What are the requirements and effects of pH value when using polyaluminium chloride for water treatment?
Publish Time: 2025-05-14
When using polyaluminium chloride (PAC) for water treatment, pH value is a crucial factor. It not only affects the solubility and chemical form of polyaluminium chloride, but is also directly related to its coagulation effect and the stability and safety of the final water quality. Understanding the effect of pH value on the mechanism of action of polyaluminium chloride is crucial to optimizing the water treatment process.Under different pH environments, polyaluminium chloride exhibits different chemical behaviors. When the pH value is at a low level, the concentration of hydrogen ions in the solution is high, which may cause the molecular structure of polyaluminium chloride to change, making it tend to decompose into smaller particles or ionic states. In this case, the active ingredients of polyaluminium chloride may not fully demonstrate their due coagulation ability, resulting in a decrease in treatment efficiency. In addition, the low pH environment may also promote the occurrence of certain side reactions, which may interfere with the normal coagulation process and even generate undesirable byproducts.On the contrary, under higher pH conditions, the number of hydroxide ions in the solution increases, which poses a challenge to the chemical stability of polyaluminium chloride. In alkaline environment, polyaluminium chloride tends to form larger aggregates. Although such aggregates theoretically have strong adsorption and precipitation capabilities, excessive particle size sometimes leads to too fast sedimentation speed, reducing the chance of contact with pollutants, thereby reducing the overall removal efficiency. More importantly, water treatment processes under high pH conditions need to pay more attention to equipment corrosion, because alkaline substances tend to be more corrosive to metal materials.In order to achieve the best treatment effect, it is usually recommended to adjust the pH value of the water body to an appropriate range. In this range, polyaluminium chloride can maintain a relatively stable chemical structure, neither excessively decompose nor form too large aggregates. At this time, polyaluminium chloride molecules can effectively combine with suspended matter, colloids and certain soluble organic matter in the water, and achieve rapid and efficient coagulation and precipitation through charge neutralization and adsorption bridging mechanisms. In this state, not only can the removal rate of suspended matter be significantly improved, but also the transparency and sensory quality of the effluent can be improved.In addition to directly affecting the coagulation performance of polyaluminium chloride, changes in pH value will also indirectly affect the behavior of other chemical components in the water body. For example, under certain pH conditions, some heavy metal ions may be more likely to bind to the flocs formed by polyaluminium chloride and be removed together; under other conditions, the same heavy metal ions may remain dissolved and difficult to be effectively removed. Therefore, when designing a water treatment solution, it is equally important to consider the impact of pH on the chemical balance of the entire system.It is worth noting that although there is a theoretical optimal pH range, in actual operation, it still needs to be flexibly adjusted according to the specific water source characteristics and treatment goals. Each water source has a unique chemical composition and physical properties, which means that even the same type of polyaluminium chloride requires differentiated application strategies in different situations. In addition, considering factors such as seasonal changes and fluctuations in raw water sources, dynamic monitoring and timely adjustment of pH values are also one of the key measures to ensure long-term stable operation.In short, pH plays an indispensable role in the process of using polyaluminium chloride for water treatment. By accurately controlling the pH value, the coagulation efficiency of polyaluminium chloride can be maximized while avoiding unnecessary side effects. This is of great significance for improving water quality standards, protecting public health and protecting the environment. Understanding and mastering the laws of action of this variable will help to formulate more scientific and reasonable water treatment plans and promote the development of sustainable use of water resources.
