Residual Aluminum Research Articles

Thermal transformation of Na-LTA zeolite into low-carnegieite: The influence of residual sodium and aluminium species

The influence of residual sodium and aluminium species on the mechanism of commercial and laboratory-synthesized Na-LTA zeolite thermally induced transformation (ZTIT) was investigated. A phase transformation route between zeolite and low-temperature carnegieite (lt-carn) during heating, is evolving in two different pathways. In one aspect, Na-LTA zeolite transforms directly into lt-carn, while in the other, transformation unfolds through amorphous state. The samples with significant amount of sodium and aluminium residues: (1.05–1.06) Na 2O:(1.02–1.07) Al 2O 3:2SiO 2 did not show intermediate amorphous state during heat treatment. It was implicitly shown that investigated ZTIT process is enhanced by residual species. The residues are extracted from all investigated samples during refluxing treatment at 100 °C. The intermediary amorphous states were created from all refluxed Na-LTA samples. Common characteristics of such prepared amorphous NaAlSiO 4 states are narrow temperature stability range (cca. 50 °C) and low-density.

Prediction of Aluminum Nitride Embrittlement in Heavy Section Steel Castings

Aluminum Nitride (AlN) embrittlement is a problem in heavier section (>4″) steel castings. AlN precipitates at higher residual aluminum and nitrogen levels and slow cooling rates. In load critical components, the formation of AlN will embrittle the casting, reducing the impact strength and ductility of the steel. The precipitation diagram for AlN from Hannerz is reviewed and his more accurate equation plotted. In addition, this information is matched to simulated cooling curves in slab castings to plot maximum aluminum content against section size to avoid embrittlement. However, these rules of thumb can be misleading in analyzing geometries without final rigging or production information like the sand properties. The most important information in predicting AlN is the cooling rates in the production setting. Therefore, the equations are incorporated into casting simulation software to use the simulated cooling curves to locate embrittled volumes. Two example castings serve to show the use of the AlN embrittlement indicator. This prediction will help to avoid AlN embrittlement in the design of heavy section steel castings and rigging.

Preparation of TiAl3-Al Composite Coating by Cold Spray and Its High Temperature Oxidation Behavior

A novel TiAl3-Al coating was prepared by cold spray for high temperature protection of titanium aluminum-based alloy. The substrate alloy was orthorhombic-Ti-22Al-26Nb (at.%). The composite coating was mainly composed of TiAl3 embedded in the matrix of residual aluminum. An interlayer about 10 μm was formed between the coating and the substrate. The oxidation test indicated that this composite coating was very effective in improving the high-temperature oxidation resistance of the substrate alloy at 950 °C in the tested 150 cycles without any sign of degradation. The microstructure analysis of the oxidized composite coating showed that an Al2O3 scale with a complex structure can be formed outside the interlayer during oxidation and no oxides beneath the interlayer were detected, which indicated that the complex continuous Al2O3 and the interlayer provide the protection of the substrate at high-temperature oxidation condition.

Abundance and diversity of ammonia-oxidizing archaea and bacteria on biological activated carbon in a pilot-scale drinking water treatment plant with different treatment processes

The effects of different placements of rapid sand filtration on nitrification performance of BAC treatment in a pilot-scale plant were evaluated. In this plant, rapid sand filtration was placed after ozonation-BAC treatment in Process (A), while it preceded ozonation-BAC treatment in Process (B). Analysis of amoA genes of ammonia-oxidizing archaea (AOA) and bacteria (AOB) combined with nitrification potential test was conducted. BAC from Process (A) demonstrated slightly higher nitrification potential at every sampling occasion. This might be due to higher abundances of AOB on BAC from Process (A) than those on BAC from Process (B). However, AOA rather than AOB could be predominant ammonia-oxidizers in BAC treatment regardless of the position of rapid sand filtration. The highest nitrification potential was observed for BAC from both processes in February when the highest abundances of AOA-amoA and AOB-amoA genes were detected. Since rapid sand filtration was placed after BAC treatment in Process (A), residual aluminum concentration in BAC influent was higher in Process (A). However, adverse effects of aluminum on nitrification activity were not observed. These results suggest that factors other than aluminum concentration in different treatment processes could possibly have some influence on abundances of ammonia-oxidizing microorganisms on BAC.

Developing a physically consistent model for gibbsite leaching kinetics

Leaching aluminium hydroxide from bauxite ores is the first step of the Bayer process which is widely used in the aluminium industry. This paper aims to develop a better understanding of the gibbsite leaching kinetics which can allow for subsequent process optimisation. Comparison of many conventional kinetic models developed for gibbsite leaching with experimental data showed poor agreement. Several new kinetic models have been developed and validated experimentally. The model equations were numerically integrated applying the fourth-order Runge–Kutta technique. Unknown model parameters were estimated by comparing numerical solutions with available experimental data using nonlinear regression analysis with the Levenberg–Marquardt algorithm. The new model for the gibbsite leaching controlled by diffusion through the surface ash/product layer did not compare well with the data. Taking into account the actual irregular surface morphology of the dissolving solids, the fractal geometry of this irregular surface was considered in the development of newer models. With the inclusion of the fractal dimension, the new models agreed better with the experimental data. Finally, the residual aluminium concentration remained in the solid phase after leaching was given consideration in the development of the new model which showed perfect agreement with the data. A physically consistent model for gibbsite leaching was thus obtained by considering these last two factors: fractal geometry of the shrinking gibbsite particles and residual aluminium concentration.

The possibility of a fully automated procedure for radiosynthesis of fluorine-18-labeled fluoromisonidazole using a simplified single, neutral alumina column purification procedure

A novel fully automated radiosynthesis procedure for [(18)F]Fluoromisonidazole using a simple alumina cartridge-column for purification instead of conventionally used semi-preparative HPLC was developed. [(18)F]FMISO was prepared via a one-pot, two-step synthesis procedure using a modified nuclear interface synthesis module. Nucleophilic fluorination of the precursor molecule 1-(2'-nitro-1'-imidazolyl)-2-O-tetrahydropyranyl-3-O-toluenesulphonylpropanediol (NITTP) with no-carrier added [(18)F]fluoride followed by hydrolysis of the protecting group with 1M HCl. Purification was carried out using a single neutral alumina cartridge-column instead of semi-preparative HPLC. The maximum overall radiochemical yield obtained was 37.49+/-1.68% with 10mg NITTP (n=3, without any decay correction) and the total synthesis time was 40+/-1 min. The radiochemical purity was greater than 95% and the product was devoid of other chemical impurities including residual aluminum and acetonitrile. The biodistribution study in fibrosarcoma tumor model showed maximum uptake in tumor, 2h post injection. Finally, PET/CT imaging studies in normal healthy rabbit, showed clear uptake in the organs involved in the metabolic process of MISO. No bone uptake was observed excluding the presence of free [(18)F]fluoride. The reported method can be easily adapted in any commercial FDG synthesis module.

Benefits of Residual Aluminum in Ductile Iron

Two main chemistry systems of micro-inclusions can be identified in ductile iron: Ca-S-X and Mg-Si-O-X with the majority of the inclusions regardless of treatment type and location being of the second type, silicates. Laboratory investigations have shown that simple silicates were present in the matrix, while more complex silicates were present in conjunction with graphite, probably acting as graphite nucleation sites. In these more complex silicates, elevated levels of Al, Ca, Ce and La were typical. Comparing micro-particles embedded in iron matrix and graphite nodules of iron treated with pure Mg-metal and iron treated with MgFeSi alloy showed a higher amount of complex silicates with elevated Al-levels in the iron treated with MgFeSi. Further laboratory investigation was undertaken to explore which source of Al and which range of residual Al would have a favorable impact on the graphite nucleation in ductile iron. The work showed that a residual aluminum of 0.005 to 0.020 wt.% appears to be beneficial for improving ductile iron solidification characteristics without the incidence of pinholes. Greatest benefits were achieved when introducing the Al into the iron via an inoculant late during processing or via a pre-conditioner to the base iron. Al added via the MgFeSi provided less benefit. Some case studies illustrating the effect of Al in ductile iron are also presented, as Al-containing pre-conditioner or/and Al-bearing, FeSi inoculant application.

Optimization of the process parameters for the removal of boron from drinking water by electrocoagulation—a clean technology

AbstractBACKGROUND: There are a number of articles related to removal of boron by electrocoagulation using aluminium electrodes, but there are fewer articles describing the use of magnesium as the anode material. The main disadvantage of aluminium electrodes is the residual aluminium present in the treated water due to cathodic dissolution, which can create health problems. In the case of magnesium electrodes, there is no such disadvantage. This paper presents the results of studies on the removal of boron using magnesium and stainless steel as anode and cathode, respectively.RESULTS: Results show that a maximum removal efficiency of 86.32% was achieved at a current density of 0.2 A dm−2 and pH of 7 using magnesium as the anode and stainless steel as the cathode. The adsorption of boron fitted the Langmuir adsorption isotherm, suggesting monolayer coverage of adsorbed molecules. The adsorption process follows second‐order kinetics. Temperature studies showed that adsorption was endothermic and spontaneous in nature.CONCLUSIONS: The magnesium hydroxide generated in the cell remove the boron present in the water and reduced to a permissible level and making it drinkable. The process scale up results was consistent with the results obtained from the laboratory scale, showing the robustness of the process. Copyright © 2010 Society of Chemical Industry

Experimental design approach applied to the elimination of crystal violet in water by electrocoagulation with Fe or Al electrodes

An experimental design methodology was applied to evaluate the decolourization of crystal violet (CV) dye by electrocoagulation using iron or aluminium electrodes. The effects and interactions of four parameters, initial pH (3–9), current density (6–28 A m −2), substrate concentration (50–200 mg L −1) and supporting electrolyte concentration (284–1420 mg L −1 of Na 2SO 4), were optimized and evaluated. Although the results using iron anodes were better than for aluminium, the effects and interactions of the studied parameters were quite similar. With a confidence level of 95%, initial pH and supporting electrolyte concentration showed limited effects on the removal rate of CV, whereas current density, pollutant concentration and the interaction of both were significant. Reduced models taking into account significant variables and interactions between variables have shown good correlations with the experimental results. Under optimal conditions, almost complete removal of CV and chemical oxygen demand were obtained after electrocoagulation for 5 and 30 min, using iron and aluminium electrodes, respectively. These results indicate that electrocoagulation with iron anodes is a rapid, economical and effective alternative to the complete removal of CV in waters. Evolutions of pH and residual iron or aluminium concentrations in solution are also discussed.

Residual aluminium in water defluoridated using activated alumina adsorption – Modeling and simulation studies

The removal of fluoride from drinking water by the method of adsorption on activated alumina is found superior than other defluoridation techniques mostly due to the strong affinity between aluminium and fluoride. Dissolution of aluminium from the alumina surfaces into its free and hydroxide ions in the aqueous medium is reported to be very low, but the presence of high fluoride concentrations may increase its solubility due to the formation of monomeric aluminium fluoride and aluminium hydroxyl fluoride complexes. An Activated Alumina Defluoridation Model Simulator (AAD) has been developed to represent fluoride adsorption on the basis of the surface complexation theory incorporating aspects of aluminium solubility in presence of high fluoride concentrations and pH variations. Model validations were carried out for residual aluminium concentrations in alumina treated water, by conducting a series of batch fluoride adsorption experiments using activated alumina (grade FB101) treating fluoride concentrations of 1–10 mg/L, at varying pH conditions. The total residual aluminium in the defluoridated water is due to presence of both dissolved and precipitated Al–F complexed forms. The Freundlich adsorption isotherm was found fit for fluoride adsorption capacity versus residual fluoride concentrations for pH = 7.5, and the relationship is given by the linearised equation log ( x/ m) = log k + (1/ n) log C e with values of k = 0.15 mg/g and 1/ n = 0.45 indicating favorable adsorption. The relationship is linear in the region of low fluoride concentrations, but as concentrations of fluoride increased, the formation of the dissolved AlF 3 0 complexes was favored than adsorption on alumina, and hence makes the isotherm nonlinear. The AAD simulations can predict for operating fluoride uptake capacity in order to keep the residual aluminium within permissible limits in the alumina treated water.

Effect of pH on the coagulation performance of Al-based coagulants and residual aluminum speciation during the treatment of humic acid–kaolin synthetic water

The fractionation and measurement of residual aluminum was conducted during the treatment of humic (HA)–kaolin synthetic water with Al 2(SO 4) 3, AlCl 3 and polyaluminum chloride (PAC) in order to investigate the effect of pH on the coagulation performance as well as residual aluminum speciation. Experimental results suggested that turbidity removal performance varied according to the following order: AlCl 3 > PAC > Al 2(SO 4) 3. HA removal performance of PAC was better than that of AlCl 3 under acidic condition. The optimum pH range for AlCl 3 and Al 2(SO 4) 3 was between 6.0 and 7.0 while PAC showed stable HA and UV 254 removal capacity with broader pH variation (5.0–8.0). For the three coagulants, majority of residual aluminum existed in the form of total dissolved Al (60–80%), which existed mostly in oligomers or complexes formed between Al and natural organic matter or polymeric colloidal materials. PAC exhibited the least concentration for each kind of residual aluminum species as well as their percentage in total residual aluminum, followed by AlCl 3 and Al 2(SO 4) 3 (in increasing order). Moreover, PAC could effectively reduce the concentration of dissolved monomeric Al and its residual aluminum ratio was the least among the three coagulants and varied little at an initial pH between 7.0 and 9.0.

NF membrane fouling by aluminum and iron coagulant residuals after coagulation–MF pretreatment

The effects of coagulant residuals on fouling of a nanofiltration (NF) membrane were investigated. Experiments were carried out with a laboratory-scale microfiltration (MF)–NF setup and a pilot MF–NF plant. In the laboratory-scale experiments, NF feed water was pretreated with poly-aluminum chloride (PACl) or alum followed by MF. NF membrane permeability declined when the feed water contained residual aluminum at 18 μg/L or more, but not when it was lower than 9 μg/L. When pretreated with ferric chloride, no substantial decline of NF membrane permeability was observed; residual iron did not affect the permeability. When SiO 2 was added to the water before the pretreatment with PACl, the NF membrane permeability declined at about double the speed. Thermodynamic calculations and elemental analysis of foulants recovered from the membranes indicated that the majority of inorganic foulants were compounds composed of aluminum, silicate, and possibly potassium. In the pilot plant, NF feed was pretreated by PACl. Transmembrane pressure for NF doubled over 4.5 months of operation. Although the aluminum concentration in the NF feed was not high (30 μg/L), analysis of membrane foulants revealed excessive accumulation of aluminum and silicate, also suggesting that aluminum residuals caused the membrane fouling by alumino-silicates or aluminum hydroxide.

Novel inorganic-organic composite coagulants based on aluminium

In this study, the preparation of a novel coagulant is examined, by introducing into PACl a cationic polyelectrolyte (CPE). For this purpose, poly-diallyldimethylammonium chloride (p-DADMAC) was used, a commonly applied cationic polyelectrolyte in water and wastewater treatment. Several possible derivatives of the composite coagulant were prepared, based on different CPE content (Al/CPE ratio, w/w). The products were characterized by means of polymerization degree (aluminium species distribution), chemical bonding (FT-IR spectroscopy), conductivity, turbidity and pH, in order to examine the impact of CPE addition in the properties of PACl. Moreover, their coagulation performance was evaluated for the treatment of contaminated tap water and compared to the respective performance of the combined application of PACl and CPE but as separated reagents. Finally, the kinetics of coagulation-flocculation was studied by aims of a Photometric Dispersion Analyzer (PDA). From the results obtained it was revealed that despite the deterioration of the charge neutralization capability when the two reagents are combined into one, the composite coagulants are more efficient in water treatment due to more effective particles aggregation. The most important advantages of the new coagulants are the significant reduction of CPE dosage (or content) and the lower residual aluminium concentration. Specific attention has to be given to the CPE content, in order to produce an improved coagulant which can achieve efficient charge neutralization combined with enhanced particles aggregation, leading to more efficient and cost-effective treatment.

Influence of residual aluminium on solidification pattern of ductile iron

The present study describes the effect of a large range of final residual Al contents (0·002–0·05%) on thermal analysis parameters when added to a base iron (less than 0·003%Al) through preconditioning (FeSi, 5%Al), tundish-cover nodularisation (MgFeSi, 0·1–3%Al) or ladle inoculation (CaFeSi, 0·1–5%Al) in hypoeutectic (carbon equivalent=3·95–4·25%) ductile irons. The most important parameters of thermal analysis were beneficially influenced by residual Al and consequently resulted in higher eutectic temperatures and lower undercooling, higher temperature at the end of solidification, higher cooling rates at this temperature, etc. Aluminium residual of 0·005–0·02% appears to be beneficial, without the incidence of pinholes. The greatest benefits were achieved when Al was introduced into the iron via the inoculant. The second best was to have Al present in the base iron, added as Al bearing preconditioner. Aluminium added via the MgFeSi provided minor benefits.

Synthesis and characterization of acrylamide‐based aluminum flocculant for turbidity reduction in wastewater

AbstractPolymeric flocculants of aluminum hydroxide‐poly[acrylamide‐co‐(acrylic acid)], AHAMAA, were prepared by solution polymerization using aluminum hydroxide as a coagulant in the presence of acrylamide (AM) and acrylic acid (AA) as a comonomer pair with N,N′‐methylenebisacrylamide as a crosslinking agent. The crosslinking was initiated by ammonium persulfate with N,N,N′,N′‐tetramethylethylenediamine as an initiator. The water absorbency of crosslinked poly[AM‐co‐AA] was always higher than that of AHAMAA and was found to be correlated to the storage modulus of the polymers, which was higher for AHAMAA than that of crosslinked poly[AM‐co‐AA]. The residual aluminum concentration of AHAMAA (0.09–0.2 mg L−1) indicated the stability of the polymer flocculant which was in good agreement with the observed tan δ and the higher G′′ and G′ values. Both the crosslinked poly[AM‐co‐AA] and AHAMAA satisfactorily reduced the turbidity of kaolin suspensions, but the latter gave a better reduction performance. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Optimization of material structure of ploy-Si thin film based on Al induced crystallization

Based on Al induced crystallization (AIC) method, influences of different material structures on formation and characteristics of ploy-silicon thin films were studied and optimized. Al-Si films on glass with different structures (Si/Al/Glass, Al/Si/Glass, Si/Al/.../Si/Al/Glass) were deposited on glass substrates by sputtering method. All samples were annealed for MIC with varied time processes under 500°C N2 environment. X-ray diffraction test and scanning electron microscope were adopted to characterize crystallization performance and surface topography of AIC poly-silicon samples after removing residual aluminum. The electrical properties were also characterized by Hall test method. Quick process and high performance of AIC ploy-silicon thin film can be both obtained by use of periodic structure samples.

Modeling and Simulation studies for Aluminium - Fluoride Interactions in Nalgonda Defluoridation Process

A model simulator NALD-2 has been developed to study the interactions of fluoride and aluminium in the Nalgonda Defluoridation Process, which principally involves the preferential adsorption of fluoride ions onto insoluble aluminium hydroxides that are formed from alum hydrolysis reactions and undergo precipitation. This model represents the defluoridation mechanism taking into account the charged behavior of the amphoteric aluminium hydroxide colloids, charged site densities, and fluoride complexation reactions in order to predict the extent of defluoridation and concentrations of dissolved and colloidal aluminium in the treated water as functions of pH, alum dosage and raw fluoride concentrations. Model validations were carried out using secondary data of Selvapathy & Arjunan (1995) for total residual aluminium in Nalgonda treated water. Slight variations in pH into the acidic range cause substantial increase in colloidal aluminium and hence pH and alum dosages are important control parameters to limit residual aluminium in treated water. The NALD-2 simulator helps in predicting optimum alum dosages for minimum residual aluminium in the treated water. It was concluded that the dosages of alum recommended in the Nalgonda method cannot bring down the residual Al below the permissible limit of 0.2mg/L in the treated water.

Defluoridation of drinking water by electrocoagulation/electroflotation in a stirred tank reactor with a comparative performance to an external-loop airlift reactor

Defluoridation using batch electrocoagulation/electroflotation (EC/EF) was carried out in two reactors for comparison purpose: a stirred tank reactor (STR) close to a conventional EC cell and an external-loop airlift reactor (ELAR) that was recently described as an innovative reactor for EC. The respective influences of current density, initial concentration and initial pH on the efficiency of defluoridation were investigated. The same trends were observed in both reactors, but the efficiency was higher in the STR at the beginning of the electrolysis, whereas similar values were usually achieved after 15 min operation. The influence of the initial pH was explained using the analyses of sludge composition and residual soluble aluminum species in the effluents, and it was related to the prevailing mechanisms of defluoridation. Fluoride removal and sludge reduction were both favored by an initial pH around 4, but this value required an additional pre-treatment for pH adjustment. Finally, electric energy consumption was similar in both reactors when current density was lower than 12 mA/cm 2, but mixing and complete flotation of the pollutants were achieved without additional mechanical power in the ELAR, using only the overall liquid recirculation induced by H 2 microbubbles generated by water electrolysis, which makes subsequent treatments easier to carry out.

APPLICATION OF SEVERAL ALUMINIUM PREHYDROLYSED COAGULANTS IN SURFACE WATER TREATMENT FOR POTABILIZATION

A prehydrolyzed aluminium chloride (PAC), commercial product selected from a previously studied series, and the electrochemically obtained PAC (E-PAC) were tested as coagulants, comparatively with the classical aluminium sulfate (alum). A new method for producing E-PAC has been applied. The level of turbidity, the amount of total organic carbon, the UV-254 absorbance and the residual aluminium were evaluated, for determining the efficiency of the coagulation process in all situations of using PAC, E-PAC and alum as coagulants. The aim of the paper was to improve coagulation flocculation process in laboratory conditions, as first step for later use in the surface water treatment plant for potable utility of Timisoara town (Romania), which has Bega River as raw water source. It can be estimated that the E-PAC offered the better alternative for practical use in drinking water processing.

Effects of Sodium Acetate and Residual Aluminum on the Hydrogenation Rate, Optical Yield and Catalyst Durability for the Enantio-Differentiating Hydrogenation of Methyl Acetoacetate Over Tartaric Acid-Modified Raney Nickel Catalysts

The effects of Na acetate and residual aluminum on the hydrogenation rate, optical yield and catalyst durability for the enantio-differentiating hydrogenation of methyl acetoacetate were studied over tartaric acid-modified Raney nickel catalysts with the in situ modification. There was an optimal Na acetate amount at which the highest optical yield and high hydrogenation rate were achieved. The addition of Na acetate in the repeat use could improve the catalyst durability significantly. The amount of the residual aluminum in Raney nickel catalysts also played an important role in this catalyst system. The highest optical yield of 61.6% was achieved over the improved T-1 RNi catalyst. Compared with previous literatures, this is the best result for the enantio-differentiating hydrogenation of methyl acetoacetate over in situ modified Raney nickel catalysts.