Polymers: Anionic and Cationic
What is an anionic polymer?
An anionic polymer is a long chain of millions of carbon atoms on which negatively charged spots are attached along the chain. The negatively charged spots act like tiny hooks. They are attracted to positively charged particles. Remember science class, opposites attract? It’s the same with anionic flocculants, aka flocculents. The hooks attach themselves to the tiny particles in solution to amass together to form larger “flocs”. This is known as the flocculation process.
For example, many minerals such as calcite and heavy metals such as copper can be effectively flocced. Floccing means removing suspended solids from a water solution by an anionic polymer or flocculant or flocculent. An anionic polymer flocculant causes tiny particles to come together. When they do, they build into a much larger “floc” particle. Then gravity takes over and the “floc” masses sink to the bottom of the treatment vessel, called a clarifier.
Dropping out solids is the desired objective to clean the solution of the solids which may be either unwanted contaminants or valuable products.
Anionic polymer flocculants reduce the cloudiness of water by removing the finely suspended solids. Anionic polymers have molecular weights which range from a few million to more than twenty million weight units.
What is a cationic polymer?
A cationic polymer is a long chain of millions of carbon atoms on which positively charged spots are attached around the perimeter. The positively charged spots act like tiny hooks to attract negatively charged particles. The cationic polymer brings all the tiny solids together to form much larger masses. When they get large enough, they drop to the bottom of the treatment tank. This is known as the flocculation process.
For example, some clays have negative charges on their perimeter. This means that they can be removed from solution by a cationic polymer. A cationic polymer flocculant or flocculent causes tiny particles to come together. When this happens they build size into a much larger “floc” particle. Then gravity takes over and drops the “floc” masses to the bottom of the tank. The treatment tank is often called a clarifier or thickener. Removing suspended from solution is the desired objective to clean the solution. The solids may be unwanted contaminants or valuable products. Cationic polymer flocculants reduce the cloudiness, aka turbidity, of water by removing the finely suspended solids.
Cationic polymers have molecular weights which range from a few hundred thousand to over ten million weight units.
Flocculation and Polymer Principles for Cationic and Anionic Polymers
Cationic and anionic flocculants, aka, flocculents greatly enhance separating solids from water solutions. The solids may be an unwanted contaminant or may be a valuable by-product. Separation success is achieved by building tiny suspended solids into large masses. Then, gravity takes over and solids drop out of solution leaving behind clear water.
These anionic and cationic flocculants are long chains of acrylamide. The term flocculation is often confused with coagulation. The two refer to entirely different processes.
Flocculation occurs when either an anionic flocculant or a cationic flocculant forms a bridge between particles to make larger masses. Anionic and cationic flocculants make solids removal possible due to the larger mass of solids which drops out of solution due to gravity.
Coagulation Water Treatment
What is coagulation water treatment?
Coagulation water treatment affects any suspended fines which should be removed from the aqueous solution. These principles are in evidence in any water treatment or wastewater treatment application. Coagulation water treatment is an electrical reaction. Tiny particles can merge together when a coagulant removes the like charges on the suspended solids. The like charges keep the particles in suspension. The coagulant neutralizes the like charges so that the particles may come together.
Theory of Flocculation
What is flocculation?
Flocculation means the suspended particles are physically precipitated to the bottom of a treatment tank. Clarifier is a more specific type of treatment tank. Particles precipitate, or drop out of solution, by both the flocculant or flocculent and the force of gravity. It functions because the flocculant or flocculent has increased suspended solids’ mass by agglomerating fines into larger particles. When that happens, gravity can operate without electrical repulsion interference. Anionic and cationic flocculants or flocculents function in this fashion whether the application is in water treatment or wastewater treatment.
All particles exert mutual attraction forces, valid only at short distances of separation. Natural coagulation can then occur. Coagulation/flocculation would happen at once if the suspension were not so tightly bound. However, suspensions are rendered stable by repulsion forces, like charges. They prevent particles from coming close enough for these attraction forces to take effect.
There are two primary sources of these repulsion forces: (a) Water is absorbed from the surroundings onto the surface of the particles which repel one another. (b) Electrical charges – all particles carry an electrical load on their surfaces. Electrical load intensity depends on the nature of the surface and the chemistry of the suspension. Repulsion prevents particles from coming together. It also retards settling by keeping the particles in constant motion. Charge repulsion effects are most noticeable with tiny particles.