The optimal pH range of polyaluminum chloride in papermaking wastewater

When Polyaluminum Chloride is used to treat papermaking sewage, the best pH range is affected by many factors. Different studies and practical applications give slightly different ranges, generally between 6 and 9. The following are the specific situations in different data:

-pH should be between 6 and 8: Within this range, polyaluminum chloride can achieve optimal flocculation and coagulation. At lower pH levels (acidic conditions), polyaluminum chloride releases more aluminum hydroxide ions, enhancing flocculation. However, if the pH is too low, it may lead to acid corrosion and instability, so the pH should be maintained above 6. Conversely, at higher pH levels (alkaline conditions), the flocculation effect of polyaluminum chloride diminishes. In highly alkaline conditions, the aluminum ions in polyaluminum chloride form aluminum hydroxide precipitates, reducing its flocculation ability. Therefore, to ensure optimal performance, the pH should be kept below 8.

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-pH 7-9: Experiments have shown that under alkaline conditions (pH 7-9), when the dosage of polyaluminum chloride exceeds 750mg/L, the removal rate of suspended solids can exceed 95%, and it can remove 20-50% of the CODCr. When polyaluminum chloride is used to treat paper mill wastewater, it shows good treatment effects within this pH range.

-pH 6.8-8.5: Based on Water Treatment experience, the aluminum ions in polyaluminum chloride are amphoteric. Generally, water treatment processes with a pH value between 6 and 9 can function normally, with the optimal pH value being between 6.8 and 8.5. When the water's pH is acidic, the aluminum ions do not form aluminum hydroxide colloids and remain as free aluminum ions, thus failing to effectively remove pollutants from wastewater. Conversely, when the water's pH is strongly alkaline, aluminum hydroxide colloids can react with hydroxide ions to form aluminate, thereby losing their adsorption and co-precipitation capabilities.

Due to the differences in wastewater quality among various paper mills, such as variations in pollutant composition and concentration, the optimal pH range for polyaluminum chloride may vary. In practical applications, experiments and adjustments should be conducted based on the specific wastewater quality of paper mills to achieve the optimal dosage of polyaluminum chloride and the optimal pH control range.

# aluminium polychlorid #