Release Of Aluminum Research Articles

A comparative evaluation of ion release from different commercially-available orthodontic mini-implants – an in-vitro study

Abstract Background Titanium alloy mini-implants have become popular in recent times and have been extensively used and studied. Although corrosion resistance of orthodontic materials has always been of concern, this property has been the least explored. The present study aimed to assess the composition, surface characterisation and corrosion resistance of five commercially available mini-implants by assaying ion release in artificial saliva. Methods Ten mini-implants each from five companies were obtained: Group 1 – AbsoAnchor (Dentos Inc, South Korea); Group 2 – Microimplant Anchorage System (MIA, Biomaterials Korea); Group 3 – The Orthodontic Mini Anchorage System (TOMAS, Dentaurum, Germany); Group 4 – mini-implants (Denticon, Maharashtra, India); Group 5 – orthodontic mini-implants (J.J.Orthodontics, Kerala, India). One mini-implant from each group was subjected to characterisation and surface microstructure analysis using Energy Dispersive Atomic Spectrometry (EDAX) and Scanning Electron Microscope (SEM), respectively. Ten miniimplants were immersed for 30 days in Fusayama-Meyer artificial saliva solution and the release of titanium, aluminium and vanadium ions was detected with Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES). The Kruskal-Wallis test was used for multi-variate analysis. In order to determine the significant differences between the groups on independent samples, the Mann-Whitney U test (bi-variate analysis) was applied. Results and conclusion All groups showed machining defects but surface pitting after immersion was mostly evident in Group 4. Although the composition of all the implants was comparable, there was a statistically significant difference in the Ti, Al and V release between Group 4 – the group with maximum release – and Group 2, the group with least release.

Mechanical properties of titanium-niobium alloy and morphological characterization of nanotubes obtained by anodizing technique

Event Abstract Back to Event Mechanical properties of titanium-niobium alloy and morphological characterization of nanotubes obtained by anodizing technique Aline Rossetto Da Luz1, Neide Kazue Kuromoto1, 2 and Carlos Maurício Lepienski1 1 Universidade Federal do Paraná, Programa de Pós-Graduação em Engenharia e Ciência dos Materiais - PIPE, Brazil 2 Universidade Federal do Paraná, Física, Brazil Introduction: Titanium and titanium alloys are the metals used to produce metallic biomaterials. The alloy frequently used for orthopedic prostheses is the Ti-6Al-4V. However, there has been toxic effects due to the release of aluminum and vanadium ions. There are studies being directed on developing new alloys, specifically the type β-Ti alloys containing Nb, Mo, Zr, Sn or Ta, which are considered non-toxic, corrosion resistant and have mechanical properties suitable for biomaterials[1]. Nanotubular surface modification of metallic implants by the anodizing technique can improve the biocompatibility when compared to conventional materials[2]. The purpose of this study was to determine the elastic modulus of the Ti-20Nb and obtain the growth of the nanotubes over the binary alloy by anodization technique. Materials and Methods: The precursor materials used were commercially pure titanium grade 2 (cp-Ti) with 99.7% purity and niobium (Nb) with 99.8% purity. For the fusion of elements it was used an arc-melting furnace with copper crucible water cooled, non-consumable tungsten electrode and an argon-controlled atmosphere. Titanium ingots with a weight percentage of 20 wt. (%) of Nb were obtained after melting process[3]. Disks with 9 mm of diameter and 2 mm of thickness were polished with a suspension of 0.05-mm colloidal SiO2. The samples were ultrasonically cleaned in acetone, isopropyl alcohol and deionized water, and dried at 40 °C for 24h. The microstructure of the chemically etched alloys was analyzed using optical microscope. The elastic modulus of the Ti-20Nb alloy were obtained by instrumented indentation by Oliver-Pharr method[4]. The nanotubes were obtained using anodic oxidation technique under potentiostatic mode in 0.5 M Na2SO4 + 0.1 wt.% HF electrolyte, using voltage of 20 V and anodizing time of 1.5 h, at room temperature. A platinum sheet was used as the counter-electrode. The morphology of the nanostructured surface was analyzed using scanning electron microscopy. Results and Discussion: Optical microscope analysis of the Ti-20Nb alloy showed a structure composed of α’/α” phases and the metastable β phase. Figure 1 shows the elastic modulus value of the Ti-20Nb alloy is of (103 ± 2) GPa at greater depth (~ 2560 nm), which is smaller than the value of cp-Ti that is 130 GPa. This decrease in the elastic modulus is due to the presence of the β phase and can reduce the effect of stress shielding between implant and bone tissue. Figure 2 shows the surface morphology of the anodized Ti-20Nb alloy, highly ordered titania nanotubes were produced. This morphology can improve osteoblasts adhesion ability and osseointegration compared to metal implants without surface treatment[2]. Conclusion: The adding niobium as β stabilizing element reduced significantly the elastic modulus, compared to cp-Ti. An ordered titania nanotube arrays successfully were obtained on the Ti-20Nb alloy, by anodization technique. We would like to thank the Center of Electron Microscopy - UFPR and the Labnano - UFPR for the facilities, and the CAPES for the financial support.

Acid Elution of Aluminum and Calcium from Human Deciduous Enamel in Relation to Dental Caries

Although aluminum itself was reported to prevent dental caries, previous in vitro studies reported that the aluminum level in the whole saliva of children was independent of caries prevalence. Purposes of this study were to compare the elution levels of aluminum and calcium from deciduous enamel into acidic artificial saliva, and determine whether the degree of aluminum elution reflects individual caries risk. One hundred and eleven extracted human deciduous teeth were collected. Concentrations of aluminum and calcium eluted from sound regions of enamel into artificial saliva (pH 6.2 or 5.5) were determined using atomic absorption spectrophotometry. One hundred and four and 108 available data samples were obtained for aluminum and calcium evaluation, respectively, and were compared based on the sex, tooth type, caries history, and the number of the donor’s carious teeth at each pH. Calcium elution was not affected by the sex; however, more aluminum was eluted from boys’ than from girls’ teeth at pH 5.5. The aluminum release depended on the tooth type, and was significantly higher in incisors than in molars at a pH of 5.5. In relation to the caries history, aluminum (at pH 5.5) and calcium (at pH 6.2) dissolved more from sound regions of the enamel of caries-experienced teeth than from the enamel of teeth without caries experience. Moreover, aluminum markedly dissolved from enamel in artificial saliva at both pH 6.2 and 5.5 when the donor had more carious teeth, regardless of the presence or absence of caries experience in the sampled teeth. There is a possibility that the rate of aluminum elution from enamel into acidic fluid reflects individual caries sensitivity.

Effect of Ge/Si ratio on genotoxicity of germanium-containing glass ionomer cements

Glass ionomer cements have been discussed across broad and progressive applications from dentistry to orthopedics. However, in orthopedic applications, adverse patient outcomes that have been clinically linked to the release of aluminum from conventional alumino-silicate GICs, demonstrate a critical need for the development of new aluminum-free materials. Accordingly, the present study uses an Ames Screen to evaluate the preliminary genotoxicity profiles of a series of promising new germanium-containing, aluminum-free GICs. The results herein reveal that in addition to the already demonstrated superior handling characteristics and suitable mechanical strength, these cements are non-mutagenic to bacteria strains Salmonella typhimurium (TA98) and Escherichia coli (WP2uvrA). The results of this study provide strong positive evidence regarding the genotoxicity of these novel GICs, warranting further investigation into the biocompatibility of these materials for numerous in vivo applications.

Oil refinery wastewater treatment using coupled electrocoagulation and fixed film biological processes

Oil refinery wastewater was treated using a coupled treatment process including electrocoagulation (EC) and a fixed film aerobic bioreactor. Different variables were tested to identify the best conditions using this procedure. After EC, the effluent was treated in an aerobic biofilter. EC was capable to remove over 88% of the overall chemical oxygen demand (COD) in the wastewater under the best working conditions (6.5 V, 0.1 M NaCl, 4 electrodes without initial pH adjustment) with total petroleum hydrocarbon (TPH) removal slightly higher than 80%. Aluminum release from the electrodes to the wastewater was found an important factor for the EC efficiency and closely related with several operational factors. Application of EC allowed to increase the biodegradability of the sample from 0.015, rated as non-biodegradable, up to 0.5 widely considered as biodegradable. The effluent was further treated using an aerobic biofilter inoculated with a bacterial consortium including gram positive and gram negative strains and tested for COD and TPH removal from the EC treated effluent during 30 days. Cell count showed the typical bacteria growth starting at day three and increasing up to a maximum after eight days. After day eight, cell growth showed a plateau which agreed with the highest decrease on contaminant concentration. Final TPHs concentration was found about 600 mgL−1 after 30 days whereas COD concentration after biological treatment was as low as 933 mgL−1. The coupled EC-aerobic biofilter was capable to remove up to 98% of the total TPH amount and over 95% of the COD load in the oil refinery wastewater.

Relationships of diboride phases in Al–Ti(Zr)–B alloys

The relationships of diboride phases in Al–Ti(Zr)–B alloys with a variable Ti/B ratio close to the stoichiometry of TiB2 were studied. The formation of diboride solid solutions was confirmed. A grain refinement mechanism is proposed as that diboride particles in the Al–Ti–B master alloys reacting with aluminium upon adding into an aluminium melt and release titanium into the melt through forming a (Ti,Al)B2 solid solution and maintain a thin dynamic Ti rich layer on the surfaces of the (Ti,Al)B2 particles, which nucleates α-Al grains in solidification. The poisoning effect of zirconium on grain refinement of aluminium by Al–Ti–B master alloys is also discussed.

Aluminum release from microwave-assisted reaction of coal fly ash with calcium carbonate

Coal fly ash (CFA) is a potential aluminum resource alternative to bauxite. Because most aluminum in CFA exists in an inert mullite phase, the way in which CFA can be activated is becoming important. Thermal activation with the addition of calcium carbonate (CaCO3) is a common method for recovering aluminum from CFA; however, the lower energy efficiency of conventional heating has limited its application. In this investigation, microwave irradiation (MWI) was found to be an energy-saving method for CFA activation, and 95wt% of aluminum was released from the specimen treated by MWI at 800°C for 60s. Compared to conventional thermal activation, MWI reduced the sintering temperature by nearly 400°C and shortened the reaction time by 20 times. Anisothermal reactions, which occurred due to the selective heating of the microwave, controlled the decomposition rate of CaCO3 and the formation rate of anorthite. MWI also accelerated the formation of fused phase and contributed to the formation of well-ordered hexagonal anorthite.

Survey on electrode type effectiveness on electro coagulation process as a method for polluted water treatment in emergencies

Aims: The aim of this study was the comparison of different electrode types on water quality characteristics in electro coagulation treatment. Materials and Methods: After electrolysis of water samples with commercial electrodes separately (iron and aluminum together), and with coal electrode (as control), quality parameters of hardness, alkalinity, pH, electrical conductivity (EC), and total dissolved solids (TDS) were evaluated by standard methods before and after the electrolysis. After data analysis, the averages of water quality parameters resulting from electrolysis with different electrodes were compared together using the SPSS-20 software. Results: The pH of samples increased significantly after using the iron and commercial electrodes (P 0.05). Total hardness, calcium, magnesium, and alkalinity were also increased significantly after using the iron and commercial electrodes (P < 0.05); and remained unchanged after using the aluminum and commercial electrodes. EC and TDS statistically significantly increased after applying all types of the electrodes. The color of samples turned brown-red after applying the iron and commercial electrodes and turned opaque white after applying the aluminum and commercial electrodes; and did not change after using the coal electrode. Except when using coal electrode, in all cases sludge was produced, which was green to black while using iron electrode alone and also using commercial electrodes, and it was opaque white when using the coal electrode. The above results do not include distilled water samples. Conclusion: Water electrolysis with studied commercial electrodes cause discoloration and sludge production as a result of aluminum and iron ions release, and leads to the production of turbid and black water, which is wrongly assumed as water impurities. Therefore, these electrodes are fraudulent and used seeking profit. Health authorities should increase the public awareness and collect them from the market.

Corrosion and solubility in a TSP-buffered chemical environment following a loss of coolant accident: Part 1 – Aluminum

Bench experiments were conducted to investigate the effect of the presence of trisodium phosphate (TSP) on the corrosion and release of aluminum from metallic aluminum surfaces under conditions representative of the containment pool following a postulated loss of coolant accident at a nuclear power generating facility. The experiments showed that TSP is capable of passivating the aluminum surface and preventing continued corrosion after about 24h at the conditions tested. A correlation that describes the rate of corrosion including the passivation effect was developed from the bench experiments and validated with a separate set of experiments from a different test system. The saturation concentration of aluminum was shown to be well described by the solubility of amorphous aluminum hydroxide for the majority of cases, but instances have been observed when aluminum precipitates at concentrations lower than the calculated aluminum hydroxide solubility. Based on the experimental data and previous literature, an equation was developed to calculate the saturation concentration of aluminum as a function of pH and temperature under conditions representative of a loss of coolant accident (LOCA) in a TSP-buffered pressurized water reactor (PWR) containment. The corrosion equation and precipitation equation can be used in concert with each other to calculate the quantity of solids that would form as a function of time during a LOCA if the temperature and pH profiles were known.

Conditions and mechanisms of the transformation of gibbsite into taranakite in phosphate solutions

Structural changes in gibbsite (an Al-containing soil mineral) in NH4H2PO4 solutions of different concentrations (from 10−6 to 2 M) were studied. As the concentration of the solution was increased, increasing release of aluminum from gibbsite to the liquid phase was observed along with binding of phosphate anions. The resulting soluble complex (aluminophosphate) anions were responsible for gibbsite dissolution. The most intense gibbsite dissolution occurred in 1 M and 2 M phosphate solutions. Evidence was obtained to show that this phenomenon is associated with the formation of aluminum complexes with pyro(poly)phosphate ligands. Along with intense gibbsite dissolution, a phosphate mineral (ammonium taranakite) formed, which was confirmed instrumentally. The key role of anionic aluminum pyro(poly)phosphate complexes in the formation of taranakite crystals was revealed. Sequential changes in the ligands in the complexes, associated with increasing phosphate loading, are discussed.

Effect of citric acid treatment on release of phosphorus, aluminium and iron from three dissimilar soils of India

To evaluate different mathematical models for describing cumulative release of phosphorus (P), aluminium (Al) and iron (Fe) by citric acid (CA) from soil, an experiment was conducted in packed soil columns with three contrasting soils viz. Alfisol, Vertisol and Inceptisol. The soils were saturated with CA at 0, 5, 10, 20, 40 and 100 mg L−1, the leachate were collected by liquid displacement at 15, 30, 45, 60 day intervals, and P, Al and Fe releases were analyzed. The release data were fitted to linear, quadratic, exponential, logarithmic, and power form of equations. The results revealed that the highest cumulative release of P, Al and Fe was observed in the 40 mg L−1 CA treatment. In the majority of cases, the relationship between CA concentration and cumulative release of ions fitted well in quadratic equation (y = ax2 + bx + c). The Fe and Al releases with time were fitted well in power-form (y = atb), while the cumulative P release in linear equation (y = mx + c). The study also revealed that a substantial amount of released P could serve as potential source of plant nutrient in fixation prone soils. The study demonstrated that CA can be used as a ‘solubilizer’ of soil P, 40 mg L−1 dose released the highest P, 0–20 mg L−1 dose was observed to be economical and 5 mg L−1 was the most promising dose in Alfisol.

Characterization of greywater in an Indian middle-class household and investigation of physicochemical treatment using electrocoagulation

Wastewater produced from all the domestic uses of water sans toilet flushing is known as greywater. It is often the major component in the domestic wastewater but has fewer pollutant load. Recycling and reuse of treated greywater for non-potable purposes may significantly reduce the stress on the fresh water requirement. This article presents the result of a study undertaken for characterization as well as laboratory-based investigation for treatment of greywater generated from an Indian single household. The greywater constituted at least 80% of the total wastewater with maximum contribution (44%) from the kitchen. The treatment studies, undertaken in an electrochemical reactor where the voltage and current were varied for sacrificial aluminum anodes, revealed that about 70% of the total COD and more than 99.9% pathogens could be removed with an energy consumption of 0.3kWh/m3 of wastewater. COD removal reached a maximum of 70%, irrespective of the applied voltage and current density, at an aluminum release from the anode at a rate of 15mg/L as aluminum. The electrochemical reactor aluminum electrodes, operated with maximum potential difference of 12V, showed potential for scale-up for real-life use in households for removal of pathogens, turbidity and COD contents of greywater.

ALUMINIUM IN BIOLOGICAL ENVIRONMENTS: A COMPUTATIONAL APPROACH

The increased availability of aluminium in biological environments, due to human intervention in the last century, raises concerns on the effects that this so far “excluded from biology” metal might have on living organisms. Consequently, the bioinorganic chemistry of aluminium has emerged as a very active field of research. This review will focus on our contributions to this field, based on computational studies that can yield an understanding of the aluminum biochemistry at a molecular level. Aluminium can interact and be stabilized in biological environments by complexing with both low molecular mass chelants and high molecular mass peptides. The speciation of the metal is, nonetheless, dictated by the hydrolytic species dominant in each case and which vary according to the pH condition of the medium. In blood, citrate and serum transferrin are identified as the main low molecular mass and high molecular mass molecules interacting with aluminium. The complexation of aluminium to citrate and the subsequent changes exerted on the deprotonation pathways of its tritable groups will be discussed along with the mechanisms for the intake and release of aluminium in serum transferrin at two pH conditions, physiological neutral and endosomatic acidic. Aluminium can substitute other metals, in particular magnesium, in protein buried sites and trigger conformational disorder and alteration of the protonation states of the protein's sidechains. A detailed account of the interaction of aluminium with proteic sidechains will be given. Finally, it will be described how alumnium can exert oxidative stress by stabilizing superoxide radicals either as mononuclear aluminium or clustered in boehmite. The possibility of promotion of Fenton reaction, and production of hydroxyl radicals will also be discussed.

Effect of strong acids on red mud structural and fluoride adsorption properties

The removal of fluoride using red mud has been improved by acidifying red mud with hydrochloric, nitric and sulphuric acid. The acidification of red mud causes sodalite and cancrinite phases to dissociate, confirmed by the release of sodium and aluminium into solution as well as the disappearance of sodalite bands and peaks in infrared and X-ray diffraction data. The dissolution of these mineral phases increases the amount of available iron and aluminium oxide/hydroxide sites that are accessible for the adsorption of fluoride. However, concentrated acids have a negative effect on adsorption due to the dissolution of these iron and aluminium oxide/hydroxide sites. The removal of fluoride is dependent on the charge of iron and aluminium oxide/hydroxides on the surface of red mud. Acidifying red mud with hydrochloric, nitric and sulphuric acid resulted in surface sites of the form SOH2+ and SOH. Optimum removal is obtained when the majority of surface sites are in the form SOH2+ as the substitution of a fluoride ion does not cause a significant increase in pH. This investigation shows the importance of having a low and consistent pH for the removal of fluoride from aqueous solutions using red mud.

Solubility, pH Changes and Releasing Elements of Different Bioceramic and Mineral Trioxide Aggregate Root Canal Sealers Comparative Study

Introduction: Bioceramic technology has been introduced recently in endodontics to benefit from the formation of hydroxyapatite during the setting reaction in the presence of tissue fluid and establish a chemical bond at the dentin interface. Objectives: To evaluate some of physiochemical properties of new different Bioceramic (iRoot-SP, EndoSequence, Smartpastebio) versus mineral trioxide aggregate (MTA-Fillapex) root canal sealers. Adseal and ActiV-GP sealers were used as control. Methods: Standard discs (10 for each) were prepared and immersed in 20 ml deionized water. After 1, 7, 14 and 28 days, solubility, pH changes and released elements were calculated and statistically analyzed with ANOVA test. Results: A significantly greater solubility and higher alkalinity were displayed by the tested sealers (in descending order) Smartpastebio, iRoot-SP, EndoSequence and MTA-Fillapex (P<0.05). Their solubility exceeded the acceptable limit (3%). Their maximum alkaline pH was exhibited after 7 days. Adseal and ActiV-GP exhibited initial neutral and acidic pH respectively. Finally both had neutral pH. EndoSequence exhibited the significantly greatest calcium release followed by iRoot-SP, Smartpastebio and MTA-Fillapex, whereas, ActiV-GP and Adseal exhibited the significantly lowest values (P<0.05). There was no silicon released from iRoot-SP, Smartpastebio and MTA-Fillapex. ActiV-GP exhibited the greatest silicon, aluminum and iron release. The greatest phosphorous, manganese and magnesium content was obtained by Adseal, MTA-Fillapex and EndoSequence respectively. Conclusion: Under the condition of this study, the prolonged alkalinity of calcium silicate sealers was synchronized with their ongoing solubility. The higher calcium ions released indicated strong alkalinity. The inequality in aluminum, iron, manganese and magnesium released by the tested sealers may expect the variance in their behaviors.

Micronucleus assay assessment of possible genotoxic effects in patients treated with titanium alloy endosseous implants or miniplates

The use of titanium and its alloys (Ti-6Al-4V) for oral surgery has increased dramatically in recent years. Ti is a stable biocompatible metal suitable for oral applications and it has been used for endosseous subperiosteal implants and miniplate fixation for more than 25 years. Dental implants are typically made of Ti or Ti alloys. The alloys are potentially toxic due to release of vanadium and aluminum. We tested the possible genotoxicity of Ti alloy endosseous implants and miniplates on the oral mucosal tissues of two groups of patients: 17 patients receiving Ti miniplate and screw fixation, and 37 endosseous dental implant placement patients. Preoperative and postoperative mucogingival cell samples were collected. Genotoxicity was assessed by the micronucleus assay (MN). There were slight but not statistically significant increases in the frequencies of MN (p=0.087 and p=0.047) post-operation in both groups. In summary, neither of the applications showed genotoxicity in the oral epithelial cells of patients.

A high-capacity aluminum hydroxide-based adsorbent for water defluoridation

In this study, the properties and fluoride-uptake capacity of aluminum hydroxide-based (AO) adsorbent has been investigated. AO was synthesized, characterized, and tested in batch and column experiments. The surface area of the AO was found to be 37.7 m2 g−1. The composition was determined to be 90% Al(OH)2.8(SO4)0.1 (or 78.3% Al(OH)3 plus 10.7% Al2(SO4)3) with 10% Na2SO4 (as an impurity). The material is X-ray amorphous and scanning electron microscopic (SEM) studies show AO to be a network of fibers with a size range of 200–300 nm. Fluoride uptake was found to be unaffected by sodium salts of chloride and sulfate in concentrations up to 500 mg/L. A reduction of fluoride uptake with increasing concentrations of hydroxide and bicarbonate was ascribed to the pH dependence of fluoride sorption, while phosphate appeared to compete with fluoride for sorption sites. The surface site concentration determined by acid–base titrations is 0.5 meq/g (equivalent to a surface site concentration of 8 sites/nm2) and an acidic component of 1.4 meq/g. Continuous packed column experiments showed that at a flow rate of 100 empty bed volumes (eBV) per day using deionized water, the fluoride uptake capacity was 26.2 mg F/g. The pH of treated water ranged between 4.4 and 7.0. In solutions representing buffering conditions of Ethiopian groundwaters (pH 8 ± 0.2, 10mM NaHCO3, 3,000 ppm CO2) uptake capacities at 100 and 10 eBV/day were 4.65 and 9.0 mg F/g, respectively. Aluminum was initially released in concentrations ranging from 0.6 to 2.0 mg/L in solutions when the pH is less than 5. Initial salt concentrations were in the g/L range. With the introduction of calcite postcolumn treatment, the pH was maintained in the range of 7.5–8.5, which significantly reduced salt concentrations due to gypsum precipitation and prevention of early aluminum release were achieved. Due to its high uptake capacity compared with all commercially available adsorbents for fluoride removal, AO is a highly promising material for water defluoridation both at household and community levels.

Zinc Interaction with Glass-Ionomer Restorative Materials

The purpose of this study was to evaluate the effect of addition of zinc sulfate to conventional and resin-modified glass ionomer restorative materials. The samples were prepared by addition of zinc sulfate to glass ionomer at different concentrations. The samples were tested for fluoride, zinc and aluminum release at different time intervals. The antibacterial activity of the restorative materials was tested at 24 and 48 hours. The hardness and diametral tensile strength were measured at 24 hours and 2 weeks. All materials showed highest initial fluoride, zinc and aluminum release rates during the first 2 to 3 days, dropping quickly over 2 weeks and becoming largely stabilized near the test period. The conventional materials released more fluoride and aluminum than that of resin-modified material. Zinc addition increased inhibition of S. mutans growth without threatens the diametral tensile strength and hardness of the tested glass-ionomer materials. Conventional glass-ionomer showed inhibition activity against S. mutans greater than that of resin-modified materials did. Resin-modified glass ionomer showed no significant difference in the inhibitory action. There was highly positive correlation between fluoride, zinc and aluminum release. Chemically-activated materials showed positive and highly significant correlation between ionic release and antibacterial action, while light cured materials showed no significant correlation. There were highly negative correlation between fluoride, zinc, aluminum released and mechanical properties, i.e., restorative materials with high fluoride, aluminum release have lower mechanical properties. Storage of specimens in water for 2 weeks leads to increased diametral tensile strength and hardness of all materials.

Synthesis, characterization and application of lanthanum-impregnated activated alumina for F removal

Elevated fluoride (F) in groundwater presents an obvious environmental concern. Adsorption using activated alumina (AA) is currently the best available technology for F removal, despite its low efficiency, pH dependence, and aluminium (Al) release. The motivation for our study is to synthesise a new F adsorbent by impregnating commercially available granulated AA with lanthanum oxide (LAA), and to explore its F adsorption mechanism on the molecular scale. Five cycles of lanthanum impregnation on AA followed by calcination at 573 K increased the La content up to 19.1% and the F removal from 18.1% by pristine AA to 92.4% by LAA. The SEM, TEM, XRD, TGA, and EXAFS results demonstrated that the 5–20 nm thin flakes of LaOOH on LAA were in an amorphous form, with 7.6 oxygen atoms around each La. This LaOOH layer was uniformly distributed inside the micropores of the 1–3 mm AA granules. LAA exhibited four fold higher F adsorption capacity than AA in the pH range 3.9 to 9.6, with substantially reduced Al release. The ability to regenerate and reuse LAA makes it an attractive sustainable material. Multiple complementary spectroscopic analyses demonstrated that ligand exchange between F and surface hydroxyl groups is the mechanism for F adsorption on LAA. Our work improves the understanding of F interaction with metal oxides on the molecular scale and presents an alternative solution for elevated F water treatment.

The effect of broadleaf woodland on aluminium speciation in stream water in an acid-sensitive area in the UK

Acidification can result in the mobilisation and release of toxic inorganic monomeric aluminium (Al) species from soils into aquatic ecosystems. Although it is well-established that conifer trees enhance acidic atmospheric deposition and exacerbate soil and water acidification, the effect of broad-leaved woodland on soil and water acidification is less clear. This study investigated the effect of broadleaf woodland cover on the acid–base chemistry and Al species present in stream water, and processes controlling these in the acid-sensitive area around Loch Katrine, in the central Highlands, Scotland, UK, where broadleaf woodland expansion is occurring. A nested sampling approach was used to identify 22 stream sampling locations, in sub-catchments of 3.2–61ha area and 0–45% broadleaf woodland cover. In addition, soils sampled from 68 locations were analysed to assess the influence of: (i) broadleaf woodland cover on soil characteristics and (ii) soil characteristics on stream water chemistry. Stream water pH was negatively correlated with sub-catchment % woodland cover, indicating that woodland cover is enhancing stream water acidification. Concentrations of all stream water Al species (monomeric total, organic and inorganic) were positively correlated with % woodland cover, although not significantly, but were below levels that are toxic to fish. Soil depth, O horizon depth and soil chemistry, particularly of the A horizon, appeared to be the dominant controls on stream water chemistry rather than woodland cover. There were significant differences in soil acid–base chemistry, with significantly lower O horizon pH and A horizon base saturation and higher A horizon exchangeable Al in the wooded catchments compared to the control. This is evidence that the mobile anion effect is already occurring in the study catchments and suggests that stream water acidification arising from broadleaf woodland expansion could occur, especially where tree density is high and acid deposition is predominantly in dry or occult forms.