Dispersants are special chemicals that are used in water and wastewater treatment to improve the distribution of fine particles and sediments in a liquid and to prevent particles from clumping or flocculating. In industrial water technology and wastewater treatment, dispersants prevent the formation and deposition of solids on surfaces, which plays an important role in circulation systems, pipelines and heat exchangers. Their application is particularly relevant for cooling water treatment, boiler water treatment and for membrane-based water treatment systemsto reduce the risk of fouling and scaling.

Technical background and function of dispersants

Dispersants work by modifying the surface charge of particles or by forming an electrostatic protective film around the particles. This creates repulsive forces that prevent the particles from sticking to each other and combining to form larger aggregates. These mechanisms support the stable distribution of solids in the water and help to minimize deposits in water treatment plants.

Mechanisms of dispersion

1. Electrostatic stabilization:

   • Dispersants influence the surface charge of the particles in the solution. This generated charge leads to electrostatic repulsion between the particles, which prevents clumping. This property is particularly important in order to avoid deposits in narrow flow areas.

2. Steric stabilization:

   • Some dispersants accumulate in a layer around the particles and create a steric barrier that separates the particles from each other. This barrier prevents the particles from coming closer together and thus forming larger aggregates or deposits.

3. Change in the particle surface:

   • Dispersants change the surface properties of the particles and make them more hydrophilic, which improves their distribution in the water. Especially in systems with hard water conditions, in which calcium and magnesium ions tend to precipitate, dispersants prevent these particles from reaching surfaces and settling.

Types of dispersants and their specific applications

Dispersants can be divided into different categories depending on the type of water treatment and the chemical structure:

1. Anionic dispersing agents:

   • Anionic dispersants have a negative charge and are suitable for stabilizing particles that have a positive surface charge. They are often used in cooling systems and in boiler water treatment to prevent the formation of calcium carbonate and magnesium deposits.

2. Cationic dispersants:

   • These positively charged dispersants are used in applications where the particles have a negative charge. In wastewater treatment, cationic dispersants can be helpful in preventing floc formation in the treatment of industrial wastewater.

3. Non-ionic dispersing agents:

   • Non-ionic dispersants have no charge and are stable in a wide range of pH conditions. These dispersants are useful for applications where the particle surfaces have different charges or the pH varies widely. They are widely used in membrane systems where the water composition is variable.

4. Polymer-based dispersants:

   • Polymeric dispersants, such as polyacrylates and polyphosphates, have long molecular chains that wrap around the particles and create steric hindrances. They are particularly effective against calcium and magnesium deposits and are well suited for cooling and boiler water treatments.

Applications of dispersants in practice

Dispersants play an important role in various industrial water treatment processes to improve the efficiency of the systems and minimize the risk of deposits and fouling.

1. Cooling water treatment:

   • Dispersants are used in open and closed cooling systems to prevent the build-up of calcium carbonate, magnesium salts and other mineral solids. The addition of dispersants keeps the cooling water clear and maintains heat transfer efficiency, reducing operating costs and extending system life.

2. Boiler water treatment:

   • In boiler systems, dispersants prevent the formation of deposits on heat exchangers and heating surfaces, which would impair heat transfer. Especially in systems with hard water, where calcium and magnesium ions tend to precipitate, dispersants are essential to maximize boiler performance and minimize downtime due to cleaning.

3. Membrane processes in water treatment:

   • In reverse osmosis and ultrafiltration systems, dispersants prevent fouling of the membranes by solids and colloids. By using dispersants, the service life of the membranes can be extended as the risk of clogging and a reduction in the filtration rate is reduced. The dispersants often work synergistically with antiscalants.

4. Textile and dyeing industry:

   • Textile processing and dyeing often produce waste water with high concentrations of solids, which can lead to deposits and discoloration. Dispersing agents prevent the formation of deposits and help to keep production facilities clean. They also help to ensure that dye particles remain dispersed in the water and are not deposited on machine surfaces.

5. Paper and pulp industry:

   • In paper production, dispersants prevent the build-up of fillers, clay and fibers on machines and surfaces. This leads to more efficient production, reduces maintenance and minimizes downtime.