CEH Report

Table of Contents

Abstract

Chelating agents (or chelants) include a number of compounds, all having the ability to coordinate with metal ions at a minimum of two sites. Typically this bidentate coordination solubilizes or otherwise inactivates these metal ions, reducing any adverse effects the metals might have on the system in which they are used.

The chelants discussed in this report include aminopolycarboxylic acids and salts (EDTA, HEDTA, DTPA and NTA [nitrilotriacetic acids and salts]), hydroxycarboxylic acids and salts (gluconic acid and salts, and sodium glucoheptonate), and organophosphonates. Although these products largely perform as chelating agents, there are other applications in which these products are used and when important in volume, they are briefly discussed in this report. Organophosphonates are largely used as scale inhibitors, disturbing the crystal structure to keep the scale particles small, versus chelating agents, which keep everything soluble.

The choice of a particular chelant is dependent on several factors, including the pH and temperature range of the system in which they are used, which metal ions are to be controlled and the overall economics of the system. As a result, the three broad classes of chelants discussed in this report usually are not easily interchangeable and usually do not compete with each other. However, products within the three major groups covered are often interchangeable with each other. Recently, products with biodegradability have been introduced to the market in response to environmental pressures.

The following pie chart shows world consumption of chelating agents:

During the past few years, more biodegradable or greener aminopolycarboxylate chelating agents have been introduced. Many of these were the result of European initiatives with respect to biodegradability and human risk. Several of the compounds introduced include glutamic acid (GLDA), methylglycinediacetic acid (MGDA), L-aspartic acid N,N-diacetic acid tetrasodium salt (ASDA), DEG/HEIDA (sodium diethanolglycine/2-hydroxyethyliminodiacetic acid, disodium salt), iminodisuccinic acid and salts (IDS), and ethylenediaminedisuccinic acid and salts (EDDS). All of these are considered aminopolycarboxylates. All are more readily biodegradable than the classical aminopolycarboxylates.

Chelating agent usage spans a large number of diverse end-use markets. Important applications include pulp and paper processing; industrial water treatment; household, institutional and industrial cleaning compounds; metal finishing; agriculture; photography; rubber processing; use in food, pharmaceuticals, cosmetics and toiletries; and textile treatment.

Growth varies widely among the chelant types. Classical aminopolycarboxylates are the most widely consumed chelating agent in the world, accounting for 37.8% of consumption in 2009. The new greener aminopolycarboxylates are projected to be the fastest growing during 2009–2014, at just over 10% annually. The only chemistry declining in consumption is NTA, with further loss in consumption projected at –6.0% annually because of the persisting concerns over its toxicity. Overall chelating agents growth is forecast at 4.0% annually during 2009–2014.