The Role and Principles of Scale Inhibitors in Water Treatment

In China, as the industry has developed rapidly, the water consumption has increased, and recycled water has become an important means of saving water resources. Industrial recycled cooling water accounts for 70% to 90% of the total industrial water consumption. With the widespread use of scale inhibitors, various types and properties of scale inhibitors have been produced to adapt to the applications of various industries.

What are scale inhibitors?

Scale inhibitors are a type of chemicals that can disperse insoluble inorganic salts in water, prevent or interfere with the precipitation and scaling of insoluble inorganic salts on metal surfaces.

What are the main components of reverse osmosis scale inhibitors?

Reverse osmosis scale inhibitors mainly include some natural dispersants, phosphonic acids, phosphonocarboxylic acids and phosphonosulfonic acids, and high molecular weight polymers. Currently, most of the scale dispersants used are high molecular weight polymers. They can disperse insoluble inorganic salts in water, prevent or interfere with the deposition and scaling of insoluble inorganic salts.

For the convenience of use and selection, we need to understand the types of scale inhibitors. The common classifications are:

Polycarboxylic acid scale dispersant

Polycarboxylic acid compounds have excellent scale inhibition effect on calcium carbonate scale, and their amount is also very small. The commonly used ones are polyacrylic acid PAA, hydrolyzed maleic anhydride HPMA, AA/AMPS, and copolymers.

Organic phosphonic ester

Organic phosphonic ester has a better effect on inhibiting calcium sulfate scale, but a worse effect on inhibiting calcium carbonate scale. Its toxicity is low and it is easy to hydrolyze.

Organic phosphonic acid scale inhibitors

The commonly used ones are ATMP, HEDP, EDTMPS, DTPMPA, PBTCA, BHMTPMPA, etc., which have good effects on inhibiting the precipitation or deposition of calcium carbonate, hydrated iron oxide, or calcium sulfate.

Polyphosphates

The commonly used polyphosphates are sodium tripolyphosphate and sodium hexametaphosphate. They form long-chain anions in water that are easy to adsorb on small calcium carbonate crystals. At the same time, this kind of anion is easy to substitute with CO₃^2-, thus preventing the precipitation of calcium carbonate.

Performance of scale inhibitors

We know that scale inhibitors have a scale inhibition function, which is due to their ability to prevent the growth of small carbonate crystal grains and distort the lattice, thereby preventing carbonate salts from forming hard scales on the surface of heat exchangers in circulating cooling water. At the same time, through the characteristics of the organic phosphates and other ingredients in their composition, they can combine with calcium ions in circulating cooling water, and play a role in preventing corrosion of metals. Our company's product PH has a wide range of uses and can have scale inhibition and corrosion inhibition effects between PH7.0~10.0, making industrial production operations simple and avoiding problems such as corrosion and scaling caused by losing control of PH.

Mechanism of scale inhibitors

• The complex and solubilization effect in the scale inhibitor is co-polymerized in water to generate negatively charged molecular chains. It forms soluble complexes or chelates with Ca²⁺, thus increasing the solubility of inorganic salts and playing a role in scale inhibition.

• The lattice distortion is caused by some functional groups in the molecule occupying a certain position on the inorganic salt nucleus or microcrystal, hindering and destroying the normal growth of the inorganic salt crystal, slowing down the growth rate of the crystal, and thereby reducing the formation of scale.

• The electrostatic repulsion effect is that the copolymer is adsorbed on the microcrystals of inorganic salts after being dissolved in water, increasing the repulsion force between the particles, hindering their agglomeration, keeping them in a good dispersion state, thus preventing or reducing the formation of scale.

Therefore, scale inhibitors can effectively disperse insoluble inorganic salts, and their chemical components can effectively hinder the agglomeration of dirt, thereby achieving the role of scale inhibition. At the same time, they also have great development prospects in the industry.

The difference between reverse osmosis scale inhibitors and circulating water scale inhibitors

Due to the different situations faced by the two, the requirements for them are different:

The operating environment of circulating water requires long-lasting and bacteria-resistant effects, and can use a large amount of polymer dispersants to provide a dispersed effect on suspended matter to increase the scale inhibition effect. The circulating water system has a large volume and operates outdoors, so the purity requirements for the medication are not high.

Reverse osmosis scale inhibitors require quick and efficient action due to the short action time. In addition, if polymer dispersants are used, it will cause bigger problems due to the narrow internal channels of the membrane. At the same time, the scale inhibition process takes place on the surface of the membrane, and high impurities content will also affect the stable operation of the system.

A significant advantage of high concentration scale inhibitors is that they can reduce transportation costs. For a single type of scale inhibitor, the higher the concentration, the narrower its stable range. For compound scale inhibitors, because the stable ranges of each single agent are different, it is more difficult to increase the concentration of the product. In addition, the higher the concentration of the scale inhibitor, the faster it will change during storage, and the higher its impurity content will be.