Nickel-Zinc accumulator

The Nickel-Zinc (Ni-Zn) accumulator was developed in the 1930s to replace the Silver-Zinc (Ag-Zn) accumulator. 

Its negative electrode is made of zinc and its positive electrode of nickel oxyhydroxide (NiOOH), which is reduced to Nickel hydroxide (Ni(OH)2) during the course of discharge. The electrolyte is an aqueous alkaline solution of KOH. 

The overall electrochemical reaction (read from left to right during discharge) is  

The Ni-Zn accumulator exhibits the advantage of having a lower cost than Ni-Cd and not being affected by directive 2006/66/EC. Its operational voltage is also 25% higher. It is robust, reliable, safe, maintenance-fiee and easily recyclable. 

The main drawback to this technology is its lifetime. It presents poor cycling resistance due to the solubility of the zinc in the alkaline electrolyte, which creates dendrites of zinc that may canse short-circuits between the two electrodes. If the zinc comes into contact with a particle of nickel, hydrogen is released and the zinc is corroded [VAN 06]. 

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In fishes, additive or more-than-additive toxicity occurs with mixtures of salts of copper and mercury, copper-zinc-phenol, and copper-nickel-zinc (Birge and Black 1979). Accumulation of copper in gills of fathead minnows during exposure to 16 pg Cu/L is reduced by added ionic calcium, which competes with Cu for gill binding sites (Playle et al. 1992). 

The metals of most concern are the heavy metals, especially cadmium, lead, and mercury. Although it is a metalloid with characteristics of both metals and nonmetals, arsenic is commonly classified as a heavy metal for a discussion of its toxicity. Though not particularly toxic, zinc is abundant and may reach toxic levels in some cases. For example, zinc accumulates in sewage sludge and crop productivity has been lowered on land fertilized with sludge because of zinc accumulation. Copper may be toxic to plants. Aluminum, a natural constituent of soil, may be leached from soil by polluted acidic rainwater and reach levels that are toxic to plants. Other metals that may be of concern because of their toxicides include chromium, cobalt, iron, nickel, and vanadium. Radium, a radioactive alpha particle-emitting metal, can be very toxic at even very low levels in water or food. 

The toxic metals present in industrial effluent streams include heavy metals such as silver, lead, mercury, nickel, zinc, and chromium. These heavy metals accumulate in soil and are eventually transferred to the human food chain. In irradiation treatment the general strategy is the reduction of higher oxidation state ions to lower oxidation state ions in lower oxidation state the solubility is usually lower, so often the reduced ions can be separated by precipitation. The reduction is done by the hydrated electron and hydrogen atom (under oxygen-free conditions) and/or by other reducing-type radicals formed in hydroxyl radical + alcohol or in hydroxyl radical + acetic acid reaction (see for instance reaction (O 23.34) and (O 23.144)) (Haji-Saeid 2007 Chaychian et al. 1998 Belloni and Mostafavi 2004 Belloni and Remita 2008). 

Indian mustard greens (Brassica juncea) Accumulates selenium, sulfur, lead, chromium, cadmium, nickel, zinc, and copper... 

Zinc/carbon and alkaline/manganese cells are primary battery systems lead, nickel/cadmium, and nickel/metal hydride accumulators are secondary batteries with aqueous electrolyte solutions. Their per-... 

The widespread use of many metals such as silver, cadmium, copper, mercury, nickel, lead, and zinc has resulted in their accumulation in the environment. Sediments are often the repositories of toxic metals (e.g.. Table 15-2). For example, copper is used as an anti-biofouling agent in marine paints and many harbor sediments contain markedly elevated levels of copper. 

Bagatto, G. and M. Alikhan. 1987. Zinc, iron, manganese, and magnesium accumulated in crayfish populations near copper-nickel smelters at Sudbury, Ontario, Canada. Bull. Environ. Contam. Toxicology 38 1076-1081. 

Heavy metals. The most common heavy-metal pollutants are arsenic, cadmium, chromium, copper, nickel, lead, and mercury. Some metals, such as manganese, iron, copper, and zinc, are essential micronutrients. Each type of heavy metal in its own way affects water ecosystem biochemistry and can accumulate in bottom deposits and in the biomass of living elements. 

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