THE
NEUTRALIZATION AND DESTRUCTION OF
HAZARDOUS
CHEMICAL IN THE LABORATORY
This bulletin is a collection of techniques
for destroying or making the hazardous chemical innocuous in the laboratory.
DESIRABLE
PROPERTIES OF A DESTRUCTION TECHNIQUE
 |
Destruction of the
hazardous chemical should be complete |
|
The effectiveness
of the technique should be easy to verify analytically |
|
The equipment and
reagents should be readily available, cheap and easy and safe to use |
SAFETY
CONSIDERATION
 |
Follow a code of good laboratory practice |
|
The destruction of hazardous chemicals
are handled only by those workers who have received the appropriate training |
|
The destruction technique is performed
on the lab scale only; if the scale is greatly increased, unforeseen hazards
may occur, particularly with effect to the production of large amounts
of heat |
|
All destruction should be carried out
in a properly functional fume hood |
|
Any chemical method for destruction of
hazardous chemicals should be vetted by an experienced chemist before being
applied to a mixed lab waste. The chemist should consider the following:- |
|
i) All the components
of the mixture (including contamination)
ii) Review the likely
products, and any possibility of side reactions,
including
catalysis or inhibition by small amounts of active compounds |
|
Appropriate personal protective equipment
should be worn |
NEUTRALISATION
For the treatment and disposal of acidic
and alkaline wastes including used solutions, liquid effluents and solid
residues or sludges. The main aim is to adjust the pH to between 6.0-9.0
for disposal to sewer. Neutralisation can be performed in batch or flow-through
system.
Note:
For acidic wastes, the use of
alkaline neutralisation agents, may often have the additional advantage
of also precipitating other undesirable waste components, such as metal
ions, at the same time.
Acid
Neutralisation
Common agents: Ca(OH)2, NaOH, Na2CO3,
CaCO3
Alkali
Neutralisation
Common agents: HCl, H2SO4, NaHSO4
SAFETY PRECAUTION
Do not treat a strong alkali directly with
a strong acid, or vice versa. Dilute with water before treatment.
Neutralise a weak base with weak acid and
a strong base with strong acid---after dilution.
OXIDATION
Oxidation processes are important detoxification
processes for many classes of compounds in aqueous solution. The aim is
complete mineralisation or, if that is not possible, the conversion into
partial oxidation products which are non-toxic.
Important
Oxidising substances
 |
chlorine in the forms of hypochlorite
or chlorine gas |
|
potassium permanganate |
|
hydrogen peroxide |
|
ozone |
General
procedure
An aqueous solution
of hypochlorite can be used to destroy wastes such as mercaptans, hydrazine
and inorganic cyanides
Inorganic cyanide
is oxidised by hypochlorite in basic solution to the much less toxic cyanate
ion.
MERCAPTANS,
INORGANIC SULPHIDES AND OTHER SULFUR DERIVATIVES
Mercaptansare
organic compound of the general formula R-SH where R is an alkyl or aryl
group. The alkyl compounds are also known as thiols and the aromatic compounds
are also called thiophenols.
Most liquid and some solid mercaptans
are volatile and possess an overpowering objectionable odour.
Alkali sulphides:
eg sodium sulphide etc
Other sulfur derivatives
(Thioether) : dimethylsulphide,
diphenyl sulphide etc
Principle
of Destruction
|
Mercaptans are oxidised by hypochlorite
to the corresponding sulfonic acid.
The compounds are generally non-volatile
and odorless. |
|
Inorganic sulphide is oxidised to sulphate |
|
Thioethers are oxidised to sulfoxides
and finally to sulfon |
CYANIDES
Principle
of Destruction
|
Inorganic cyanides are oxidised by hypochlorite
in basic solution to the much less toxic cyanate ion which is degraded
into carbon dioxide and nitrogen by acidification of the solution, followed
by excess hypochlorite. |
|
Complexation to ferrocyanide (for cyanide
compounds soluble in water)
An alkaline solution of cyanide treated
with an excess of ferrous sulfate gives ferrous ferrocyanide and than transformed
into ferric ferrocyanide by oxidation in the presence of a ferric salt
(ferric sulfate)
Carbon disulfide
(CS2) possess a special problem. It is highly volatile (b.p 46oC), highly
toxic and readily forms ignitable or explosive mixtures with air.
This chemical is
destroyed by hypochlorite oxidation to carbon dioxide. |
CAUTION
Reaction is very exothermic
The presence of strong base (eg NaOH) can
cause explosive polymerization of HCN, acrylonitrile, plastic monomers
and many organic compounds containing double bonds.
PHENOL
Principle
of Destruction
|
Phenols are oxidised with 30% hydrogen
peroxide at a controlled maximum temperature of 60oC. The phenol is dissolved
in water along with about half its weight of ferrous sulphate. The pH is
adjusted to between 5 and 6, and oxidant added. |
CAUTION
Chlorine containing
oxidisers must not be used because of the formation of chlorinated phenols
as byproducts of the reaction.
OXALIC
ACID
Principle
of Destruction
|
Destroy by heating with conc. sulfuric
acid to carbon dioxide and carbon monoxide |
|
By oxidation with an acid solution of
KMnO4 held at 80oC for 1 hour |
|
Oxalic acid can also be precipitated in
water solution by the addition of excess of CaCl2. The insoluble calcium
oxalate is filtered off |
ALDEHYDES
AND KETONES
Principle
of Destruction
|
The majority of these chemicals are oxidised
to carboxylic acids (less toxic and less volatile) by KMnO4 |
|
For methyl ketones, destruction is achieved
by contact with excess of sodium hypochlorite solution |
|
Aldehydes and certain unhindered ketones
form a bisulfite addition product with an excess of sodium bisulfite |
AMINES
This class of chemicals
includes the aliphatic (eg methyl, ethyl etc) and aromatic (eg phenyl)
amines. Most of the common aliphatic amines are flammable liquids and are
severe irritants, while most aromatic amines are toxic liquids or solids
and some are known to be carcinogenic.
Principle
of Destruction
|
Aliphatic amines are transformed into
water-soluble salt by the action of sulphuric acid , NaHSO4 or sulfamic
acid |
|
Aromatic amines (eg aniline, 2-naphthylamine,
benzidine etc) are destroyed by transformation into their corresponding
aromatic hydrocarbons. This reduction is effected by first converting the
aromatic amine into a diazonium salt by the action of sodium nitrite in
the presence of HCl.
The diazonium salt is then treated with
excess hypophosphorous acid |
|
Aromatic amines may be oxidised with KMnO4
in sulfuric acid. The products of this reaction have not been identified |
HYDROGEN
PEROXIDE AND DERIVATIVES
| Peroxides |
: |
sodium peroxide, alkyl peroxides |
| Peracids |
: |
peracetic acid, perbenzoic acid |
| Hydroperoxides |
: |
t-butyl hydroperoxide |
| Peresters |
: |
t-butyl perbenzoate |
| Peranhydrides |
: |
benzoyl peroxide |
Principle
of Destruction
|
Hydrogen peroxide and its principal derivatives
may be destroyed by various powerful reducing agents (eg sodium sulfite,
sodium bisulfite, ferrous sulfate etc) |
|
Peranhydrides that are poorly soluble
in water, such as benzoyl peroxide, is destroyed by treatment with a solution
of an alkali iodide in HCl |
ALKYL,
ALLYL OR BENZYL HALIDES
Principle
of Destruction
|
These halides are decomposed by hydrolysis
in a strongly alkaline medium, with the formation of the corresponding
alcohols. Depending on the structure of the halide, this reaction may be
accompanied by secondary reaction ; formation of ethers, alkenes and so
on |
ACID
HALIDES AND ANHYDRIDES
Principle
of Destruction
|
Acid halides and anhydrides are hydrolyzed
by mineral bases : sodium carbonate, sodium bicarbonate, ammonium hydroxide
and sometimes sodium/potassium hydroxide for certain derivatives such as
benzyl chloride |
CAUTION
Reaction is very
exothermic and must be carefully controlled.
ORGANOMETALLIC
HYDRIDES AND DERIVATIVES
eg LiH, NaH, LiBH4, LiAlH4,
AsH3, B2H6, PH3, SiH4,
Grignard
reagents, R-Mg-X, (CH3)2Zn
Principle
of Destruction
|
Most of these compounds often react violently
with water. Water-sensitive compounds may be destroyed by contact with
a higher alcohol such as n-butanol |
Destruction
of LiAlH4
CAUTION
This compound reacts
violently with water and with many compounds that have a mobile hydrogen
atom (eg alcohols, acids etc) or that are easily reduced (eg esters etc)
Contact of solid LiAlH4 with small quantity
of water (humidity) may lead to spontaneous combustion. Working under an
inert atmosphere (nitrogen, argon) is thus strongly recommended.
An excess of this hydride (usually 2-4
times the theoretical quantity) is generally used for the reduction of
organic compounds and this excess must be destroyed at the end of the reaction.
In large scale operations, destruction of the hydride by addition of small
quantity of ice-cold water is always very dangerous due to the liberation
of large quantity of hydrogen that may burn or explode. In this case it
is preferable to use 10% solutions of sodium hydroxide or ammonium chloride.
The alumina which precipitate is then easily removed by filtration. If
the reaction products are sufficiently stable, excess LiAlH4 may be destroyed
by the addition of an ice-cold solution of 20% NaOH(5N)
Best
Method of Destruction
The best method of destruction of excess
LiAlH4 is by using ethyl acetate. This ester destroys this hydride without
liberating hydrogen.
CAUTION
Reaction is exothermic.
NONMETALLIC
HYDRIDES
Principle
of Destruction
|
Nonmetallic hydrides such as B2H6,
PH3, AsH3, SiH4 are very sensitive to
oxidising agents and may spontaneously ignite in air. These hydrides may
be destroyed by oxidation in the presence of an aqueous solution of CuSO4
in an inert atmosphere (dry nitrogen) |
ISOCYANATE
AND DIISOCYANATES
CAUTION
Organic isocyanates
are strongly irritating to eyes, skin and respiratory mucous membranes.
Methyl isocyanate is particularly toxic and its inhalation may lead to
rapid death.
Principle
of Destruction
|
Organic isocyanates are destroyed by contact
with water, mineral bases or methanol. These reactions are exothermic.
Thus in the presence of an alcohol, an isocyanate is converted into a carbamate |
PEROXIDE-FORMING
SUBSTANCES
Peroxide-forming
organic compounds possess, as a general rule, a hydrogen atom which is
easily activated in the presence of oxygen (ie free radical reaction).
In most cases, the
peroxidation of organic compounds first leads to formation of a hydroperoxide
(detectable by the KI test) which may then evolve either to a peroxide
(undetectable by the KI test) or to a peroxidized polymer
While hydroperoxides
are often easily destroyed by reduction, this is not so for peroxides and
polymers which require much more drastic techniques.
Principle
of Destruction
|
SnCl2 is an excellent agent for the reduction
of the peroxides formed in secondary alcohols and in ethers (eg THF, dioxane,
etc) |
|
Ferrous salts in solution are very effective
in destroying hydroperoxides. Solid ferrous sulphate is not effective |
|
CAUTION |
|
Reaction is exothermic. Check that the
solvent does not contain any sodium wire or pellets of NaOH (often added
for drying purpose) |
|
In alkaline media (pH 9.5) sodium sulfite
is a good reducer of hydroperoxides |
|
A column of activated, basic alumina is
used to remove peroxide derivatives. This very simple technique of
peroxide elimination may be used for the majority of ethers, tetralin and
decalin |
|
Peroxides may be eliminated from ethers
by percolation through a column containing molecular sieves. |
ALKALI
AMIDES
eg LiNH2,
NaNH2
Principle
of Destruction
|
Alkaline amides may be destroyed by the
action of excess solid NH4Cl, ammonia being liberated in the
process |
|
Alkaline amides may be destroyed by the
action of excess solid NH4Cl, ammonia being liberated in the
process |
CAUTION
Commercial sodium
amide is an unstable product which, during storage, absorbs moisture and
oxygen, becoming covered with a yellowish film (peroxide derivatives?).
This aged product becomes very unstable and may spontaneously explode.
When this aged amide is immersed in water, no reaction is observed at first.
However, the reaction quickly becomes violent and explosive.
This aged amide
can be destroyed by controlled incineration.
ALKALINE
METALS
Principle
of Destruction
|
The destruction of alkaline metals is
generally effected by carefully controlled addition of an alcohol. Ethanol
may be used for sodium, while a higher alcohol (eg butanols, amyl alcohols
etc) is used for the more reactive alkaline metals |
|
CAUTION |
|
The alkaline metals react violently with
water, liberating hydrogen which may ignite. The reactivity with water
increases in the order Li<Na< K<Ru<Cs |
|
The reaction of Li with cold water is
moderate, but with hot water, the reaction is vigorous and the hydrogen
liberated may ignite. With sodium, the action of water is not explosive
below 40oC |
|
In contrast, the highly exothermic reaction
of water with potassium may be explosive even at 20 oC and the hydrogen
formed ignite spontaneously |
|
With rubidium and especially cesium, the
reaction with cold water is very violent and leads to the immediate ignition
of hydrogen. The reaction with simple alcohols (eg methanol, ethanol, IPA
) is similar. |
PHOSPHORUS
AND ITS DERIVATIVES
eg white phosphorus, red phosphorus, PH3,
PCl3, P205
Note:
White phosphorus is very reactive
and very toxic.
Red phosphorus is poorly reactive and
practically nontoxic.
Principle
of Destruction
|
White phosphorus, PH3 , phosphides
may be destroyed by oxidation with CuSO4. |
|
Phosphides are easily eliminated by oxidation
in the presence of excess sodium hypochlorite |
|
Red phosphorus is destroyed by KClO3 |
|
Phosphorus halides, oxyhalides, pentasulfide
may all be destroyed by treatment with ice-cold water or, better, with
an alkaline solution of sodium hydroxide, sodium bicarbonate) |
MERCURY
AND ITS DERIVATIVES
CAUTION
Mercury is a very
toxic heavy metal and is unique in being the only metal to be a liquid
at room temperature. Considerable care is required in handling this substance
as the vapor concentration above the liquid can readily attain harmful
levels. All mercury compounds are toxic and are cumulative poison. The
dispersion of 1 ml of mercury in a medium-size laboratory may be dangerous.
Principle
of Destruction
|
Formation of insoluble, non-volatile mercuric
sulfide with calcium polysulfide and sulfur. |
|
Mercury readily forms solid amalgams with
various metals (Cu, Zn, Sn, Fe)
HgS as well as amalgams may be eliminated
as solid wastes. |
METALS
AND THEIR DERIVATIVES
eg metals, metal salts, organometallic
compounds
Principle
of Destruction
|
In the metallic state or in insoluble
forms (oxides, sulfides etc) metals may be directly eliminated as solid
waste |
|
In the form of water-soluble salts or
of liquid-soluble organometallic derivatives, metals must be transformed
into insoluble compounds (hydroxide or sulfide) which can be discarded
as solid wastes |
|
In a few particular cases, the insoluble
salts may be sulfates (eg barium, lead), carbonates (eg barium, lead) |
|
Organomercury compounds such as R2Hg and
RHgX, should not be incinerated because some Hg may be volatilized. These
chemicals may be destroyed by oxidation with hypochlorite |
| Sb, As, Bi |
| These elements and their derivatives,
in the form of water-soluble chlorides, are precipitated by an excess of
H2S in a slightly acidic medium. After drying, the sulfide so obtained
may be destroyed with other metallic wastes. |
| Ag, Cd, Hg, Os,
Pb |
| The water-soluble nitrates of these elements
and their derivatives are precipitated by NH4HS in strongly acidic media
(pH ~1) in the form of insoluble sulfides. |
| Ba and Strontium |
| Ba and St salts and oxides form insoluble
carbonates in the presence of sodium or ammonium carbonate. |
| Be, Cr |
Water-soluble derivatives of Be and Cr
precipitate in the form of insoluble hydroxides when treated with excess
ammonia in an ammonium medium
(eg NH4OH) |
| Co, Sn, Ni, Thallium |
| Water-soluble forms of these elements
may be precipitated by ammonium bisulfide in a weakly acidic medium (acetic
acid, sodium acetate) in the form of insoluble sulfides. |
References:
-
Destruction of Hazardous Chemicals in the
Laboratory by George Lunn & Eric B. Sansone
-
Prudent Practices for Disposal of Chemicals
from Laboratories
-
Handbook of Laboratory Waste Disposal by Martin
J. Pitt & Eva Pitt
-
Safety in the Chemistry and Biochemistry Laboratory
by Andre Picot and Phillippe Grenouillet
-
Hazardous Chemicals Handbook by PA Carson
& CJ Mumford
-
Manual of Hazardous Chemical Reactions….National
Fire Protection Association, USA
|
