Mercury in batteries

Liquid mercury was once used in the extraction of gold and silver. Added to the crushed ore, it formed liquid amalgams with the noble metals. After the amalgams were squeezed out of the ore, the mercury was removed by distillation, leaving metallic gold or silver. 

In the chlor-alkali process for chlorine production, a sodium chloride solution is electrolyzed with mercury as the cathode material. Na ions are discharged and sodium metal formed spontaneously is alloyed with mercury as a sodium amalgam  

When Na amalgam is removed from the cell and treated with water, sodium hydroxide and hydrogen gas are formed  

The liquid mercury is recycled back to the electrolytic cell. 

A serious drawback with the process described above is mercury loss to the environment. A modern, alternative process without mercury, the membrane cell technique, is described in Chapter 50 Halogens. 

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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). 

The problem was the lack of knowledge that mercury could be converted from a nonlipophilic form into a lipophilic form in situ in the sediment. Most industrial sources of mercury are now under control except for municipal solid waste incinerators, in which the main problem seems to be mercury in batteries. 

The mercury battery of the type frequently used in watches, calculators, and hearing aids is a primary cell. Although mercury in the water supply is known to cause health problems, no conclusive evidence has been found that the disposal of household batteries contributes to such problems. Nevertheless, manufacturers are working to decrease the amount of mercury in batteries. In recent years, the amount of mercury in alkaline batteries decreased markedly at the same time, the life of such batteries has increased dramatically. 

An Act To phase out the use of mercury in batteries and provide for the efficient and cost-effective collection and recycling or proper disposal of used nickel cadmium batteries, small sealed lead-acid batteries, and certain other batteries, and for other purposes. 

Insofar as mercury and cadmium are concerned, and lead to a lesser extent, no matter how the incinerators are operated, a significant fraction of these materials will be volatilized during incineration and enter the ecosystem via the airborne path, unless recovered from the flues by fly ash precipitation and vapor condensation, methods of questionable merit for large scale MSW operations, uie remainder of the cadmium and lead will end up in the incinerator ash and in the incinerator residues, but all the mercury may be expected to be volatilized. This means that unless the reduction of the toxic materials at the source can be practiced, the incinerator residues and flues will need to be processed to remove lead and cadmium for recycling or for safe disposal in some other manner. The most effective and also the most economical way to prevent mercury from entering the environment from batteries is to phase out the use of mercury in batteries to the ftillest extent possible, an effort already instituted by the battery manufacturers, and to maintain an effective collection system for the mercury batteries still in use. 

There is environmental pressure to remove not only the mercury but also cadmium and lead from the zinc cans. A couple of decades ago, California announced a prohibition on the sale of C-Zn and alkaline cells containing mercury. The restriction on the use of mercury in batteries eliminates the need for recycling, thereby eliminating storage and transportation problems. In other words, the restriction on the use of zinc plus the need to remove mercury would favor the sale... 

AppHcations of mercury include use in batteries (qv), chlorine and caustic soda manufacture (see Alkali and chlorine products), pigments (see Pigments, inorganic), light switches, electric lighting, thermostats, dental repair (see Dental materials), and preservative formulations for paints (qv) (1—3). As of the end of the twentieth century, however, increased awareness of and concern for mercury toxicity has resulted in both voluntary and regulatory reduction of mercury usage (see also Mercury compounds). 

California and Minnesota have placed restrictions on the disposal of fluorescent light tubes, which contain from 40—50 mg of mercury per tube, depending on size. After batteries, fluorescent lamps are the second largest contributor of mercury in soHd waste streams in the United States (3,14). A California law classifies the disposal of 25 or more fluorescent lamp tubes as hazardous waste. In Minnesota, all waste lamps generated from commercial sources are considered hazardous waste. Private homes are, however, exempt from the law (14). Other states have proposed similar regulations. Several companies have developed technologies for recovering mercury from spent lamps (14). 

Mercuric chloride is widely used for the preparation of red and yellow mercuric oxide, ammoniated mercury/7(9/USP, mercuric iodide, and as an intermediate in organic synthesis. It has been used as a component of agricultural fungicides. It is used in conjunction with sodium chloride in photography (qv) and in batteries (qv), and has some medicinal uses as an antiseptic. 

An improved solidification (cementation) technology has been used by Dr. Lawrence K. Wang of the Lenox Institute of Water Technology, Massachusetts, USA, for successful solidification of mercury-containing batteries in concrete blocks. The concrete blocks, which are environment friendly, can then be properly buried in the government-approved hazardous waste landfill sites.3... 

Nitration of the surface of polypyrrole and the subsequent reduction of the nitrate groups has been reported [244] and Bidan et al. [306, 307] have investigated the electrochemistry of a number of polymers based on pyrroles with /V-substituents which are themselves electrochemically active. Polypyrrole has also been successfully deposited onto polymeric films of ruthenium complexes [387], and has been used as an electrode for the deposition and stripping of mercury [388], As with most conducting polymers, several papers have also appeared on the use of polypyrrole in battery systems (e.g. [327, 389] and Ref. therein). 

Two common types of button batteries both use a zinc container, which acts as the anode, and an inert stainless steel cathode, as shown in Figure 11.11 on the next page. In the mercury button battery, the alkaline electrolyte paste contains mercury(II) oxide, HgO. In the silver button battery, the electrolyte paste contains silver oxide, Ag20. The batteries have similar voltages about 1.3 V for the mercury cell, and about 1.6 V for the silver cell. 

The reaction products in a mercury button battery are solid zinc oxide and liquid mercury. The two half-reactions and the overall equation are as follows. 

UNIDEMP was developed in Europe and is based on 10 years of experience with the demercurization of mercury-containing batteries. The equivalent process for batteries, DEBATOX, has been field tested in Europe. This technology is ready for commercial application. 

Mercury Recovery Services, Inc. (MRS), has developed the Mercury Removal/Recovery Process (MRRP) to treat media contaminated with mercury. The ex situ process uses medium-temperature thermal desorption to remove the mercury from contaminated wastes. Process wastes are heated in a two-step process to recover metallic mercury in a 99% pure form. MRS claims MRRP can be applied to soils, activated carbon, mixed waste, catalysts, electrical equipment, batteries, lamps, fluorescent bulbs, mercurous and mercuric compounds, mercury-contaminated waste liquids, and debris. 

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. 

Common procedures of qualitative mercury analysis, i.e. using aluminum foil hooked up to a battery to determine the presence of mercury in a solution (mercury metal forms on the surface of the aluminum foil), suggested the use of aluminum as a cathode. This principle was applied on a larger scale using aluminum wire which had to be flattened to a certain thickness for the voltage used. 

Modern exposure to mercury is seen in miners of cinnabar (HgS), in workers in the chlor-alkali industry, in dental workers, and in battery manufacturing. Almost all of these exposures are now under control. 

Various forms of inorganic mercury are used in industry in battery production and as catalysts. Mercuric nitrate was previously used in tanneries and the fur trade (see pp. 166-7). Clearly these can cause both pollution and human poisoning. However, the form of mercury most likely to be associated with environmental pollution and to cause problems is organomercury. This is because in this form mercury is soluble in fat and can accumulate in animals in the food chain. The cases of serious environmental mercury pollution and poisoning illustrate this well. 

Various forms of mercury have more recently been used in industrial processes as an electrode, in electrical equipment, in batteries, as a catalyst, and in fungicides. Some of these, especially its use in fungicides and as a catalyst, have caused serious human poisoning, as have have seen. 

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