7.1 Concentrated Solutions of Acids and Bases7.1 Concentrated Solutions of Acids and Bases
Corrosive acids and bases are common wastes generated in laboratories on campus. Corrosivity is the only hazardous waste characteristic that may be treated by a generator onsite without an EPA permit.
Generators of corrosive wastes which have no other hazardous characteristics should neutralize the wastes to a pH between 5.5 and 9.5. The neutralized non-hazardous waste may then be drain disposed followed with a good water flush (20 parts of water).
Procedures for neutralizing acids and bases are described in the following three sections. Note: Neutralization is recommended only for very small volumes of corrosive acids and bases. You should only perform neutralization of corrosives if you have been trained, you feel confident that you understand the process, you have the proper personal protective equipment, and are comfortable doing it.
7.1.1 General Neutralization Procedures7.1.1 General Neutralization Procedures
- Do neutralizations in a fume hood behind a safety shield, as vapors and heat may be generated. Wear lab coat or apron, gloves and goggles. A face shield in combination with safety goggles is recommended. Please note, a face shield alone is not sufficient, safety goggles must be worn when using a face shield.
- Keep containers cool during process, such as placing a beaker in a bucket with slushy ice.
- Work slowly.
- After neutralization is complete, dispose of down the drain followed by 20 parts water to the neutralized solution.
- Follow the specific neutralization procedures below for the acid or base you are trying to neutralize.
7.1.2 Acid Neutralization7.1.2 Acid Neutralization
While stirring, add acids to large amounts of an ice water solution (1:10) of base such as sodium carbonate, calcium hydroxide, or sodium hydroxide for concentrated acids.
When a pH of at least 5.5 to 9.0 is achieved, dispose of the solution down the drain followed by 20 parts water to the neutralized solution.
7.1.3 Base Neutralization7.1.3 Base Neutralization
- Add the base to a large vessel containing water (1:10). Slowly add a 1M solution of Hydrochloric acid.
- When a pH of 5.5 to 9.0 is achieved, dispose of solution down the drain followed by 20 parts water to the neutralized solution.
7.1.4 Chromic Acid7.1.4 Chromic Acid
Chromic acid is a powerful oxidizing agent that is both toxic and corrosive and can explode on contact with organic materials. Chromium (VI), or hexavalent chromium, is also classified as a carcinogen. Accidents involving chromic acid cleaning solutions can result in burns to both skin and clothing.
Chromic acid cleaning solutions leave a residue of chromium (VI) on the glass surface, which is difficult to remove. This residue has been known to interfere with certain research procedures since the material can leach into solution. EHS highly recommends that you consider using chromic acid alternatives such as “NOCHROMIX”, “Alconox”, or similar type products which can be ordered through one of Cornell’s eShop preferred suppliers such as VWR Inc. Due to the reactive and toxic nature, do not attempt to neutralize chromic acid - dispose of chromic acid waste through the hazardous waste management program.
7.1.5 Hydrofluoric Acid7.1.5 Hydrofluoric Acid
Hydrofluoric acid is a strong corrosive and highly toxic chemical that causes severe burns from dilute solutions and can be fatal upon exposure of concentrated solutions. Bench top use of hydrofluoric acid is not permitted; it must only be used in a fume hood.
Anyone using Hydrofluoric acid must contact the Gannett Health Center and purchase a tube of Calcium gluconate gel, which is used as an initial response to skin exposure of Hydrofluoric acid. The quantities of Hydrofluoric acid that are used and stored should be kept to an absolute minimum. All users of hydrofluoric acid must attend hydrofluoric acid training. More information on hydrofluoric acid can be found in the Laboratory Safety Manual and Chemical Hygiene Plan.
Due to the toxic nature, do not attempt to neutralize hydrofluoric acid - dispose of hydrofluoric acid waste through the hazardous waste management program. Because of hydrofluoric acid’s ability to etch glass, the chemical and waste must be stored in plastic containers. As a safety precaution, EHS recommends that calcium hydroxide be added to any mixtures or dilute solutions of Hydrofluoric acid waste to help bind the fluoride ions.
7.1.6 Perchloric Acid7.1.6 Perchloric Acid
Perchloric acid is a strong oxidizer and corrosive acid. Perchloric acid can react with metal to form shock sensitive metal perchlorates. This can occur when perchloric acid is used in a regular (non-perchloric acid) fume hood. More information on Perchloric acid can be found in the Laboratory Safety Manual and Chemical Hygiene Plan. Due to the reactive nature, do not attempt to neutralize perchloric acid - dispose of perchloric acid waste through the hazardous waste management program.