Chelating agent

A chelating agent is a chemical compound used in laundry detergents to remove dissolved minerals such as calcium and magnesium, and reduce yellow discoloration caused by iron and manganese. These water softeners suspend the minerals, allowing the detergent to do a better job. Unlike precipitating builders such as sodium carbonate that cause the minerals to fall out of solution as insoluble compounds which build up on fabrics and laundry equipment, these keep the minerals in solution so they can be rinsed away.

Sodium citrate is a good example of an environmentally friendly chelating agent. Phosphates also perform well, but contribute to algae growth in lakes and ponds. EDTA (ethylene diamine tetraacetic acid) is a well-known chelating agent used in laundry detergents. However, substitutes have been developed because EDTA does not biodegrade in the environment.

Reference:

Dr. Bassam Z. Shakhashiri, University of Wisconsin, from the Science is Fun Web site.