Self-neutralisation is often used, where a waste acid and waste alkali neutralise each other.
•Otherwise, lime or sodium hydroxide are the most widely used neutralising agents for acids.
•Sulphuric and hydrochloric acid are the most commonly used neutralising agents for alkalis.
Each neutralisation process must be previously tested in a laboratory to avoid reactions which may be too slow, too rapid or have undesired gas emissions.
Neutralisation is a batch process, usually at a rate of 10m3 at a time. The variability of the waste does not permit a continuous process.
The pH of the mixture must be continuously monitored, and the neutralised liquid is usually sent for sedimentation.