Weak Alkaline Solution Research Articles

A study of Trace Gold Chloride and Hydroxide Speciation in Weak Alkaline Solution by Ion Chromatography Inductively Coupled Plasma Mass Spectrometry

A study of Trace Gold Chloride and Hydroxide Speciation in Weak Alkaline Solution by Ion Chromatography Inductively Coupled Plasma Mass Spectrometry

Predominance diagrams for Zn(II)–NH3–Cl−−H2O system

The thermodynamics in zinc hydrometallurgical process was studied using a chemical equilibrium modeling code (GEMS) to predict the zinc solubility and construct the species distribution and predominance diagrams for the Zn(II)–NH3–H2O and Zn(II)–NH3–Cl−−H2O system. The zinc solubilities in ammoniacal solutions were also measured with equilibrium experiments, which agree well with the predicted values. The distribution and predominance diagrams show that ammine and hydroxyl ammine complexes are the main aqueous Zn species, Zn(NH3)42+ is predominant in weak alkaline solution for both Zn(II)–NH3–H2O and Zn(II)–NH3–Cl−−H2O systems. In Zn(II)–NH3–Cl−−H2O system, the ternary complexes containing ammonia and chloride increase the zinc solubility in neutral solution. There are three zinc compounds, Zn(OH)2, Zn(OH)1.6Cl0.4 and Zn(NH3)2Cl2, on which the zinc solubility depends, according to the total ammonia, chloride and zinc concentration. These thermodynamic diagrams show the effects of ammonia, chloride and zinc concentration on the zinc solubility, which can provide thermodynamic references for the zinc hydrometallurgy.

Ionically and Covalently Cross-Linked Hydrogels Based on Gelatin and Chitosan

The formation of double cross-linked (ionic and covalent) gelatin (G) and chitosan (CS) hydrogels was studied. The covalent cross-linking consists in the reaction between the carbonyl groups of glutaraldehyde with the free amine groups from the two polymers; the ionic cross-linking is based on sulfate anions interaction with protonated amine groups of the polymers solubilized in acetic acid. The structural and morphological characterization of the obtained hydrogels was performed using FT-IR and scanning electron microscopy (SEM). The influence of different parameters on the cross-linking density (indirectly assessed by water swelling capacity) and the ability to include hydrosoluble active principles such as the ratio between polymers (G/CS), the amount of ionic cross-linker, and the cross-linking time were investigated. The morphological and structural characteristics, mechanical stability, elasticity of the network, the interaction with aqueous weak alkaline solutions, and the capacity to load and release a model drug were analyzed for the obtained hydrogels. Rheological tests were performed to study the mechanical stability of the hydrogels and the results show, generally, elastic and stable networks.

Poly(m-phenylenediamine)–Prussian blue hybrid film formed by one-step electrochemical deposition for glucose biosensor

Hybrid film of poly(m-phenylenediamine) (PMPD) and Prussian blue (PB) has been formed on a glassy carbon (GC) electrode by one-step electrochemical deposition process for the construction of a highly sensitive and selective glucose biosensor. Due to the nanosized PB particles (ca. 40nm) in the PMPD–PB hybrid film, the modified GC electrode exhibited good electrochemical activity towards hydrogen peroxide reduction. The PMPD–PB modified electrode responded to hydrogen peroxide in the linear range from 0.0055mM to 1.0mM with a detection limit of 0.6μM (S/N=3). The PMPD–PB modified electrode showed good stability in neutral or weak alkaline solutions, and also strong anti-interference ability to other interfering electroactive species such as ascorbic acid and uric acid. Glucose biosensor was further constructed by immobilizing glucose oxidase on the PMPD–PB hybrid-modified electrode surface using gold nanoparticles and chitosan. The present biosensor responded linearly to glucose in the concentration range from 0.025mM to 0.65mM with a detection limit of 1.0μM (S/N=3). The response time was 10s and the sensitivity was 2.54mA/M. The present biosensor did not show any interference from large excess of ascorbic acid and uric acid. The constructed biosensor had good stability and reproducibility, thus could be applied to the glucose analysis of serum samples in practice.

Effect of Additive Elements on Corrosion Behavior for Aluminum in Weak Alkaline Solution at High Temperature

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Glucose biosensor based on three dimensional ordered macroporous self-doped polyaniline/Prussian blue bicomponent film

In this paper, a three dimensional ordered macroporous self-doped polyaniline/Prussian blue (3DOM SPAN/PB) bicomponent film was fabricated via the inverted crystal template technique using step-by-step electrodeposition. In this bicomponent film, PB not only acted as a redox mediator, but also presented increased stability in neutral or weak alkaline solution by the protection of SPAN layer on the top. A novel glucose biosensor was fabricated based on the large active surface area and excellent conductivity possessed by the 3DOM SPAN/PB film. The applying experimental conditions of the glucose biosensor have been optimized. Under the optimal conditions, the biosensor showed a wide linear range over three orders of magnitude in glucose concentrations (from 2 to 1600μM) and a low detection limit of 0.4μM. Moreover, the biosensor exhibited short response time, high selectivity and excellent operation stability, which can be applied to detect the blood sugar in real samples without any pretreatment.

SELECTIVE DETERMINATION OF GOLD ION IN RIVER WATER BY SOLVENT EXTRACTION WITH 2-THIAZOLIDINETHIONE, 4-(1-METHYLETHYL)-, (4S)-, FOLLOWED BY REVERSED PHASE HPLC

A determination method for gold (Au) ion in river water has been developed by reversed phase HPLC. The Au(III) ion was quantitatively extracted into benzene from a weak alkaline solution as 2-thiazolidinethione, 4-(1-methylethyl)-, (4S)- (TTM) chelate. The extracted Au-TTM chelate was then separated on a C18 column with an eluent of methanol/ethanol/ 0.01 mol/L TTM (70:30:0.1, v/v) and detected at 270 nm. The correlation coefficients of the calibration curves obtained with 5 mL Au standards were more than 0.999 in the range of 1 µg/mL (ppm) to 10 ppm. The detection limit of the Au ion in 5 mL of water was estimated as 0.08 ppm, by a signal-to-noise ratio (S/N) = 3. Relative standard deviations of peak areas (n = 6) for 5 ppm Au standards was 1.0%. The recoveries with a spiked river water sample for 5 ppm Au ion (n = 6) was 99.2 ± 0.6%. Effects of foreign ions on the determination of 2 ppm Au were investigated with 57 metal ions. Almost none of the ions interfered except for Ag(I), Cd(II), and Ti(IV) ions.

Visual in-situ monitoring of the behavior and phase states of water-hydrocarbon inclusions at high temperatures and pressures

Experiments aimed at examining interactions between hydrothermal solutions and caustolithic rocks, oil, and its major fractions were carried out to obtain model water-hydrocarbon fluids (WHCF) and study their behavior and phase states at high P-T parameters. Simultaneously we experimentally synthesized and grew quartz crystals with inclusions as the major source of information on the behavior and phase state of the model WHCF. The inclusions were then examined with the application of conventional and local IR spectroscopy, gas and liquid chromatography, fluorescent and X-ray diffraction analysis, and the microthermometry of fluid inclusions. Interactions between hydrothermal solutions and caustolithic rocks were proved to result in the synthesis of an oil-like liquid, gaseous hydrocarbons (mostly methane), and solid bitumen. The behaviors and phase states of WHCF generated at temperatures below 260–320°C and above 330–500°C (under saturated vapor pressure and higher) were proved to be different, with these differences predetermined by oil cracking in hydrothermal solutions at temperatures above 330°C (particularly at 350–500°C) with the synthesis of predominantly light and intermediate hydrocarbon fractions. As the temperature was increased, the WHCF generated at temperatures of 260–320°C were transformed into two-phase oil-water fluids without free gas. In contrast to them, the heating of the fluids generated at 330–500°C first resulted in two-phase gas-liquid fluids with light oil fractions dissolved in them. As soon as the critical point (370–380°C) was reached, these fluids passed into a homogeneous supercritical state. The content of oil dissolved in hydrothermal weakly alkaline and alkaline solutions (visual estimations at temperatures of 260–400°C and pressures up to 90 MPa; the inclusions decrepitated at higher pressures) increased from a few hundredths and a few tenths of a percent to 8–10 vol % or, upon oil cracking at 380–450°C, to 20–30 vol % and more.

Effects of pH and anions on the sorption of selenium ions onto magnetite

This study analyzes the influence of carbonate and silicate, which are generally abundant in granitic groundwater, on the sorption of selenium ions onto magnetite in order to understand the behaviors of selenium in a radioactive waste repository. Selenite was sorbed onto magnetite very well below pH 10, but silicate and carbonate hindered the sorption of selenite onto magnetite. On the other hand, little selenate was sorbed onto magnetite in neutral and weak alkaline solutions of 0.02 M NaNO 3 or NaClO 4, matching the ionic strength in a granitic groundwater, even though silicate or carbonate was not contained in the solutions. The surface complexation constants between selenite and magnetite were obtained by using a geochemical program, FITEQL 4.0, from the experimental data, and the formation of an inner-sphere surface complex such as =FeOSeO 2 − was suggested for the sorption of selenite onto magnetite from the diffuse double layer model calculation.

Stability of ZnMgO oxide in a weak alkaline solution

Zinc oxide (ZnO) is a chemical compound of great interest used, for example, as photocatalyst in the purification of wastewater or polluted air. However, neither dissolution, nor photo-dissolution of ZnO is negligible: indeed, both processes reduce significantly the efficiency of photocatalysis and then lead to a secondary pollution by free Zn2+. In the present study, the stability of ZnMgO thin films in weak alkaline solution is investigated. We demonstrate that the replacement of Zn2+ ion with Mg2+ ion results in the production of a Zn0.84Mg0.16O solid solution, whose stability is higher than that of the ZnO sample. This alloy, thus, constitutes an alternative to the use of ZnO in photocatalysis applications. To gain more insights into the higher resistance of such alloys to the dissolution process, X-Ray photoelectron spectroscopy measurements were performed. They highlighted the role of OH group adsorption in the experimentally observed enhancement of ZnMgO stability.

Modifying of etching anisotropy of silicon substrates by surface active agents

Abstract The influence of alcohol additives on etch rate anisotropy of Si(hkl) planes has been studied. The etching processes were carried out in 3 and 5 M KOH aqueous solutions saturated and non-saturated with alcohols. Isopropanol, 1-propanol and tert-butanol were examined. It has been showed that the etching process cannot be controlled only by the surface tension of the solution. Saturation of the etching solution with alcohols modifies etch rate anisotropy, lowering the ratio of the etch rate of (110) and vicinal planes to the etch rate of (100) plane. The morphology of Si(hkl) planes etched in 3 M KOH solution saturated with tert-butyl alcohol has been studied in detail. Smooth (331) and (221) planes have been achieved in this solution. The (100) plane turned out to be densely covered by hillocks, opposite to the (100) plane etched in weak-alkaline solution saturated with isopropanol. To explain this phenomenon, the mechanism of hillocks formation on Si(100) surface has been proposed.

Absorption of atmospheric oxygen by agitated weakly alkaline solutions of surfactants

Volumetric analysis of the decomposition kinetics of sodium hydroxymethylsulfinate was performed to study the absorption of atmospheric oxygen by surfactant solutions agitated in various modes at 353 K. The application of the Danchwerts model of surface renewal made it possible to evaluate the contribution made by changes in driving forces in the stages of O2 absorption and solvation to the overall effect of accelerated gas absorption. The intensifying influence of surfactants on the process of oxygen absorption, manifested in an immobile fluid and at slow solution agitation rates, is eliminated by the oppositely directed changes in the mass transfer and solubility of oxygen at the phase boundary in the transition and turbulent flow modes.

Fillers and Dissolvent in Porous Self-Generating Fine Super-Hard Abrasive Tool

In order to obtain low surface damage and high machining efficiency for advanced ceramics, overcome clogging and dressing difficulties of traditional metal bonded super-hard abrasive, a novel fine super-hard abrasive with porous self-generating ability is proposed in this paper. And the matching of filler and dissolvent in abrasive are studied. Soluble filler is a key technology of porous self-generating fine super-hard abrasive. In this paper, metal, metal oxide and non-metallic oxide are respectively used as soluble fillers. Results of the experimental shows: In metal bonded super-hard abrasive, metal, metal oxide and non-metallic oxide as soluble filler are feasible, correspondingly, FeCl3 solution, aqueous solution and weak alkaline solution are used as dressing dissolvent, respectively. It can be met the requirement of high precision machining for advanced ceramic materials, hard and brittle machining materials.

Quantum-chemical and correlation study of deprotonation and complexation of 1-amino-4-hydroxyanthraquinone

Existing views on the deprotonation and complexation of 1-amino-4-hydroxyanthraquinone are wrong. This compound, its anions, and complexes with metals are not individual substances, but they form a dynamic equilibrium mixture of keto-enol (keto-oxide) and amino-imine tautomers. Different samples of the same compound differ by the tautomeric composition, the respective information is contained in their electron absorption spectra. In weak alkaline solutions the deprotonation occurs exclusively at the hydroxy group. Most typical structure of 1-amino-4-hydroxyanthraquinone anions is 1,10-quinoid, its metal complexes have 9,10-and 1,10-quinoid structures. The ground states of molecules are more responsible for the tautomeric transformations than the excited states. Quantum-chemical calculations of tautomeric anthraquinones by semiempirical PPP methods are more reliable than modern ab initio calculations.

ChemInform Abstract: The Inhibition of Zinc Corrosion by Bisaminotriazole and Other Triazole Derivatives.

Abstract The inhibition of zinc corrosion by various triazole derivatives was investigated with respect to dependence on pH, potential E , inhibitor concentration c Inh , zinc ion concentration c Zn 2+ , and exposure time t . Current potential curves and measurements of weight loss show that 3-amino-5-heptyl-1,2,4-triazole (AHT) is an excellent inhibitor of zinc corrosion in acid and weak alkaline solutions, while bisaminotriazole (BAT4) gives the best inhibition efficiency expecially at pH 9 and low inhibitor concentrations. Capacity potential curves and XPS-measurements show the formation of protective triazole layers with a maximum thickness of about 3 nm. The chemical analysis of insoluble zinc triazole complexes precipitated in solution yields a stoichiometric ratio of Zn 2+ and the triazole ring of 1 : 2. The presence of zinc triazole complex on the zinc surface is shown by XPS spectroscopy. The solubility, adsorbability and hydrophobicity of the triazole molecules and the stability of the zinc-triazole complexes are found to be the most important factors influencing the inhibition efficiency of the triazole derivatives under varying conditions.

Heat and mass transfer in hydrogen production by electrolysis of a water-coal suspension

The possibility of electrochemical gasification of a water-coal suspension at a temperature of 180–460°C and a pressure of 7–20 MPa has been proved experimentally. The obtained producer gas contains mainly hydrogen and carbon dioxide as well as traces of methane, propane, and carbon monoxide. After washing carbon dioxide with weak alkaline solutions hydrogen is dispatched for use in power engineering. The liquid phase contains an insignificant amount of hydrocarbons. Heat and mass transfer between reacting media in the electrolyzer under the conditions of phase transitions with partial absorption of the formed gases has been considered.

A novel reusable platinum nanocatalyst

Recyclability of noble metal catalysts is a challenging issue when dealing with their industrial applications. Smart pH-sensitive Pt nanoparticles were successfully prepared for the first time by using octa(N,N-diacetic acid phenylamine)silsesquioxane (OAPAS) as a macromolecular protective agent. As-prepared Pt nanoparticles can self-aggregate or redisperse by only changing the pH of the system solution. In the weak acidic or alkaline solution (pH > 4.0), the Pt nanoparticles dispersed homogenously; while in the acidic solution (pH = 2.5), they self-aggregated. The dynamic self-aggregation and redispersion processes of the Pt nanoparticles driven by pH changes were revealed by transmission electron microscopy measurements. Electrocatalytic experiments proved that the platinum nanoparticles as a recyclable catalyst showed excellent activity for the hydrogenation of aldehyde after runs of five times. Such platinum nanoparticles are thereby anticipated to have great potential functioning as “smart” catalysts for industrial applications.

The effects of vitamin C on ZnO crystal formation

We have studied the effects of L(+)-ascorbic acid (vitamin C) on the formation of ZnO crystals. We carried out a series of experiments under weak acidic to alkaline conditions. We obtained ZnO structures with various distinct morphologies by varying the concentration of vitamin C dissolved in the weak acidic and alkaline solutions. Under weak acidic conditions, if the concentration of added vitamin C exceeds 0.5 mM, mixed amorphous/crystalline vitamin C–ZnO (VitC–ZnO) nanostructures are obtained. We also found that the ZnO content of the VitC–ZnO nanostructures can be controlled by adjusting the concentration of vitamin C added to the reaction solution. On the basis of our results, we propose a mechanism for the formation of the various ZnO structures and VitC–ZnO nanostructures in the presence of vitamin C.

Chemical speciation of environmentally significant metals with inorganic ligands. Part 3: The Pb2+ + OH–, Cl–, CO32–, SO42–, and PO43– systems (IUPAC Technical Report)

Abstract Complex formation between PbII and the common environmental inorganic ligands, Cl–, OH–, CO3 2–, SO4 2–, and PO4 3–, can be significant in natural waters with low concentrations of organic matter. Numerical modeling of the speciation of PbII amongst these inorganic ligands requires reliable values for the relevant stability (formation) constants. This paper provides a critical review of such constants and related thermodynamic data. It recommends values of log10 β p,q,r ° valid at I m = 0 mol kg–1 and 25 °C (298.15 K), along with the equations and empirical coefficients required to calculate log10 β p,q,r values at higher ionic strengths using the Brønsted–Guggenheim–Scatchard specific ion interaction theory (SIT). Some values for reaction enthalpies, Δr H, are also reported. In weakly acidic fresh water systems (–log10 {[H+]/c°} < 6), the speciation of PbII is similar to that of CuII. In the absence of organic ligands, PbII speciation is dominated by Pb2+(aq), with PbSO4(aq) as a minor species. In weakly alkaline solutions, 8.0 < –log10 {[H+]/c°} < 9.0, the speciation is dominated by the carbonato species PbCO3(aq) and Pb(CO3)2 2–. In weakly acidic saline systems (–log10 {[H+]/c°} < 6), the speciation is dominated by PbCl n (2– n )+ complexes, (n = 0–3), with Pb2+(aq) as a minor species. In this medium (and in seawater), the speciation contrasts with that of CuII because of the higher stability of the Pb2+-chlorido- complexes. In seawater at –log10 {[H+]/c°} = 8.2, the calculated speciation is less well defined, although it is clearly dominated by the uncharged species PbCO3(aq) (41 % of [Pb]T) with a significant contribution (16 %) from Pb(CO3)Cl– and minor contributions (5–10 %) from PbCl n (2– n )+, (n = 0–3) and Pb(CO3)2 2–. The uncertainty in calculations of PbII speciation in seawater arises from (a) the large uncertainty in the stability constant for the apparently dominant species PbCO3(aq), (b) the reliance on statistical predictions for stability constants of the ternary species Pb(CO3)Cl– and Pb(CO3)OH–, and (c) the uncertainty in the stability constant for PbCl4 2–, the available value being considered "indicative" only. There is scope for additional detailed high-quality measurements in the Pb2+ + CO3 2– + Cl– system.

Hydrosulfide/sulfide complexes of zinc to 250°C and the thermodynamic properties of sphalerite

The solubility of synthetic ZnS (cr) was measured at 25–250 °C and P = 150 bars as a function of pH in aqueous sulfide solutions (~ 0.015–0.15 m of total reduced sulfur). The solubility determinations were performed using a Ti flow-through hydrothermal reactor. The solubility of ZnS (cr) was found to increase slowly with temperature over the whole pH range from 2 to ~ 10. The values of the Zn–S–HS complex stability constant, β, were determined for Zn(HS) 2 0 (aq) , Zn(HS) 3 − , Zn(HS) 4 2− , and ZnS(HS) − . Based on the experimental values the Ryzhenko–Bryzgalin electrostatic model parameters for these stability constants were calculated, and the ZnS (cr) solubility and the speciation of Zn in sulfide-containing hydrothermal solutions were evaluated. The most pronounced solubility increase, about 3 log units at m ( S total ) = 0.1 for the temperatures from 25 to 250 °C, was found in acidic solutions (pH ~ 3 to 4) in the Zn(HS) 2 0 (aq) predominance field. In weakly alkaline solutions, where Zn(HS) 3 − and Zn(HS) 4 2− are the dominant Zn–S–HS complexes, the ZnS (cr) solubility increases by 1 log unit at the same conditions. It was found that ZnS(HS) − and especially Zn(HS) 4 2− become less important in high temperature solutions. At 25 °C and m ( S total ) = 0.1, these species dominate Zn speciation at pH > 7. At 100 °C and m ( S total ) = 0.1, the maximum fraction of Zn(HS) 4 2− is only 20% of the total Zn concentration (i.e. at pH t ~ 7.5), whereas at 350 °C and 3 <pH t <10, the fraction of Zn(HS) 4 2− and ZnS(HS) − is less than 0.05% and 2.5% respectively, of the total Zn concentration and Zn(HS) 2 0 and Zn(HS) 3 − predominate. The measured equilibrium formation constants were combined with the literature data on the stability of Zn–Cl complexes in order to evaluate the concentration and speciation of Zn in chloride solutions. It was found that at acidic pH, and in more saline fluids having total chloride > 0.05 m, Zn–Cl complexes are responsible for hydrothermal Zn transport with no significant contribution of Zn–S–HS complexes. The hydrosulfide/sulfide complexes will play a more important role in lower salinity (< 0.05 m chloride) hydrothermal solutions which are characteristic of many epithermal ore depositing environments. The value of Δ f G ° (β-ZnS (cr) ) = − 198.6 ± 0.2 kJ/mol at 25 °C was determined via solubility measurements of natural low-iron Santander (Spain) sphalerite.