無機酸の安全な取り扱い

Mineral acids derived from inorganic materials are widely used in research laboratories as well as in chemical industry. Due to their hazardous properties it is important to learn how to safely handle these chemicals.

Most mineral acids range from very strong acids such as hydrochloric-, sulfuric-, chromic- and nitric acid to strong acids such as phosphoric-, hydrofluoric-, and boric acids. These acids are very corrosive.

Additionally, mineral acids such as nitric acid and sulfuric acid are strong oxidizing agents and can react violently causing explosions.

This video will illustrate the hazardous nature of mineral acids, how to safely handle, dispose, and store these chemicals; and what to do in case of an emergency, like skin contact or spill.

In order to understand why safe handling of mineral acids is important and which safety precautions to follow, let us first take a closer look at the hazardous nature of mineral acids.

As mentioned earlier, mineral acids are corrosive and will cause irritation and damage to human tissue. If inhaled the acid will react with the mucus membrane of the respiratory tract resulting in coughing, burning of the throat, and possibly pulmonary edema. Ingestion can cause severe damage of the digestive tract, while skin contact can lead to burns and eye contact to blindness.

If we want to ensure safe handling of mineral acids we need to understand their reactivity and properties. Oxidizing acids such as nitric acid, or aqua regia, will react with metals and can release toxic or explosive gases, for example nitrogen dioxide or hydrogen.

In addition to being a strong oxidizer, sulfuric acid has also dehydrating properties and will react violently with organic compounds such as household sugar. The reaction is highly exothermic and yields in carbon, water, sulfur dioxide and carbon dioxide gas. The heat released during the reaction brings the water to boil, which could lead to burns.

Now that we know about the hazardous properties of mineral acids, let’s learn how to safely handle them so that we don’t cause any accidents.

While working with mineral acids, always wear proper personal protective equipment, or PPE, which includes safety goggles or a face shield. Furthermore, long sleeves and full-length pants should be worn along with closed-toed shoes.

Additionally wear a reusable or disposable apron or lab coat made of rubber, neoprene or PVC. Traditional cotton-polyester lab coats can readily absorb the mineral acids in case of a spill and are not recommended.

Always use double nitrile, neoprene, or PVC gloves when working with mineral acids. Remember to replace gloves whenever a splash occurs.

Mineral acids should be handled in a properly functioning chemical fume hood, which are cleared of clutter and incompatible materials. The fume hood sash should provide optimal safety while allowing execution of the task in an unencumbered manner.

Mineral acids with concentrations of 3 molar or less may be handled on a bench top. Remember, these acids are still corrosive.

When transferring acids from a big bottle to a beaker use secondary containers to hold the smaller container.

At this point you have learned how to protect yourself when working with mineral acids. Now let’s learn how to safely use, dispose and store these chemicals.

Many acids will react exothermically upon dilution with water. Never add water to the acid; always add small amounts of acid to the water. Otherwise the released heat could bring the solution to boil and splash acid out of the container.

Remember to never mix nitric acid with organic materials. Nitric acid is a strong oxidizer and can react violently with organic materials leading to explosions or fire.

Furthermore, always inform yourself about the safety hazards when working with mineral acids. The safety guidelines can be found in the safety data sheets provided by chemical vendors.

Every time you work with acids you need to ensure proper disposal of any waste. Any mineral acid waste should be kept separate from organic waste and disposed through the organization’s chemical waste management system. The waste container has to be labeled according to EH&S regulation including contact information, content, hazards as well as start- and end date.

Furthermore the waste container should be ideally equipped with a pressure regulating safety funnel or checked periodically for gas evolution. Avoid over-pressurized containers, which may violently erupt. Always store the waste container in a secondary container such as a plastic bin.

Alternatively, the acid waste could be disposed in the drain, but you have to make sure that the waste solution does not contain any metals. The acid waste has to be neutralized starting with the dilution using ice water.

Followed by the addition of an aqueous basic solution, such as 1 M sodium hydroxide or saturated sodium bicarbonate until the pH is neutral. The neutralized solution may then be poured down the drain.

Mineral acid containers should be stored together in an acid cabinet. This cabinet should be labeled as Inorganic Acids. Due to their corrosive nature mineral acids should preferably not be stored in a metal cabinet or shelf.

If possible, a secondary container made of plastic should be used, especially for nitric acids.

Furthermore mineral acids should not be stored together with bases, oxidizing agents, organic materials, and combustibles. All containers have to be stored upright in a dry and well-ventilated place away from heat or ignition sources.

Additionally, nitric acid, which is a strong oxidizer, should be stored separately in a chemically resistant secondary container made of polyethylene, PYREX, or Nalgene.

If a mineral acid has to be transferred into a smaller container, make sure the container is acid compatible and clearly displays a label matching the information of the manufacturer’s label.

By now you have learned how to safely work with mineral acids. However, it is important that you also familiarize yourself with crucial procedures in case of an emergency.

In case of skin contact, immediately remove contaminated clothing and rinse thoroughly with water for at least 15 min.

In case of eye exposure, immediately rinse eyes with copious amount of water for at least 15 min and then promptly seek medical attention.

In case of large amount of vapor inhalation, move person to fresh air and then seek medical attention. If mineral acid is ingested, immediately seek medical attention.

In case of a small chemical spill, clear the surrounding area immediately and try to control the spill from spreading further. Use a spill kit to clean up the spill, which is an absorbent material that can be swept up with a broom. Further decontamination and neutralization may be required using solid sodium bicarbonate or calcium carbonate.

In case of a large spill, evacuate the area immediately alerting others and call 911. Make sure someone is near the scene to provide information about the chemical spilled and the accident. Have the product information and the safety data sheet (SDS) available. All spills must be reported to the Environmental Health and Safety (EH&S) agency regulating requirements and standards.

Now you have learned how to handle most mineral acids and respond in case of an emergency, however, you have to be extra careful when handling hydrofluoric acid.

Hydrofluoric acid is not like most other mineral acids. It is not only highly corrosive, but also reacts with most materials, even glass and ceramics.

Furthermore hydrofluoric acid is very toxic and can penetrate skin. Once absorbed it reacts with calcium and magnesium ions in the body causing sever tissue damage and chemical burns. Therefore, in addition to normal PPE, special gloves made of neoprene, or thick butyl rubber, have to be worn.

In case of skin contact the area is flushed with water for at least 15 minutes, and then treated with calcium gluconate to bind fluoride ions. Seek immediate medical attention.

You’ve just watched JoVE’s video on safe handling of mineral acids. You should now understand the hazards of mineral acids, the appropriate safety precautions while using, disposing, and storing of these chemicals. In addition, you should also know what to do in case of an emergency like a skin contact or a spill. As always, thanks for watching.