Waste treatment and disposal

Written by J.A Dobado | Last Updated on April 22, 2024

What is waste treatment and disposal?

Wastes generated in an organic chemistry laboratory must be managed appropriately, according to their potential risk. There must be a waste collection plan in these facilities. Under no circumstances should they be discharged into drains or bins. The laboratory should be equipped with suitable containers for storage and subsequent treatment of these wastes (see Figure). Their location and use should be known by students.

Classification of chemical waste

Since not all the residues exhibit the same treatment, and to reduce costs of hazardous waste management, these are classified according to their nature into 7 groups:

Group I (halogenated solvents)

Are organic liquids, very toxic, irritants, and in some cases, carcinogenic, with some content greater than 2 % of a halogen. Also included are mixtures of solvents, halogenated and non-halogenated (provided that the content of halogens of the mixture is higher than the 2 %).

For example: CH₂Cl₂, CHCl₃, CCl₄, PhBr, etc have to be careful not to use any container of aluminum for its storage.

Group II (non-halogenated solvents)

Are organic liquids flammable and toxic that contain less than 2 % in halogen. For example: R-OH, R-CHO, R-CO-R’, R-COO-R’, R-H, R-CN, etc

As far as possible it is important, in this group, avoid mixtures of solvents immiscible, due to the appearance of phases makes it difficult to post-treatment.

Group III (liquids and aqueous solutions “non-acidic”)

Because it is a very large group as they include aqueous solutions of both organic compounds such as inorganic, are subdivided into:

• Inorganic: Aqueous solutions basic, aqueous solutions of heavy metals and aqueous solutions of hexavalent chromium (VI).
• Organic: Aqueous solutions of dyes, solutions of fixing organic, mixtures of water / solvent.

Group IV (acid)

Include inorganic acids and their aqueous solutions concentrated > 10 % in volume. We must take precautions because the mixture of some of these acids, can produce a chemical reaction exothermic or detachment of toxic gases.

Group V (oils)

It consists of mineral oils derived from operations of maintenance, baths, heaters, etc

Group VI (solids)

It is made up of chemicals in the solid state (both organic and inorganic, that should not be mixed with each other. They are subdivided into:

• Organic solids: Chemical products of organic nature or contaminated with organic chemicals, such as activated carbon or silica gel impregnated with an organic solvent.
• Inorganic solids: Chemical products of inorganic nature as salts of heavy metals.
• Disposable materials contaminated: Material contaminated with various chemicals.

Group VII (special products)

It encompasses all the chemical products (solid or liquid) which due to their high toxicity or hazard may not be included in any of the other groups, as well as the reagents pure obsolete or expired. Should not be mixed with each other. Whenever possible, be kept in its original container, if the amounts are less than a liter.

Among this group we can highlight: Oxidising (peroxides), compounds are pyrophoric (magnesium metal powder),
compounds very reactive acids as fumantes, alkali metals, hydrides, compounds peroxidables, as remnants of reaction, products are not labeled, compounds with halogens assets, polymerisable compounds, compounds highly toxic osmium tetroxide, mix crómica, cyanides, sulfides, etc, as well as compounds not identified.

Disabling of wastes

It is recommended that before disposing of waste in the container, an appropriate deactivation to minimize the risks in the storage and transport of the same:

• Acids and bases: Aqueous solutions of acids and bases you should turn off by adjusting the pH to a range 6-8. The neutralization of the acids can be performed using a solution of NaOH, or sodium bicarbonate, and the basic residues with dilute HCl.
• Alkali metals: Before you turn off the solid residues of these metals need to be cut into pieces as small as possible. Must be entered in a container with a solvent inert as, for example, toluene or hexane. To turn it off will be added gradually EtOH, with the caution that, as a byproduct to form hydrogen gas. The process is terminated by adding water with extreme caution. You must perform all these operations in showcase.
• Nitriles and thiols: Deactivated by oxidation with sodium chlorate, and the excess of sodium chlorate is destroyed with sodium thiosulfate.
• Peroxides and other oxidants Br₂, I₂, etc): Is deactivated with an aqueous solution of sodium thiosulfate.
• Cyanides: Disabled oxidizing with a solution of H₂O₂ at pH = 10-11.
• Hydrides, amiduros and borohidruros: Add MeOH at the same time it cools the outside of the container with the residue. The deactivation is completed by adding water with a lot of caution. To disable LiAlH₄ is suspended in ether and added dropwise ethyl acetate, always in an inert atmosphere, and agitate strongly. At the end of the reaction, water is added slowly.
• Azides: Deactivated with iodine in presence of sodium thiosulfate, in the process it follows gaseous nitrogen.
• Halides and alkyl sulfates: Should exercise caution as they tend to be carcinogenic. Are turned off by adding them to drop on an aqueous solution of saturated ammonium hydroxide. There is that cool outwardly.
• Halides-acid: Disabled converting them into the corresponding esters with MeOH at acidic pH. Subsequently neutralized with NaOH.
• Aldehydes: Is deactivated with an aqueous saturated sodium bisulfite, giving the corresponding combinations bisulfíticas.
• Organometallic compounds sensitive to moisture: To turn them off, there is that added drop by drop (typically found with organic solvents) on n-butanol, and combustible vapors given off are eliminated in the fume cupboard. The process is terminated by adding with extreme caution water.

Disposal of chemical wastes

Once we have the waste classified in seven groups mentioned above, and, to the extent possible, deactivated it will be removed by the storage of the same in the containers and containers designed for this purpose and that must be available on all Organic Chemistry lab.

These containers should be in perfect conditions and closed, we should also take the precaution of replacing the containers once they are these full and not stored in the laboratory excessive material waste. The containers must be placed in a ventilated place and away from sources of heat or spark.