The surplus-chemical stockroom is not a depository for any chemical that will not be wanted in the laboratory within a reasonable period (e.g., 2 to 3 years); such materials are to be disposed of properly. Rooms that are used as general depositories of unwanted chemicals become mini-Superfund sites because of lack of control.

Academic institutions could recycle common organic solvents from one research laboratory to another, or from research laboratories to teaching laboratories. For example, chromatography effluents such as toluene could be collected from research laboratories, distilled, and checked for purity before reuse. Commercial distillation systems are available for such purposes, but laboratory personnel performing the distillations or working in the immediate vicinity need appropriate training. (See Chapter 7 for hazards associated with distillation.)

Laboratory-to-laboratory exchange can be an effective alternative to a central surplus-chemical stockroom in organizations unwilling or unable to manage a central storeroom properly. In such a system, trained laboratory personnel retain responsibility for the storage of unwanted chemicals but notify colleagues periodically of available materials. A chemical tracking system as described above facilitates an exchange system greatly. If colleagues within the same laboratory are using the same hazardous material, particularly one that is susceptible to decomposition on contact with air or water, they should try to coordinate the timing of their experiments.

5.D.3 Recycling of Chemicals and Laboratory Materials

5.D.3.1 General Considerations

Chemical recycling takes many forms. 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 occurs on-site or off-site. On-site recycling occurs at the laboratory or at a central location that collects recyclables from several laboratories. Because on-site recycling can be very time and energy intensive, it may not be economically justifiable. In some cases, although the amount of waste may be quite small, it can require very expensive disposal if a commercial vendor must be used. Before a decision on recycling is made, the cost of avoided waste disposal should be calculated. Because of the difficulty of maintaining the needed level of cleanliness and safety, on-site recycling of mercury and other toxic metals is no longer recommended. Another significant issue is whether recycling activities require a waste treatment permit under the Resource Conservation and Recovery Act (RCRA). More information about this regulation can be found in Chapters 8 and 11. State and local regulations must also be considered.

Off-site commercial firms recycle, reclaim, purify, and stabilize vacuum pump oil, solvents, mercury, rare materials, and metals. Off-site recycling is preferable to disposal, and sometimes is less expensive. Another off-site option is to work with suppliers of laboratory chemicals who accept return of unopened chemicals, including highly reactive chemicals. Gas suppliers sometimes accept returns of partially used cylinders.

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 separate container, because the distillation process gives a better product with fewer materials to separate. Steps should also be taken to avoid getting mercury into oils used in vacuum systems, and oil baths. Similarly, certain ions in a solution of waste metal salts have a serious negative impact on the recrystallization process. Identify users for a recycled product before time and energy are wasted on producing a product that must still be disposed of as a waste. Recycling some of the chemicals used in large undergraduate courses is especially cost-effective because the users are known well in advance.

Many recycling processes result in some residue that is not reusable and will probably have to be handled as a hazardous waste.

5.D.3.2 Solvent Recycling

Because the choice of a distillation unit for solvent recycling is controlled largely by the level of purity desired in the solvent, 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 is probably required. Stills with automatic controls that shut down the system under conditions such as loss of cooling or overheating of the still pot are highly recommended, because they 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 are accumulated before the distillation process is begun.

5.D.3.3 Recycling Containers, Packaging, and Labware

Laboratory materials other than chemicals, such as containers or packaging materials and parts of labora-



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