After entering the water, polyaluminium chloride (solid) will first undergo a dissolution and ionization process, which is the starting point for its coagulation effect. When solid particles come into contact with water, they will gradually disperse and release positively charged aluminum ions and their polymers. These charged particles, like tiny charge carriers, can quickly interact with impurities in the water, laying the foundation for subsequent coagulation reactions. At this time, the colloidal particles and suspended impurities in the water originally carried negative charges, and the attraction between positive and negative charges began to emerge, creating conditions for further aggregation.
In the charge neutralization stage, the positively charged particles released by polyaluminium chloride (solid) will actively meet and interact with the negatively charged colloidal particles in the water. The reason why colloidal impurities in water can be stably suspended is largely because their surfaces carry the same negative charge, which repel each other and prevents them from aggregating. The positive charge provided by polyaluminium chloride (solid) will gradually neutralize the negative charge on the surface of the colloid, causing the colloidal particles to lose the electrical basis for their stable existence. When the charge on the surface of the colloidal particles is neutralized to a certain extent, the original repulsive force is weakened or even disappears, and the particles can get close to each other.
As the charge neutralization proceeds, the high molecular polymers in polyaluminium chloride (solid) begin to play a bridging role. The molecular structure of these polymers is like a long chain, one end of which can be adsorbed on the surface of a colloidal particle, and the other end can connect to another colloidal particle, connecting the dispersed particles to each other and forming a larger floc. This bridging effect not only accelerates the aggregation of particles, but also allows smaller particles to combine into relatively stable groups, preparing for subsequent precipitation and separation.
In the adsorption and sweeping process, the hydroxide flocs formed by polyaluminium chloride (solid) play an important role. These flocs themselves have strong adsorption capacity. When they gradually grow and become larger in the water body, they will be like an invisible net, constantly adsorbing the surrounding fine particles and impurities that have not been neutralized during the movement. Even some particles whose charges are not completely neutralized will be wrapped and rolled by these larger flocs, and captured together with the growth of the flocs. This process is like using a rag to collect scattered dust during a general cleaning, so that various impurities originally dispersed in the water can be effectively gathered, further improving the purification effect of the water body.
The growth and stability of flocs are the key stages of coagulation. Under the combined effect of the above processes, fine particles continue to gather, and the flocs formed gradually increase in size and become more compact in structure. At this time, the weight of the flocs themselves also increases, and the original state of suspension in the water is difficult to maintain. At the same time, the flocs will collide and merge with each other, causing the volume and weight to continue to grow, providing favorable conditions for subsequent sedimentation and separation. In this stage, the transparency of the water body begins to gradually increase, the original turbid state slowly changes, and the impurities appear in the form of visible flocs.
When the flocs grow to a certain extent, gravity begins to dominate, causing them to settle to the bottom of the water body. This process marks the entry of coagulation into the separation stage. Because their own weight exceeds the buoyancy of water, larger flocs will slowly sink and settle to the bottom of the water like falling snowflakes. In this process, most of the suspended impurities and colloidal particles in the water body are wrapped in flocs and settle together. The originally turbid water gradually becomes clear, and the impurity content in the water is greatly reduced, which reduces the burden on subsequent filtration and other treatment processes.
The coagulation effect of polyaluminium chloride (solid) is also reflected in the treatment of tiny organic matter and some soluble substances in water. In addition to colloids and suspended particles, some tiny organic matter and soluble impurities in water will also be adsorbed or wrapped by flocs. Although these substances are difficult to remove by simple precipitation, they will be separated as the flocs are settled under the action of flocs formed by polyaluminium chloride (solid). This comprehensive effect makes the water not only visually clear, but also significantly reduces the content of its inherent pollutants, thereby achieving the purpose of purifying water quality and meeting the requirements of subsequent water use or discharge.
