Experimental work was carried out to explore the possibility of using filamentary Ni powder to enhance the rate capability and reduce the usage of cobalt in pasted Ni(OH)(2) electrodes for high-drain-rate application. Testing results showed that an extra fine filamentary nickel powder, type 210, as an additive significantly improved the active mass utilization, gravimetric capacity, and volumetric capacity of pasted Ni(OH)(2) electrodes at high rates. In addition, the performance gain could be achieved in thicker electrodes using reduced Co content. Coarser filamentary Ni powder, type 255, was also found effective but in a lesser degree than type 210. The major contribution of a filamentary Ni powder was believed to be enhancement of conductivity by means of a secondary conductive network in the active mass within the Ni foam cells, equivalent to a reduction in Ni foam cell size. (C) 2003 The Electrochemical Society.

The effect of high surface area, filamentary Inco nickel powders Type 210 and 210H, and of standard battery grade Ni powder Type 255, on the internal pressure of Ni/metal hydride (MH) cells was studied in starved cells. When used as additive to the Teflon bonded AB/sub 5/ metal hydride electrode in a range of 2.5 to 5 wt%, the high surface area powders were found highly effective in accelerating oxygen recombination and suppressing hydrogen evolution and accumulating during overcharge. This led to significantly lower internal pressure in Ni/MeH cells during cycling. The pressure reduction, as well as the MH electrode capacity improvement, was found directly proportional to the specific surface area of the added nickel powder rather than to their ability to improve conductivity. The benefit of the nickel addition is believed to relate to their catalysis to the electrode reactions InNi/MH cell.

The solubility of crystalline samples of scorodite, synthetic and natural, was found to be about two orders of magnitude lower than those reported by earlier authors for apparently amorphous ferric arsenate. Congruent dissolution was observed between pH 1.0 and 2.4. Congruent dissolution data obtained with the synthetic sample were used to calculate the solubility product of scorodite at 23 o C and the free energy of formation

Basic ferric arsenates precipitated from hydrometallurgical liquors by hydrolysis are shown to be very insoluble over a range of pHs. The stability range (solubilities <1 mg l−1) becomes wider with increasing Fe/As ratios. Precipitates with Fe/As ratio=8 have solubilities <1 mg l−1 between Ph=3 and 8. The As solubility did not increase during aging over a 2–3.7 yr period. Naturally occurring iron oxide samples with Fe/As ratios=3–4 show even lower As solubilities than precipitates with the same Ar/As ratios. The solubility of crystalline scorodite, FeAsO42H2O, was found to be about two orders of magnitude lower than reported in the literature for apparently amorphous FeAsO4H2O. The solubility and the free energy of formation were recalculated for crystalline scorodite. This investigation shows that basic ferric arsenates appear to be suitable for safe disposal of arsenic.

AbstractThe passivation of copper anodes due to precipitation of copper sulfate on the anode surface was investigated as a function of electrolyte composition and temperature, and of anode composition. The slime layer present on the anode surface was shown to be the primary factor in causing passivation by inhibiting the diffusion of copper ions. Factors such as temperature, free acid level, Ni2+ and Cu2+ ion levels were also important in so far as they affected the mass transfer characteristics of Cu2+ ions and the solubility of copper sulfate. Résumé La passivation des anodes de cuivre due à la précipitation du sulfate de cuivre sur la surface de l'anode a été étudiée en fonction de la composition et la température de l'électrolyte et aussi en fonction de la composition de l'anode. Nous avons montré que la couche d'impuretés présente sur la surface de l'anode est la cause première de la passivation car elle empêche la diffusion des ions cuivre. D'autres facteurs tels que la température, le niveau d'acide libre, le niveau d'ions Ni2+ et Cu2 sont également importants en ce qu'ils affectent les caractéristiques de transport de matière des ions Cu2+ et la solubilitédu sulfate de cuivre.

Nickelic hydroxide is an important metallurgical reagent used for precipitating cobalt from nickel sulfate solutions. Existing methods of preparation of nickelic hydroxide involve electrolytic oxidation of Ni(OH)2 or the use of strong oxidizing agents such as chlorine, ozone and persulfate. The present paper describes a new method for chemical preparation of nickelic hydroxide, developed in INCO laboratories, by a technique consisting of reacting nickelous hydroxide suspensions with a slurry of calcium sulfite in the presence of air or oxygen. The main advantage of the process is the cost of reagents and an absence of soluble by-products (e.g. Cl−). The chemistry of this process is unusual since the redox potential obtained during the reaction exceeds the theoretical potential of the oxygen electrode. The effect of CaSO3, therefore, is not just a catalytic acceleration of the reaction Ni(OH)2 + O2, for the SO32− must be involved in the stoichiometry of the overall reaction by producing, in the initial phase, some strongly oxidizing intermediate species, most likely the peroxomonosulfate ion SO52−.

The enhancing effect of gas bubbles generated at an anode, on the ionic mass transport rate at the associated cathode is analysed by means of an experimental laboratory-scale copper electrowinning cell in which the bubbles were (a) permitted to rise freely in the entire cell and (b) restricted in their motion by a copper baffle-plate placed between the two electrodes. The improvement in mass transfer observed in the unrestricted case has been correlated via statistical regression analysis to the intensity of bubble motion and pertinent cell parameters.

The acid mist generated during copper electrowinning can be effectively suppressed by a froth covering the electrolyte surface stabilized by the addition of the sulphonic acid, Dowfax 2AO. If the spent electrolyte is then used to strip copper from the loaded solvent extraction reagent LIX65N, these two organics and any degradation products will be mixed. In order to determine whether these organics are compatible, a small-scale continuous solvent extraction/electrowinning system was therefore studied for an extended period.Successive passes of organic around the circuit resulted in decomposition of the LPX65N such that its ability to extract copper was greatly reduced. After seven hundred organic phases, the phase separation in both the loading and stripping stages seriously deteriorated and even with the addition of impractical amounts of Dowfax 2AO it was impossible to maintain the froth over the electrowinning cell. Thus, it is clear that Dowfax 2AO cannot be allowed to contaminate a copper sol...

Agitation of the electrolyte by gas sparging was studied as a means of intensifying the electrowinning of copper. Diffusion layer profiles at the cathode were quantitatively measured using a new technique based on the mass transfer controlled codeposition of a tracer metal ion. Smooth, good quality cathodes were produced in a prototype cell at current densities up to 30 A/dm2 (270 asf).

AbstractHorizontal and vertical mapping of the cathode mass transfer coefficient was used to compare the hydrodynamics of full height model electrowinning cells employing either natural convection or two methods of forced convection. The most sgnificant improvement in performance was achieved with uniform agitation resulting from sparging gas over the cathode surface.

AbstractEine einfache Methode zur Bestimmung des Massentransportkoeffizienten wird diskutiert.