Cadmium, in batteries

There are two main uses for cadmium in batteries (particularly Ni-Cd batteries), which account for almost three quarters of the consumption, and in pigments and plastics stabilizers. 

A very limited number of studies have been devoted to the analysis of the presence of batteries in municipal solid waste (MSW). The specific presence of Ni-Cd portable batteries has received some recent attention due to the increasing use of cadmium in batteries. In this context. Chandler s study is usually taken as a reference even if it was performed on a limited amount (2.5 tonnes) of materials (Chandler-1995). 

An important aspect of lead is that it is a recoverable resource. It has been estimated that more than 95% of the batteries sold in the United States are ultimately recycled, and it takes considerably less energy to recycle lead, a low-melting metal (mp 327.4°C), than to produce the metals used in other storage battery systems (nickel, iron, zinc, silver, and cadmium) in battery-grade quality. 

Hydrogen-storage alloys (18,19) are commercially available from several companies in the United States, Japan, and Europe. A commercial use has been developed in rechargeable nickel—metal hydride batteries which are superior to nickel—cadmium batteries by virtue of improved capacity and elimination of the toxic metal cadmium (see BATTERIES, SECONDARYCELLS-ALKALINe). Other uses are expected to develop in nonpolluting internal combustion engines and fuel cells (qv), heat pumps and refrigerators, and electric utility peak-load shaving. 

Batteries. Many batteries intended for household use contain mercury or mercury compounds. In the form of red mercuric oxide [21908-53-2] mercury is the cathode material in the mercury—cadmium, mercury—indium—bismuth, and mercury—zinc batteries. In all other mercury batteries, the mercury is amalgamated with the zinc [7440-66-6] anode to deter corrosion and inhibit hydrogen build-up that can cause cell mpture and fire. Discarded batteries represent a primary source of mercury for release into the environment. This industry has been under intense pressure to reduce the amounts of mercury in batteries. Although battery sales have increased greatly, the battery industry has aimounced that reduction in mercury content of batteries has been made and further reductions are expected (3). In fact, by 1992, the battery industry had lowered the mercury content of batteries to 0.025 wt % (3). Use of mercury in film pack batteries for instant cameras was reportedly discontinued in 1988 (3). 

To reduce or eliminate the scattering of cadmium in the environment, the disposal of nickel —cadmium batteries is under study. Already a large share of industrial batteries are being reclaimed for the value of their materials. Voluntary battery collection and reclaiming efforts are under way in both Europe and Japan. However the collection of small batteries is not without difficulties. Consideration is being given to deposit approaches to motivate battery returns for collection and reclamation. 

In 1988 the estimated apparent consumption pattern for cadmium was batteries (qv), 32% coating and plating, 29% pigments (qv), 15% plastics and synthetic products, 15% and alloys and other uses, 9% (16). 

Battery technology continues to advance at a steady pace. Lithium batteries and nickel-metal-hydride batteries are now commonplace. These new rechargeable batteries eliminate the need for toxic cadmium and store more energy per unit mass. The detailed chemistry that underlies the newest advances in battery technology involves principles that are beyond the scope of an introductory course. 

Nowadays, such hydride electrodes are used widely to make alkaline storage batteries which in their design are similar to Ni-Cd batteries but exhibit a considerably higher capacity than these. These two types of storage battery are interchangeable, since the potential of the hydride electrode is similar to that of the cadmium electrode. The metal alloys used to prepare the hydride electrodes are multicomponent alloys, usually with a high content of rare-earth elements. These cadmium-free batteries are regarded as environmentally preferable. 

In landfills, heavy metals have the potential to leach slowly into soil, groundwater, or surface water. Dry cell batteries contribute about 88% of the total mercury and 50% of the cadmium in the MSW stream. In the past, household batteries accounted for nearly half of the mercury used in the United States and over half of the mercury and cadmium in the MSW stream. When burned, some heavy metals such as mercury may vaporize and escape into the air, and cadmium and lead may end up in the ash. 

Nickel-cadmium rechargeable batteries are being researched. Alternatives such as cadmium-free nickel and nickel hydride systems are also being researched, but nickel-cadmium batteries are unlikely to be totally replaced. Nickel-cadmium batteries can be reprocessed to reclaim the nickel. However, currently, approximately 80% of all nickel-cadmium batteries are permanently sealed in appliances. Changing regulations may result in easier access to these nickel-cadmium batteries for recycling. 

Subcategory A encompasses the manufacture of all batteries in which cadmium is the reactive anode material. Cadmium anode batteries currently manufactured are based on nickel-cadmium, silver-cadmium, and mercury-cadmium couples (Table 32.1). The manufacture of cadmium anode batteries uses various raw materials, which comprises cadmium or cadmium salts (mainly nitrates and oxides) to produce cell cathodes nickel powder and either nickel or nickel-plated steel screen to make the electrode support structures nylon and polypropylene, for use in manufacturing the cell separators and either sodium or potassium hydroxide, for use as process chemicals and as the cell electrolyte. Cobalt salts may be added to some electrodes. Batteries of this subcategory are predominantly rechargeable and find application in calculators, cell phones, laptops, and other portable electronic devices, in addition to a variety of industrial applications.1-4 A typical example is the nickel-cadmium battery described below. 

Many types of rechargeable batteries are much more portable than a car battery. For example, there is now a rechargeable version of the alkaline battery. Another example, shown in Figure 11.20, is the rechargeable nickel-cadmium (nicad) battery. Figure 11.21 shows a nickel-cadmium cell, which has a potential of about 1.4 V. A typical nicad battery contains three cells in series to produce a suitable voltage for electronic devices. When the cells in a nicad battery operate as galvanic cells, the half-reactions and the overall cell reaction are as follows. 

Uses. The metal is used in electroplating, in solder for aluminum, as a constituent of easily fusible alloys, as a deoxidizer in nickel plating, in process engraving, in cadmium-nickel batteries, and in reactor control rods. Cadmium compounds are employed as TV phosphors, as pigments in glazes and enamels, in dyeing and printing, and in semiconductors and rectifiers. 

Cadmium is a widely distributed metal used in manufacturing and is present in a number of consumer products. Dietary exposure to cadmium is possible from shellfish and plants grown on cadmium-contaminated soils. Absorption is increased when associated with low levels of iron or calcium in the diet. Some plants, such as tobacco, can concentrate cadmium from even low levels in the soil. The lung readily absorbs cadmium, thus cigarette smokers have elevated cadmium exposure. Cadmium is also used as a metal alloy, in paint, and in batteries (Ni-Cad, nickel-cadmium). Workplace exposure can occur in welding and battery manufacture. 

Cadmium hydroxide is used in storage battery anodes, in nickel-cadmium and silver-cadmium storage batteries, and in cadmium plating. It also is used to prepare other cadmium salts. 

Cadmium (Cd) is a transition metal widely used in industry. Workers are exposed to cadmium in the manufacture of nickel cadmium batteries, pigments, low-melting-point eutectic materials, in solder, television phosphors, and in plating operations. 

Beryllium connections and contacts are employed for switchgear and relays. Beryllium oxide is used as substrata for electronic circuits. Cadmium is used in television and fluorescent light phosphors. Cadmium, nickel and mercury are employed in batteries such as "nicad" cells and mercury cells. Mercury is used in fluorescent lamps, electrical switches, and outdoor lamps, as well as instruments for measuring pressure, temperature, and density. Selenium is employed as a photoreceptor in copying machines, and as a semiconductor in rectifiers. Lead applications include lead add storage batteries, a component in color television glass, and, in its oxide form, use as a dielectric material. 

Cadmium is close to lead and mercury as a metal of current toxicological concern.12346 Extraction of lead and zinc ores, which contain cadmium, pollutes the environment with cadmium. The use of cadmium before 1900 was infrequent however, its valuable metallurgical properties, such as resistance to corrosion, increased its use markedly, for example in the manufacture of alloys and as a coating on steel. It is also now widely used in nickel cadmium ( nicad ) batteries. Coal and other fossil fuels contain cadmium which is released into the environment on combustion. 

Silver-cadmium satellite batteries have been used, in cyclic periods of five hours or more with discharge times of 30-60 min. Operational and test programs have shown cycle life periods of 3 yr at low temperatures. At temperatures of 40°C and 50°C, the cycle life is 1 yr and 0.2 yr, respectively. The cycle life at intermediate temperatures is L.4-2.0 yr. 

To reduce or eliminate the scattering of cadmium in the environment, the disposal of nickel-cadmium batteries is under study. Already a large share of industrial batteries are being reclaimed for die value of iheir materials. 

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