Classification and Principles of Scale Inhibitors

Commonly used scale inhibitors in water treatment include polyphosphates, organophosphonic acids, phosphonic acids, organophosphonic acid esters, and polycarboxylic acids.

Polyphosphates

Commonly used polyphosphates include sodium tripolyphosphate and sodium hexametaphosphate. In water, they generate long-chain anions that readily adsorb onto tiny calcium carbonate crystals. These anions also readily replace CO32-, thus preventing calcium carbonate precipitation.

Organophosphonic acids

Effective agents include HEDP and EDTMP, which are very effective at inhibiting the precipitation or sedimentation of calcium carbonate, hydrated iron oxide, or calcium sulfate.

Organophosphonic acid esters

Organophosphonic acid esters are effective at inhibiting calcium sulfate scale, but less effective at inhibiting calcium carbonate scale. They have low toxicity and are easily hydrolyzed.

Polycarboxylic acids

Polycarboxylic acid compounds have good scale inhibition properties against calcium carbonate scale, and are used in very small quantities. Commonly used ones include polyacrylic acid and hydrolyzed maleic anhydride.