Scale Inhibitors for Industrial Circulating Water Systems: A Review

Presence and deposition of sparingly soluble salts, known as scale, has been one of utmost damaging problems of circulating water. In industry, the scaling phenomenon may cause technical problems such as reduction of heat transfer efficiency in cooling systems and obstruction of pipes. Therefore, adding scale inhibitors that exhibit desired efficiencies to control scale is so important to mitigate adverse effect in water circulation systems because of their high tolerance for cations, such as Ca2+, Mg2+, and their ability to efficiently dissolve the unstable polymorphs of inorganic salts at the early stages of crystallization, thus impairing scaling. This paper reviews the research progress and state-of-the-art developments of scale inhibitors, including natural scale inhibitors and synthetic scale inhibitors. Natural scale inhibitors, including natural organic and plant extract scale inhibitors, are non-toxic, inexpensive, widely used, biodegradable and in line with the characteristics of green chemistry. Synthetic scale inhibitors mainly composed of phosphorous, polycarboxylic acid and polyaspartic acid are widely used due to their excellent performance. Detailed comparison between natural scale inhibitors and synthetic additives alongside future directions towards antiscalant are also discussed. The former are less water-soluble, while the latter require a large dosage, which causes a great burden to the environment. In particular, the need for developing green, efficient, easy preparation, and pollution-free scale inhibitors, studying the interactions between scale inhibitors and metal ions is stressed. It is expected that this paper could offer an insight in deeper understanding the scale inhibitors in industry and provide some clues for exploring more advanced scale inhibitors technologies.