By Burt Process Equipment

What Is Neutralization?

The simplest neutralization definition is “the result of a base and an acid reacting with each other in a chemical process.” For neutralizing acids and adjusting their pH, you must add hydroxide ions (OH-), which is a base. To neutralize a base, you must add hydrogen ions (H+), which is an acid. When neutralization occurs, water and salt (calcium chloride) are produced. The pH of a neutral solution will depend on how much acid was contained in the original substance. 

What is a Neutralization System Used For?

Industrial neutralization examples include drinking water and wastewater treatment. Neutralization systems are used in a wide variety of industries, from semiconductors and metal finishing to pharmaceutical manufacturing.

How Do You Neutralize an Acid?

The most common chemicals used for neutralizing acids or bases are sodium hydroxide (50%) and sulfuric acid (98%). To raise the pH of an acidic liquid, sodium carbonate (soda ash), ammonium hydroxide, calcium hydroxide (lime) or magnesium hydroxide can also be used. To lower the pH of a base liquid, phosphoric acid, hydrochloric acid (HCI), nitric acid or carbon dioxide can be used, in addition to sulfuric. These are all effective chemicals for pH adjustment.

Considerations for Neutralization Chemicals

Before selecting the right neutralization chemicals for your application, there are important considerations. Worker health and safety is a primary concern. A potentially dangerous reaction or toxic gas release may occur when combining chemicals. Extreme caution must be used when using chemicals for neutralization. If low cost is important, certain chemicals may be more cost-effective than others. Also, consider the concentration, as this can affect the cost as well as convenience. The application environment and storage location are also important. The various reagents have specific physical properties which may render them inappropriate for your use. For example, sodium hydroxide in a 50% concentration will start to freeze below 600 degrees Fahrenheit.

Acids Used to Neutralize a Base

Here is a list of acids and bases that can be used to alter a liquid’s pH.

Carbon Dioxide (CO2) – Though not an acid, when exposed to water, it forms carbonic acid. Since it’s difficult to use, it isn’t often used in neutralization systems. However, it is sometimes used for certain wastewater treatment.

Hydrochloric Acid (HCI) – HCI is the second most common acid used in industrial settings, after sulfuric acid. It’s inexpensive and effective, though it’s more expensive than sulfuric since it’s not as potent. A concentration that’s more than 10 percent creates hydrogen chloride vapor that becomes highly corrosive when it’s combined with humidity. This resulting gas can corrode metal, such as stainless steel and copper wiring. It is recommended that HCI is used in a well-ventilated space or outdoors only. HCI also releases heat.

Nitric Acid (HNO3) – HNO3 is more expensive than HCI or H2SO4. Like hydrochloric acid, nitric acid combines with humidity to create a corrosive gas. It is also oxidizing and shouldn’t be used if organic material is present. During neutralization, nitric liberates heat.

Phosphoric Acid (H3PO4) – Generally safe, phosphoric acid is frequently used to produce detergents and agricultural fertilizers. It’s inexpensive, but not as cost-efficient as HCI or sulfuric. Since it’s a weaker acid, there usually isn’t an issue with released gasses. It is slower to react, making it more controllable. However, due to its availability and cost, it typically isn’t used for neutralization.

Sulfuric Acid (H2SO4) – This is the most commonly used and least expensive neutralization chemical. Typical concentrations are 25 to 96 percent. It’s more potent than all acids, apart from phosphoric acid, and is safer and easier to use than nitric or hydrochloric acid. However, sulfuric acid must be used with caution, since it will decompose any organic material, including the skin. It also releases heat.

Bases Used to Neutralize an Acid

Ammonium Hydroxide (NH4OH) – Ammonium hydroxide is not a good choice as a chemical for neutralizing, because it’s difficult to handle, creates dangerous corrosive gasses and is expensive. If used, storage and treatment tanks must be properly ventilated.

Calcium Hydroxide or Lime (Ca(OH)2) – Ca(OH)2, since it must be used as a slurry, is more difficult to use than other bases. It’s also not very water-soluble. However, its reaction time is less than magnesium hydroxide, and it can be economically cost-effective, as it’s much cheaper than NaOH.