Dilute Hydrochloric Acid Solution Research Articles

Electrochemical corrosion characteristics of type 316 stainless steel in simulated anode environment for PEMFC

The corrosion behavior of type 316 stainless steel in simulated anode environment for proton exchange membrane fuel cell (PEMFC), i.e., dilute hydrochloric acid solutions bubbled with pure hydrogen gas at 80 °C, was investigated by using electrochemical measurement techniques. The main purpose is to offer some fundamental information for the use of stainless steels as bipolar plate material for PEMFC. Both polarization curve and electrochemical impedance spectroscopy (EIS) measurements illustrate that 316 stainless steel cannot passivate spontaneously in the simulated environments. The absorbed (and/or adsorbed) hydrogen atoms from cathodic corrosion reactions on the steel surface may deteriorate the passivity and corrosion resistance. The oxidation of these hydrogen atoms gives rise to a second current peak in the anodic polarization curve, and the current increases with immersion time. EIS spectra also reveal that a porous corrosion product layer formed on the steel surface during the active dissolution in the test solutions. 316 stainless steel exhibits the similar corrosion behavior in sulfate ions containing dilute hydrochloric acid solution.

Thiosubstituted Organophosphinic Acids as Selective Extractants for Mercury(II) from Acidic Chloride Solutions

This paper reports results on the extraction behavior of mercury (II) from dilute hydrochloric acid solutions using mono‐ and di‐sulphur analogs of bis(2,4,4‐trimethylpentyl)phosphinic acid, namely, bis(2,4,4‐trimethylpentyl)monothiophosphinic acid (CYANEX 302) and bis(2,4,4‐trimethylpentyl)dithiophosphinic acid (CYANEX 301). The effect of various parameters such as, concentrations of mineral acid, metal ion, extractant, and the nature of the diluent on the extraction of mercury (II) has been investigated. The results clearly demonstrate that CYANEX 302 and CYANEX 301 do not behave as cation‐exchange extractants but as solvating extractants, owing to the strong affinity of sulphur atom of the extractant for the soft metal ion mercury. The extraction equilibrium of mercury (II) can be represented as: where HX represents CYANEX 302 and CYANEX 301. The equilibrium constants of the extracted complexes have been calculated by non‐linear regression analysis with the aid of suitable chemical model. IR spectral studies of the extracted complex have been used to further clarify the nature of the extracted complex. The potential of CYANEX 301 for decontaminating mercury from the brine‐sludge of a Chlor‐Alkali plant has been assessed.

Variation among three Crinum species in alkaloid content

Dilute hydrochloric acid solution extraction, followed by gas chromatographic analysis, was used to investigate the interspecific variation in the alkaloid content of three Crinum species, C. bulbispermum, C. macowanii, and C. moorei over two consecutive years. The identified alkaloids showed that C. moorei had the highest levels of all individual alkaloids, except crinamine, when compared to C. bulbispermum and C. macowanii. The detected alkaloids can be used to make a chemotaxonomic distinction between C. moorei on the one hand and C. bulbispermum and C. macowanii on the other. The results suggest that C. macowanii is more closely related to C. bulbispermum.

Synthesis and properties of stereoregular cyclic polysilanols: cis-[PhSi(O)OH](4), cis-[PhSi(O)OH](6), and tris-cis-tris-trans-[PhSi(O)OH](12).

New stereoregular cyclic polysilanols of the general formula [PhSi(O)OH]n (n = 6 and 12) have been selectively obtained in high yields by the reaction of cagelike oligophenylmetallasiloxanes with dilute solutions of hydrochloric acid at low temperatures. An alternative method was used to prepare cis-[PhSi(O)OH](4) from sodium phenylsiloxanolate, cis-[(Na(+))(4)[PhSi(O)O(-)](4)].(1-butanol)(x). All compounds were fully characterized by NMR and IR spectroscopy and molecular weight determinations. The structure of cis-[PhSi(O)OH](6) was confirmed by single-crystal X-ray analysis. Furthermore, a series of stereoregular cyclosiloxanes containing triorganylsiloxy groups at each silicon atom was prepared by the reactions of the cyclic polysilanols with triorganylchlorosilanes Me(3)SiCl, Me(2)ViSiCl, and Me(2)(CH(2)Cl)SiCl.

Optimum reaction conditions for in situ polyaniline films

The deposition of the polyaniline (PANI) films was monitored using the quartz crystal microbalance (QCM) technique. The films were grown from an aqueous dilute hydrochloric acid solution by the chemical oxidation of aniline using ammonium persulphate (APS) as an oxidizing agent. The effect of initial molar ratios of the APS/aniline on the yield and the thickness as well as on the growth rate of the PANI films was studied. The most efficient initial molar ratio of APS/aniline is found to be ∼1.15±0.1. This is in close agreement with the corresponding one obtained during the PANI powder formation in the bulk solution. The higher APS/aniline initial molar ratio results in a degradation of the PANI films.

Effect of acid treatment on the consolidation and plasto-elasticity of tapioca powder

Purpose: The effects of treating the tapioca (the fibrous residue obtained after up to 90% of the proportion of starch has been removed from the peeled and rasped roots of cassava tubers powder with dilute solutions of hydrochloric acid) in order to find an approach for rendering an otherwise poorly compressible material to a directly compressible powder. Method: The parameters measured were the degree of consolidation of the powder after compression (i.e. the packing fraction of resulting tablets), the plasto-elasticity of the powders as reflected by the brittle fracture index (BFI) of the tablets made from the powders and the viscosities of mucilages derived from the powders. The influence of time of exposure and the concentration of acid used in the treatment were studied. Results: The degree of consolidation of the powder increased slightly with increase in duration of exposure to acid (24 — 72 h) but drastically with increase in the acid concentration from 0.1 to 0.4 mol. L—1. On the other hand, the plasto-elasticity of the powders as measured by the BFI values and the viscosities of mucilages derived from the powders decreased slightly with duration of exposure but drastically with increase in acid concentration. A change in acid concentration was therefore the more determinant factor with regards to the consolidation and plasto-elasticity properties of the powders. The decrease in the viscosities of the mucilages following acid treatment of the powders was indicative of a breakdown of polymeric structure in the powder Conclusion: Acid treatment of tapioca powder imparted plasticity in tapioca powder which became compressible. Key words: Plasto-elasticity, brittle fracture index, tapioca powder. Trop J Pharm Res, June 2002; 1(1): 45-49

EXTRACTION OF MERCURY(II) WITH DICYCLOHEXANO-18-CROWN-6, AND ITS APPLICATION TO INDUSTRIAL WASTES

As part of the study of hazardous metal ion separation from industrial wastes, the extraction behavior of Hg(II) from dilute hydrochloric acid solutions with dicyclohexano-18-crown-6 (DC18C6) in 1,2-dichloroethane was investigated. For comparison, extraction studies also were carried out with 18-crown-6 (18C6), benzo-18-crown-6 (B18C6), and dibenzo-18-crown-6 (DB18C6). The extraction data were analyzed by both graphical and theoretical methods that account for aqueous phase complexation with inorganic ligands and all plausible complexes extracted into the organic phase. The results demonstrate that Hg(II) is extracted into dichloroethane as HgCl2·2Crown Ether. The HgCl2·DC18C6 solid complex was prepared and characterized by elemental analysis, and IR (infrared) and 1H-NMR (nuclear magnetic resonance) spectral studies. The possible means of extracting and separating Hg(II) from other metal ions, such as Mg(II), Ca(II), Ba(II), and Fe(III), that are present in the industrial wastes of the chlor-alkali industry is discussed. The potential of the DC18C6 for decontaminating mercury from the brine sludge of a chlor-alkali plant has been assessed.

Studies on the liquid–liquid extraction of mercury(II) from acidic chloride solutions using Cyanex 923

The extraction of mercury(II) from dilute hydrochloric acid solutions has been investigated using Cyanex 923 (=TRPO) as an extractant. The extraction data have been analysed by both graphical and theoretical methods taking into account aqueous phase speciation and all plausible complexes extracted into the organic phase. The results demonstrate that mercury(II) is extracted into xylene as HgCl 2·3TRPO. IR spectral studies of the extracted complex were used to further clarify the nature of the extracted complex. The loading capacity of the solvent was determined. The effect of the diluent on the extraction process of mercury has been studied and correlated with dielectric constants. The developed extraction procedure has been explored for the recovery of mercury from the brine–sludge of Chlor-Alkali industry.

Electrochemical corrosion behaviour of type 316 stainless steel in acid media containing fluoride ions

The corrosion behaviour of type 316 stainless steel has been investigated in F- containing dilute hydrochloric acid and acetic acid solutions aerated with oxygen gas at 25degreesC using electrochemical measurement techniques. Both electrochemical impedance spectroscopy spectra and polarisation curves illustrate that 316 stainless steel can passivate in these solutions at the corrosion potential. The passive impedance decreases slightly with increasing F- concentration. The anodic polarisation curves show that low concentrations of F- ion have 170 significant influence on the passivity of 316 stainless steel, but the passivity is reduced by high concentrations of F- ions. In 0.1 M NaF solutions, an anodic current peak occurs at below the pitting potential. This does not appear in solutions with low concentrations of NaF, and is related to the F- accelerated reactions. During anodic polarisation, the selective dissolution of the Fe component takes place in the above solutions.

Ester hydrolysis and enol nitrosation reactions of ethyl cyclohexanone-2-carboxylate inhibited by beta-cyclodextrin

Both the ester hydrolysis and the nitrosation reactions of the enol tautomer of ethyl cyclohexanone-2-carboxylate (ECHC) are investigated in the absence and presence of beta-cyclodextrin (beta-CD). The ester hydrolysis reaction is studied in dilute H2O and D2O solutions of hydrochloric acid and in aqueous buffered solutions of carboxylic acids (acetic acid and its chloro derivatives). The pseudo-first-order rate constant increases with both the [H+] and the total buffer concentration, indicating that the hydrolysis is subject to acid and general base catalysis. Substantial solvent isotope effects in the normal direction (kH/kD > 1) for the acid-catalyzed hydrolysis was observed. Addition of beta-CD strongly slows the hydrolysis reaction. The variation of the observed rate constant (k(o)) with [beta-CD] exhibits saturation behavior, consistent with 1:1 binding between the enol of ECHC and beta-CD. The binding is quite strong, and bound ECHC-enol is unreactive. The nitrosation reaction of ECHC in aqueous acid medium, using sodium nitrite in great excess over the concentration of ECHC, yields perfect first-order kinetics, indicating that the slow step is the nitrosation of the enol tautomer. This finding suggests that a great percentage of the total ECHC concentration must exist in the enol form. The nitrosation reaction is of first order in [nitrite] and is catalyzed by the presence of Cl-, Br-, or SCN- ions, which indicates that the attack of the nitrosating agent is the slow step. The nitrosation reaction is also strongly inhibited by the presence of beta-CD because of the formation of unreactive inclusion complexes between the host, beta-CD, and the guest, the enol of ECHC. In alkaline medium, the formation of the enolate ion is observed, which absorbs at higher wavelengths (lambda(max) = 256 nm in acid medium shifts to lambda(max) = 288 nm in alkaline medium). This anion also undergoes ester hydrolysis spontaneously, but shows neither specific basic catalysis nor appreciable effect by the presence of beta-CD. From kinetic and spectroscopic measurements the pKa of the enol of ECHC has been determined as 12.35.

Chemical stability of doped ZnO thin films

We present the results of a chemical etching stability study carried out on ZnO thin films doped with several elements deposited by spray pyrolysis. Prior to the etching, a structural study was done by X-ray diffraction and the texture of the samples was obtained by scanning electron microscopy. The samples were etched employing a solution of dilute hydrochloric acid. The etching rates obtained for the different samples depend on the dopant element and our results confirm that films doped with Cr present the highest stability against chemical etching.

塩酸服用による重症腐蝕性上部消化管炎の１救命例

A 28-year-old man attempted suicide by drinking a glass of dilute solution of caustic hydrochloric acid and was admitted to the Sapporo Medical University Hospital 3 hours later. Laboratory examination on admission showed metabolic acidosis, BE -8.9mEq/l. Endoscopic examination showed corrosive changes indicating injury to the deep layer of the upper gastrointestinal tract. The patient underwent surgery for severe caustic ingestion injury of the esophagus, stomach and duodenum to prevent perforative complications. After 84 days, esophageal reconstruction using the right colon with the terminal ileum was conducted, with excellent results were obtained. He was transferred to another hospital without further complication. Diagnosis and surgical treatment of caustic ingestion injuries remain controversial. After severe caustic injuries, patient survival is closely related to the delay between ingestion and surgical treatment. Our experience indicated that the decision for early operative intervention played a basic role in preventing of perforative complications.

Routine staining of drill core to determine carbonate mineralogy and distinguish carbonate alteration textures

Carbonate staining has long been utilized with thin sections. Similar techniques are also extremely useful for distinguishing the mineralogy and texture of different carbonate minerals in drill cores. The simplest method for routine staining of whole drill core utilizes a dilute hydrochloric acid solution containing both alizarin red S and potassium ferricyanide. This solution is painted on to the drill core to allow for the rapid identification of calcite, ferroan calcite, ferroan dolomite (ankerite), and rhodochrosite. Production-scale staining of whole drill core rapidly provides a wealth of information on carbonate mineralogy and textural relationships in a number of deposit types. Examples from the Irish Zn-Pb district, the McArthur River Zn-Pb-Ag district, the Ruby Creek Cu-Co deposit, and the Kansanshi copper deposit are presented to illustrate the type of information that can be gained through use of this inexpensive and rapid technique.

A Novel Immobilized Enzyme Flow-Injection System for Urea with a Bulk Acoustic Wave Impedance Sensor as Detector

The urea-urease system was chosen as a model system to explore the suitability for the use of a bulk acoustic wave impedance sensor (BAWIS) as a detector in an immobilized enzyme FIA system. In the proposed FIA sysem, the urea in samples was hydrolyzed into ammonium and bicarbonate under the catalysis of the immobilized urease. The ammonium formed was converted into ammonia in an alkaline stream, and the ammonia diffused across a gas-permeable membrane into a recipient solution of dilute hydrochloric acid. The conductance change caused by the trapped ammonia was followed by a BAWIS detector. The system was applied to the analysis of urea in blood and urine samples. It exhibited a linear frequency response up to 10 mM urea with a detection limit of 10 μM. The through-put was 50 h-1, and the relative standard deviation of the peak heights (n=6) ranged between 0.63-1.97%. The effects of several factors, including those affecting the enzymatic reaction, detector performance, and gas-diffusion process, were also investigated. Compared with those conventional enzymatic methods for urea determination, the proposed immobilized urease FIA/BAWIS system is characterized by its rapid throughput, high reproducibility, low-cost apparatus, and easy manipulation.

Determination of rare earth elements and yttrium in rocks by inductively coupled plasma atomic emission spectrometry after solvent extraction with a mixture of 2-ethylhexyl dihydrogenphosphate and bis(2-ethylhexyl) hydrogenphosphate

The importance of rare earth elements in petrogenetic studies is well known. The inductively coupled plasma atomic emission spectrometry (ICP-AES) technique is mostly used for the determination of rare earth elements after its separation by the ion exchange method. An alternative, rapid, solvent extraction method involving a mixture of (2-ethylhexyl) dihydrogenphosphate and bis(2-ethylhexyl) hydrogenphosphate in kerosene suitable for the separation and preconcentration of REE in silicate rock is described. Major elements, such as Mg, Ca, Mn, Na and K, are not extracted appreciably from dilute hydrochloric acid solution. The extraction of the major fraction (>95%) of iron is prevented by its reduction with ascorbic acid. Titanium, Th, U and Zr are also extracted quantitatively and Al is extracted partially (∼6%). The REE are selectively stripped from the organic phase after the addition of tri-n-butyl phosphate with 4.5 mol dm –3 hydrochloric acid. Major fractions of co-extracted interfering elements (residual Fe, Th, U, Zr and Ti) remain in the organic phase. The aluminium is also stripped along with the REE; however, aluminium does not cause any interference in the determination of REE by ICP-AES. The method is applied for the preconcentration of REE in silicate rocks and its validity is checked by analyzing some Standard Reference Materials. The results are in good agreement with the recommended value. The method is simple, rapid, and suitable for the determination of REE in a silicate rock sample.

還元剤として過酸化水素および亜硫酸ナトリウムを用いたコバルトリッチクラストの塩酸浸出

Hydrochloric acid leaching of Co, Ni, Cu, Mn and Fe from the cobalt-rich ferromanganese crust under reducing conditions was performed using hydrogen peroxide and sodium sulfite as reducing agents. Hydrochloric acid concentration more than 3.0 mol/dm3 is required to obtain the high extraction of Co and Ni without reducing agents at ambient temperature. The high extraction of Cu in dilute hydrochloric acid solution without reducing agents at ammbient temperature explains the different form of Cu from other metals present in cobalt-rich ferromanganese crusts. When hydrogen peroxide or sodium sulfite was used as reducing agent, the high extraction of Co and Ni was obtained with dilute hydrochloric acid at ambient temperature. In particular, hydrogen peroxide extracts metals in stoichiometric amounts. The extraction of Ni depends significantly on the leaching temperature, regardless of the presence or absence of reducing agents.

Face selectivity in the reactions of Grignard reagents with 5-substituted-2-dicyanomethyleneadamantanes

Reactions of 5-substituted-2-dicyanomethyleneadamantanes (4-Z) with benzylmagnesium bromide (C6H5CH2MgBr) or alkylmagnesium halides (RMgX) generated the 1,4-addition (5-Z (R)) and/or the hydrogenation (5-Z (H)) products. A variety of substituents X were used: hydro, fluoro, chloro, bromo and phenyl groups. The generation of the different isomeric products from the zu-face or en-face by the transfer of the benzyl or alkyl groups, or the hydride from the Grignard reagents is discussed in terms of the electrostatic field influence and the steric hindrance between the Grignard reagents and the substrate 4-Z. Reactions of 4-Br or 4-Ph with phenylmagnesium bromide generated 1,2-addition products 6-Br, 7-Br or 8-Ph when the intermediate A was added to dry methanol or to dilute ice-cold hydrochloric acid solution.

Uptake of mercury (II) from wastewater by activated carbon from an unwanted agricultural solid by-product: coirpith

Adsorption studies of mercury (II) from aqueous solutions on coirpith carbon were investigated under the varying conditions of agitation time, metal ion concentration, adsorbent dose and pH. Adsorption equilibrium reached in 10, 25, 30 and 40min for 10, 20, 30 and 40mgl−1 Hg(II) concentration. Adsorption followed both Langmuir and Freundlich isotherms. The adsorption capacity was 154mgg−1. The percent removal increased with the increase of pH from 2 to 5 and remained constant up to pH11.00. Desorption studies were performed with dilute hydrochloric acid and potassium iodide solutions.

Rapid Detection of Pectolytic Erwinia sp. in Aglaonema sp.

The purpose of this research was to develop a rapid microplate assay for detecting and presumptively identifying pathogenic pectolytic Erwinia sp. in ornamental propagative stock and to readily distinguish them from nonpathogenic bacteria associated with Aglaonema. The assay was developed by modifying an existing crystal violet-sodium polypectate (CVP) medium to visualize the depolymerization of pectate by addition of bromcresol purple (BCP), then acidifying with a dilute hydrochloric acid (HCl) solution. The assay was sufficiently sensitive to detect latent (symptomless) infections in small sections of leaf or stem tissue. Based on inoculum titration assays, 40 to 600 colony-forming units (CFU) of Erwinia chrysanthemi (Burkholder et al.) were required to produce symptoms in Aglaonema stems and leaves, respectively. The microplate assay was able to detect the pathogen at low levels (40 to 60 CFU) in tissue segments of ≈1 cm2. In tests of bacterial strains isolated from 211 samples from Aglaonema `Silver Queen', `Emerald Beauty', and `San Luis' grown in Hawaii, only the pectolytic and pathogenic Erwinia sp. reacted positively in the microplate assay. Other bacteria associated with Aglaonema, including Pseudomonas paucimobilis (Holmes), P. vesicularis (Galarneault and Leifson), and nonpectolytic Erwinia sp., were not detected by the assay. Pectolytic strains of Ralstonia (Pseudomonas) solanacearum (Smith) were differentiated from pectolytic Erwinia sp. by the yellow color that developed in wells of the latter strains after acidification of the medium with dilute HCl. The test is visual and can be performed with minimal equipment and cost.

Hydrometallurgical process for recovery of metal values from spent nickel-metal hydride secondary batteries

A completely hydrometallurgical process has been developed for the recovery of metal values such as cobalt, nickel and rare earths from spent nickel-metal hydride (Ni-MH) secondary batteries. Effects of hydrochloric acid concentration, temperature, reaction time and solid-to-liquid ratio on leaching of metals contained in the electrode materials of the batteries were studied. The optimal operating conditions were found to be 3 M HCl at a temperature of 95°C and a 3-h leach time, and it was possible to treat up to 5.5 g of scrap in 50 ml of acid solution where the recoveries 100% of cobalt, over 96% of nickel and 99% of rare earths were achieved. A typical chemical composition of the resulting leach liquor was approximately, in grams per liter, 23.4 Ni, 1.7 Co, 3.4 Fe, 0.72 Zn, 0.46 Al, 1.2 Mn, 4.2 La, 0.26 Ce, 0.82 Pr, 2.6 Nd and 0.074 Sm, as well as 50 Cl. The pH of the solution was around 1.2. The rare earth values can be readily recovered from the leach liquor by the use of a solvent extraction circuit with 25% bis(2-ethylhexyl) phosphoric acid (D2EHPA) in kerosene, in which a two-stage counter-current extraction at an O:A ratio of 3:1 at an equilibrium pH of 2.0, a single-stage cobalt scrubbing with 0.3 M hydrochloric acid at an O:A ratio of 22:1, and a stripping operation with 2.0 M hydrochloric acid in one contact at an O:A ratio of 5:1 are involved. A mixed rare earth oxide of over 99% purity was obtained by selective precipitation with oxalic acid, and calcination of the precipitate. The total yield of rare earths approached 98%. The cobalt and nickel in the raffinate are effectively separated by selective extraction of cobalt with 25% TOA in kerosene after concentration (up to [Cl −]≈220 g l −1). Nearly complete recovery of cobalt can be achieved by using a three-stage counter-current extraction at an O:A ratio of 2:1, followed by stripping with a dilute hydrochloric acid solution (pH 2.0) in a single stage at an O:A ratio of 4:1. Subsequently the cobalt in the strip liquor and the nickel remained in the raffinate are separately recovered as oxalates by the addition of ammonium oxalate. A pure cobalt product and a nickel oxalate with a purity close to 99.9% were obtained. The total recoveries of cobalt and nickel were found to be approx. 98% and 96%, respectively.