Nickel charging process

Write a balanced equation for the reaction that occurs when a nickel-cadmium battery is recharged. If 10.0 g of Ni(OH)2 is oxidized in the charging process, how many grams of cadmium are formed ... 

Nickel batteries use P-Ni(OH)2 as electrode material. This material converts to P-NiOOH during the charging process and this rearranges to y-NiOOH when it is overcharged. This last process is accompanied by a significant expansion, because of the difference in density between P-NiOOH and y-NiOOH, which may result in poor electric contact between the current collector and P-Ni(OH)2/p-NiOOH, with concomitant decrease in the discharge capacity of the battery. Among others, layered double hydroxides of Ni and other metals, often termed stabilized a-Ni(()H), or doped Ni(0H)2, have been tested as electrode materials (Bernard et al., 1996). The effect of the interlayer anions on the electrochemical performance of layered double hydroxide electrode materials has been recently studied by Lei et al. (2008) (see Chapter 6). 

There are three classes of SX reagents, viz. acidic, basic and solvating. Acidic extractants exchange for metal ions, basic extractants are positively charged and extract anionic metal complexes and solvating extractants solubilize neutral metal complexes or ion pairs in the organic phase. For Ni/Co extraction and separation in nickel laterite processing, only acidic and... 

FIGURE 28.27 Charge process of sealed nickel-cadmium batteries. (a) Charge efficiency at 20°C. Charge—O.IC x 16 h discharge—0.2°C end voltage—1 V. (b) Charge efficiency vs. 

The importance of the nickel cadmium cells lies in the fact that, by a special design, they can be made dry giving the portability and freedom of dry primary batteries and the economy of a storage battery. Toward the end of the charging process, both hydrogen and oxygen are liberated at the electrodes, the electrode reactions being... 

In the Edison alkaline accumulator, a 20% solution of potassium hydroxide is electrolysed between a cathode of iron/ferrous hydroxide and an anode of nickel hydroxide. These electrode materials are pressed into perforated steel containers along with mercury and finely divided nickel at cathode and anode respectively to raise the conductivity (which is low for hydroxides). During the charging process the following reactions occur. 

In all of these oxide phases it is possible that departures from the simple stoichiometric composition occur dirough variation of the charges of some of the cationic species. Furthermore, if a cation is raised to a higher oxidation state, by the addition of oxygen to tire lattice, a conesponding number of vacant cation sites must be formed to compensate tire structure. Thus in nickel oxide NiO, which at stoichiomen ic composition has only Ni + cations, oxidation leads to Ni + ion formation to counterbalance the addition of extra oxide ions. At the same time vacant sites must be added to the cation lattice to retain dre NaCl sUmcture. This balanced process can be described by a normal chemical equation thus... 

The effect of physical processes on reactor performance is more complex than for two-phase systems because both gas-liquid and liquid-solid interphase transport effects may be coupled with the intrinsic rate. The most common types of three-phase reactors are the slurry and trickle-bed reactors. These have found wide applications in the petroleum industry. A slurry reactor is a multi-phase flow reactor in which the reactant gas is bubbled through a solution containing solid catalyst particles. The reactor may operate continuously as a steady flow system with respect to both gas and liquid phases. Alternatively, a fixed charge of liquid is initially added to the stirred vessel, and the gas is continuously added such that the reactor is batch with respect to the liquid phase. This method is used in some hydrogenation reactions such as hydrogenation of oils in a slurry of nickel catalyst particles. Figure 4-15 shows a slurry-type reactor used for polymerization of ethylene in a sluiTy of solid catalyst particles in a solvent of cyclohexane. 

Unlike the cells above, which are all primary cells, this is a secondary (i.e. rechargeable) cell, and the two poles are composed in the uncharged condition of nickel and cadmium hydroxides respectively. These are each supported on microporous nickel, made by a sintering process, and separated by an absorbent impregnated with electrolyte. The charging reactions are ... 

Oxygen evolution occurs on nickel oxide electrodes throughout charge, on overcharge, and on standby. It is the anodic process in the self-discharge reaction of the positive electrode in nickel-cadmium cells. Early work in the field has been reviewed [9], No significant new work has been reported in recent years. 

All tests reported here were performed with a special methanation catalyst developed by BASF, Ludwigshafen, for the process. The catalyst had a relatively high nickel content on a carrier. It was charged to reactors D2 and D3 in unreduced form and had to be activated by reduction with hydrogen. 

These tests demonstrated that the Lurgi Rectisol process provides an extremely pure synthesis gas which can be charged directly to the metha-nation plant without problems of sulfur poisoning of the nickel catalyst. However, in order to cope with a sudden sulfur breakthrough from Rectisol as a result of maloperation, a commercial methanation plant should be operated with a ZnO emergency catchpot on line. 

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