Scale Control 101

Threshold Inhibition

Threshold Inhibition is the extension of solubility of an otherwise insoluble salt beyond its saturation limits using an additive at sub-stoichiometric levels. Polymers such as INITIA™ Polymer Additives are exceptional threshold inhibitors for mineral scales such as CaCO3, CaSO4, and BaSO4. INITIA™ Polymer Additives work sub-stoichiometrically which differentiates it from materials that function according to strict stoichiometric ratios such as EDTA.

Mechanistically, INITIA™ Polymer Additives achieve Threshold Inhibition in three basic steps: Surface Adsorption, Directional Growth Blocking, and Crystal Dissolution.


Sequestration is the complexation of a metal ion such that the ion does not retain its original reactive properties. Unlike threshold inhibition, sequestration does not imply either stoichiometry or specific functionality. In other words, sequestration does not describe how or how much of an additive is necessary; rather it describes what happens to the metal ion properties in solution. INITIA™ Polymer Additives sequester ions such as calcium, magnesium, barium, iron and zinc and prevent them from forming insoluble complexes with compounds such as carbonate, phosphate and sulfate.


A Chelate is a coordination compound in which a central metal ion such as Ca2+ is attached by coordinate links to two or more non-metal atoms in the same molecule, called ligands. A Chelating Agent is one that “grabs” a metal ion at two or more points within the agent molecule.

By definition, INITIA™ Polymer Additives act as chelating agents with most muti-valent ions. However, using common use of the terms Chelate or Chelation tend to imply a more permanent or substantive relationship between the ion and the ligand where stoichiometry is exact and predictable (i.e. Calcium-EDTA.) INITIA™ Polymer Additives generally do not meet the common definition because their association with metals are temporary and their functionality is sub-stoichiometric.


The concept of Stabilization can have two meanings with respect to polymer interactions with metal ions: Colloidal Stabilization is where precipitation in a fluid (water) occurs but the polymer prevents agglomeration of particles beyond 1 micron in size. These particles are thus stabilized via electrostatic interactions with the polymer and remain suspended throughout the water phase. These sub-micron particles are typically not visible to the naked eye. A notable exception to this is stabilized iron particles which can be visible due to the orange-brown color associated with most oxidized (Fe3+) iron complexes. The term Stabilization can also be a synonym for sequestration where a coordination complex between the polymer and soluble ions or surface interaction between the polymer and forming crystal lattices occurs and prevention of precipitation is achieved. In this case, threshold inhibition is not the prevailing mechanism since stoichiometry is undefined. INITIA™ Polymer Additives are highly effective for Iron Stabilization, Calcium Phosphate Stabilization, and Zinc Stabilization in water treatment applications.

Particulate Dispersion

Particulate Dispersion may be the most straightforward of the six concepts for scale control. A formal definition of Particulate Dispersion is where a mixture of finely divided particles, called the internal phase (often of colloidal size) is distributed in a continuous medium, called the external phase. More simply stated, Particulate Dispersion is a suspension of particulates in an aqueous solution. These can be Inorganic (i.e. calcium carbonate), Organic (i.e. biomass) or a mixture of the two. Polymer composition and Mw are key determinants in deriving functionality for effective particulate dispersion. INITIA™ Polymer Additives are effective particulate dispersants for a wide-range of particulate types and applications.

Crystal Habit Modification

Crystal Habit Modification is the basis for the control of mineral scales such as calcium carbonate, calcium sulfate, and barium sulfate. INITIA™ Polymer Additives are highly effective crystal habit modifiers.

A Crystal Habit is defined as the normal size and shape of a precipitated substance in a given set of environmental conditions. The formation of crystals such as calcium carbonate and their subsequent deposition onto surfaces follow a simplified process of Nucleation, Lattice Formation and Propagation, Bulk Precipitation and Surface Deposition. Crystal Habit modification can be described in instances where a “poison” such as a polymer, phosphonate, or other contaminant disrupts normal lattice formation. The crystal lattice poison, in turn, produces crystals that either tend to re-dissolve or precipitate in abnormal forms. This effect reduces the cohesion of the crystals to each other (dispersion) and the adhesion of the crystal to system surfaces (scaling).