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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals
eral information, it is usually advisable to carry out the hazard categorization process before the materials are removed from the laboratory. Having the analysis done at the laboratory is also usually cheaper than having it performed by the treatment disposal facility or an outside contractor.
Generally, it is not necessary to determine the molecular structure of the unknown material precisely. Hazard classification information usually satisfies the regulatory requirements and those of the treatment disposal facility. However, it is important to establish that the disposal facility will accept the analytical data that are ultimately provided.
The first concern in identification of an unknown waste is safety. The laboratory worker who carries out the procedures should be familiar with the characteristics of the waste and any necessary precautions. Because the hazards of the materials being tested are unknown, it is imperative that proper personal protection and safety devices such as fume hoods and shields be employed. Older samples can be particularly dangerous because they may have changed in composition, for example, through the formation of peroxides. (See Chapter 3, section 3.D.3.2, and Chapter 5, section 5.G.3, for more information on peroxides.)
The following information is commonly required by treatment disposal facilities before they will consider handling unknown materials:
pH and possibly also neutralization information,
presence of oxidizer,
presence of sulfides or cyanides,
presence of halogens,
presence of radioactive materials,
presence of biohazardous materials, and
presence of toxic constituents.
The following test procedures should be readily accomplished by a trained laboratory worker. The overall sequence for testing is depicted in Figure 7.1 for liquid and solid materials.
Physical description. The physical description should include the state of the material (solid, liquid), the color, and the consistency (for solids) or viscosity (for liquids). For liquid materials, describe the clarity of the solution (transparent, translucent, or opaque). If an unknown material is a bi- or tri-layered liquid, describe each layer separately, giving an approximate percentage of the total for each layer.
After taking appropriate safety precautions for handling the unknown, including the use of personal protection devices, remove a small sample for use in the following tests.
Water reactivity. Carefully add a small quantity of the unknown to a few milliliters of water. Observe any changes, including heat evolution, gas evolution, and flame generation.
Water solubility. Observe the solubility of the unknown in water. If it is an insoluble liquid, note whether it is less or more dense than water (i.e., does it float or sink?). Most nonhalogenated organic liquids are less dense than water.
pH. Test the material with multirange pH paper. If the sample is water-soluble, test the pH of a 10% aqueous solution. It may also be desirable or even required to carry out a neutralization titration.
Ignitability (flammability). Place a small sample of the material (<5 milliliters (mL)) in an aluminum test tray. Apply an ignition source, typically a propane torch, to the test sample for one-half second. If the material supports its own combustion, it is a flammable liquid with a flash point of less than 60 °C. If the sample does not ignite, apply the ignition source again for one second. If the material burns, it is combustible. Combustible materials have a flash point between 60 and 93 °C.
Presence of oxidizer. Wet commercially available starch-iodide paper with 1 N hydrochloric acid, and then place a small portion of the unknown on the wetted paper. A change in color of the paper to dark purple is a positive test for an oxidizer. The test can also be carried out by adding 0.1 to 0.2 grams (g) of sodium or potassium iodide to 1 mL of an acidic 10% solution of the unknown. Development of a yellow-brown color indicates an oxidizer. To test for hydroperoxides in water-insoluble organic solvents, dip the test paper into the solvent, and then let it evaporate. Add a drop of water to the same section of the paper. Development of a dark color indicates the presence of hydroperoxides.
Presence of sulfide. The test for inorganic sulfides is carried out only when the pH of an aqueous solution of the unknown is greater than 10. Add a few drops of concentrated hydrochloric acid to a sample of the unknown while holding a piece of commercial lead acetate paper, wetted with distilled water, over the sample. Development of a brown-black color on the paper indicates generation of hydrogen sulfide. Because of the toxicity of the hydrogen sulfide formed during this test, only a small sample should be tested, and appropriate ventilation should be used.
Presence of cyanide. The test for inorganic cyanides is carried out only when the pH of an aqueous solution of the unknown is greater than 10. Prior to testing for