Coagulants

Coagulation destabilises colloidal particles by neutralising their charge with an added chemical. Coagulants are generally metal salts such as iron chloride, ferric chloride and polyaluminium chlorides, usually dosed as liquids. They may also form part of a formulated powder or a separate first treatment stage. They are sometimes grouped with flocculants because small flocs appear after dosing.

However, a flocculant or polyelectrolyte produces effective floc growth. Coagulants are important for streams containing paint and ink pigments, whose dispersions and emulsions benefit from coagulation before solids flocculation.

Positively charged iron or aluminium ions neutralise the negative charge on colloidal particles. Coagulants are therefore often based on iron or aluminium chlorides or modified variants. Neutral particles no longer repel one another and can aggregate, settle or float. Coagulation is often the first stage in physicochemical treatment.

Chemtrade International supplies coagulants in small packs, including 10 kg cans, and IBCs. We can test which product suits your application. Sulphate free products with low chloride content are available where needed, particularly in closed circuits where chloride accumulation is undesirable and conductivity must remain low. High conductivity and salt loading can accelerate corrosion of wetted plant components, such as water cooled saw blades in natural stone processing. Salt deposits can also cause fouling or blockages.

Most coagulants are acidic, sometimes as low as pH 1, so dosing affects the water’s pH. Effective flocculation requires a neutral pH. If a large dose is needed to break emulsions and dispersions, neutralisation with an alkaline agent such as sodium hydroxide or milk of lime is necessary.

There is much to consider in treatment, and we can advise you. Contact us to discuss the options.