Difference between revisions of "Proper disposal of chemicals"

Revision as of 22:51, 28 August 2022

Most chemicals used by the amateur chemist come from every day use and do not require special treatment before being discarded in the usual way. However there are many chemicals, such as heavy metal compounds or organic solvents, that require special disposal techniques. In the interest of keeping lab costs low, though, it may be a good idea to look into ways to recycle and recover chemicals such as solvents, which can be reclaimed by distillation.

IMPORTANT NOTE!!!

The information posted in this article is merely a collection of observations from various amateur chemists and is NOT meant for professionally disposing large amounts of chemicals and should NOT be used as a guideline on neutralizing reagents. For the disposal of large amounts of hazardous reagents or for special reagents, ask the help of professional hazardous chemical disposal entities. ALWAYS CHECK THE LOCAL LAWS BEFORE DISPOSING OF ANY REAGENT! This wiki will NOT take any responsibility (legal or other) for any (failed) attempts at neutralizing hazardous reagents. Do not treat the written disposal guidelines as absolute.

Standard procedures

Acids

Acids are best neutralized with a base, such as carbonate/bicarbonate, hydroxide (calcium hydroxide e.g.) best as aqueous solution. Before neutralizing them, always dilute the acid first, to limit splashing or boiling the acid. ALWAYS POUR THE ACID IN WATER AND NOT THE OTHER WAY AROUND! After you diluted the acid, dissolve the base in water or, if it's insoluble, add just enough water to turn it into a suspension. Slowly add the base in the diluted acid, and watch out for foaming or, if it's a strong acid, boiling. Never add solid alkali bases in strong acids, as this will cause the acids to violently boil and splash acid everywhere. After neutralization, you're left with a solution containing the salt of the neutralized acid. Salts of hydrochloric, sulfuric, phosphoric acids can be further diluted then safely poured down the drain, or recycled if you want.

The soluble salts of halogen acids and oxoacids (except perchloric and chloric acids) can be safely poured down the drain. Special acids and their salts, such as hydrazoic acid and azides must not be poured directly down the drain, they must be treated with nitrous acid to destroy them.

Oxidizing mixtures, such as aqua regia, piranha solution or the nitrating mixture must also never be poured down the drain, as they're much more dangerous than simple acids, and can wreak havoc on your plumbing. Instead, they must be neutralized first.

Bases

Alkali hydroxides can be left in open air to absorb carbon dioxide as well as corrosive and unpleasant gases, forming carbonates and salts. However, as the carbonate is formed, it will creep out of the flask, covering it. For quicker results, alkali bases can be neutralized with any acid, though for practical and economical purposes, acetic acid or citric acid are sufficient. Just make sure to dilute the bases first. Bases may be reused to absorb acidic vapors in a desiccator, which mitigates their dangers. Care must be taken to avoid excess heating with strong bases.

Cyanides

Waste containing cyanide, either from gold refining or from organic extractions of alkaloids from cyanide containing plants, must be neutralized with bleach or hydrogen peroxide, to turn them into less harmful cyanates. The resulting cyanates will slowly hydrolyze in basic environment to ammonium carbonates, while excess bleach/oxidizer will further convert them to nitrogen and carbon dioxide.

Cyanides must never be poured down the drain before neutralization.

Heavy metals

Since the biggest hazard comes from the volatile and soluble heavy metal compounds, it's best to convert them into insoluble compounds, which are less toxic.

Heavy metals, such as mercury, can often be neutralized with a mixture of zinc and sulfur powders, which yields mercury sulfide aka cinnabar. This compound is insoluble in water and acids, showing little reactivity.

Very dangerous heavy metals such as cadmium, thallium and arsenic should always be properly disposed of at designated facilities, as their effects on human life and the environment is sometimes catastrophic.

Inorganic anions

Inorganic anions, based on halogens, sulfur, phosphorus, nitrogen, carbon and silicon can be flushed down the drain with lots of water. Examples of these are sulfide, sulfate, chloride, chlorate, nitrate, nitrite, thiocyanate.^[1]

Metal ions

A good rule of thumb for transition metals is to convert solutions of their ions to the insoluble carbonate or oxide, often one of the most stable and nontoxic forms of these elements, prior to disposal. Another simple solution is to reduce the ions back to the metal.

Copper salts are dangerous to the environment and should be reduced with iron to elemental copper, that can be reused, and the iron salts produced are less toxic.

Nickel-containing compounds, especially organonickel compounds, are carcinogens, and are also dangerous to many other forms of life. It is a good idea to take these to a proper waste disposal facility.

Cobalt salts may be carcinogenic and should be taken to a proper waste disposal facility.

Aluminium compounds generally should not be disposed in the sewage. They can, however, be converted to aluminium sulfate, which is safe to dispose of in soil, though it will cause a decrease in pH (it is used as a fertilizer for this purpose), and in diluted form can be poured down the drain, as at low concentrations it's used in the treatment of water. It is a good idea to dispose of aluminium sulfate and a safe basic compound (such as calcium carbonate) at the same time.

Many compounds of chromium, especially chromium(VI), are poisonous and carcinogenic. These should be converted to the +3 oxidation state; hydrogen peroxide as well as sulfites or thiosulfate will do this, which is typically the least harmful, preferably to chromium(III) oxide. Chromium dioxide may be another feasible option, as it is found in cassette tapes and can be recycled with them.

Zinc compounds can be refined to zinc metal using electrowinning. It's not recommended to use zinc compounds obtained from technical sources as zinc supplements for soil or livestock, as it may contain traces of heavy metals, such as cadmium.

Some MSDS sheets recommend that rare earths be converted to their oxalates or carbonates and disposed of in the trash.

Alkali metals are minimally toxic as their salts and may be dumped down the drain.

Organic compounds

Organic solvents should be poured in labeled waste tanks, such as: halogenated, non-halogenated solvents. Flammable organic solvents that are safe in low exposures, such as ethanol, methanol, and acetone can often simply be burned outside for disposal, as most often their combustion products are simply carbon dioxide and water. It may be a better idea just to recover them by distillation, though. An alcohol burner can be used to burn these liquids.

Halogenated compounds like chloroform can be neutralized with a strong base, although this neutralization should not be done without safety precautions.

A good, though resource-intensive way to destroy halogenated and aromatic compounds is with Fenton's reagent, which breaks them down to simpler non-toxic compounds. It's best however, to avoid dumping large quantities of waste, as the reaction in exothermic and may splash or volatilize some of the waste, so it's best to perform the neutralization in small steps. Many methods described in literature involve slowly bubbling the organic compound with a carrier gas in the Fenton solution, as this increases oxidation and limits splashing. However, because only small amounts of compound gets neutralized at a time, this process takes a while. For safety, you will need to use diluted hydrogen peroxide, meaning that at the end of the neutralization process you will be left with a large volume of water filled with iron precipitate and some organic residues that did not decompose completely, though they're generally not as toxic as their parent compound.

Chromic acid and it's derivatives can also be used to destroy hazardous chemical compounds, as it neutralizes them to carbon dioxide and water. However, chromic acid will (violently) oxidize alcohols to their respective aldehydes or ketones, which cannot be oxidized further by the acid alone, which limits it's use in neutralizing many compounds.

Piranha solution is an excellent material for the disposal of organic compounds. The decomposition is highly exothermic and the resulting smoke is very dangerous. As such, this method is generally considered a last resort in disposal, and it's mostly used for cleaning rather than disposal.

Organic salts, such as acetates and oxalates can be pyrolyzed to carbonates and water vapors. The decomposition works best in oxygen-rich atmosphere.

Recycling

Sometimes it is an option to purify waste products into chemicals that are pure enough to be used again. While this can sometimes be time consuming, it can often be more environmentally and economically friendly than discarding the waste in one manner or another is. Before discarding waste, think about what all it contains, and if there is some way that it could be used.

Down the drain vs. into the soil

The availability of these disposal methods varies depending on where you live. If you live in an apartment block, you only have the drain. If you live in a suburban house, you have both. If you live in some quaint rustic shithole paradise like the author of this edit, you only have the "into the soil" option.

Generally, the soil option is safer, because there is no plumbing you should worry about, but some chemicals shouldn't be released into the soil, either. In general, your designated place for pouring chemicals into the soil should be far from any gardens, horticulture or any other agricultural objects. Chemicals marked as "Oh yes!" in the table below are harmless and even useful in agriculture as fertilizers. These you can pour down in your garden.

Lists of various chemical compounds that can be safely released in the ground or down the drain can be found here, here or here.

Other

Heavy metal salts or solutions can be mixed with cement, and trapped by making a concrete block. The resulting block can also be covered in another layer of cement, to reduce the diffusion of the heavy metals. Unless the concrete is damaged, broken or dissolved in acid, the heavy metal ions will not be released. However, this merely is a method to prevent the heavy metals from being released in the environment and is not a permanent way of disposal.

Legal considerations

Releasing hazardous chemicals in the environment is a crime in all jurisdictions and carries heavy fines or even jail time. While properly neutralized reagents may be poured down the drain, dumping very large amounts of said reagents is frowned upon. Incineration is attractive as it's a good method of getting rid of wastes, but unless you're using an incinerator, some material will not be destroyed and instead it will be scattered in air. Likewise, it's forbidden to burn certain materials in open air, such as aromatic compounds or organosulfur compounds and for those, special incinerators are a must.

Always check the local laws before choosing the disposal method.

Chemical disposal table

References

1. ↑ http://woelen.homescience.net/science/chem/exps/rules.html
2. ↑ http://www.atsdr.cdc.gov/toxprofiles/tp187-c5.pdf
3. ↑ http://link.springer.com/article/10.1007%2FBF02318626
4. ↑ http://pubs.rsc.org/en/Content/ArticleLanding/2007/EM/b709571f#!divAbstract
5. ↑ http://www.google.com/patents/US2519284
6. ↑ Chemical Technology and Emission Control, 2012, M.B. Hocking, p. 216
7. ↑ http://www.drugfuture.com/chemdata/cuprous-sulfite.html
8. ↑ http://www.inchem.org/documents/sids/sids/115775.pdf
9. ↑ http://pubs.acs.org/doi/abs/10.1021/es7029703?journalCode=esthag

Relevant Sciencemadness threads

• Lab Waste Disposal
• Waste disposal
• Safe disposal/handling of lead in a domestic setting