We are all aware that the efficacy of
polyaluminium chloride is closely and directly related to its active component, aluminium trioxide. The content of aluminium trioxide varies between 20% and 30%. Therefore, we require testing of its purity. In other words, we need to ascertain its content to gain an understanding of its quality.
Currently, when testing the content of polyaluminium chloride, we generally follow the national standard procedure. This involves dissolving the product sample, then adding acid. Under the action of the acid, the polyaluminium undergoes degradation. Subsequently, zinc chloride is added for titration. Finally, by analysing the ions present in the sample, relevant usage data is obtained. Calculating based on this data yields the actual content of the product. However, as this is a manual experimental process, some deviation is inherent in the calculations. For liquid products, this deviation must not exceed 0.1%, while for solid products, it must not exceed 0.2%. Consequently, purchasing products with purity slightly below the stated level is common. Provided the deviation remains within these permissible ranges, it is considered normal and there is no need for undue concern regarding purity.
What precautions should be taken when using polyaluminium chloride products? Avoid direct addition prior to use. It is advisable to determine the appropriate formulation and dosage based on the characteristics of the source water. As this is an inorganic polymer compound, it dissolves readily in water but possesses certain corrosive properties. Therefore, experimental testing according to the source water quality is recommended to establish the optimal dosage. For ease of transportation and storage, solid formulations are commonly selected. Prior to use, dissolution is essential. Mix at a ratio of solid to clean water of 1:5 for dissolution, followed by dilution with additional water. Generally, concentrations below 1% may undergo hydrolysis, diminishing efficacy. Conversely, excessively high concentrations risk wastage.
It is advisable to prepare a 5-10% aqueous solution for application. Adjustments should be made during use: insufficient dosage typically results in sparse flocculation and high turbidity in sedimentation tanks, while excessive dosage often causes large, floating flocs. Prompt adjustments are essential to ensure effective treatment.
