Hydrofluoric Nitric Acid Research Articles

A comparison of two digestion methods and heavy metals determination in sediments

Abstract This study was conducted to evaluate the levels of heavy metal concentrations in sediments and also involves a comparison of two different digestion protocols. The first digestion procedure was done with a mixture of hydrochloric acid and nitric acid while the second digestion method was done using the United States Environmental Protection Agency method 3052 which comprises nitric acid, hydrofluoric acid, hydrochloric acid, and hydrogen peroxide. The sediment samples were analyzed for cadmium, copper, iron, lead, zinc, chromium, manganese, nickel (Cd, Cu, Fe, Pb, Zn Cr, Mn, and Ni) with the aid of atomic absorption spectrophotometer. Concentrations of metals ranged 0–7.0 mg/kg for Cr, 0.5–20.0 mg/kg for Cd, 10.8–112.0 mg/kg for Fe, 0.10–7.20 mg/kg for Pb, 45.69–184.96 mg/kg for Cu, 1.0–73.75 mg/kg for Zn, 1.5–19.7 mg/kg for Mn and nd −3.0 mg/kg for Ni. The order of concentrations of the metals in the samples are Cu > Fe > Zn > Cd > Mn > Pb > Cr > Ni. The second digestion method yielded higher levels of metal concentration. Comparison with theWorld Health Organization (W.H.O) standards for marine sediments showed that the average concentrations of heavy metals were within the permissible limits. Close monitoring and more publicity are further needed to discourage further pollution of the area.

The Influence of Surface Iron Contamination on the Localized Corrosion Resistance of Austenitic and Duplex Stainless Steel, Studied with a Novel Rust Deposition Method

The influence of iron contamination on a stainless steel surface was evaluated based on a novel rust deposition procedure. The main variables that control the corrosion process and the influence of iron contamination on localized corrosion resistance of austenitic and super duplex stainless steel were investigated. Cyclic potentiodynamic polarization tests and environmental exposure with different rust surface contamination degrees were performed. Potentiodynamic polarization curves showed that iron contamination deteriorated the local corrosion resistance of both stainless steels. Environmental salt-spray exposure results indicated that the alloy resistance to rust contamination increased with the materials’ pitting resistance equivalent. Likewise, the extent of localized corrosion decreased with the rust contamination degree. These findings suggested that preferential corrosion from rust contamination was associated with the occluded solution chemistry. Environmentally friendly cleaning methods, including chemical treatments and laser cleaning, were evaluated as alternatives to hazardous pickling based on hydrofluoric-nitric acid. Last, practical recommendations for rust contamination of stainless steel are addressed.

Development of a Sulfamic Acid-Based Chemical Formulation for Effective Cleaning of Modified 9Cr–1Mo Steel Steam Generator Tubes

A new sulfamic acid-based formulation is developed for the effective chemical cleaning of modified 9Cr–1Mo steel as a replacement for the conventional corrosive nitric acid (HNO3) and hydrofluoric acid (HF) mixture. The effect of sulfamic acid concentrations and inhibitor (2-mercaptobenzimidazole, MBI) on the metal loss during cleaning of modified 9Cr–1Mo steel was studied using weight loss and electrochemical impedance spectroscopic methods. The metal loss was found to increase with increase in acid concentration, but it was significantly lower with increasing inhibitor concentration, with an efficiency of > 90%. The corrosion rates of modified 9Cr–1Mo steel with 10% sulfamic acid + 2 mM MBI, 10% sulfamic acid without inhibitor and HNO3 + HF mixture were 1290, 6426, and 303,515 μm year−1 respectively. The optimal composition for efficient cleaning, with least base metal loss, was found to be 10% sulfamic acid + 2 mM MBI. Laser Raman spectroscopic (LRS) analysis of the corrosion products obtained during chemical cleaning process revealed that a protective chromium oxide film was formed during the cleaning with sulfamic acid + inhibitor as compared to iron oxide-based films with HNO3 + HF mixture and 10% sulfamic acid solutions.

Risk assessment of heavy metals content in different hair dyes and their users’ urine samples

ABSTRACT Human toxicity of heavy metals is the result of long-term exposure to pollutants found in hair dyes. In this study, levels of lead (Pb), cadmium (Cd), mercury (Hg) and urine were evaluated in various hair dyes products sold in local stores in Riyadh using inductive coupled plasma optical emission spectrometry (ICP-OES) after digestion with a mixture of nitric acid (HNO3), hydrofluoric acid (HF) and hydrogen peroxide (H2O2) for hair dyes, while a mixture of HNO3 and H2O2 was used for urine. The mean concentrations of the selected heavy metals in hair dye ranged (0.0015–0.0035 ppm) from Cd, (0.003–0.014 ppm) from Pb, which were within the permissible international limits, while for Hg (1.1–4.3 ppm) from Hg was higher than the permissible international limits. The mean concentrations of the selected heavy metals in urine ranged (0. 002, 0.011 and 1.3 ppm) from Cd, Pb, and Hg respectively in the urine. However, in the case of urine samples, the average concentration of Pb was higher than the permitted international limits. The current study showed that the use of hair dyes exposes users to low concentrations of toxic heavy metals that can cause potential health damage to users.

Effect of Nitric Hydrofluoric Acid Treatment on Brazing of Alumina Ceramics and Pure Titanium

Effect of Nitric Hydrofluoric Acid Treatment on Brazing of Alumina Ceramics and Pure Titanium

Two-step extraction method for lead isotope fractionation to reveal anthropogenic lead pollution

ABSTRACTThis study developed the 2-step extraction method which eluted the Pb adsorbing on the surface of sediments in the first solution by aqua regia and extracted the Pb absorbed inside particles into the second solution by mixed acid of nitric acid, hydrofluoric acid and hydrogen peroxide solution. We applied the method to sediments in the enclosed water area and found out that the isotope ratios of Pb in the second solution represented those of natural origin. This advantage of the method makes it possible to distinguish the Pb between natural origin and anthropogenic source on the basis of the isotope ratios. The results showed that the method was useful to discuss the Pb sources and that anthropogenic Pb in the sediment samples analysed was mainly derived from China because of transboundary air pollution.

Chemical Milling of Cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo Alloys in Hydrofluoric-Nitric Acid Solutions

The behavior of cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo during chemical milling in hydrofluoric-nitric (HF-HNO3) acid solutions with 1:3 and 1:11 molar ratios was investigated using electrochemical and atomic force microscopy (AFM) techniques. Faster corrosion rate in 1:3 solutions was measured for Ti-6Al-4V than for Ti-6Al-2Sn-4Zr-2Mo, whereas in 1:11 solution Ti-6Al-2Sn-4Zr-2Mo exhibited higher corrosion rate. Scanning Kelvin probe force microscopy measurements revealed difference in the Volta potential between the α-laths and the β-layers in the Widmansttaten microstructure indicating operation of microgalvanic cells between the microconstituents when in contact with HF-HNO3 solution. The AFM topography measurements demonstrated faster corrosion of the α-laths compared to the β-layers, in both alloys. In 1:3 solutions, higher α/β height difference was measured in Ti-6Al-4V, whereas in 1:11 solution, the difference was higher in Ti-6Al-2Sn-4Zr-2Mo. The results revealed that the chemical milling behavior o...

Characterization of the products obtained from the reactions of Zircaloy-4 with an acid mixture of concentrated HNO3and dilute HF with the aim of understanding pickle salts of zirconium alloys

Pickling of zirconium alloys in nitric-hydrofluoric acid has been widely used in the nuclear materials industry. However, the pickle salts still remain a curiosity and a thorough knowledge of the products of the system Zr–(HNO3–HF) still needs to be well established. The present study investigated the products obtained from the reactions of Zircaloy-4 with an acid mixture of HNO3 (65 wt%) and HF (40 wt%) in a volume ratio of 94 : 6, similar to the one used under nuclear industry conditions. It shows that after the reactions, a gel-like solution was present. When drying it at a high relative humidity (at 25 °C and 70 ± 5% RH), an amorphous solid product formed, while in the case of at a low relative humidity (at 15/25 °C and 25 ± 5% RH), besides the amorphous solid, crystalline zirconium hydroxide nitrates Zr(OH)2(NO3)2·4.71H2O and Zr(OH)2(NO3)2·1.65H2O (possible) with low degree of crystallinity formed. These compounds were identified with the help of successfully synthesizing completely crystalline Zr(OH)2(NO3)2·4.71H2O from the gel-like solution by ultrasonication, which in itself was a breakthrough. Such a study can be expected to provide a deep understanding of pickle salts of zirconium alloys in practical use.

Determination of oxygen in acid-treated high-purity niobium by X-ray photoelectron spectroscopy

ABSTRACTHigh-purity niobium was immersed in nitric acid and hydrofluoric acid for two minutes and the resulting product was characterized. Scanning electron microscopy was employed to characterize the morphology of the acid treated product. Inert gas fusion was used for determination of oxygen in the high-purity niobium. X-ray photoelectron spectroscopy was employed to characterize the surface ratio of oxygen to niobium. The oxygen concentration was 30 ppm in the acid-treated material and 70 ppm in the untreated material. X-ray photoelectron spectroscopy was employed to characterize the reduction of oxygen at the surface. The ratio of oxygen to niobium decreased from 9.75 to 2.60 without treatment compared to acid treatment for two minutes. The concentrations of adsorbed water and niobium oxide decreased following etching. The acid-treated high-purity niobium was characterized by argon ion bombardment; adsorbed water molecules and niobium oxides were not present but non-lattice oxygen was observed.

Determination of Trace Germanium in Plant Samples by Dry Ashing-Atomic Fluorescence Spectrometry

To reduce the limit of detection (LOD) and allow the accurate determination of Ge, a dry ashing method was performed to enrich the Ge in plant samples. A method for the determination.of trace Ge in plant samples by HG-AFS was established. Study of the effect of temperature on the ashing of plant samples showed that no volatile loss of Ge occurred even at 900 °C. Additional experiments indicated that a 4 h burning process at 600 °C would be sufficient to fully ash the plant samples. Various digestion methods (involving nitric acid, hydrofluoric acid, and sulfuric acid digestion methods) for ashed samples were investigated. High-temperature ashing with large sample weights was used, which could reduce the reagent doses and the method's LOD effectively and simultaneously, the precision of the method was improved. The method's LOD was 0.27 ng · g(-1), and the relative standard deviation was 3.99%-6.81%. Verified with national biological reference materials (grade I), the proposed method was accurate and reliable.

Development of fine-grain size titanium 6Al–4V alloy sheet material for low temperature superplastic forming

Fine-grained titanium 6Al–4V alloy, which typically has a grain size of about 1–2μm, can be made to superplastic form at around 800°C with special processing. The normal temperature for superplastic forming (SPF) with conventional titanium 6Al–4V sheet material is 900°C. The lower temperature performance is of interest to the Boeing Company because it can be exploited to achieve significant cost savings in processing by reducing the high-temperature oxidation of the SPF dies, improving the heater rod life for the hot presses, increasing operator safety and replacing the chemical milling operation to remove alpha case contamination with a less intensive nitric hydrofluoric acid etchant (pickle). In this report, room temperature tensile tests and elevated temperature constant strain rate tensile tests of fine-grained Ti–6Al–4V sheets provided by the Baoti Company of Xi׳an, China, were conducted according to the test method standards of ASTM-E8 and ASTM-E2448. The relationships among the processing parameters, microstructure and superplastic behavior have been analyzed. The results show that two of the samples produced met the Boeing minimum requirements for low-temperature superplasticity. The successful material was heat-treated at 800°C subsequent to hot rolling above the beta transus temperature, Tβ-(150–250°C). It was found that the sheet metal microstructure has a significant influence on superplastic formability of the Ti–6Al–4V alloy. Specifically, fine grains, a narrow grain size distribution, low grain aspect ratio and moderate β phase volume fraction can contribute to higher superplastic elongations.

The Surface Treatment Effect on Combination of Ni-Ti Alloy Fiber and Epoxy Resins

Surface treatment of Ni-Ti fibers were processed by using various chemical solutions, including the hydrochloric acid, the mixture solvent of hydrofluoric-nitric acid and the solvent of potassium dichromate-vitriol. Scan electric microscopy (SEM) and fiber pull-out test were adopted to characterize the corrosive effect of the chemicals and the shear strength of the fiber/resin interface. The results showed that the surface of the alloy fiber is corroded most seriously after acid treatment with the mixture of hydrofluoric acid and concentrated nitrate. Tensile test result also shows that the maximum interfacial bonding strength is obtained by treatment with this acid. The effect of the cross-link agent in epoxy was also discussed.

Distillation Separation of Hydrofluoric Acid and Nitric Acid from Acid Waste Using the Salt Effect on Vapor–Liquid Equilibrium

This study presents the distillation separation of hydrofluoric acid with use of the salt effect on the vapor–liquid equilibrium for acid aqueous solutions and acid mixtures. The vapor–liquid equilibrium of hydrofluoric acid + salt systems (fluorite, potassium nitrate, cesium nitrate) was measured using an apparatus made of perfluoro alkylvinylether. Cesium nitrate showed a salting-out effect on the vapor–liquid equilibrium of the hydrofluoric acid–water system. Fluorite and potassium nitrate showed a salting-in effect on the hydrofluoric acid–water system. Separation of hydrofluoric acid from an acid mixture containing nitric acid and hydrofluoric acid was tested by the simple distillation treatment using the salt effect of cesium nitrate (45 mass%). An acid mixture of nitric acid (5.0 mol · dm−3) and hydrofluoric acid (5.0 mol · dm−3) was prepared as a sample solution for distillation tests. The concentration of nitric acid in the first distillate decreased from 5.0 mol · dm−3 to 1.13 mol · dm−3, and the concentration of hydrofluoric acid increased to 5.41 mol · dm−3. This first distillate was further distilled without the addition of salt. The concentrations of hydrofluoric acid and nitric acid in the second distillate were 7.21 mol · dm−3 and 0.46 mol · dm−3, respectively. It was thus found that the salt effect on vapor–liquid equilibrium of acid mixtures was effective for the recycling of acids from acid mixture wastes.

Routine to estimate composition of concentrated metal–nitric–hydrofluoric acid pickle liquors

Hydrometallurgical processes need feasible methods for controlling the composition of concentrated metal and acid solutions that provide real-time measurements of the main process parameters. A large contrast between controlling methods appears when accuracy and speed are evaluated. This paper proposes a new titration method for determining the composition of concentrated solutions of nitric, hydrofluoric acids containing iron, chromium and nickel, originating from stainless steel pickling. Methods for controlling this process depend usually on probes in direct contact with the pickling bath which are used to calculate, in an approximate manner, bath composition. The proposed analysis consists of determining the pickling bath composition by fitting simulated titration curves to experimental plots, using various metals, acid and anion concentrations as parameters. Sodium and potassium hydroxide were used to titrate 12 synthetic pickling liquors. Results show that sodium hydroxide cannot be used as titration agent as sodium–fluoride ion interaction displaces equilibrium and makes singular points of titration curves to overlap. Titration with potassium hydroxide provides good correlation indexes and low errors in concentration prediction and is recommended for composition measurement. Mean relative error for metal concentrations is 0.4% for iron and nickel and 1.4% for chromium; while the mean relative error for anions is 4% for fluoride and 1% for nitrate.

Pitting corrosion of sheets of a nickel-base superalloy

Cold rolled sheets of a nickel-base superalloy are used in building gas turbine engines. After rolling to the final gauge, the sheets were annealed at 1180 °C. Pickling of the sheets was carried out to remove the scale and the oxidized layer. It was observed that there was heavy incidence of pitting with perforations at several locations due to pits penetrating through the thickness. The sheets got rejected, resulting in heavy loss. The superalloy contains 25 wt% chromium, 15 wt% tungsten. Tungsten provides high resistance to pitting corrosion. With such a high level of W, the grade has a high Pitting Resistance Equivalent. Further it is a single-phase material. Pitting attack is thus totally unexpected. The failure was analyzed. Pickling process for this material normally involves the usage of salt bath, sulfuric acid, nitric acid, and/or hydrofluoric-nitric acid baths. In the case under study, satisfactory pickling was not achieved this way; discoloration and deposits were persistently present on the sheet surface. In order to improve the surface quality, the sheets were dipped in hydrochloric acid bath for a long time. Hydrochloric acid bath was in aged condition; by that point of time, the bath went through extensive usage for pickling of different grades of steels. Consequently there was significant accumulation of iron salts in the bath. It is known that ferric and chloride ions cause significant acceleration in pitting. The bath was stagnant and the time of immersion of the sheets in the bath was long. The material failed under the combination of these adverse conditions. The paper brings out the details of the failure analysis carried out.

Metal Pollution Assessment of Surface Sediments Along a New Gas Pipeline in the Niger Delta (Nigeria)

Chromium, nickel, copper, zinc and cadmium were determined in sediments of the Niger Delta (Nigeria) in order to discriminate between natural metal sources and anthropogenic ones. Surface sediments were collected at seven sites along a new gas pipeline near Port Harcourt, between the New Calabar River and the Bonny River towards Bonny town. Chemical characterisation is obtained by hydrofluoric-nitric acid digestion procedure, providing the 'total' ('residual') metal contents. Information about the anthropogenic metal fraction was obtained by cold diluted hydrochloric acid extraction procedure. This 'labile' acid soluble fraction of metals, perhaps due to relatively recent inputs in the sediments, constitutes the fraction more likely to be available to marine organisms, and furnishes a first evaluation of the possible toxicity of sediments of this sensitive ecosystem. Zinc appears to be the most available of all the heavy metals: its 'labile' fraction attains 40-50% of the 'total' zinc in sediment. Sites near Port Harcourt city are the most contaminated. All the examined metals are one order of magnitude below the respective values proposed as a limit for toxicity and are comparable with those observed by other authors in similar Niger Delta areas. Some anomalous data found near Port Harcourt city suggest that zinc and cadmium are the metals that require further monitoring. Their anthropogenic source could be derived from urban and industrial sewage.

ステンレス鋼およびチタンの硝ふっ酸酸洗におけるNOxガス抑制のための新技術開発

ステンレス鋼およびチタンの硝ふっ酸酸洗におけるNOxガス抑制のための新技術開発

Electrolytic pickling of stainless steel studied by electrochemical polarisation and DC resistance measurements combined with surface analysis

A tightly adhering oxide scale is formed on stainless steels when they are annealed. The removal of the oxide scale and chromium-depleted subscale is one of the most important processes during the stainless steel production. Electrolytic pickling in neutral sodium sulphate is widely used for oxide scale removal. This study describes the different stages of the oxide scale removal on Polarit 725 (EN 1.4301) stainless steel in sodium sulphate solution. A mechanism of the scale dissolution is also proposed. The dissolution is proposed to proceed by the electrochemical reactions of the scale in three successive stages. At the beginning of the pickling process chromium and manganese of the outer oxide layer were preferentially dissolved. When the chromium content of the outer layer decreased, the scale was enriched of iron. The electrode potential was then increased and the scale thickness greatly reduced. Finally a steady state was obtained and a thin oxide layer, rich in iron and silicon, was left on the surface. Silicon could not be removed by the electrolytic pickling and post-treatment in nitric–hydrofluoric acid is required.

Influence of surface preparation on performance of chromate conversion coatings on Alclad 2024 aluminium alloy: Part I: Nucleation and growth

The microstructure and morphology of the surface of aluminium alloys strongly affect the nucleation, growth, and protective properties of chromate conversion coatings. Samples of AA 2024-T3 cladded with AA1230 were pretreated with two different procedures before they underwent a chromating process, which consisted of dipping in a commercial Alodine 1200 solution. In one procedure, an extra step, consisting of immersion in nitric–hydrofluoric acid solution for 30 s (desmutting bath), was carried out after immersion in sulfuric –phosphoric acid solution (acid pickling bath). Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and electrochemical investigations highlighted the fact that this extra step in the pretreatment route gave rise to a more etched, but less reactive surface, due to the removal of a large amount of cathodic sites, mainly related to AlFeSi precipitates present in the clad layer. A similar effect, but on a smaller scale, was caused also by the increase of the time of immersion in sulfuric –phosphoric acid solution. The decrease of galvanic coupling gives rise to a more homogeneous nucleation of the chromate conversion coating on the surface of the Alclad 2024-T3. Moreover, the chromate film tends to be denser and with fewer defects.

A multi-element profile of house dust in relation to exterior dust and soils in the city of Ottawa, Canada

This paper presents multi-element profiles of indoor dust versus exterior soils and dusts from 50 residences located in 10 neighborhoods across Ottawa, the capital city of Canada. Mercury concentrations were determined using nitric–sulphuric acid digestion and cold vapor AAS. Concentrations of 31 other elements were determined using nitric–hydrofluoric acid digestion and ICP-MS. Comparisons of household dust, garden soil and street dust at the individual residence scale and at the community scale were based on a consistent 100–250 μm particle size fraction. Results showed housedust samples to contain significantly higher concentrations of many key elements, including lead, cadmium, antimony and mercury, than either street dust or garden soil samples. Also, housedust profiles revealed a distinct multi-element signature in relation to exterior dust and soil samples. Interestingly, garden soil contained higher concentrations of aluminum, barium and thallium than either house or street dust. Geometric mean concentrations (mg/kg) of these elements in household dust/garden soil were: lead 233/42; cadmium 4.42/0.27; antimony 5.54/0.25; mercury 1.728/0.055; aluminum 24281/55677; barium 454/763; and thallium 0.14/0.29. Street dust contained lower geometric mean concentrations than garden soil for 23 out of a total of 32 elements. In general, indoor/outdoor concentration ratios varied widely from one element to another, and from one residence to another within the community. In the case of Ottawa, which is a city with a low concentration of heavy industries, it would be difficult-to-impossible to accurately predict indoor dust concentrations based on exterior soil data. It is concluded that dust generated from sources within the house itself can contribute significantly to exposures to certain elements, such as lead, cadmium, antimony and mercury.