Anionic or cationic polyelectrolyte: how to choose
How charge decides between anionic and cationic flocculants, with the typical use for each Sunfloc grade.
The charge on the polymer decides what it can grab. Most suspended solids in water carry a negative charge, but the best polymer depends on what else is in the water.
Anionic polymers
Anionic polymers bridge particles that have already been brought together by a metal-salt coagulant such as alum, ferric chloride or PAC. They are the usual choice after coagulation in effluent treatment, in municipal clarifiers and for mineral slurries.
Cationic polymers
Cationic polymers are attracted to negatively charged organic matter and biological solids. They are used for sludge conditioning ahead of belt presses, centrifuges and filter presses, and for organic-rich effluents.
HQ and MQ
Sunfloc comes in HQ and MQ grades for each charge. HQ grades are packed in 25 kg bags; MQ grades in 10 kg bags. Their specification sheets give different sets of values, so check the grade table before you compare them.
Do not guess
Charge choice is a first filter, not the final answer. Confirm with a jar test.
A decision in three questions
First, what is the charge of the particles? Most mineral and clay solids carry a negative surface charge and respond to anionic polymer, usually after a coagulant or lime has done its job. Organic solids such as sludge, fats, proteins and colour-bound floc carry negative charge too, but are often better held by a cationic polymer.
Second, what is the pH? Charge on both particle and polymer changes with pH, so correct it before comparing grades. Third, what is the water used for next? A stream going to reuse or an RO unit needs a clear overflow, and that is the test to judge by.
When the answer is not obvious, test both on the same sample in the same jar run. Sugar research is a useful illustration: SASRI notes that cane juice suspended matter is mainly negatively charged, which is why anionic polymers are standard there. A jar test is the fair way to compare options: the same water, the same stirring, one variable at a time. ASTM D2035 describes the practice, and it is the right starting point for any new stream.
Sources: SASRI: flocculation of cane juice, where suspended matter is mainly negatively charged; ASTM D2035-19, Coagulation-Flocculation Jar Test of Water.
Not sure which grade suits your water?
Send us a one-litre sample or describe your process. We test it in our lab free of charge and recommend a grade and starting dose.