Electrolytes are substances that give conductive properties to water after being dissolved in water. Polyelectrolyte is a chain of electrolytes. When these substances enter water, a large number of charged groups are formed in the water. Therefore, suspended substances can be absorbed and form clots.
From polyelectrolyte, they are added to water in order to remove fine and suspended particles. These materials are polymer compounds that are used in the process of coagulation and flocculation in water purification . In the following, we discuss the properties of polyelectrolytes and their applications.
What is polyelectrolyte?
Polyelectrolyte is one of the best and most widely used coagulant aids. Its other name is polyacrylamide PAM, which is marketed in three categories: anionic, cationic and nonionic.
This compound has polymeric and electrolytic properties and is used to remove colloids and suspended impurities in water, sewage and sewage. Coagulants are used to complete the coagulation process and create larger and heavier clots.
Its appearance is a solid, white, odorless crystal, and it is soluble in water, ethanol, ether, and chloroform. The settling speed of polyelectrolytes is about twice the settling speed of other coagulant and coagulant aids. Polyacrylamide is mostly in powder form, but liquid polyelectrolyte is used to make things easier.
Where is polyacrylamide or polyelectrolytes used?
Polyacrylamide or PAM has different uses in different industries. Among them, the following can be mentioned:
- Water and wastewater treatment
- Industrial wastewater treatment
- Papermaking (production of paper pulp and factory waste)
- Food factories
- Oil, gas and petrochemicals
- drilling
- dyeing
- leather manufacturing
- Production of agricultural pesticides
What are the benefits of polyelectrolytes?
- A lower dose of coagulant is required
- A smaller volume of sludge remains after the treatment process is completed
- Less increase in ionic charge of purified water
- Reducing aluminum content in treated water
- Cost savings of up to 25-30%
- Very high dissolution power and speed
- In the process of purification and removal of suspended and colloidal particles, less sludge is produced.
- The low required amount of these materials compared to other coagulants
- Clots produced by these polymeric materials have a larger volume and size
- The settling speed of coagulated particles is higher than other materials
- No formation of harmful and dangerous compounds in the process of purification and removal of suspended particles
Polyelectrolyte properties
Homogeneous polyelectrolytes have a charged group. But the heterogeneous type of polyelectrolyte has both positive and negative charge groups. These substances are soluble in water. But when they absorb suspended substances, they become insoluble. Liquid polyelectrolytes are classified into three categories: low molecular weight, medium molecular weight, and high molecular weight.
Before buying polyelectrolyte, the pH of the water should be measured. Because these materials are sensitive to water pH. And not using them at the specified pH may lead to a decrease in the efficiency of the polyelectrolyte.
How is the production of polyelectrolyte?
Polyelectrolyte is produced in two forms, liquid and powder. Liquid polyacrylamide is used to produce polyelectrolyte. Polymerization or polyelectrolyte production process is done at 60 degrees Celsius. This reaction is carried out using microwave radiation, which causes the formation of polymer chains in water.
Liquid polyelectrolyte
Polyelectrolytes exist both synthetically and naturally. Among the natural polyelectrolytes used in wastewater and water treatment are modified polymers, gelatin, chitosan and cellulose and starch compounds. Synthetic polyelectrolytes mainly include polyacrylamide. But they are polyphosphate, polyacrylamide copolymer, acrylate and ammonium monomers.
Liquid polyelectrolytes are classified based on molecular weight and charge density. But to buy polyelectrolyte for use in water purification, its coagulation potential should be considered.
Cationic polyelectrolyte
Cationic polyelectrolytes usually have quaternary ammonium groups. These electrolytes have a positive charge regardless of the pH of the water. Therefore, they are called strong polyelectrolytes. Weak cationic polyelectrolyte includes a polyelectrolyte that becomes cationic when dissolved in an acidic environment. Among the most important cationic polyelectrolyte materials, cationic polyacrylamide, chitosan, epichlorohydrin and polydiallyl dimethylammonium chloride can be mentioned.
Cationic nanoparticles are called acrylamide, which have a positive charge, or cationic polyelectrolyte. These polyamines are made from epichlorohydrin and secondary amines such as dimethylamine.
There are many types of cationic polymers. Among them, the following can be mentioned:
- Polydiallyl dimethyl ammonium chloride
- Epichlorohydrin / dimethylamine
- Cationic polyacrylamide
- Natural cationic polymers such as chitosan
Where are the applications of cationic polyelectrolyte?
These polyamides are used for coagulation of various chemicals in the following cases:
- Domestic sewage treatment plant or municipal sewage,
- paper making, oil and gas and petrochemical industry,
- Mining and textile industries
Anionic polyelectrolyte
Acrylamide, which has a negative electric charge, is called anionic polyacrylamide or anionic polyelectrolyte. This linear polymer is completely soluble in water. It is also synthesized under high temperature polymerization. It is almost insoluble in aliphatic solvents, acetone, benzene, ether and other organic solvents, but it has valuable properties.
Where are the applications of anionic Polyelectrolyte Package?
These materials can easily perform coagulation, thickening, shearing, dispersion, so they are used in cases such as the following:
- Oil recycling, stone quarrying factories
- Mineral processing, coal washing
- Metallurgy, coagulation of chemicals, papermaking
- Textile industry, sugar production
- In pharmaceuticals, environmental protection
- Concrete and building materials, agriculture
- and other industries
Read more: Application of polyelectrolyte in wastewater treatment
Nonionic polyelectrolyte
Nonionic polyelectrolyte is the third type of this material. In that load, there is no dominant positive or negative and it is neutral. This material is actually the same homopolymers that are practically neutral and have no electric charge. Uncharged or practically neutral acrylamide is called nonionic or nonionic polyelectrolyte.
The difference between polyelectrolytes
The difference between cationic and anionic polyelectrolytes is in the charge that each of them has. According to the type of load they carry, their use is also different. Also, each of them is used in different environments. On the other hand, another type of polyelectrolytes is the non-ionic and non-charged (neutral) type.
Some special properties of polyelectrolytes compared to uncharged polymers:
- High solubility of this polymer in water
- Ability to swell and connect with large amounts of water
- High interaction capability with heterogeneously charged macromolecules
The difference between polyelectrolytes is when they enter water. Cationic polyelectrolyte forms positively charged polymers when entering water. Therefore, it can absorb negatively charged materials on both sides and cause them to settle and finally purify water. But anionic polyelectrolyte forms negatively charged polymers after entering water. Therefore, knowing the type of water to be purified is effective when buying polyelectrolyte.
What is the difference between mineral and organic clots?
Inorganic flocculants and organic flocculants have coagulation or flocculation properties. Mineral flocculants are mostly substitutes for coagulants or flocculants. But organic flocculations are polymers with high molecular weight because they have sedimentation and there are solutes in them. The help of mineral coagulants are salts obtained from multipurpose metals such as iron and aluminum, whose deposition process is completely different from organic flocculation.
The correct way to choose between polyelectrolytes
The correct choice of the type of flocculation depends on the electric charge of colloids suspended in the solution. The electrostatic force of attraction is very important for the formation of clots between the suspended particles of colloids and flocculations because this force is created by using the attraction force between the dissimilar charges of colloids and flocculations.
So, in choosing between electrolytes, we must first identify our wastewater load. After identification, we select the electrolyte according to the wastewater load. For example, we use positively charged electrolyte for negatively charged wastewater. This action creates attraction between the particles and the clot.