Aluminum Sulfate

FAQ

• What should I do if flocculation is poor and no flocs are forming?

  Possible causes include improper dosage, unsuitable pH, or inadequate mixing. Both under-dosing and over-dosing can affect performance. First, check whether the water pH is within the optimal range of 5.5 to 8.0, then confirm the optimal dosage through jar testing. Additionally, ensure sufficient intensity during the rapid mixing stage to achieve thorough dispersion of the chemical.

• What should be done if flocs are fine and settle slowly?

  This may be caused by excessive rapid mixing or insufficient slow flocculation. Excessive stirring can break up newly formed small flocs; therefore, the intensity or duration of rapid mixing should be appropriately reduced, and sufficient time must be allowed during the slow flocculation stage for flocs to grow. Low temperatures (<10°C) also slow down the flocculation reaction, requiring an appropriate extension of the flocculation time.

• Can aluminum sulfate still be used if it has clumped due to moisture absorption?

  Aluminum sulfate is hygroscopic, and clumping due to moisture absorption is common. For slight clumping, it may be possible to crush and use the product in a low-humidity environment. However, severe clumping can lead to inaccurate weighing and difficulty in dissolution; therefore, it is recommended to use freshly opened product for critical experiments.

• Is it normal for the prepared solution to have precipitate or turbidity?

  The presence of a small amount of insoluble material when preparing the solution may be normal (e.g., in crude products). However, if the solution becomes cloudy or milky, it could indicate that aluminum sulfate has hydrolyzed to form aluminum hydroxide precipitate, which is more likely to occur in weakly alkaline or alkaline solutions and may affect flocculation performance. To resolve this, adjust the pH of the solution to approximately 3.0–4.0 using dilute sulfuric acid; the precipitate will then redissolve.

• Is there a risk from aluminum residue in water after treatment with aluminum sulfate?

  There is a certain risk. After using aluminum-based coagulants, some aluminum may remain in the treated water (for example, in one study, the aluminum concentration in sedimentation tank effluent was approximately 0.09 mg/L). Long-term consumption of water with high aluminum levels may be associated with skeletal disorders and neurological diseases (such as dialysis dementia). The safe threshold for aluminum content in tap water in China is set at 0.2 mg/L. Therefore, drinking water treatment plants must strictly control dosing and ensure that residual aluminum in the effluent remains below this limit.