mfety in the chernicol loborotory
edited by MALCOLM M. RENFREW University of ldaho Moscow, ldaho 83843
Chemical Waste Management and Disposal Margaret-Ann A r m w r University of Alberta, Edmonton, AB, Canada T6G 262
Practical chemical laboratory classes generate quantities of waste chemicals that must he recycled or disposed of by safe and environmentally acceptable methods. Supervisors of such classes must be aware of appropriate disposal methods. Thus, college instructors who are training future high school teachers need to help prepare their students to cope with the disposal problems that they will meet in the classroom. Many hazardous chemicals can be treated by simple and efficient techniques so that nontoxic and nonhazardous residues are formed ( I ) . This provides an alternative to disposal by incineration, packing for landfilling, or using a commercial disposal company. For the past five years, a group a t the University of Alberta has developed and tested laboratory methods for treating some commonly used hazardous or toxic chemicals. Our ideal is to convert these chemicals to products that can he safely washed into thedrain, disposed of in the normalgarbage, or at least be more easily transported to a Margaret-Ann Armour recslved her BSc horn tne University of Edlno~rghin 1961 ana worked as a research chemist in the papermak ng mdustry. ~n1970 she oo-
secure landfill and he more environmentally acceptable in such a landfill. I t should be noted that what can be washed into the drain, even after treatment, is ultimately controlled by local regulations. Our goal is to document exact reaction conditions so that the methods can he performed reproducibly by persons having some training in chemistry (2). Several of these methods will be described, toeether with an overview of the manageme& of waste and surplus chemicals. ~
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General Rules for Management of Waste Chemlcals from School Laboratories (3) Plan Ahead Before beeinnine " ..an exveriment, d a n s for the recycling or disposal of all surplus matrr d s or products from thr experiment should be in place. Reuse or Recycle As far as possible, experiments should he planned so that the products can either he used as starting materials in another experiment, perhaps illustrating a disposal method for thevroduet (4).or can be recycled for use in theaame experiment the next time it is performed. Segregate Wastes and Label Clearly Where wastes have to be disposed of by incineration or in a landfill, they must be segregated appropriately and the containers for collecting the waste in the labaratow clearly labelled. For example, halogenated solvents such as chloroform, carbon tetrachloride, and dichlorometbane can be mixed together and labelled as "halogenated salvents". Similarly, nonhalogenated flammable solvents such as petroleum ether, diethyl ether, toluene, and methanol can be mixed, preferably in a container with a fireproof screen, and labelled as nonhalogenated solvents. Before being sent for disposal, these wastes must be packaged and labelled in accordance with the disvoser's directions.
three laboratmy manuals and n chemical education, hazardsposal, and women m science mber of the Chemical lnstltute he American Chemical Socl-
New York Academy of Scl-
A64
Journal of Chemical Education
. .- -- .- - -Safely In ~ e c o n d & School dheinistry Laboratories at the 19th Central Regional ACS meeting. Columbus, OH, June 25. 1987.
Dispose of Wastes Soon After Coflection Wastes should not be allowed to accumulate hut should be dis~osedof as soon as poss~bleafter the experrment r~ complete. Accumulat~unsof unlalrellcd materldl are especially hazardous, and it can be eatremely difficult to know how to dispose of them safely (5) General Techniques for the Dlsposal of Waste or Surplus Chemlcals Before performing any of the techniques described in the following paragraphs, appropriate personal protection such as goggles, gloves, and laboratory coat should be worn. A c i d B a s e Neutralization Waste or surplus dilute mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, or acetic acid can be neutralized with waste or surplus dilute solutions of sodium hydroxide, potassium hydroxide, or other dilute base. Water should be added to the acid or base solutions until they are not more than 1M in strength. The base is then slowly added to the acid while stirring or in such a way that efficient mixing occurs. If necessary, ice should be added to the solution to keep the temperature below 40 "C. The pH of the final mixed solution should he about 7, or neutral to litmus. If only waste acid is available for disposal, it can be neutralized by dilution to less than 1M followed by slow addition of either solid sodium carbonate (soda ash) or 5%sodium hydroxide, with efficient mixing, until the solution is neutral to litmus. Similarly, if only waste base is available. it should be diluted to less 1 M or ahout 5% concentration and than ~~~~~~-~ dilute (1 M) hydrochloricarid or acetrc acid addedslowly with stirring. The neutralrol~tion is washed into the drain with water. ~
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Volume Reduction of Dilute Solutions of Inorganic Salts When an experiment yields a large volume of dilute aqueous solution containing toxic heavy metal ions that should not be washed into the drain, the solution can be placed in a large evaporating dish (or other container providing a large surface area of the solution) in the fume hood and allowed to evaporate. The residue is packaged and labelled for disposal. (Continued on page A66)
Solvent Recycling Where a considerable quantity of a solvent is used in an experiment, it can be economically feasible to collect the solvent in the laboratory in specially marked coutainers and to distil it for ;ewe in the same experiment the next time it is performed. Solvents such as dichloromethane, alcohols, and petroleum ether are especially well handled by this procedure. The distillations should he performed in the fume hood, remembering that alcohols and petroleum ether are flammable. Specific Disposal Reactions Certain chemicals can be disposed of or recycled by simple treatment within the laboratory. Several of these disposal or recycling methods are described in the following paragraphs. Strong Oxidizing Agents Solutions of compounds such as potassium permanganate, sodium chlorate, sodium bromate, sodium iodate, sodium periodate, sodium uersulfate. and calcium bvooehlorite shoild be redukd hefore heing discarded into the drain t o avoid uncontrolled reactionsin thesewer system. The reductioncan be accomplished by treatment with a freshly prepared 10% aqueous solution of sodium hisulfite. Precise quantities and conditions for these reactions are detailed. ~
Potassium Permnnganate
indicates t h a t oxidizing agent is still present. Continue t o add sodium bisulfite solution t o the initial sodium chlorate solution until the test on a 3-mL sample yields a colorless or pale yellow liquid, indicating that no oxidizing agent remains. Neutralize the acidic solution by slow addition, with stirring, of solid sodium carbonate, and wash into the drain with water. Sodium Bromote.
Prepare a 10% aqueous solution of the waste sodium bromate, or estimate the concentration of the waste solution, and, if neeessary, dilute t o not greater than 10% with water. In the fume hood, slowly and with stirring add 10% aqueous sodium hisulfite solution until the yellow color of the sodium bromate is discharged. About 20 mL of sodium bisulfite solution is required for each 10 mL of 10%bromate solution. Neutralize the clear solution hy sl
