Which chemical is most commonly used to neutralize acidic waste streams?

Caustic soda, also known as sodium hydroxide (NaOH), is typically the most effective chemical for neutralizing acidic waste streams due to its strong alkaline properties. When caustic soda is added to an acidic solution, it reacts with the acid to form water and a salt, effectively raising the pH of the solution toward neutrality. This reaction is exothermic, meaning it releases heat, which can aid in the neutralization process but also requires careful handling to avoid dangerous conditions.

The versatility of caustic soda makes it a popular choice in various industrial applications, especially for treating wastewater that needs pH correction before being discharged or further processed. It's also relatively cost-effective compared to some alternatives and can be stored and handled safely with proper precautions.

In contrast, lime (calcium hydroxide) is also a common neutralizing agent but tends to be used when treating large volumes of acidic waste or in situations where a slower reaction is acceptable. Soda ash (sodium carbonate) is a milder alkalizing agent, which may not be as effective as caustic soda for strong acids. Sulfuric acid is, of course, an acid itself and would not be suitable for neutralizing acidic waste streams.