Chelants are defined as complexing agents that form stable, but water-soluble, complexes with metal ions. The interesting feature about the action of metal chelating agents is that although they leave the metal ions in solution, they prevent them from reacting as normally expected.
Metal chelating agents are added to an aqueous system to limit the available concentration of a particular metal ion. This prevents precipitation of insoluble salts of this metal ion or some other adverse reaction.
Using glycolic acid to replace more hazardous inorganic acids delivers several benefits to the user. Glycolic acid does not fume. It does not produce objectionable odours, even at elevated temperatures. Glycolic acid also chelates metal ions that might otherwise react and interfere with the metal chelation process.
Glycolic acid is able to chelate, or complex, metal salts introduced by hard water or by the metals being processed. These glycolic acid metal salt complexes are very water soluble, especially vs. sulphate or phosphate salts, so they do not precipitate.
Glycolic Acid is useful in a wide variety of metal cleaning applications, including the cleaning of copper or aluminium parts and equipment, stainless steel boilers, heat exchangers and other process equipment, dairy and other food processing equipment, water wells, and many other industrial metal surfaces. The properties listed below contribute to glycolic acid’s effectiveness and versatility.
- It is a relatively strong organic acid. The pH of a 4% solution of glycolic acid in water is below 2.0.
- It is a non-volatile acid. This means no corrosive fumes evolve on heating. Low acid yield loss is experienced, even when hot solutions are used.
- It has a very mild odour versus the strong objectionable odour created by other acids like acetic. It does not fume as some mineral acids do.
- It dissolves carbonate, oxide, and most casein scales readily. The resulting salts are water soluble. This gives good rinsing properties.
- As supplied, it is already in complete solution. It is easy to handle as a liquid. There are no “incomplete dissolving” problems, and the 70% concentrate can be quickly diluted to any desired strength with water.
- It has a relatively low corrosion rate on metals. Specific corrosion data are available upon request from DuPont. These low rates of corrosion can be further reduced by addition of a corrosion inhibitor.
- It contains essentially no chlorides. It can be used for cleaning stainless steels without the possible chloride cracking or embrittlement sometimes experienced in acid chloride systems.
- In formulation, it is compatible with many cleaning additives. These can include surfactants, biocidal agents, corrosion inhibitors, scents, colours, other acids, and of course, water.
- It possesses complexing properties. This characteristic may preclude the need to add a special chelating or complexing agent. It enhances the rinsibility property of the cleaner.
- It is a relative safe acid to store and handle. Always be sure to follow material safety data sheet guidelines for chemical handling.
- It is readily biodegradable, but does not support the growth of bacteria in use.