH)2+ and Al(OH)4−, and the buffering effect of F− inhibited the transformation of the precipitated Al(OH)3 into soluble aluminates due to the formation of Al-OH-F complexes. The residual aluminum and fluorine contents were on average 0.0065 g/L and 0.042 g/L, respectively, in the mother liquor after neutralization at pH 9. The loss of lithium increased from 1.1% to 5.4% as the pH increased from 5 to 9. These findings imply that aluminum and fluorine can play significant roles in the recovery of alkali metals from lepidolite, and the precipitation of aluminum from leaching solutions as alums can cause a loss of lithium.

The effects of silicon substrate thickness and annealing temperature on surface coverage for aluminum-induced crystallization of germanium films

This work investigates polycrystalline germanium films for photovoltaic applications that were developed using aluminum-induced crystallization on silicon substrates coated with 500 nm of thermally grown silicon dioxide. Five silicon substrate thicknesses were investigated between 200 and 525 µm and the samples were annealed for 50 hours at either 365 °C, 375 °C, or 385 °C. When annealed, the amorphous germanium films deposited on the 200 µm silicon substrate developed into discrete monocrystalline germanium islands with an average grain size of 10.76 µm, but poor overall surface coverage between 50% and 59%. The germanium films deposited on silicon substrates with thickness between 250 and 375 µm and annealed below 385 °C revealed the highest and most uniform polycrystalline germanium surface coverage between 80% and 97% and demonstrated ~300 nm grain size. The 525 µm silicon substrate exhibited dense island formation at 385 °C as well as high residual aluminum content, and cracks in the film at lower temperatures.

Optimization of conventional treatment of the surface water treatment plant of the city of Khenifra

Treatment of the surface water of the city of Khenifra combines a conventional treatment and a membrane process unit (reverse osmosis). The conventional treatment in question uses an aluminium base reagentin the form of Aluminum sulphate that may cause leaks of Aluminum called "residual Aluminum" in the filtered water. The objective of this work is to study the elimination of residual aluminum, resulting from the conventional treatment, for a better operation of the demineralization unit by Reverse Osmosis, located downstream. Indeed, according to the requirements of the supplier of the membranes, the residual aluminum content should not exceed 0.05mg/L. The jar test remains the most used test, at the level of the laboratories, which allows optimizing the doses of treatment reagents to be used in a treatment plant; particularly the aluminum sulfate coagulant. Trials of the jar test were performed and had been optimized by the application of Doehlert experimental design.The effectiveness of the treatment and the optimum conditions through the stages of treatment are achieved by monitoring the parameters: pH, turbidity and residual aluminum.

Production of ferroboron by using redesigned ESR process called electroslag melting for alloying by reductions (ESMAR)

Ferroboron is produced economically for decades by the carbothermic process. However, the carbon content of ferroboron, is above 0.5% as a result of the carbothermic process, which adversely affects the properties of permanent magnets. On the other hand, the requirement of aluminium for reduction of iron ore in the aluminothermic process increases the production costs. In this study, ESR process was redesigned for the production of ferroboron to take advantages of the process. In this study, a new process was developed with the name of Electroslag Melting for Alloying by Reduction (ESMAR) by using the advantages of ESR process and the feasibility of ferroboron production by using this process was investigated. Since the steel ingot in the ESMAR process will be used as a consumable electrode, the iron content of the ferroboron to be produced can be obtained from these ingots without the use of iron ore, thus eliminating the need for aluminium for iron ore reduction. The boron content of ferroboron will be obtained by reducing the boron oxide in the slag with aluminum. At the end of the experiments, ferroboron products containing different ratios of boron and residual aluminum (15.23% B and 1.19% Al; 18.39% B and 5.44% Al) were obtained. These products are of commercial quality. Since this new process did not require Al for the reduction of iron ore, the consumption of Al decreased by 3.37 grams per gram of boron. As a result, it was found out that the ESMAR Process is a suitable method for ferroboron production and that the process can be improved by optimization of process parameters.

Influence of the Coagulation Mechanism on the Coagulation Performances Using New Composite Coagulants: Role of the Raw Water Characteristics

To improve the coagulation performances, new composite coagulants were used to treat different water samples. The results indicate that Ca2+ has no significant effects on the removal efficiency for turbidity in the kaolin system. The residual aluminum decreased from 0.15 mg·L-1 to 0.10 mg·L-1 (AlCl3 was used as coagulant and the coagulant dosage was 0.10 mmol·L-1). The presence of Ca2+ led to the decrease of the amount of negative charges in the HA system and the residual aluminum decreased due to the decrease of the complexation between the HA molecules and Al-based coagulants. When the raw water contained BSA molecules and the coagulant dosage was 0.16 mmol·L-1, the flocs formed by PACl with Ca2+ were larger (~50 μm) than the flocs generated by PACl and the settleability also improved. Under alkaline conditions (pH=8.5), the DOC concentration decreased after coagulation process by~0.2-0.6 mg·L-1 and the residual aluminum decreased by~0.4-0.7 mg·L-1 using composite coagulants. Under acidic conditions (pH=5.5), the concentrations of DOC and residual aluminum did not significantly differ.

Revisiting of coagulation-flocculation processes in the production of potable water

Water Treatment Plants treat "flushy" raw waters and the majority use electrolytes and polyelectrolytes for the removal of the solid and organic impurities included in surface waters. The dose of the used reagents depend strongly on the nature of the incoming surface water and its turbidity. Turbidity is due to the suspended particles in the source water and up to date is main criterion for the appropriate choice of the electrolyte and polyelectrolyte nature and dosage. One of the main findings of the present work is that the selection of the appropriate dose of coagulants and flocculants as a linear function of turbidity is not right, especially for the large values of turbidity. The most common electrolytes Aluminum sulfate and PolyAluminiumChloride together with the polyelectrolyte PolyAcrylaMide, are tested for their effectiveness in the removal of suspended particles and their results discussed based on the particle’s ζ-potential and size distribution. These common reagents have raised public health concerns due to the residual aluminium and acrylamide which remain in treated water and at produced sludge. Thus, the present work examined and suggests the use of polymers as the natural Chitosan and CMInulin and the synthetic PolyDiallylDiMethylAmmoniumChloride, as alternative, environmentally friendly coagulants, for their performance on the treatment of potable water. The new reagents proved to reduce the turbidity of the surface water up to 96%.

Applying GMDH-type neural network for modeling and prediction of turbidity and free residual aluminium in drinking water

Applying GMDH-type neural network for modeling and prediction of turbidity and free residual aluminium in drinking water

Optimizing the removal of humic acid with polyaluminum chloride and polyaluminum ferric chloride as green coagulants using response surface methodology

Humic acid is a major precursor of chlorinated byproducts that need to be removed from water, via treatment, given their adverse effects on human health. The current study aimed at identifying the optimal conditions to remove humic acid from surface water, using coagulants such as polyaluminum chloride (PACl) and polyaluminum ferric chloride (PAFCl). The effects of independent variables such as total organic carbon (TOC) concentration (1.6–7 mg/L), pH level (5–9), and coagulant dosage (10–50 mg/L) on humic acid removal were studied using response surface methodology and central composite design. A coagulant dose of 15.72 mg/L (for PACl and PAFCl), TOC concentration of 2.66 mg/L, and pH of 7.84 comprised the optimal conditions, and the removal efficiencies of 97.55% and 98.18% were obtained with PACl and PAFCl, respectively. Zeta potential analysis showed that the leading mechanism for coagulation, with both coagulants, was charge neutralization. PACl and PAFCl had adequate potential to remove humic acid from surface water, but PAFCl had a better performance regarding the treatment of aluminum residuals. Keywords: Coagulation; Humic acid; Polyaluminum chloride; Polyaluminum ferric chloride