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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals
Store liquid organic peroxides at the lowest possible temperature consistent with the solubility or freezing point. Liquid peroxides are particularly sensitive during phase changes.
Inspect and test peroxide-forming chemicals periodically (these should be labeled with an acquisition or expiration date) and discard containers that have exceeded their safe storage lifetime.
Store particularly sensitive materials or larger amounts of explosive materials in explosion relief boxes.
Restrict access to the storage facility.
Assign responsibility for the storage facility to one primary person and a backup person. Review this responsibility at least yearly.
4.E.6Storing Toxic Substances
The following precautions should be taken when storing toxic substances:
Store chemicals known to be highly toxic (including carcinogens) in ventilated storage in unbreakable, chemically resistant secondary containers.
Keep quantities at a minimum working level.
Label storage areas with appropriate warning signs, such as
CAUTION! REPRODUCTIVE TOXIN STORAGE
CAUTION! CANCER-SUSPECT AGENT STORAGE
and limit access to those areas.
Maintain an inventory of all highly toxic chemicals. Some localities require that inventories be maintained of all hazardous chemicals in laboratories.
4.FRECYCLING OF CHEMICALS, CONTAINERS, AND PACKAGING
Recycling of chemicals can take many forms, from solvent distillation to cleaning of mercury to precipitation and purification of heavy metal salts. In each case a material that is not quite clean enough to be used as is must be brought to a higher level of purity or changed to a different physical state. Recycling processes can be very time-and energy-intensive and may not be economically justifiable. Before a decision on recycling is made, the cost of avoided waste disposal must be figured into the equation.
Another significant issue is whether recycling activities require a waste treatment permit under the Resource Conservation and Recovery Act (RCRA). This issue is discussed in Chapter 9. State and local regulations must also be considered.
A general comment applicable to all recycling is that a recyclable waste stream needs to be kept as clean as possible. If a laboratory produces a large quantity of waste xylene, small quantities of other organic solvents should be collected in a different container, because the distillation process will give a better product with fewer materials to separate. Steps should also be taken to avoid getting mercury into oils used in vacuum systems, oil baths, and other applications. Similarly, certain ions in a solution of waste metal salts may have a serious negative impact on the recrystallization process.
It is also important to identify users for a recycled product so that time and energy are not wasted on producing a product that must still be disposed of as a waste. Recycling some of the chemicals used in large undergraduate courses may be especially cost effective because the needs of the users are known well in advance.
Among the factors to be considered when ordering from a supplier of laboratory chemicals is whether the supplier will accept return of unopened chemicals, including highly reactive chemicals. Materials other than chemicals, such as containers or packaging materials and parts of laboratory instruments, can also be recycled. Examples include certain glass and plastic containers, drums and pails, plastic scrap and film scrap, cardboard, office paper, circuit boards, and metals such as steel and aluminum.
The choice of a distillation unit for solvent recycling is controlled largely by the level of purity desired in the solvent, and so it is useful to know the intended use of the redistilled solvent before equipment is purchased. A simple flask, column, and condenser setup may be adequate for a solvent that will be used for crude separations or for initial glassware cleaning. For a much higher level of purity, a spinning band column will probably be required. Stills with automatic controls that shut down the system under conditions such as loss of cooling or overheating of the still pot enhance the safety of the distillation operation greatly. Overall, distillation is likely to be most effective when fairly large quantities (roughly 5 L) of relatively clean single-solvent waste can be accumulated before the distillation process is begun.
The simplest method of cleaning mercury of entrained particulates or small quantities of water is