Greener Chelating Agents

Chelating agents (chelants for short) form complexes with metal ions in solution either to prevent metal ions from causing undesirable reactions or to transport metal ions to where they are needed. Chelants are normally used in water-based systems where metal ions are nearly always present and require control. To understand how and why chelants are used, it is worth spending a short time considering water as a solvent and the effect that metal ions have on the use of water as a solvent in industry and the home. 

Water is the most common solvent used by humans. It is readily available in most parts of the world and is used for drinking, washing, cleaning, and industrially as a solvent. Water quality varies widely from region to region, from heavily polluted to purified drinking water quality. Water hardness and impurities are even more variable depending on the source of the water. 

Water is an excellent solvator and dissolves many chemicals, particularly metal ions. Since some metal ions are essential to human health in the right dose, removing them completely to make demineralized water is not desirable. Hence metal ions will be part of the water used by humans, not just for drinking but also during domestic chemistry such as washing and cleaning, and for most industrial chemistry. However, metal ions can be undesirable for some domestic or industrial chemistry applications. 

Calcium can deposit out of water to leave scale on surfaces, such as kitchen worktops and glass in the bathroom, or in dishwashers and washing machines. 

Handbook of Green Chemistry Volume 9 Designing Safer Chemicals, First Edition. Edited by Robert Boethling and Adelina Voutchkova. 

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