The electrochemical recovery of nickel from plating residues

In view of the increasing demand for nickel and its compounds, the recovery of nickel values from any secondary source is of great importance, particularly in countries such as India where there is no domestic source of the metal. The buildups (or nodules) that accumulate during the nickel plating processes are one secondary source of metal. To take advantage of this resource, an electrochemical approach has been attempted to recover the nickel from plating wastes in the form of nickel sulfate. The approach involves selective anodic dissolution of the nickel nodules in a sulfuric acid medium and crystallization of the resultant nickel sulfate. Acidity, nickel concentration in the electrolyte and the extent of dissolution of the nodules have been examined with the intent of avoiding the loss of nickel at the cathode and reducing copper contamination in the electrolyte.     

Current efficiency during the electrochemical machining of iron and nickel

Current efficiency determinations from weight-loss measurements were made on pure iron and pure nickel anodes in 4M NaClO₃ solution in a flow cell at flow rates between 500 and 3000 cm/s in a current range from 5 to 50 A/cm². The current efficiency for metal removal was virtually independent of current density and flow rate on iron anodes. On nickel anodes the current efficiency increased strongly with current density. In the high current density region, the current efficiency decreases with flow rate up to 2000 cm/s and then increases with higher flow rates. This behavior was accounted for by differences in the nature and properties of the anodic films formed on iron and nickel anodes.     

Thermodynamics of chemical and electrochemical stability of brasses

Based on the theory of “regular” solutions, the thermodynamic properties of α-, β-, γ-, ɛ-, and η-phases of the Cu-Zn system are described. The surface activity of the elements in the phases is assessed. Potential-pH diagrams for the general system Cu-Zn-H₂O and the manganese brass system H₂O at 25°C are plotted. The nature of passivating films on conventional and special brasses and their composition are elucidated in different pH and potential ranges.     

The penetration by sulfur of NiO scales growing on nickel

The transport of sulfur through growing scales may occur by chemical (solution and diffusion) or physical (gas molecule permeation) mechanisms. Both possibilities are examined theoretically for the case of NiO growing on nickel. Experiments are designed and carried out to establish which mechanism plays the major role in sulfur transport. The results indicate that the physical mechanism is likely to be predominant.     

Effect of products of nitric acid reduction on active dissolution and passivation of nickel

For nickel in HNO₃ solutions, the passivation process is impeded and the range of its active dissolution is broadened, as opposed to in solutions of nonoxidative acids, which is stipulated by the interaction processes between metal surface and the products of cathode reduction of the solution. It has been shown that the products of cathode reaction promote the occurrence of a new electronegative reaction of nickel dissolution in the form of a complex with ammonia, the ligand formed on the cathode. Moreover, the intermediate products of NO reduction to NO₂ by interacting with nickel surface displace passivating oxygen and, therefore, retard the process of electrode passivation. The kinetic control of the cathode reaction of HNO₃ reduction within the potential range of active dissolution of nickel is connected with the complicated NO desorption from nickel surface, which virtually eliminates the possibility of the development of homogeneous autocatalysis within a certain potential range.     

Initial stages of nickel passivation and dissolution in acidic sulfate solutions

Regularities of the electrochemical dissolution of freshly formed surface (FFS) of iron and nickel are similar as a whole, but exhibit a number of distinctions. At an oxidation stage Me⁰-Me⁺, a water molecule chemisorbs to form a surface complex with charge transfer; however, a mean fraction of transferred charge in the complex of nickel (0.8) is significantly higher than that of iron (0.5). In weakly acid sulfate solutions (pH 1.7–3.2), the iron FFS dissolution is predominantly inhibited by hydrogen atoms formed by the discharge of hydroxonium ions and adsorbed at the dissolution centers. On nickel at pH > 2.7, the inhibition is caused by the formation of adsorbed oxygen corresponding to more positive potentials in a range of active nickel dissolution. Original Russian Text ? A.N. Podobaev, I.I. Reformatskaya, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 1, pp. 73–75.     

Transport of sulfur in the scale growing on nickel in sulfur dioxide atmosphere at 873 K

SO₂ labeled with³⁵S radioisotope was used to study the diffusion of sulfur in scales growing on nickel in sulfur-dioxide atmosphere at 873 K. It was observed that in addition to the inward molecular transport of SO₂, outward diffusion of sulfur also occurred. This diffusion occurred mainly through the grain boundaries of the scale [D_G873=3×10^–7cm²/s]. The liberation of sulfur inside the scale was caused by the reaction of Ni₃S₂ with oxygen or with sulfur dioxide.     

Effect of sulfur electrode composition on the electrochemical property of lithium/PEO/sulfur battery

The lithium/sulfur cell is very attractive because of its high theoretical specific capacity and low production cost. The sulfur electrode is prepared from sulfur, with carbon as an electronic conductor and PEO as an ionic conductor. We changed the carbon content of a 50 wt.% sulfur electrode from 10 wt.% to 40 wt.%. The lithium/PEO/sulfur cell showed two plateau potential regions (2.4 V, 2.1 V) and high discharge capacity, i.e., 1484 mAh/g (88% utilization) for optimum composition. The discharge capacity decreased drastically by charge-discharge cycling. The degradation rate as well as the first discharge capacity depended on the composition of the sulfur electrode. The optimum composition of the 50 wt.% sulfur electrode was 30 wt.% carbon and 20% PEO.     

Thermodynamics of chemical and electrochemical stability of copper-nickel alloys

With the use of the substitution solution model, thermodynamic properties of Cu-Ni solid solutions are described in the stratification region. Cross sections of the Cu-Ni-O phase diagram and potentialpH diagrams of the German silver-H₂O systems, such as CuNi19-H₂O and MNZhMts30-1-1-H₂O, at 25°C and 1 bar are plotted. The homogeneity region of NiO _x phase at equilibrium with atmospheric oxygen is estimated at various temperatures. Thermodynamic features of the corrosion-electrochemical behavior of copper-nickel alloys are analyzed.     

Influence of the oxyanion nature of the electrolyte on the corrosion/passivation behaviour of nickel

The electrochemical behaviour of nickel in the presence of various electrolyte solutions at 0.1 mol/L concentration exhibits a distinction according to the oxyanion nature of the investigated anions. Passivity is achieved with oxyanions whereas it fails with anions not containing oxygen. SIMS and XPS measurements performed from isotopic and non isotopic KNO₃ electrolytes indicate that the oxygen and nitrogen atoms from nitrate oxyanions are incorporated into the passive film during anodic polarization and with evidence of a direct bonding between nitrogen and nickel surface.     

Porosity of nickel electrodeposits on mild steel using electrochemical impedance spectroscopy

Abstract

Impedance spectroscopy recorded at the open circuit potential in 1M H₂SO₄ at 293 K is shown to provide a convenient test for detecting the degree of through porosity in electroplated nickel coatings, electrodeposited from a Watts bath, on mild steel. The impedance data can be interpreted in terms of a simple equivalent circuit, and the corrosion resistance provides a reliable guide to the quality of the deposit. The quantitative estimation of porosity from these data is considered.     

Simulation analysis of electrochemical nature of real passive films with artificial passivation films

Simulation experiments using oxide thin films with analogues composition and thickness of passive films on Fe-Cr alloys have been performed to reveal the function of alloying elements in passive films. The objective of the present paper is to review recent results of the simulation experiments using Fe₂O₃-Cr₂O₃ films. The thinning rate of the films was measured as a function of potential in 1 M HCl by in-situ ellipsometry. The potential-dependent change of the rate well simulated the potential-dependent dissolution behavior of Fe-Cr alloys. The composition of the films having resistance against given environment was obtained by the simulation experiments.     

Effect of a marker material on the oxidation of nickel in sulfur dioxide

A marker study of nickel oxidation in SO₂ at 600°C has proved that after the reaction metallic markers (Au, Pt, W) are covered with a sulfide rim. This effect is not observed on quartz markers. The metallic markers make the intermediate NiO layer adjacent to them increase, whereas the quartz marker makes this layer disappear.     

Thermodynamics of chemical and electrochemical stability of corrosion active nonmetal inclusions

Diagrams potential-pH are plotted for different phase components of corrosive nonmetal inclusions in steels in sulfide-containing media at 25°C, 1 atm (air), and a _i = 10⁻³ mol/l. Thermodynamic peculiarities of their corrosion and electrochemical behavior are analyzed. Original Russian Text ? A.G. Tyurin, I.Yu. Pyshmintsev, I.V. Kostitsyna, I.M. Zubkova, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 1, pp. 39–49.     

The effect of medium on the corrosion and electrochemical behavior of nickel

Electrochemical and corrosion properties of nickel in neutral, alkaline, and acidic solutions are studied. Chemical and phase composition of surface films and surface morphology are examined. The effect of electrolyte composition and concentration on the metal removal rate in the course of broaching is determined. Optical, electrochemical, and gravimetrical methods, x-ray diffraction analysis, and thermogravimetry were used in the work. Original Russian Text ? V.V. Parshutin, N.L. Bogdashkina, G.P. Chernova, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 1, pp. 64–70.     

硫化矿生物浸出过程的热力学

计算并绘制了主要金属硫化物氧化反应的Ｅ－ｐＨ图,并与细菌存活区对比,对主要金属硫化物的细菌浸出进行了热力学分析。     

调压铸造中铝液真空除气的热力学和动力学分析

从热力学角度对调压铸造中的铝液真空除气过程进行了分析,并对真空除气动力学环节进行分析,推导出铝液平均氢浓度与真空处理时间的数学模型,为调压铸造真空除气的压力规范设计提供了参照依据.     

The adsorption of anions on iron during anodic passivation in neutral solution

Abstract

The adsorption of phosphate and ο-iodohippurate ions on iron surfaces has been measured at varying potential during anodic passivation in near neutral solution. Considerable adsorption of both anions occurs in the active potential region, this adsorption being potential dependent. The phosphate adsorption is about three times that of ο-iodohippurate at the same potential. The adsorption of phosphate ions increases with pH in the range 7–9 and with increasing concentration in the range 4 × 10^?5 to 4 × 10^?4 M. When the iron surface is converted from the active to the passive state, the surface coverage with adsorbed anions is an appreciable fraction of a monolayer. The larger the anion adsorption on the active surface, the more easily does passivation occur. Considerable uptake of phosphate ions occurs into the passive film on the iron surface, indicating that passivation is associated with a three-dimensional film.