Application of surfactants in water treatment

The mechanism of action of surfactant (water treatment agent) in water treatment is a matter of concern to people. After years of research and practice, the following views have been preliminatively obtained:

1. Corrosion inhibition mechanism

Surfactants used as corrosion inhibitors first require its polar groups to have a great affinity for the metal surface, that is, physical adsorption and chemisorption can occur on the metal surface to form an adsorption layer, its non-polar groups are carrying the metal to the water arrangement, thus forming a water-repellent barrier, separating the metal surface from the water, so as to protect the metal. Secondly, the adsorption film formed by it must be firm and tight, and the solubility in water is very low, otherwise it is vulnerable to damage and be dissolved in water and lose its protective effect.

From the point of view of molecular structure, the length of its long chain group is closely related to the corrosion inhibition, because the longer the carbon chain, the greater the surface activity, the more conducive to its dispersion and adsorption on the interface, but if it is too long, it affects the solubility of the surfactant itself in water, so there should be an optimal chain length range. In addition, the degree of firmness and stability of the adsorption film is related to the structure and properties of the polar groups, such as surfactants with chelating groups, because they can form stable chelate films with metal surface ions and show strong corrosion inhibition ability.

Surfactants with good corrosion inhibition ability only need to form a single molecule adsorption film to meet the corrosion inhibition requirements, so that its use concentration can be much lower than its critical micelle concentration CMC. On the contrary, some surfactants have corrosion inhibition ability only when the concentration in water is greater than CMC, indicating that the adsorption on the metal surface at this time is micellar adsorption.

2. Killing mechanism

Water treatment for sterilization, algae killing agents called biocides, cationic surfactants, such as germinate, new germinate, often used as non-oxidizing biocides in water treatment. It is generally believed that their killing function is due to the adsorption of the positive charge with the negatively charged bacteria in water after ionization in water, and the formation of electrostatic bonds with the negatively charged parts on the bacterial cell wall, resulting in pressure on the cell wall, causing the dissolution and death of the cell. They can also destroy the tissue of the cell's semi-permeable membrane, intracellular metabolic substances and coenzymes, make proteins and cause cell death.

3. Scale inhibition mechanism

Some water-soluble polymers (mostly polyelectrolytes) are used as scale inhibitors in water treatment. Although the scale inhibition mechanism is complex, the condensation and dispersion of these polymers due to their surface activity is one of the important scale inhibition mechanisms. According to the surface view, these polymers can be regarded as widely used surfactants.