Laboratory Safety Manual

Reviewed May 2012

Appendix D
Neutralization of Spent Acids and Bases

Spent mineral acids, straight-chain fatty acids, and bases (hydroxides) comprise a large portion of the unwanted chemicals being stored in campus laboratories. As a part of regular laboratory procedures, campus labs should neutralize spent inorganic acids, acetic acid, straight-chain fatty acids, and bases (hydroxides) that do not contain metal or organic contaminants. These chemicals will be managed in an "elementary neutralization unit" and, therefore, are not considered a part of the hazardous waste stream for the campus. An "elementary neutralization unit" is a container used for neutralizing corrosive wastes.

Neutralization is a relatively simple procedure that is best done by and in the laboratory that uses inorganic acids, acetic acid, straight-chain fatty acids, and bases (hydroxides) on a regular basis. The laboratory that generates spent corrosives usually has the facilities and expertise to neutralize them, and therefore will be responsible for doing so. The following procedures (see A - D) describe the proper technique for neutralization of spent inorganic acids, acetic acid, straight-chain fatty acids, and bases (hydroxides) as a part of regular laboratory procedures. At the end of this appendix are lists of corrosives to be managed in-house by campus laboratories. Aqueous corrosive wastes shall NOT contain sulfides, cyanides, metals, or other materials that can give off hazardous fumes upon reaction with the acid or base.

Do NOT use these procedures for:

• INORGANIC ACIDS THAT CONTAIN HEAVY METALS (e.g., Atomic Absorption Standards, arsenic, cadmium, chromium, lead, mercury, nickel, selenium, silver, thallium. Solutions containing sodium, potassium, magnesium, iron can be neutralized as long as the anion is also non-hazardous.)
• ESTERS OF INORGANIC ACIDS
• CHROMIC ACID
• PERCHLORIC ACID
• HYDROFLUORIC ACID
• ORGANIC ACIDS EXCEPT ACETIC ACID AND STRAIGHT-CHAIN FATTY ACIDS

• LARGE QUANTITIES OF NITRIC ACID

Chemicals shall not be disposed in the sanitary sewer for two reasons. First, Stillwater does not allow the disposal of most chemicals in the wastewater flow. Second, strong reactions can take place if the chemical carries unknown contaminants or contacts an incompatible chemical in the wastewater.

A.  Equipment Needed for Neutralizing Acids and Bases

1. Sodium carbonate (Soda ash), baking soda, or diluted inorganic base (hydroxide) for neutralization of an acid, or a diluted inorganic acid for neutralization of a base.

2. Polyethylene bucket - 1 or 2 gallon size, as personal preference dictates. Remember that 1 gallon weighs approximately 8 pounds or greater.

3. Protective equipment (goggles, apron, gloves).

4. 500 ml beakers.

5. pH Indicator Strips, or other pH test method.

B.  Personal Protective Equipment

Read the Material Data Safety Sheet (MSDS) for detailed information. Call the Environmental Health & Safety Department Hazard Communications Section if an MSDS is not available. The MINIMUM recommended personal protection needed when performing the neutralization procedure is:

• Ventilation
  Work in a fume hood
• Gloves
  Use neoprene, natural rubber, butyl, polyethylene, nitrile butadiene, or polyvinyl chloride depending on the MSDS information
• Clothing
  Apron (rubber is preferred), lab coat (or protective suit or coveralls), and closed-toe shoes.

• Eye Protection
  Splash-proof or dust-proof goggles AND a face-shield (8 inch minimum)

Hands shall always be washed after working with these chemicals. An eyewash station and quick-drench facility shall be located in the area. All employees shall locate these emergency facilities before starting to work.

WARNING: Remember that extreme heat can be productd by this procedure unless it is done very slowly and well-diluted. Closely monitor the amount of heat produced by touching the outside of the neutralization container. Use ice bath if necessary.

C.  Neutralization Procedure for Acid

1. Make a saturated solution of sodium carbonate (soda ash) in a beaker or use an inorganic base diluted in water (1:10 ratio) - set aside.

2. Put tap water into 1 or 2 gallon polyethylene bucket.

3. Dilute acid at least 1:10 (1 part acid to 9 parts of water) by slowly pouring and stirring the acid into the water. For concentrated acids and bases, neutralization must be done slowly and with vigorous stirring. If there are any questions, or if you are hesitant about attempting this procedure with any spent acid or alkali waste, please call Environmental Health & Safety, Hazardous Materials Section, at 4-7241. The recommended time for the neutralization procedure is when the wastewater flow is at a peak, e.g., 9:00 a.m.

4. Slowly add soda ash or other basic solution into diluted acid with stirring, or save diluted acid to neutralize bases as described below.

5. Monitor pH with pH meter, pH indicator strips, or other pH test method.

6. When pH is between 6 and 9, dispose in a drain followed with excess water. A pH near 7 is preferred to reduce the possibility of plumbing damage.

HELPFUL HINT: When neutralizing an acid, the pH can be tested quickly by the following method. Make a saturated solution of sodium bicarbonate in water. A small amount of sodium bicarbonate solution poured into the acid will make a "fizz", which is a release of carbon dioxide. Since carbon dioxide evolves from these procedures, insure adequate ventilation is available. This "fizz" will indicate that the solution is still acidic, and needs more base to be added. Always stir the mixture and do a final check of the pH before pouring the neutralized acid down the drain.

D.  Base Neutralization

1. Put tap water into 1 or 2 gallon polyethylene bucket.

2. Dilute alkali wastes at least 1:10 (1 part alkali to 9 parts water) by slowly pouring and stirring the base into the water. For concentrated acids and bases, neutralization must be done slowly and with vigorous stirring. If there are any questions, or if you are hesitant about attempting this procedure with any spent acid or alkali waste, please call Environmental Health & Safety, Hazardous Materials Section, at 4-7241. The recommended time for the neutralization procedure is when the wastewater flow is at a peak, e.g., 9:00 a.m.

3. Neutralize the diluted alkali solution with a previously diluted inorganic acid.

4. Monitor pH with pH meter, pH indicator strips, or other pH test method.

5. When pH is between 6 and 9, dispose in a drain followed with excess water. A pH near 7 is preferred to reduce the possibility of plumbing damage.

NOTE:

For concentrated acids and bases, neutralization must be done slowly and with vigorous stirring. If there are any questions, or if you are hesistant about attempting this procedure with any spent acid or alkali waste, plase call Environmental Health Services, Hazardous Materials Section, at extension 47241. The recommended time for the neutralization procedure is when the wastewater flow is at a peak, e.g., 9:00 a.m.

INORGANIC ACIDS

INORGANIC BASES

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