Desalination Pretreatment: Antiscalant

Antiscalants are surface active materials that interfere with precipitation reactions in three primary ways:

• Threshold inhibition: it is the ability of an antiscalant to keep supersaturated solutions of springly soluble salts.
• Crystal modification: it is the property of an antiscalants to distort crystal shapes, resulting in soft non adherent scale. As a crystal begin to form at the submicroscopic level, negative groups located on the antiscalant molecule attack the positive charges on scale nuclei interrupting the electronic balance necessary to propagate the crystal growth. When treated with crystal modifiers, scale crystals appear distorted, generally more oval in shape, and less compact.
• Dispersion: dispersancy is the ability of some antiscalants to adsorb on crystals or colloidal particles and impart a high anionic charge, which tends to keep the crystals separated. The high anionic charge also separates particles from fixed anionic charges present on the membrane surface.

Threshold Mechanism

Dispersancy

Calculation procedures exist for predicting the likelihood of scale formation. Use of these predictors depends upon an up-to-date water analysis and a knowledge of system design parameters. The ions contained in the feed water concentrate through the RO system, the point of maximum scale potential is the concentrate stream. Antiscalant type and dosage is therefore based upon the mineral analysis at this point.
It is important to find the optimization of antiscalant treatment with respect to type and dosage, identifying the proper antiscalant to use and the dosage-induction type relationship for the extended level of super saturation.

Lenntech can help you in the selection of the best antiscalant for your particular application.