Electropolishing of metals in alcoholic solution of sulphuric acid

The potentiodynamic polarization curves of iron, nickel, cobalt, molybdenum, copper and iron-nickel and cobalt-nickel alloys were measured in the polishing solution of 1M H₂SO₄ in CH₃OH. The above mentioned metals and alloys may be divided into three groups: metals and alloys with high dissolution rate in the active state in which the polishing follows immediately behind the active dissolution region (Fe, Co and Ni-Fe and NiCo alloys with a low nickel content), metals and alloys with low passivating current density that become passive at first and the polishing takes place behind the region of localized corrosion (nickel and NiFe and NiCo alloys with a high nickel content) are metals that are polished in the transpassive region (molybdenum).     

Reclamation of nickel from spent nickel catalyst

Spent nickel catalyst containing an average 9.6% nickel was obtained locally from an oil hydrogenation industry. It was digested with 1–3N HCl, HNO₃, H₂SO₄ and mixtures thereof in one to three stages of durations ranging from one to three hr at 100°C using spent nickel catalyst to acid proportions of 1:3 to 1:8 (w/v). Nickel recoveries of over 94% were obtained when one part of spent catalyst was digested for three hr with six or more parts of 3N mixture of HCl and HNO₃ (3:1, v/v). Acid extracts of spent nickel catalyst obtained using HCl, H₂SO₄ and mixtures thereof were treated with NaOCl to convert their content of iron in the ferric form. The iron from the nickel extract was precipitated out in the form of ferric hydroxide at pH 6.0. Nickel from the iron-freed acid extracts was recovered at pH 8.5±0.5 as nickel hydroxide. Nickel formate was prepared by refluxing nickel hydroxide with 10% formic acid in about 6% excess to stoichiometric requirements for 30 min. The dried nickel formate was reduced in peanut oil at 230°C to 270°C for 0.25 to 2.75 hr. The reduction at 260°C on kieselguhr support, employing nickel formate:oil:support in ratio of 50:43:7, for two hr provided catalyst of maximum activity. The hydrogenation activity of the reclaimed catalyst, assessed by standard AOCS procedure, was greater than that of the parent catalyst. Presented at the AOCS Meeting in New Orleans, LA, in May 1987.     

INTERFACIAL ACTIVITY OF HDEHP AND KINETICS OF NICKEL EXTRACTION IN VARIOUS DILUENTS

ABSTRACT

The interfacial behavior of HDEHP at various diluents/0.05M (H₂,Na₂)SO₄ interfaces was examined using the Drop Volume Method. Different adsorption isotherms such as the Gibbs and Szyszkowski were found as fits well to the experimental interfacial tension isotherms. The values of surface excess at saturated interface,calculated according to them by using the concentration of individual species (e.g. organic monomeric species),increase in the order: MIBK<chloroform <benzene～toluene～xylene<CCl₄ <n-hexane～n-heptane

The interfacial activity data were used to discuss the mechanism and kinetics of nickel extraction. It was shown that the interfacial mechanism is very probable and the extraction limiting step is the reaction between HDEHP molecules present near the interface and the intermediate 1:2 complex just as following

Ni(H₂O) ₄A_2(int,0) +2H₂A_2(int,0) =Ni(H₂O) ₂A₂˙2H₂A_2(int,0) +2H₂O_(int,0)

The investigation of the influence of diluent on the extraction rate supports the mechanism suggested.     

Inorganic–organic hybrid metal complexes: 24-membered hexaazamacrocyclic dinuclear nickel complexes hybridized with CdBr42−

The 24-membered macrocyclic mononuclear cadmium complex reacts with Ni(ClO₄)₂ in solution and unexpected dinuclear nickel complex was obtained with [CdBr₄]²⁻ as counter ions. In the homodinuclear nickel complex, two different coordination environmental entities were observed. One of these is a five-coordinated dinuclear species, the other is a six-coordinated dinuclear species [Ni(1A)₂C₂₆H₄₀N₆O₂(H₂O)₂]. In [Ni(1A)₂C₂₆H₄₀N₆O₂(H₂O)₂], nickel ion is coordinated to three nitrogen atoms, one phenolic oxygen from the macrocyclic ligand, and with one exogenous water molecule to complete an octahedron. In [Ni(1B)₂C₂₆H₄₀N₆O₂], each nickel ion is five-coordinated without solvent interaction. [CdBr₄]²⁻ anions are located in the lattice and serve as hybrid bridges to connect two different molecules and form two layer arrays along the c axis. The whole molecule is described as an ion pair with a two-dimensional hydrogen bonding network. The average bond lengths of Ni–N and Ni–O(phenolic oxygen) are 2.083, 2.028 Å.     

Coloured coatings on aluminium produced by varying the duration of a.c. electrolysis treatment I. Thin coatings

Variously coloured coatings on aluminium were obtained by varying the duration of the a.c. electrolysis in a bath containing H₃BO₃, Ni(CH₃COO)₂ and (HOCH₂ CH₂)₂ NH, after an initial d.c. pretreatment in a mixture of H₃PO₄ and H₂SO₄. Electron-optical observation of the micro structure reveals that many tiny columns grow on the outer layer of the anodic film and the column consists of fine nickel particles, together with amorphous material.     

Selective Recovery of Cadmium,Cobalt, and Nickel from Spent Ni–Cd Batteries Using Adogen® 464 and Mesoporous Silica Derivatives

Spent Ni–Cd batteries are now considered an important source for many valuable metals. The recovery of cadmium, cobalt, and nickel from spent Ni–Cd Batteries has been performed in this study. The optimum leaching process was achieved using 20% H₂SO₄, solid/liquid (S/L) 1/5 at 80 °C for 6 h. The leaching efficiency of Fe, Cd, and Co was nearly 100%, whereas the leaching efficiency of Ni was 95%. The recovery of the concerned elements was attained using successive different separation techniques. Cd(II) ions were extracted by a solvent, namely, Adogen^® 464, and precipitated as CdS with 0.5% Na₂S solution at pH of 1.25 and room temperature. The extraction process corresponded to pseudo-2nd-order. The prepared PTU-MS silica was applied for adsorption of Co(II) ions from aqueous solution, while the desorption process was performed using 0.3 M H₂SO₄. Cobalt was precipitated at pH 9.0 as Co(OH)₂ using NH₄OH. The kinetic and thermodynamic parameters were also investigated. Nickel was directly precipitated at pH 8.25 using a 10% NaOH solution at ambient temperature. FTIR, SEM, and EDX confirm the structure of the products.     

Composite Ni/Al2O3 coatings and their corrosion resistance

Composite coatings Ni/Al₂O₃ were electrochemically deposited from a Watts bath. Al₂O₃ powder with particle diameter below 1 μm was codeposited with the metal. The obtained Ni/Al₂O₃ coatings contained 5-6% by weight of corundum. The structure of the coatings was examined by scanning electron microscopy (SEM). It has been found that the codeposition of Al₂O₃ particles with nickel disturbs the nickel coating's regular surface structure, increasing its microcrystallinity and surface roughness. DC and AC electrochemical tests were carried out on such coatings in a 0.5 M solution of Na₂SO₄ in order to evaluate their corrosion resistance. The potentiodynamic tests showed that the corrosion resistance of composite coating Ni/Al₂O₃ is better than that of the standard nickel coating. After 14 days of exposure the nickel coating corrodes three times faster than the Ni/Al₂O₃ coating. The electrochemical behaviour of the coatings in the corrosive solution was investigated by electrochemical impedance spectroscopy (EIS). An equivalent circuit diagram consisting of two RC electric circuits: one for electrode, nickel corrosion processes and the other for processes causing coating surface blockage, were adopted for the analysis of the impedance spectra. The changes in the charge transfer resistance determined from the impedance measurements are comparable with the changes in corrosion resistance determined from potentiodynamic measurements.     

The Hafnium-Selective Extraction Fom a Zirconium(Hafnium) Heptafluoride Ammonium Solution Using Organophosphorus-Based Extractants

ABSTRACT

The suitability of the organophosphorus-based extractants, DiOPA, Ionquest 801 and D2EHPA was evaluated for the selective extraction of Zr and Hf from an (NH₄)₃Zr(Hf)F₇ acidic solution using both dispersive and pertraction solvent extraction (SX). A stock solution of (NH₄)₃Zr(Hf)F₇ was dissolved in either HCl or H₂SO₄ (0.1–8 M). The following extraction variables were investigated: type and concentration of the acidic solution, the contact time, and extractant to metal ratio. Subsequently, the stripping was investigated using (NH₄)₂CO₃, CaCl₂, H₂SO₄ and C₂H₂O₄ in the concentration ranges of 0–2 M. During extraction, scrubbing and stripping using D2EHPA, CaCl₂ and C₂H₂O₄, the Zr purity was increased from 97.2% to 99.0%. When extracting from 4 M H₂SO₄ with 9 wt% D2EHPA, a Hf selectivity of 32% was observed where after stripping with C₂H₂O₄ resulted in a 98.7% recovery of Zr. With 1.2 M CaCl₂ as stripping liquor, almost no Hf and 75% Zr stripping was obtained. During the pertraction 72% Hf and 44% Zr extraction was achieved after 180 min when extracting with 9 wt% D2EHPA from 4 M H₂SO₄. Pertraction based stripping with 1.2 M C₂H₂O₄ yielded 75% of both Zr and Hf, while stripping with 2 M CaCl₂ resulted in 58% Hf stripped with almost no Zr stripping.     

Unsupported Ni/Mo(W)S2 Catalysts from Hexamethylenediammonium Thiometallates Precursors: In Situ Activation During the HDS of DBT

Unsupported Ni/MoS₂ and Ni/WS₂ HDS catalysts were prepared by in situ activation of hexamethylenediammonium thiometallates promoted with Ni. The method involved an aqueous solution reaction of ammonium thiomolybdate (ATM) or ammonium thiotungstate (ATT) with Ni(NO₃)₂·6H₂O and hexamethylenediamine. Ni-promoted precursors were then in situ activated during the hydrodesulfurization (HDS) of dibenzothiophene (DBT) producing Ni/MoS₂ and Ni/WS₂ catalysts. Solids were analyzed after the in situ activation by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and for textural properties by using the BET and BJH methods. Catalysts with relatively high surface area and type IV N₂ adsorption–desorption isotherms were obtained. The use of the hexamethylenediammonium precursor led to a significant nickel promotion of MoS₂ and WS₂ catalysts. For Ni/MoS₂, the use of this carbon-containing precursor was found to be more beneficial for the final HDS catalytic activity than using the classical ammonium tetrathiomolybdate (ATM) without carbon. For Ni/WS₂, compared to tetraalkylammonium thiosalts, the lower amount of carbon in excess formed during the decomposition of the hexamethylenediammonium precursor coupled with a lower crystallization rate of WS₂ favors a correct nickel accommodation on the WS₂ edges.     

Selective Separation of Gallium from Acidic Leach Solutions by Emulsion Liquid Membranes

Abstract

The separation and concentration of gallium from acidic leach solutions, containing various other ions such as iron, cobalt, nickel, zinc, cadmium, lead, copper, and aluminium, by an emulsion liquid membrane (ELM) technique using tributyl phosphate (TBP) as carrier has been presented. Liquid membrane consists of a diluent, a surfactant (ECA 4360J), and an extractant (TBP), and 0.1 M HCl or 0.1 M H₂SO₄ were used as the stripping solution. The important variables governing the permeation of gallium and their effect on the separation process have been studied. These variables were membrane type and composition, mixing speed, diluent type, surfactant concentration, extractant concentration, HCl concentration in the feed, acid type of stripping phase, feed concentration, and treatment ratio. The optimum conditions were determined. It was possible to selectively extract 96.0% of gallium from the acidic leach solutions, containing Fe, Co, Ni, Zn, Cd, Pb, Cu, and Al, at the optimum conditions.     

Hydrogen coevolution and permeation in nickel electroplating

Nickel coatings were electrodeposited onto a steel membrane in a conventional Devanathan cell in order to measure the diffusion rate of hydrogen into the steel substrate during electrodeposition. In most cases a Watts' solution containing various organic additives was used: butyne-2 diol-1, 4; saccharine or thiourea. The structure of the electrodeposits was studied by X-ray and Transmission electron microscopy (TEM). It was shown that the electrodeposition parameters (pH, composition of the bath, additives) have a strong effect on hydrogen permeation. The use of organic additives during Ni plating increased the penetration of hydrogen into the substrate. In particular, sulfur-containing additives cause a fast initial increase of the permeation rate, which is attributable to a high surface concentration of H_ads when steel is not totally covered with nickel. By performing permeation experiments with Ni coatings during hydrogen charging from a H₂SO₄ solution, it was shown that hydrogen permeation through nickel coatings is influenced by their fibre texture and by their grain sizes. A low permeation rate was observed in coatings plated in the presence of butyne-2 diol-1,4, which exhibit a strong 100 texture with large grains and a low density of defects. Conversely, the hydrogen diffusion rate is very high in coatings plated in the presence of thiourea or saccharine. These coatings exhibit a weak texture with very small grains.     

Pro-oxidant activity of nickel (II) pyridoxal complexes. Synthesis,characterization and peroxidase activity assays

The synthesis of Ni (II) complexes with pro-oxidant applications has demonstrated many advantages, such as accelerated reactions, solution stability and with high selectivity reactions. In this work we describe the synthesis, characterization and structural analysis of nickel ([(Ni)(C₃₀H₂₈N₄O₄S₂)]);([(Ni)(C₃₁H₃₀N₄O₄S₂)]) and ([(Ni)(C₃₃H₃₇N₄O₄S₂)]·DMF — complex 3) complexes with ligands obtained from the condensation of pyridoxal and aryl-thiol amines and their application as a pro-oxidant in the reaction of the phenol-aminoantipyrine adduct. The complexes show variation in carbon spacers between pyridoxal molecules: ethane, propane and butane. It was found that the spacer two carbons containing the most significant as the pro-oxidant activity.     

Phase Transformations of α-Alumina Made from Waste Aluminum via a Precipitation Technique

We report on a recycling project in which α-Al₂O₃ was produced from aluminum cans because no such work has been reported in literature. Heated aluminum cans were mixed with 8.0 M of H₂SO₄ solution to form an Al₂(SO₄)₃ solution. The Al₂(SO₄)₃ salt was contained in a white semi-liquid solution with excess H₂SO₄; some unreacted aluminum pieces were also present. The solution was filtered and mixed with ethanol in a ratio of 2:3, to form a white solid of Al₂(SO₄)₃·18H₂O. The Al₂(SO₄)₃·18H₂O was calcined in an electrical furnace for 3 h at temperatures of 400–1400 °C. The heating and cooling rates were 10 °C/min. XRD was used to investigate the phase changes at different temperatures and XRF was used to determine the elemental composition in the alumina produced. A series of different alumina compositions, made by repeated dehydration and desulfonation of the Al₂(SO₄)₃·18H₂O, is reported. All transitional alumina phases produced at low temperatures were converted to α-Al₂O₃ at high temperatures. The X-ray diffraction results indicated that the α-Al₂O₃ phase was realized when the calcination temperature was at 1200 °C or higher.     

Zinc electrowinning with 2-butyne-1,4-diol

The beneficial effect of 2-butyne-1,4-diol on zinc current efficiency in the presence of nickel impurity has been examined. Several techniques including HPLC, absorption spectrophotometry and constant current deposition experiments have shown that a trimer of 2-butyne-1,4-diol is responsible for the removal of Ni ions from the electrolyte, thus increasing the current efficiency of the zinc electrowinning process from sulphate solutions (60 g/L Zn + 200 g/L H₂SO₄) in the presence of Ni ions.     

Simultaneous removal of SO2, SO3 and H2SO4 mist from the gas after TiO2 calcining

Absorption of SO₂ and SO₃ in the solutions of waste ferrous sulfate (so-called ‘green salt’) and in the spent acid after TiO₂ hydrolysis, at H₂SO₄ concentrations ranging from 0–5 to 15 g/m³ (STP), was studied. The rate of SO₃ absorption has been found to rise linearly with increasing SO₃ concentration in the gas and to be independent on H₂SO₄ concentration in solution. The SO₂ absorption also rises linearly with increasing SO₂ content in the gas, but diminishes as H₂SO₄ concentration increases—an upper limit of 100 g H₂SO₄/kg H₂O is indicated. The initial concentration of the solution must not be higher than 40 g H₂SO₄/kg H₂O.     

Electrodeposition of catalytically active nickel powders from sulphate baths. I. Effect of bath constituents

A detailed study was made of the influence of the sulphate bath constituents: 0.3 - 0.0125 NiSO₄·7H₂O (I), 0.05 – 0.23 (NH₄)₂SO₄ (II), 0.1 – 0.4 H₃BO₃ (III) and 0.07 – 0.35 mol l^?1 Na₂SO₄·10H₂O (IV) on the electrodeposition of nickel powder. The cathodic polarization, current efficiency, growth morphology, crystallite size and catalytic activity of the electrodeposited nickel powders were affected to different extents by the bath constituents. A highly pure nickel powder characterized by a small crystallite size (776 Å) and moderate catalytic activity was obtained from a bath containing: 0.0125 (I), 0.23 (II), 0.1 (III) and 0.07 mol l^?1 (IV) at a current density of 10 A dm^?2 and electrolysis time 60 min. at 25 °C. Structural studies with a scanning electron microscope are given and a reaction mechanism for the electrolytic powder deposition is discussed.     

Regeneration of activated carbon after contact with sulfuric acid solution

This study deal's with the feasible use of a commercial activated carbon in the uptake of H₂SO₄ from aqueous solution and with the regeneration of the spent product. Thermogravimetry TG and FT‐IR spectroscopy are used in the analysis of samples. The activated carbon is a very effective material for the uptake of H₂SO₄. Using a 9.0 mol dm⁻³ H₂SO₄ solution, the mass increase is 37.8 wt%. From the sample obtained, the H₂SO₄ can be removed largely either by heating at 250 °C for 2 h in a N₂ atmosphere or by washing thoroughly with distilled water for 24 h. The mass loss in both cases amounts to 33.6 wt%. The FT‐IR spectroscopy results indicate that the surface chemistry of the carbon is not affected, noticeably, at least, after its contact with the H₂SO₄ solution. The behavior of H₂SO₄ toward carbon is compared with that of HNO₃. © 2000 Society of Chemical Industry     

Surface pH measurements during nickel electrodeposition

To better understand the electrochemistry of nickel electrowinning from nickel chloride solutions at the cathode-electrolyte interface, the cathode surface pH was measured using a flat-bottom combination glass pH electrode and a 500 mesh nickel-plated gold gauze as cathode. The cell was a modification of that designed by Romankiw and coworkers. The pH electrode was positioned at the back of, and in direct contact with, the gauze cathode. As expected, the cathode surface pH was always higher than the pH in the bulk electrolyte, and if the current density was sufficiently large, it could cause the precipitation of insoluble Ni(OH)₂₍₅₎ on the cathode surface. Lower bulk pH, higher nickel concentration, higher temperature, and the additions of H₃BO₃ and NH₄Cl effectively suppressed the rise of the cathode surface pH. The results provide further evidence of the buffering action of H₃BO₃ and NH₄Cl and of the enhancement of nickel deposition by H₃BO₃. At current densities less than 240 A m^–2 additions of NaCl and Na₂SO₄ suppressed the rise of the cathode surface pH but to a much smaller degree.     

Size resolved chemical composition of nanoparticles from reactions of sulfuric acid with ammonia and dimethylamine

Abstract

Nanoparticle formation and growth driven by acid-base chemistry was investigated by introducing gas-phase sulfuric acid (H₂SO₄) with ammonia (NH₃) or dimethylamine (DMA) into a flow tube reactor. A thermal desorption chemical Ionization mass spectrometer was used to measure the size-resolved chemical composition of H₂SO₄-DMA and H₂SO₄- NH₃ nanoparticles formed under dry conditions and at 60% relative humidity. In contrast with predictions for bulk aqueous systems, nanoparticles showed a strong size-dependent composition gradient and did not always reach a fully neutralized state in excess of gas-phase base. Smaller particles were more acidic, with an acid:base ratio of 0.7?±?0.1 and 1.3?±?0.3 for 8.6 and 9.5?nm H₂SO₄-DMA particles formed under dry and humid conditions, respectively, and 3.1?±?0.6 and 3.4?±?0.3 for 7.5?nm H₂SO₄-NH₃ particles formed under dry and humid conditions, respectively. The acidity of particles generally decreased as particles grew. H₂SO₄-DMA particles became fully neutralized as they grew to 14?nm, but H₂SO₄-NH₃ particles at 12?nm were still acidic and were never observed to reach bulk sample thermodynamic equilibrium for the experimental conditions in this study. Thermodynamic modeling demonstrated that the observed trends can be reproduced by modifying acid dissociation constants to minimize acid-base chemistry, which may be caused by steric or mixing effects, and by considering volatilization of the neutral base.

Copyright © 2018 American Association for Aerosol Research     

The solubilities of Fe,Ni, V and Na salts in concentrated aqueous H2SO4 solutions at temperatures between 400 and 460 K

When residual fuel oil, which contains up to 4 wt% S, is burned in boiler plant, H₂SO₄ is formed which condenses as aqueous solutions (65–90 wt% H₂SO₄) on surfaces in the cool back-end. The oil contains traces of other elements, in particular Na, V, Fe and Ni, which also deposit on these surfaces as either sulphates (Na, Fe, Ni,) or oxides (V). When designing techniques to control acid deposition and the corrosion which it subsequently causes, account must be taken of the degree to which the acid properties can be modified by taking these compounds into solution. A series of measurements of the solubilities of relevant compounds in acid solutions within the appropriate ranges of concentration and temperature (400–460 K) have been made. Sodium sulphate has by far the highest solubility (55 wt% in a solution originally containing 85 wt% H₂SO₄ at 423 K). Of the other compounds considered, only V₂O₅ exhibits a solubility of more than 2 wt%; for example, at 463 K, in 75 wt% H₂SO₄, solutions containing up to 16 wt% V₂O₅ can be formed. Solutions with up to 23 wt% V₂O₅ can be stabilised by the presence in solution of small amounts (～0.5 wt%) of Fe³⁺ ions. The structure of these solutions is discussed.