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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.

Standard proceduresEdit

AcidsEdit

Acids should be neutralized with a base, such as carbonate/bicarbonate, hydroxide (calcium hydroxide e.g.) usually as a solution. 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 mixed acid 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.

BasesEdit

Alkali hydroxides can be left in open air to absorb carbon dioxide as well as corrosive and unpleasant gases, forming carbonates and salts. For quicker results, alkali bases can be neutralized with any acid, though for practical and economical purposes, acetic acid or citric acid are sufficient. 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.

CyanidesEdit

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. Cyanates can be further neutralized to nitrogen and carbon dioxide.

Cyanides must never be poured down the drain.

Heavy metalsEdit

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 sulfur, generating mercury(II) sulfide, which is generally insoluble in water and has little reactivity.

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

Inorganic anionsEdit

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 ionsEdit

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 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). 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 as zinc supplemements for soil or livestock, as it may contain traces of 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 compoundsEdit

Organic solvents should be dumped in labeled waste tanks, such as: halogenated, non-halogenated solvents. Flammable organic solvents that 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.

A good way to destroy halogentated 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.

Organic salts, such as acetates and oxalates can be pyrolyzed to carbonates and water vapors.

RecyclingEdit

Main article: Reagent 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.

OtherEdit

Heavy metal salts or solutions can be mixed with cement, and trapped in the resulted concrete block. The resulting block can also be covered in another layer of cement, to reduce the diffusion of the heavy metals. Unless the resulting concrete is damaged, broken and 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.

Chemical disposal tableEdit

Substance Neutralization Heat treatment Down the drain Environmental considerations
Acetic acid Bicarbonates, carbonates, bases, oxides Flammable (high concentrations), no dangerous combustion products Yes Safe, biodegradable; avoid dumping large amounts, acidifies soil
Acetic anhydride Bicarbonates, carbonates, bases, oxides Flammable, no dangerous combustion products Yes Biodegradable; avoid dumping large amounts, acidifies soil
Acetone Oxidation, reducing, photolysis Flammable, no dangerous combustion products Not advised Biodegradable; not advised
Acetone peroxide Photolysis, detonation in safe area Explosive, not recommended Not advised Biodegradable; not advised
Acetylene Oxidation, photolysis Dangerously flammable Not possible Biodegradable
Acetylsalicylic acid Any base Not particularly helpful Yes Biodegradable
Aluminium chloride Treatment with water, precipitation with a base No effect Not advised
Ammonia Oxidation, neutralization with acids At high concentrations Not possible (gaseous), safe to pour (as solution) Biodegradable
Ammonium acetate Unnecessary -- Yes Safe, biodegradable
Ammonium bicarbonate Pyrolysis, hydroxides, acids Decomposes on heating Yes Safe, good fertilizer (nitrogen source)
Ammonium nitrate Pyrolysis, Hydroxides, carbonates Emits nitrous oxide, may explode if the temperature is too high Yes Safe, good fertilizer (nitrogen source)
Ascorbic acid Unnecessary Yes Safe, biodegradable
Barium manganate Sulfuric acid Not advised
Benzene Oxidation with Fenton's reagent Generates dangerous combustion products DO NOT DUMP Avoid releasing in environment
Bis(ethylenediamine)copper(II) perchlorate Crystallize and ignite safely Detonates DO NOT DUMP Copper kills aquatic life and plant roots
Bismuth trioxide Reduced to bismuth metal Will oxidize anything (yes, platinum too) when molten
Boric acid
Boron trioxide
Calcium acetate Pyrolysis Decomposes to calcium carbonate and acetone at high temperature Yes Biodegradable
Chloroform Destruction with aqueous sodium hydroxide, which can be aided by methanol or acetone; Oxidation with Fenton's reagent Boils to form vapor, should not be attempted indoors DO NOT DUMP May cause ozone depletion, dangerous to aquatic life
Copper(II) chloride Precipitate as carbonate or reduce to copper metal using aluminum Loses water, turns brown DO NOT DUMP Kills aquatic life and plant roots
Terbium(III) oxide Unnecessary, simply dump in trash Releases absorbed water or carbon dioxide Unnecessary Effects unknown, may stimulate plant growth

ReferencesEdit

  1. http://woelen.homescience.net/science/chem/exps/rules.html

Relevant Sciencemadness threadsEdit

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