Hydride wastes, disposal

However, lithinm aluminum hydride or zinc metal and HCl (5) are required as reducing agents to reduce the thiocyanate to the thiol. These reducing agents are stoichiometric reagents and aren t environmentally acceptable at this time because of their hazardous properties and waste disposal problems on a large manufacturing scale. 

Although distillation is an effective drying technique, it is laden with serious safety issues. They include fire hazards, the handling of large quantities of reactive metals or metal hydrides, quenching of the metals or metal hydrides, and waste disposal. 

It may be destroyed in several ways. One method is as follows (Aldrich 1995). The solid or its solution is dissolved or diluted in large volume of water. Diluted acetic acid or acetone is then slowly added to this solution in a well-ventilated area. Hydrogen generated from decomposition of borohydride should be carefully vented out. The pH is adjusted to 1. The solution is then allowed to stand for several hours. It is then neutralized to 7, and the solution is then evaporated to dryness. The residue is then buried in a landfill site approved for hazardous waste disposal. Sodium borohydride may be destroyed in the laboratory by alternative methods mentioned for other hydrides. 

The synthesis had a series of disadvantages, like a poor regioselectivity in the Friedel-Crafts acylation, in which the 1-isomer is also produced, accompanied by educts and by-products with safety-critical properties (nitrobenzene, sodium hydride, methyl iodide, sulfide salts) and an undesirable waste disposal problem, demanding a different synthetic path for the larger production scale. 

Excess lithium aluminum hydride and the products of the treatment described above should be placed in an appropriate container, clearly labeled, and handled according to your institution s waste disposal guidelines. For more information on disposal procedures, see Chapter 7. ... 

The successes described above notwithstanding, synthetic chemistry in the 1990s was in large measure characterized by catalysis , which encouraged development of organocopper processes that were in line with the times. The cost associated with the metal was far from the driving force that was more (and continues to be) a question of transition metal waste. In other words, proper disposal of copper salt by-products is costly, and so precludes industrial applications based on stoichiometric copper hydrides. 

At the present time, a large number of spent batteries are disposed of directly into the urban waste stream without proper controls. In addition to the most common systems such as zinc-carbon, alkaline manganese and nickel-cadmium, these now include, at an increasing rate, nickel-metal hydride and lithium cells. Such disposal is of serious concern because of the possible effects of battery components on the environment. Consequently, most countries are now evolving policies for collection and recycling. The majority of lead-acid batteries are recycled, but the number of recycling plants in operation worldwide for other battery systems is still very small due to the unfavourable economic balance of such operations (see Table A3.1). Some of the procedures for the disposal and recycling of battery materials are now briefly described. 

Alkali metals (Na or K) and metallic hydrides, on contact with water, produce hydrogen and sufficient heat to ignite the gas with explosive rapidity. Waste scraps of sodium should be added in small proportions to a high-boiling alcohol, such as propanol or butanol, and safely disposed of after all action ceases. Nonaqueous fire extinguishers such as dry soda ash are the only kind that should be used on an alkali metal fire. See also Alkali and Alkaline Earth Metals, Vol 1, p A125-L... 

Most metal hydrides react violently with water with the evolution of hydrogen, which can form an explosive mixture with air. Some, such as lithium aluminum hydride, potassium hydride, and sodium hydride, are pyrophoric. Most can be decomposed by gradual addition of (in order of decreasing reactivity) methyl alcohol, ethyl alcohol, n-butyl alcohol, or t-butyl alcohol to a stirred, ice-cooled solution or suspension of the hydride in an inert liquid, such as diethyl ether, tetrahydrofuran, or toluene, under nitrogen in a three-necked flask. Although these procedures reduce the hazard and should be a part of any experimental procedure that uses reactive metal hydrides, the products from such deactivation may be hazardous waste that must be treated as such on disposal. 

One of the ways to dispose of chemicals that are reactive with water is hydrolysis, that is, the reaction with water under controlled conditions. Inorganic chemicals that can be treated by hydrolysis include metals that react with water metal carbides, hydrides, amides, alkoxides, and halides and nonmetal oxyhalides and sulfides. An example of a waste chemical treated by hydrolysis is the reaction with water of sodium aluminum hydride (used as a reducing agent in organic chemical reactions) ... 

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