Which chemical is often used to sequester metals in water treatment processes?

The chemical that is often used to sequester metals in water treatment processes is polyphosphate. Polyphosphates function by binding to metal ions, such as calcium and magnesium, effectively preventing them from forming undesired precipitates or scales. This property is particularly important in maintaining the clarity and quality of drinking water.

In water treatment, polyphosphates are added to control scale formation in pipes and equipment, which can lead to operational issues and inefficiencies. They help keep metals in solution, thereby enhancing water quality and protecting infrastructure.

The other options, while important in their own right, do not primarily serve the purpose of sequestering metals in the same way as polyphosphate. Chlorine is primarily used for disinfection, bicarbonate plays a role in pH buffering, and sodium hydroxide is used to adjust pH but does not specifically target metal sequestration.