What are the types of antiscalants?

A large number of types of antiscalants are chemicals that can be used as antiscalants or as dispersants to improve the operation of reverse osmosis and nanofiltration (NF) systems. Antiscalants are a family of chemicals designed to inhibit the formation and precipitation of crystallized mineral salts that form scale. Most antiscalants are proprietary organic man-made polymers (e.g., polyacrylic acids, carboxylic acids, polymaleic acids, organophosphates, polyphosphates, phosphonates, anionic polymers, etc.). The molecular weight of these polymers can range from 2000 to 10,000 Da.

The reason for the multiple types of antiscalants

Antiscalant technology for RO systems was initially derived from chemistries used in cooling water and boiler water applications. It should be duly noted that the large number of different antiscalant chemistries that have evolved have produced a wide variety of results and efficacy depending on the application and organic polymer used. However, they have to be used with caution.

First: Antiscalants made of polyacrylic acid

They are susceptible to the formation of a foulant that settles on the membrane surface if there are high levels of iron. This foulant will increase feed pressure requirements but typically can be cleaned using a low pH cleaning.

Second: Antiscalants are anionic in nature (e.g., polyacrylic acids)

When a cationic-based coagulant or filtering aid is used in the pretreatment, a very viscous, sticky foulant can be produced that will increase feed pressure requirements, and it can be very difficult to clean off.

An antiscalant that was popular in the early days of RO was sodium hexametaphosphate (SHMP), but its use has been greatly reduced with the advent of proprietary antiscalants because of a number of limitations.

The most common mineral scalants of concern are:

• Calcium carbonate (CaCO3)
• Calcium sulfate (CaSO4)
• Strontium sulfate (SrSO4)
• Barium sulfate (BaSO4)

Less common mineral scalants are:

• Calcium phosphate [Ca3(PO4)2]
• Calcium fluoride (CaF2)

Dispersants

Dispersants are a family of organic man-made polymers designed to inhibit the agglomeration and deposition of foulants onto the membrane surface. T are sometimes referred to as antifoulants. Foulants tend to be a softer, noncrystalline deposit. Dispersant chemicals frequently have antiscalant properties. The efficacy of differing dispersants can vary for different foulants, so one needs to know what foulant they are treating with.

Foulants treated by dispersants are as follows:

• Mineral scales
• Metal oxides
• Hydroxides (iron, manganese, and aluminum), polymerized silica, colloidal material (defined as very small particles that stay in an infinite suspension and can be composed of clay, iron, aluminum, silica, sulfur, and/or OM)
• Biological matter

Maintaining proper dosing levels of an antiscalant/dispersant is important. Underdosing can cause scaling or fouling. Overdosing can cause a deposition of the antiscalant/dispersant onto the membrane, creating a fouling problem.

The most important types of antiscalants

Due to their widespread use and proven effectiveness in many applications. The following types are among the most important and common types of antiscalants:

Antiscalant Solution BR4000

Highly effective liquid antiscalant specially formulated for brackish water and highly brackish water RO system TDS max 20000ppm.

Antiscalant Solution BR7000 Plus

Highly effective liquid antiscalant specially formulated for sea and brackish water RO system TDS to avoid carbonate, silicate, and sulfate scale formation.

Antiscalant Solution BR 7700

A highly effective scale inhibitor intended for desalination plants that operate on river and sea salts that contain high levels of sulfates and ionized silica.

If you’re still confused about which type of antiscalant is right for your application, our Carewater experts are happy to help you decide.