In the purification of wastewater,
polyferric sulphate can be considered a highly effective water treatment chemical. It demonstrates particularly excellent efficacy in the removal of phosphorus from sewage, a capability unmatched by other water treatment agents. The superior performance of polyferric sulphate in water treatment processes is primarily attributable to its basicity, which determines its flocculation effect. However, the required basicity varies across different wastewater treatment processes. So, how does the basicity differ in various water treatment applications?
Polyferric sulphate is an inorganic polymeric flocculant. It offers advantages such as rapid hydrolysis, high floc density, and a broad pH applicability range. Moreover, the greater the number of hydroxyl groups incorporated into the sulphate iron network structure, the higher the product's basicity. This also enhances the molecular polymerisation degree, leading to superior flocculation treatment efficacy. Therefore, by modifying or adjusting the composition and ratio of acids, hydroxyl groups are more readily substituted for sulphate ions and incorporated into the network structure of the ferric sulphate molecular clusters. This enhances both the product's basicity and molecular polymerisation degree. Compared to conventional polymeric ferric sulphate, it exhibits faster hydrolysis rates, higher floc density, and rapid sedimentation, offering functions such as flocculation, decolourisation, and sludge dewatering.
When testing basicity, the fundamental method typically involves acid decomposition of the initial sample. Potassium fluoride is then added to mask iron ions, followed by sodium hydroxide solution for determination. Generally, the results obtained are sufficiently accurate. It should be noted that insufficient hydrochloric acid during decomposition of the polymeric ferric sulphate may lead to incomplete decomposition. Complete masking can result in inaccurate final determination outcomes. During testing, one may first employ a substantial quantity of hydrochloric acid for decomposition, using potassium fluoride to mask trivalent iron ions. Sodium hydroxide is then added to neutralise some acidity, followed by a dilute sodium hydroxide solution. This approach yields more precise results.
The basicity of polyferric sulphate typically falls within the range of 8-16%. Higher basicity generally enhances its hydrolytic flocculation efficacy. However, this does not imply that higher basicity is invariably preferable. Excessively high basicity leads to OH⁻ ion precipitation, resulting in a dark yellow appearance and increased susceptibility to solidification and degradation. It also becomes difficult to store. Furthermore, it may hydrolyse readily when added to wastewater. Generally, maintaining the basicity of polyferric sulphate around 16% yields optimal quality and efficacy. Thus, keeping the basicity within an appropriate range is advisable.
