Study on thermal stability of tertiary pyridine resin

The fundamental properties of tertiary pyridine resin (TPR) and its mixtures with methanol/HCl and HNO₃ were investigated in order to evaluate the thermal stability of TPR and to determine the conditions necessary to avoid runaway reactions. Based on experimental DSC results, it was found that TPR with HCl was thermally stable, but strong decomposition was possible with TPR in the presence of HNO₃. From the results of heating tests on the gram scale, TPR with HNO₃ reacted violently under high temperature regardless of HNO₃ concentration and presence or absence of methanol. However, it was considered that the violent exothermic reaction could be controlled by heating temperature.     

210Pb and210Po in tobacco-with a special focus on estimating the doses of210Po to man

Studies have been carried out on the solubility of Pu(III) oxalate by precipitation of Pu(III) oxalate from varying concentrations of HNO₃/HCl (0.5–2.0M) solutions and also by equilibrating freshly prepared Pu(III) oxalate with solutions containing varying concentrations of HNO₃/HCl, oxalic acid and ascorbic acid. Pu(III) solutions in HNO₃ and HCl media were prepared by reduction of Pu(IV) with ascorbic acid. 0.01–0.10M ascorbic acid concentration in the aqueous solution was maintained as holding reductant. The solubility of Pu(III) oxalate was found to be a minimum in 0.5M–1M HNO₃/HCl solutions containing 0.05M ascorbic acid and 0.2M excess oxalic acid in the supernatant.     

Recovery of palladium using chemically modified cedar wood powder

Japanese cedar wood powder (CWP) was chemically modified to a tertiary-amine-type adsorbent and studied for the selective recovery of Pd(II) from various industrial waters. Batch adsorption tests performed from 0.1 M to 5 M HCl and HNO₃ systems reveal stable performance with better results in HNO₃ medium. The maximum loading capacity for Pd(II) was studied in HCl as well as in HNO₃. A continuous-flow experiment taking a real industrial solution revealed the feasibility of using modified CWP for the selective uptake and preconcentration of traces of palladium contained in acidic effluents. In addition, stable adsorption performance even on long exposure to γ-irradiation and selective recovery of palladium from simulated high-level liquid waste (HLW) are important outcomes of the study.     

Assessment of copper(II) biosorption from aqueous solution by agricultural and industrial residues

In this study, newspaper scraps (NS) and maize spatha (MS) treated in turn by HNO₃ and MeOH were evaluated for the biosorption of Cu²⁺ ions, on the basis of batch experiments. The effects of several parameters were investigated, including contact time, solution pH, shaking speed, biosorbent dosage and ionic strength. Under optimal conditions, the maximum sorption capacities (Q_max) were (60.386 ± 0.006) and (44.90 ± 0.02) μmol Cu²⁺ per g of sorbent, respectively, for NS and MS chemically treated with HNO₃. The optimal parameters were pH: 5, contact time: 40 min and shaking speed: 100 rpm for NS, while for MS the same parameters were pH 5, 20 min and 150 rpm, respectively. It was found that Cu²⁺ biosorption is disfavored by an increase in ionic strength and by the presence of some interfering cations. The experimental data obtained with NS best matched the Langmuir’s sorption model (R² = 0.994) while the Temkin model best described biosorption on MS (R² = 0.987). The biosorption of Cu²⁺ on both materials followed pseudo-second order kinetics, and the desorption of Cu²⁺ ions was effective in 0.01 M HCl solution.     

Determination of inorganic and total mercury by vapor generation atomic absorption spectrometry using different temperatures of the measurement cell

A simple and inexpensive laboratory-built flow injection vapor generation system coupled to atomic absorption spectrometry (FI-VG AAS) for inorganic and total mercury determination has been developed. It is based on the vapor generation of total mercury and a selective detection of Hg^2 + or total mercury by varying the temperature of the measurement cell. Only the inorganic mercury is measured when the quartz cell is at room temperature, and when the cell is heated to 650 °C or higher the total Hg concentration is measured. The organic Hg concentration in the sample is calculated from the difference between the total Hg and Hg^2 + concentrations. Parameters such as the type of acid (HCl or HNO₃) and its concentration, reductant (NaBH₄) concentration, carrier solution (HCl) flow rate, carrier gas flow rate, sample volume and quartz cell temperature, which influence FI-VG AAS system performance, were systematically investigated. The optimized conditions for Hg^2 + and total Hg determinations were: 1.0 mol l^− 1 HCl as carrier solution, carrier flow rate of 3.5 ml min^− 1, 0.1% (m/v) NaBH₄, reductant flow rate of 1.0 ml min^− 1 and carrier gas flow rate of 200 ml min^− 1. The relative standard deviation (RSD) is lower than 5.0% for a 1.0 μg l^− 1 Hg solution and the limit of quantification (LOQ, 10 s) is 55 ng g^− 1. Certified samples of dogfish muscle (DORM-1 and DORM-2) and non-certified fish samples were analyzed, using a 6.0 mol l^− 1 HCl solution for analyte extraction. The Hg^2 + and CH₃Hg⁺ concentrations found were in agreement with certified ones.     

Adsorption behavior of 181W and 93mMo as lighter homologues of seaborgium (Sg) in HF/HNO3 on anion-exchange resin

Adsorption of carrier-free radiotracers ¹⁸¹W and ^93mMo produced in the ¹⁸¹Ta(p, n) and ^natNb(p, n) reactions, respectively, on anion-exchange resin was studied in mixed solution of HF and HNO₃ in a concentration range of 10⁻⁴–10⁻¹ M HF/0.1 M HNO₃. Distribution coefficients (K _d) of ¹⁸¹W and ^93mMo at 70 °C showed the V-shaped variation with the minimum at around 10⁻¹ M HF/0.1 M HNO₃, although variation of the K _d values for ^93mMo was quite small compared with that for ¹⁸¹W. Formation of oxofluoro complexes for W and Mo is briefly discussed.     

Size-controlled synthesis and formation mechanism of manganese oxide OMS-2 nanowires under reflux conditions with KMnO4 and inorganic acids

This study presents a simplified approach for size-controlled synthesis of manganese oxide octahedral molecular sieve (OMS-2) nanowires using potassium permanganate (KMnO₄) and different inorganic acids (HCl, HNO₃, and H₂SO₄) under reflux conditions. The morphology and nanostructure of the synthesized products are characterized by X-ray diffraction, Ar adsorption, and electron microscopy analysis, in order to elucidate the controlling effects of acid concentration and type as well as the formation mechanism of OMS-2 nanowires. The concentration of inorganic acid is a crucial factor controlling the phase of the synthesized products. OMS-2 nanowires are obtained with HCl at the concentration ≥0.96 mol/L or with HNO₃ and H₂SO₄ at the concentrations ≥0.72 mol/L. Differently, the type of inorganic acid effectively determines the particle size of OMS-2 nanowires. When the acid is changed from HCl to HNO₃ and H₂SO₄ in the reflux system, the average length of OMS-2 declines significantly by 60–70% (1104–442 and 339 nm), with minor decreased in the average width (43–39 and 34 nm). The formation of OMS-2 nanowires under reflux conditions with KMnO₄ and inorganic acids involves a two-step process, i.e., the initial formation of layered manganese oxides, and subsequent transformation to OMS-2 via a dissolution-recrystallization process under acidic conditions. The proposed reflux route provides an alternative approach for synthesizing OMS-2 nanowires as well as other porous nano-crystalline OMS materials.     

Selective synthesis of functionalized pyrazoles from 5-amino-1H-pyrazole-4-carbaldehydes with sodium nitrite: 5-Amino-4-nitrosopyrazoles and pyrazole-4-carbaldehydes

A novel and efficient redox reaction was developed to react 5-amino-1H-pyrazole-4-carbaldehyde with sodium nitrite (NaNO₂) in an acidic solution (HCl/MeOH) to generate 5-amino-4-nitrosopyrazole, pyrazole-4-carbaldehyde, or diazenylpyrazole selectively. The results showed that 5-amino-4-nitrosopyrazoles were formed as the major product in the diluted acidic solution (≤2 N HCl in MeOH solution) through redox, formylation, and nitrosation reactions of NaNO₂. Intriguingly, pyrazole-4-carbaldehyde was the main product under 6 N HCl in MeOH solution.     

Selective separation and reversed phase extraction of zirconium and hafnium from a multitracer solution

The solvent extraction of Zr and Hf was studied using 444-trifluoro-1-(2-thienyl)-1,3-butanedione (TTA) from a multitracer solution containing carrier-free radioisotopes of Zr, Hf, and other elements. The multitracer was prepared from Au foil irradiated with high-energy heavy-ion beams. Effects of HCl and HNO₃ concentrations and organic solvent on the extraction and coextraction of other radionuclides have been studied. It was found that decalin (decahydronaphthalene) was the best solvent among 14 solvents studied and the optimum aqueous phase was 2 mol·dm^–3 HCl or HNO₃. About 2–10% of Sr, Rb, Sc and Nb were coextracted with Zr and Hf. The reversed phase extraction of Zr and Hf was also developed by using ethylenediaminetetraacetic acid (EDTA) solution at pH range of 8.5–10.     

Valence properties of tellurium in different chemical systems and its determination in refractory environmental samples using hydride generation – Atomic fluorescence spectroscopy

Using HG – AFS as a powerful tool to study valence transformations of Te, we found that, in presence of HCl and at high temperature, Te can form volatile species and be lost during sample digestion and pre-reduction steps. It was also noticed that the chemical valences of Te can be modified under different chemical and digestion conditions and even by samples themselves with certain matrices. KBr can reduce Te(VI) to Te(IV) in 3.0 M HCl at 100 °C, but when HNO₃ was >5% (v/v) in solution, Br₂ was formed and caused serious interference to Te measurements. HCl alone can also pre-reduce Te(VI) to Te(IV), only when its concentration was ≥6.0 M (100 °C for 15min). Among 10 studied chemical elements, only Cu²⁺ caused severe interference. Thiourea is an effective masking agent only when Cu²⁺ concentration is equal or lower than 10 mg/L. Chemical reagents, chemical composition of sample, as well as the modes of digestion can greatly affect Te valences, reagent blanks and analytical precisions. A protocol of 2–step–digestion followed by an elimination of HF is proposed to minimize reagent blank and increase the signal/noise ratios. It is important to perform a preliminary test to confirm whether a pre-reduction step is necessary; this is especially true for samples with complex matrices such as those with high sulfide content. The analytical detection limits of this method in a pure solution and a solid sample were 100 ng/L and 0.10 ± 0.02 μg/g, respectively.     

Liquid — Liquid extraction of silver(I) by diphenyl-2-pyridylmethane in benzene from aqueous mineral acid — Thiocyanate solutions

Liquid — liquid extraction of Ag(I) by diphenyl-2-pyridylmethane (DPPM) in benzene from aqueous nitric and sulfuric acid solutions containing thiocyanate ions has been studied at ambient temperature (24±2 °C). The metal is extracted quantitatively from 0.01M HNO₃+0.02M KSCN; or 0.25M H₂SO₄+0.02M KSCN by 0.1M DPPM (optimum extraction conditions). Slope analysis indicates that two types of ion-pair complexes i.e. [(DPPMH)⁺·Ag(SCN) ₂ ^– ] and [(DPPMH) ₂ ⁺ ·Ag(SCN) ₃ ^2– ] are involved in the extraction process. Separation factors determined at optimum conditions reveal the separation of Ag(I) from Cs(I), Br(I), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Fe(III), Au(III) (from HNO₃ solution only), Cr(III), Hf(IV), Ta(V), Sn(IV) and Cr(VI). With the exception of thiosulfate, other complexing anions like ascorbate, acetate, citrate, oxalate do not hinder the extraction of Ag(I) under optimum conditions.     

Liquid-liquid extraction of 233Pa(V) with Aliquat 336</p> </p>

Summary The extraction of protactinium with Aliquat 336 (methyl-tri-caprylyl ammonium chloride) in toluene, cyclohexane and chloroform from HCl, HNO₃, H₂SO₄, HClO₄, HF and mixed HCl-HF media was investigated by radioactive tracer technique. Distribution ratios of protactinium between the aqueous solution and the organic phase were determined as a function of shaking time, concentrations of acid in aqueous solution phase, extractant concentration and type of diluents in the organic phase. Aliquat 336 can almost quantitatively extract protactinium from strong HCl solution. At the same time, small amounts of HF in HCl solutions have a strong effect on Pa distribution.</p> </p>     

Analytical evaluation of a cup-horn sonoreactor used for ultrasound-assisted extraction of trace metals from troublesome matrices

In this work, a sample preparation method based on ultrasound-assisted extraction of trace metals from a variety of biological and environmental matrices using a cup-horn sonoreactor is described. Diluted acids (HNO₃, HCl and HF) and oxidants (H₂O₂) were tried for extraction, the extracts being directly analyzed by electrothermal-atomic absorption spectrometry. The cup-horn sonoreactor combines the advantages of probe and bath sonicators, allowing a variety of conditions to be used for metal extraction from troublesome matrices. This system facilitates the use of HF to destroy the silicate lattice, application of simultaneous treatments of up to six samples and short treatment times. Quantitative metal recoveries are achieved from different matrices (animal and vegetal tissues, soil, sediment, fly ash, sewage sludge) under a set of extraction conditions ranging from the use of 3 min sonication time and 3% volume/volume HNO₃ for some animal tissues to 40 min sonication time along with 5% volume/volume HNO₃ + 20% volume/volume HF for sediment. Vegetal matter required the use of 5% volume/volume HNO₃ + 5% volume/volume HF for extraction of some elements.     

Runaway effects of nitric acid on methyl ethyl ketone peroxide by TAM III tests

Methyl ethyl ketone peroxide (MEKPO) is an unstable material above certain limits of temperature, decomposing into chain reactions by radicals. The influence of runaway reactions on this basic characteristic was assessed by evaluating kinetic parameters, such as activation energy (E _a ), frequency factor (A), etc., by thermal activity monitor III (TAM III). This was done under three isothermal conditions of 70, 80, and 90 °C, with MEKPO 31 mass% combined with nitric acid (HNO₃ 6 N) and sodium nitrate (NaNO₃ 6 N). Nitric acid mixed with MEKPO gave the maximum heat of reaction (△H _d ) and also induced serious reactions in the initial stage of exothermic process under the three isothermal temperatures. The time to maximum rate (TMR) also decreased when HNO₃ was mixed with MEKPO. Thus, MEKPO combined with HNO₃ 6 N forms a very hazardous mixture. Results of this study will be provided to relevant plants for alerting their staff on adopting best practices in emergency response or accident control.     

Cation-exchange isolation and ICP-AES determination of rare earth elements in geological silicate materials

An ion-exchange ICP-AES method for the determination of 14 rare earth elements (REEs) and Y in geological materials is described. The separation of REEs from Ba using a Dowex 50W-X8 cation resin is especially considered since Ba is an excellent internal standard for REE determination by this technique. Although total recovery with either HCl or HNO₃ may be achieved, it is advantageous to use both acids sequentially. Volume and concentration of the acids are optimized attaining a quantitative separation of REEs from Ba by the introduction of the sample solution in a 1.75 mol/l HCl medium, followed by elution with 2 mol/l HNO₃ to remove matrix elements and with 7 mol/l HNO₃ to elute the analytes. The total elution volume is significantly reduced without decreasing the efficiency. The behaviour of the matrix constituents under the selected conditions is also studied, evaluating their elution percentages in each step. The final solution obtained contains only the REEs and Y, with the bulk of Sc and minor amounts of Cr, Fe, Hf and Ta. Experimental data for 5 geological reference standards (NIM-G, GSP-1, AGV-1, NIM-L and NIM-S) are reported. Good agreement between the present results and previously accepted values by various analytical techniques is observed.     

Corrosion behavior of tantalum alloying on γ‐TiAl by double‐glow plasma surface metallurgy technique

The Ta coating with corrosion resistance is grown on the γ‐TiAl substrate by double‐glow plasma surface metallurgy technique, followed by the electrochemical test in 10 wt%, 20 wt% HCl and 10 wt%, 40 wt% H₂SO₄ solution. The data of nanohardness and elastic modulus are collected by the nanoindention test. The adhesion strength of Ta coating is investigated by means of the scratch test. The study of corrosion resistance is performed using potentiodynamic polarization and electrochemical impedance spectroscopy and measured by SEM and X‐ray diffraction. Results highlight that the Ta coating is tightly bonded to the γ‐TiAl substrate, consisting of the deposition layer and diffusion layer. Experimental data indicate that the Ta coating presents excellent corrosion resistance, which is confirmed by the high values of polarization resistance (R_p) and the low values of corrosion current density (i_corr). The surface nanohardness of the Ta coating is improved from 3.41 to 7.29 GPa, nearly twice of that of the substrate. The Ta₂O₅ formed on the coating is able to hold back the penetration of adverse ions inwardly, owing to its dense structure and adhesion effect. Copyright © 2017 John Wiley & Sons, Ltd.     

Determination of trace metals in Nile River and ground water by differential pulse stripping voltammetry

The determination of trace metals in river water and ground water by DPSV is seriously disturbed by the presence of organic complexes. The influence of these substances can be eliminated by acidification of the samples with acids. Cd, Pb and Cu were determined at pH 1.1 (HNO₃ medium) and Zn, Cd, Pb and Cu at pH 2 (HCl medium), in both the Nile river and ground water. Zn was determined at pH 3.5 in HCl and pH 4.5 in HNO₃, after neutralizing the samples with NH₃/NH₄Cl buffer. Manganese could then be determined, after further addition of ammoniacal buffer solution up to pH 7.5 and 8.5. Ni and Co were determined in the adsorptive mode after formation of dimethylglyoximates at pH 9.2. The effect of pH on the stripping peaks of manganese was studied. Good agreement was observed between DPSV and AAS results for Zn, Cd, Pb, Cu and Mn, but the concentrations of Ni and Co were below the detection limits for AAS. Good agreement was obtained between DPSV results in HCl and HNO₃ for Ni and Co. The results indicate that decomposition of organic complexes by acidification with HNO₃ is better than in the case with HCl for Zn, Pb, Cu, Ni and Co, but HCl is better than HNO₃ for Cd and Mn.     

Application of Metalfix Chelamine prior to the determination of noble metals by the inductively coupled plasma atomic emission spectrometry

Metalfix Chelamine chelating resins of two different bead sizes (150-300 and 40-80 μm) were examined and compared regarding their application for sorption of Au, Ir, Pd, Pt, Rh and Ru ions from medium of HCl, HNO₃ and mixtures of HCl and HNO₃. The quantitative enrichment of Au, Ir, Pd and Pt was established for the resin of 150-300 μm particle size and for solutions acidified with HCl and HNO₃ (3:1) up to the concentration of 0.50 mol l⁻¹. In the case of Rh and Ru, the uptake of these metals by the resin was lower than 50%. For the elution, solutions of different reagents, i.e. HCl, HNO₃, KCN, KI, KSCN and (NH₂)₂CS, were studied with respect to the complete release of the analytes retained by the resin. In addition, influence of various base metals, i.e. Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn, on the retention of the noble metals was investigated. Under the selected conditions for the retention and elution of Au, Ir, Pd and Pt, the analytical performance of the proposed pre-concentration procedure was evaluated and it was applied to the determination of these noble metals in anodic sludge sample.     

Thermal unimolecular decomposition mechanism of 2,4,6-trinitrotoluene: a first-principles DFT study

Simple C–NO₂ homolysis, 4,6-dinitroanthranil (DNAt) production by dehydration, and the nitro-nitrite rearrangement–homolysis for gas-phase TNT decomposition were recently studied by Cohen et al. (J Phys Chem A 111:11074, 2007), based on DFT calculations. Apart from those three pathways, other possible initiation processes were suggested in this study, i.e., CH₃ removal, O elimination, H escape, OH removal, HONO elimination, and nitro oxidizing adjacent backbone carbon atom. The intermediate, 3,5-dinitro-2(or 4)-methyl phenoxy, is more favor to decompose into CO and 3,5-dinitro-2(or 4)-methyl-cyclopentadienyl than to loss NO following nitro-nitrite rearrangement. Below ~1,335 K, TNT condensing to DNAt by dehydration is kinetically the most favor process, and the formations of substituted phenoxy and following cyclopentadienyl include minor contribution. Above ~1,335 K, simple C–NO₂ homolysis kinetically dominates TNT decomposition; while the secondary process changes from DNAt production to CH₃ removal above ~2,112 K; DNAt condensed from TNT by dehydration yields to that by sequential losses of OH and H above ~1,481 K and to nitro-nitrite rearrangement–fragmentation above ~1,778 K; O elimination replaces DNAt production above ~2,491 K, playing the third role in TNT decomposition; H escaping directly from TNT thrives in higher temperature (above ~2,812 K), as the fourth largest process. The kinetic analysis indicates that CH₃ removal, O elimination, and H escape paths are accessible at the suggested TNT detonation time (~100–200 fs), besides C–NO₂ homolysis. HONO elimination and nitro oxidizing adjacent backbone carbon atom paths are negligible at all temperatures. The calculations also demonstrated that some important species observed by Rogers and Dacons et al. are thermodynamically the most favor products at all temperatures, possibly stemmed from the intermediates including 4,6-dinitro-2-nitroso-benzyl alcohol, 3,5-dinitroanline, 2,6-dinitroso-4-nitro-phenylaldehyde, 3,5-dinitro-1-nitrosobenzene, 3,5-dinitroso-1-nitrobenzene, and nitrobenzene. All transition states, intermediates, and products have been indentified, the structures, vibrational frequencies, and energies of them were verified at the uB3LYP/6-311++G(d,p) level. Our calculated energies have mean unsigned errors in barrier heights of 3.4–4.2 kcal/mol (Lynch and Truhlar in J Phys Chem A 105:2936, 2001), and frequencies have the recommended scaling factors for the B3-LYP/6-311+G(d,p) method (Andersson and Uvdal in J Phys Chem A 109:2937, 2005; Merrick et al. in J Phys Chem A 111:11683, 2007). All calculations corroborate highly with the previous experimental and theoretical results, clarifying some pertinent questions.     

Thermal explosion simulation and incompatible reaction of dicumyl peroxide by calorimetric technique

Dicumyl peroxide (DCPO) is usually employed as an initiator for polymerization, a source of free radicals, a hardener, and a linking agent. In Asia, due to its unstable reactive nature, DCPO has caused many thermal explosions and runaway reaction incidents in the manufacturing process. This study was conducted to elucidate its essentially thermal hazard characteristics. In order to analyze the runaway behavior of DCPO in a batch reactor, thermokinetic parameters, such as heat of decomposition (ΔH _d) and exothermic onset temperature (T ₀), were measured via differential scanning calorimetry (DSC). Thermal runaway phenomena were then thoroughly investigated by DSC. The thermokinetics of DCPO mixed with acids or bases were determined by DSC, and the experimental data were compared with kinetics-based curve fitting of thermal safety software (TSS). Solid thermal explosion (STE) and liquid thermal explosion (LTE) simulations of TSS were applied to determine the fundamental thermal explosion behavior in large tanks or drums. Results from curve fitting indicated that all of the acids or bases could induce exothermic reactions at even an earlier stage of the experiments. In order to diminish the extent of hazard, hazard information must be provided to the manufacturing process. Thermal hazard of DCPO mixed with nitric acid (HNO₃) was more dangerous than with other acids including sulfuric acid (H₂SO₄), phosphoric acid (H₃PO₄), and hydrochloric acid (HCl). By DSC, T ₀, heat of decomposition (ΔH _d), and activation energy (E _a) of DCPO mixed with HNO₃ were calculated to be 70 °C, 911 J g⁻¹, and 33 kJ mol⁻¹, respectively.