Pure Acid Solutions Research Articles

Effect of cations on the hydrated proton.

We report on a strong nonadditive effect of protons and other cations on the structural dynamics of liquid water, which is revealed using dielectric relaxation spectroscopy in the frequency range of 1-50 GHz. For pure acid solutions, protons are known to have a strong structuring effect on water, leading to a pronounced decrease of the dielectric response. We observe that this structuring is reduced when protons are cosolvated with salts. This reduction is exclusively observed for combinations of protons with other ions; for all studied solutions of cosolvated salts, the effect on the structural dynamics of water is observed to be purely additive, even up to high concentrations. We derive an empirical model that quantitatively describes the nonadditive effect of cosolvated protons and cations. We argue that the effect can be explained from the special character of the proton in water and that Coulomb fields exerted by other cations, in particular doubly charged cations like Mg(2+)aq and Ca(2+)aq, induce a localization of the H(+)aq hydration structures.

Preparation of high purity crystalline silicon by electro-catalytic reduction of sodium hexafluorosilicate with sodium below 180 °C.

The growing field of silicon solar cells requires a substantial reduction in the cost of semiconductor grade silicon, which has been mainly produced by the rod-based Siemens method. Because silicon can react with almost all of the elements and form a number of alloys at high temperatures, it is highly desired to obtain high purity crystalline silicon at relatively low temperatures through low cost process. Here we report a fast, complete and inexpensive reduction method for converting sodium hexafluorosilicate into silicon at a relatively low reaction temperature (∼200°C). This temperature could be further decreased to less than 180°C in combination with an electrochemical approach. The residue sodium fluoride is dissolved away by pure water and hydrochloric acid solution in later purifying processes below 15°C. High purity silicon in particle form can be obtained. The relative simplicity of this method might lead to a low cost process in producing high purity silicon.

Regenerating spent acid produced by HZSM-5 zeolite preparation by bipolar membrane electrodialysis

A large amount of acid wastewaters containing sodium chloride (NaCl) is usually generated during the production of HZSM-5 zeolite (H-form Zeolite Socony Mobile Five). It can cause contamination of the environment if discharged directly. In this study, a method was reported to regenerate hydrochloric acid (HCl) and sodium hydroxide (NaOH) from the acid wastewater by bipolar membrane electrodialysis (BMED). The effects of operation parameters, such as initial base concentration and current density, on the spent acid solution regeneration were investigated. The results indicated that the initial concentration of sodium hydroxide had little or no effect on the acid wastewater regeneration. But it was also demonstrated that current density have a great influence on the acid wastewater regeneration, and a higher current density applied to the BMED stack usually resulted in lower current efficiency and higher energy consumption. After the operation of BMED process, the comparison between the recycled acid solution and the pure acid solution illustrates the recycled acid solution by BMED process can replace the pure acid solution completely. Therefore, this experiment can not only achieve the elimination of environmental pollution, but also the recycling of resources.

Collagen tissue treated with chitosan solutions in carbonic acid for improved biological prosthetic heart valves

Calcification of bovine pericardium dramatically shortens typical lifetimes of biological prosthetic heart valves and thus precludes their choice for younger patients. The aim of the present work is to demonstrate that the calcification is to be mitigated by means of treatment of bovine pericardium in solutions of chitosan in carbonic acid, i.e. water saturated with carbon dioxide at high pressure. This acidic aqueous fluid unusually combines antimicrobial properties with absolute biocompatibility as far as at normal pressure it decomposes spontaneously and completely into H2O and CO2. Yet, at high pressures it can protonate and dissolve chitosan materials with different degrees of acetylation (in the range of 16–33%, at least) without any further pretreatment. Even exposure of the bovine pericardium in pure carbonic acid solution without chitosan already favours certain reduction in calcification, somewhat improved mechanical properties, complete biocompatibility and evident antimicrobial activity of the treated collagen tissue. The reason may be due to high extraction ability of this peculiar compressed fluidic mixture. Moreover, exposure of the bovine pericardium in solutions of chitosan in carbonic acid introduces even better mechanical properties and highly pronounced antimicrobial activity of the modified collagen tissue against adherence and biofilm formation of relevant Gram-positive and Gram-negative strains. Yet, the most important achievement is the detected dramatic reduction in calcification for such modified collagen tissues in spite of the fact that the amount of the thus introduced chitosan is rather small (typically ca. 1wt.%), which has been reliably detected using original tritium labelling method. We believe that these improved properties are achieved due to particularly deep and uniform impregnation of the collagen matrix with chitosan from its pressurised solutions in carbonic acid.

A fully automated direct injection nebulizer (d-DIHEN) for MC-ICP-MS isotope analysis: application to boron isotope ratio measurements

This work presents a fully automated setup for using direct injection nebulization as an introduction system for solution measurements by MC-ICP-MS, here applied to boron isotopes in pure boric acid solutions and natural samples.

Mechanical and Electrochemical Evaluation of Organic Inhibitors Effect on Mild Steel Damage by Hydrogen

Hydrogen penetration into the bulk of steel is a risk during the whole process of the manufacturing of steel product. Hydrogen accumulation in the material structure can induce the adverse changes in mechanical/metallurgical properties, i.e. cause hydrogen blistering or even hydrogen embrittlement. Consequently, when the product is subjected to mechanical stress, cracking hazard occurs. In this study, we focus on hydrogen ingress during pickling of mild steel in strong acids (diluted sulphuric and hydrochloric acid. Generally, pickling is the critical step of the coating process. Different types of adsorption inhibitors were used as additives to pickling bath in order to prevent metal dissolution and related hydrogen evolution. The effect of inhibitors was tested by electrochemical and mechanical methods. Polarization curves measurement was used to evaluate corrosion rate of mild steel substrate in pure and inhibited acid solutions. Mechanical tests were performed using Cyclic Loading Pulsator, which is an experimental device simulating cyclic stress. Thus, the fatigue life of retaining rings for shafts exposed to the tested solutions was determined. Based on the results the most effective inhibitors were chosen.

Effect of ionising radiation on polyphenolic content and antioxidant potential of parathion-treated sage (Salvia officinalis) leaves

The γ-irradiation effects on polyphenolic content and antioxidant capacity of parathion-pretreated leaves of Salvia officinalis plant were investigated. The analysis of phenolic extracts of sage without parathion showed that irradiation decreased polyphenolic content significantly (p<0.05) by 30% and 45% at 2 and 4kGy, respectively, compared to non-irradiated samples. The same trend was observed for the Trolox equivalent antioxidant capacity (TEAC), as assessed by the anionic DPPH and cationic ABTS radical-scavenging assays. The antioxidant potential decreased significantly (p<0.01) at 2 and 4kGy, by 11–20% and 40–44%, respectively. The results obtained with a pure chlorogenic acid solution confirmed the degradation of phenols; however, its TEAC was significantly (p<0.01) increased following irradiation. Degradation products of parathion formed by irradiation seem to protect against a decline of antioxidant capacity and reduce polyphenolic loss. Ionising radiation was found to be useful in breaking down pesticide residues without inducing significant losses in polyphenols.

Comparison of Chromatographic and Titrimetric Methods for the Determination of the a-amino Nitrogen in Standard Solution and Fish Protein Hydrolysates

&lt;p&gt;Two analytical methods, reverse phase high-performance liquid chromatography (RP-HPLC) and formol titration, were compared for their accuracy and precision for the determination of a-amino nitrogen (a-AN) concentration in fish protein hydrolysates. The result showed that, when tested with pure amino acid solutions, RP-HPLC method had a better standard deviation (S. D.), coefficient of variation (C. V.), and standard error (S. E.) but a poorer recovery rate compared with formol titration technique. The observed a-AN value by RP-HPLC has good coincidence with the actual a-AN value and their correlation coefficient (r) is 0.9981, which was close to the r value (0.9995) between the a-AN by formol titration and the actual a-AN. However, when tested with protein hydrolysates, the a-AN obtained from RP-HPLC technique were significantly (p&amp;lt;0.05) lower than that from formol titration for the same sample. Therefore, the formol titration method can be used as a quick screening method to assess the quality fish hydrolystaes.&lt;/p&gt;&lt;p&gt; &lt;/p&gt;

Deterioration of tensile behavior of concrete exposed to artificial acid rain environment

This study is focused on evaluation of the tensile properties of concrete exposed to acid rain environment. Acid rain environment was simulated by the mixture of sulfate and nitric acid in the laboratory. The dumbell-shaped concrete specimens were submerged in pure water and acid solution for accelerated conditioning. Weighing, tensile test, CT, SEM/EDS test and microanalysis were performed on the specimens. Tensile characteristics of the damaged concrete are obtained quantitatively. Evolution characteristics of the voids, micro cracks, chemical compounds, elemental distribution and contents in the concrete are examined. The deterioration mechanisms of concrete exposed to acid rain are well elucidated.

Electrodialytic removal of H2SO4 from its aqueous mixture with Na2SO4

The experimental results of the separation of sulfuric acid from sodium sulfate by the membrane electrolysis method have been presented. The anion-exchange membrane Neosepta ACM has been used. It has been found that the current efficiency of H2SO4 removal is similar for pure acid solution and for the mixture H2SO4-Na2SO4 if the initial acid concentrations are the same. For the same current density effectiveness of H2SO4 removal is higher for lower initial acid concentration (63% for 0.5 M and 56% for 1 M (j = 100 mA/cm2).

The accuracy of δ11B measurements of foraminifers

Values of δ 11B reported in the literature for Holocene samples of the same foraminiferal species show large variability (6‰) relative to cited precision (< 1‰). This is indicative of significant inter-laboratory biases and raises concerns about the accuracy of foraminiferal proxy pH records. To investigate this problem we have measured the δ 11B of modern ocean carbonates using several different analytical procedures. We have used total evaporation negative thermal ionisation mass spectrometry (TE-NTIMS), with various sample preparation and loading procedures and multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS). The δ 11B of pure boric acid solutions measured by TE-NTIMS and MC-ICPMS agree well, demonstrating no fundamental biases between the techniques. Yet the δ 11B values measured by TE-NTIMS for non-foraminiferal carbonates are about 2‰ lighter than those by MC-ICPMS whereas foraminifers measured by the same standard TE-NTIMS procedure are 2 to 6‰ heavier than those by MC-ICPMS. Significantly, we found that foraminiferal samples kept in acidic solution over several months yielded lower δ 11B values (up to 5‰ lower) and better reproducibility when re-measured by TE-NTIMS. We infer that organic material, released on foraminiferal dissolution, causes biases in NTIMS measurements. No residual organics should be present in the MC-ICPMS measurements as matrix is separated from sample before analysis. Moreover we demonstrate by standard addition the absence of any matrix influence in the MC-ICPMS procedure beyond the inherent uncertainties in the standard addition approach (∼ ± 0.35‰ 2sigma). Degradation of the inferred organic residue, either by long term storage in acidic solution or by loading samples in 30% H 2O 2, reduces but does not totally remove the (variable) bias between TE-NTIMS and MC-ICPMS δ 11B measurements. Despite these problems, careful analysis of similar samples by NTIMS may permit data to be obtained with consistent relative differences that still yield valuable proxy records, but there is clearly considerable potential for inaccuracies to result in such an approach from hard to detect changes in matrix.

Fabrication of Stable Superhydrophobic Coatings with Furfural Acetone Resin/PTFE Composites

We describe a simple and inexpensive technique to fabricate superhydrophobic coatings with furfural acetone resin/poly (tetrafluoroethylene) (FAR/PTFE) composites. An interesting hierarchical structure with dispersed cavities and protuberances in microscale was achieved. The water contact angle (CA) of the superhydrophobic surface is 157° and the sliding angle is about 5°. The coatings can be applied to large substrates by spray coating with ease and possess high cohesional strength with the substrates. Meanwhile, the superhydrophobic coatings show long-term stability in pure water and acidic solutions with higher concentration.

Continuous electrodeionization for removal and recovery of Cr(VI) from wastewater

Continuous electrodeionization (CEDI) was investigated for removal and recovery of Cr(VI) from synthetic wastewater. Different anion exchange resins, including the gel strong-base resin, gel weak-base resin, macro-porous strong-base resin, and macro-porous weak-base resin, were examined. The gel strong-base resin was found to be the best one for use in CEDI. It was shown that CEDI could remove and recover Cr(VI) effectively from wastewater. After treatment, Cr(VI) concentration was reduced from initial 40–100 mg/L to 0.09–0.49 mg/L, and a pure chromic acid solution containing Cr(VI) as high as 6300 mg/L Cr(VI) was obtained. The current efficiency and energy consumption was 16.1–18.8%, and 4.1–7.3 kWh/mol Cr(VI), respectively.

Corrosion of iron in highly acidic hydro-organic solutions

In acidic water–organic solvents of ethylene glycol (EGOH), propylene glycol (PGOH), methanol (MeOH) and ethanol (EtOH), iron corrosion was studied by monitoring the corrosion potential, the potentiodynamic polarization curves and electrochemical impedance diagrams. In these aqueous glycols and alcoholic solutions containing HCl having concentrations of 0.5 up to 9 M, it has been shown by electrochemical analysis ( I– E curves) that dissolution mechanism of iron is similar to that one in pure acidic aqueous solutions if only we take into account the relative amount of water in the medium. Based in our experimental data, water has an important role in the transfer kinetics of protons to the metallic electrode and limits electro dissolution rate of iron. When water quantity is sufficient at the metal surface, the acidity is a governing factor in the evolution of corrosion process.

The Effect of the Impurities in Refinery Process from Fermentation Broth on Lactic Acid Polymerization

Polylactic acid (PLA) is synthesized by direct polycondensation without catalyst (NC-DP) method using a lactic acid (HLa) solution which had been refined by concentration, esterification and hydrolysis of fermented broth from fresh cassava roots (FCR). Higher polymerization rates and earlier thermal degradation had been observed, compared with those from a pure lactic acid solution. It is due to residual impurities in refining process, such as butanol (BuOH) and butyl lactate (BuLa), which act as an external catalyst. Additionally, it has been found that thermal degradation of PLA containing these impurities occurs via random scission with vinyl end groups, in regard to specific scission for PLA from a pure HLa solution.

FIRST‐ORDER HYDROTHERMAL OXIDATION KINETICS OF DIGESTED SLUDGE COMPARED WITH RAW SLUDGE

This article presents an assessment of the first‐order hydrothermal oxidation kinetics of a selected digested sludge at subcritical (< 374°C) and supercritical (> 374°C) temperatures in the range of 250–460°C. Furthermore, the results were compared with reported oxidation kinetics of raw sludge treated under identical experimental conditions. In the assessment, oxidation was considered to proceed in two steps: (1) decomposition of the particulate, or non‐filterable, chemical oxygen demand (PCOD); followed by (2) ultimate oxidation and removal of the total, particulate and soluble, COD. The accumulation and removal of soluble COD (SCOD) was determined from the difference between the rates of sludge decomposition and ultimate oxidation. Using results from batch and continuous‐flow hydrothermal treatment experiments, the reacting organic ingredients were separated into groups according to the ease or difficulty at which they were decomposed or removed, with Arrhenius‐type activation energy levels assigned to the different groups. The analysis confirmed that within the treatment range of 75% to more than 97% COD removal, the oxidation kinetics of the digested and raw sludges were nearly identical despite differences in the proportions of their original organic ingredients. The original organic ingredients were mostly removed above 75% COD removal, and the oxidation kinetics appeared to be dominated by the removal of acetic acid, an intermediate by‐product which constituted 50% to more than 80% of the remaining COD. Furthermore, the oxidation kinetics of both sludge types were consistent with reported first‐order oxidation kinetics of pure acetic acid solutions. The resulting kinetic models adequately represented hydrothermal oxidation of digested sludge, in terms of COD and PCOD removals, as well as accumulation and removal of the soluble SCOD.

Extraction of Am and rare-earth elements from acidic solutions by alkyl derivatives of dibenzo- and dicyclohexano-18-crown-6

Abstract Extraction of rare-earth elements (REE) and Am(III) by various crown ethers on the basis of alkyl derivatives of 18-crown-6 with phenyl- and cyclohexano-fragments from aqueous acid solutions have been studied. The recovery of REE and Am(III) in this system is increased when trichloroacetic acid (TCAA) is used in comparison with pure acid solutions of HNO 3 or HClO 4 . The distribution coefficients of the Ce subgroup in these conditions are higher than those of the elements belonging to the Y subgroup. The composition of extracted complexes of REE (M) with crown ethers (L) were determined as M:L = 1:1 in all cases. The optimal conditions for Am(III)/M(III) separation with a separation factor >50 has been found.

N,N,N′,N′-tetraoctyl-3-oxapentane-1,5-diamide impregnated magnetic particles for the uptake of lanthanides and actinides from nuclear waste streams

A novel, simple technique based on magnetically assisted chemical separation (MACS) has been developed for the uptake of lanthanides and actinides from pure nitric acid solutions as well as from Simulated Pressurized Heavy Water Reactor-High Level Waste (PHWR-SHLW). Uptake profiles of various metal ions, such as Pu(IV), U(VI), Th(IV), Am(III), Eu(III), Sr(II), Cs(I) and Fe(III) were investigated as a function of time and nitric acid concentrations usingN,N,N′,N′-tetraoctyl-3-oxapentane-1,5-diamide (TODGA) impregnated magnetic particles and compared withN,N′-dimethyl-N,N′-dibutyl tetradecyl malonamide (DMDBTDMA) and trialkyl phosphine oxide coated magnetic particles and also with TODGA coated extraction chromatographic resins. The uptake of various metal ions follows the order Eu(III) &gt; Am(III) &gt; Th(IV) &gt; Pu(IV) &gt; U(VI) &gt; Sr(II) &gt; Fe(III) &gt; Cs(I) in pure nitric acid solutions. On the other hand, distinctly high distribution coefficient (Kd) value has been observed for Pu(IV) as compared to Eu(III) and Am(III) in SHLW. Further, no significant extraction of Cs(I) or Sr(II) was observed in SHLW. Also, at any acidity theKdvalue of a given metal ion is less in the SHLW as compared to that in pure HNO3, apparently due to the co-extraction of the other metal ions present in SHLW. The loading capacity of the TODGA impregnated magnetic particles with respect to Th(IV), U(VI) and Eu(III) was determined, along with the distribution isotherms to simulate multiple contacts. The adsorption models of Langmuir and Freundlich were fitted to the experimental data and best correlations was obtained for Langmuir model suggesting monolayer adsorption is the prevalent mechanism. The stability and reusability of the TODGA coated magnetic particles was also assessed.

N, N′-dimethyl-N, N′-dibutyl tetradecyl malonamide impregnated magnetic particles for the extraction and separation of radionuclides from nuclear waste streams

Summary N, N′-dimethyl-N, N′-dibutyl tetradecyl malonamide (DMDBTDMA) coated magnetic particles are being evaluated for the possible application in the partitioning of actinides, lanthanides and fission products from pure nitric acid solutions as well as from Simulated Pressurized Heavy Water Reactor-High Level Waste (PHWR-SHLW). Uptake profiles of various metal ions, such as Pu(IV), U(VI), Am(III), Eu(III), Sr(II) and Cs(I) were obtained as a function of time and nitric acid concentration by batch studies using DMDBTDMA coated magnetic particles. The order of uptake follows the order Pu(IV)&gt;U(VI)&gt;Am(III)&gt;Eu(III)&gt;Sr(II)∼Cs(I) in both nitric acid and SHLW. The uptake of various trivalent lanthanides was also investigated as a function of nitric acid concentration and found the uptake order as Pr(III)&gt;La(III)&gt;Eu(III)&gt;Tb(III)&gt;Ho(III)&gt;Er(III)&gt;Yb(III)&gt;Lu(III). The sorption capacity of the DMDBTDMA coated magnetic particles with respect to U(VI) and Eu(III) was determined, along with the sorption isotherms to simulate multiple contacts. The maximum sorption capacity of DMDBTDMA coated magnetic particles was found to be 1.58 mmol/g and 0.36 mmol/g for U(VI) and Eu(III), respectively. The adsorption models of Langmuir and Freundlich were fitted to the experimental data and best correlations were obtained for both the models. The Langmuir model predicts a loading capacity of 1.61 mmol/g and 0.37 mmol/g for U(VI) and Eu(III), respectively, which is close to the experimental values. The stability and recycling capacity of the DMDBTDMA coated magnetic particles was also assessed.

Comparison between pure-water- and seawater-soluble nutrient concentrations of aerosols from the Gulf of Aqaba

Seawater-soluble nutrient fractions of aerosols better represent the contribution of aerosol dry deposition to the nutrient load from this source to the ocean than any estimates based on aerosol nutrients leached in pure water or acidic solutions. To understand the solubility difference between seawater and pure water, 31 pairs of aerosol samples collected from the Gulf of Aqaba were extracted in Sargasso seawater and pure water under consistent experimental conditions and procedures. Major inorganic N species (NO 3 − and NH 4 +) in the aerosols show similar solubilities in Sargasso seawater (average 44 and 23 nmol m − 3 ) and pure water (average 41 and 23 nmol m − 3 ). Seawater-soluble PO 4 3− concentrations (average 0.4 nmol m − 3 ) are slightly lower than the purewater concentrations (average 0.5 nmol m − 3 ). Total soluble N and P, which include dissolved organic compounds, extracted from the aerosols into the seawater (average 65 and 0.4 nmol m − 3 ) are significantly lower than those extracted by pure water (average 75 and 0.7 nmol m − 3 ). It was found that the dissolution of crustal-dominated trace metals (e.g. Fe and Al) strongly decrease in the seawater compared to that in pure water, while similar amounts of aerosol Zn are leached in both seawater and pure water. The percentage solubilities of non-crustal trace metals (Cu, Ni and Zn) are about one or two orders of magnitude higher than those of Fe and Al in the seawater. Our comparison experiments suggest that some previous reports may have overestimated the dry deposition inputs of aerosol P, Fe, Al, Cu, and Ni to the ocean as a result of the use of solubility estimates obtained from pure water extractions. The estimated dry deposition fluxes of soluble nutrients showed that the atmospheric nutrient input could increase the possibility of P limitation in the Gulf of Aqaba and also contribute a significant fraction of dissolved nutrients to the euphotic zone during stratification period (April to October).