Insoluble Salt Formation with Calcium Ions

Boiler Water Treatment

• Properly managed water treatment is crucial to produce quality steam, control steam purity, deposits, and corrosion.
• Boiler performance, efficiency, and service life depend on selecting and controlling feed water used in the boiler.
• Most components in feed water are soluble, but they can precipitate out as particulate solids, crystallized forms, and amorphous particles under heat and pressure.
• Boiler water must be free of deposits to allow rapid and efficient heat transfer and must not be corrosive to the boiler metal.

Hardness Salts

• Hardness salts, such as calcium and magnesium salts, are the most important chemicals in water that influence deposit formation in boilers.
• Calcium and magnesium bicarbonate dissolve in water to form an alkaline solution, known as alkaline hardness.

Water Properties

• Pure water (H2O) is colorless, odorless, and tasteless, composed of hydrogen and oxygen.
• Water can dissolve almost every naturally occurring substance on earth, earning it the term "universal solvent."
• This property makes water beneficial but also poses a major threat to industrial equipment.

Mineral Scale

• A mineral scale is a deposit of certain sparingly soluble salts, such as calcium carbonates, calcium phosphates, and calcium sulfate, from process fluids after precipitation onto tubing and process surfaces.
• Deposits include various foulants, such as corrosion products, microbiological, colloidal, or suspended matter.

Temperature and Turbidity

• Temperature determines the rate at which scale-forming salts precipitate on heat exchanger or reverse osmosis membrane surfaces, making them a major fouling problem.
• Turbidity in water is due to suspended solids dispersed throughout the water, which scatter light and must be removed through filtration.

Water Chemistry

• Aluminum-based compounds are used as coagulant aids to clarify industrial and municipal waters.
• Barium forms insoluble salts with soluble sulfate ions and fluoride ions.
• Calcium forms insoluble salts with various anions, including carbonate, fluoride, oxalate, phosphate, and polyphosphate.
• Copper is found in some natural waters and can corrode copper or copper-based alloy pipes.
• Chromium compounds are relatively water-insoluble, with trivalent chromium mainly discharged by the metal industry and hexavalent chromium in industrial wastewater.
• Iron-based compounds cause serious problems in industrial water systems, with iron(II) or ferrous ions being very soluble at low pH values.
• Magnesium forms sparingly soluble salts, such as magnesium silicate and magnesium hydroxide.
• Manganese is usually present below 0.5 mg/L in public and private water supplies.
• Sodium ions form relatively soluble salts with most ions, including bicarbonates, carbonates, sulfates, and chlorides.

Scale Deposition

• Calcium carbonate scale deposits are encountered in various industrial processes and equipment.
• Metal sulfate scale deposits, including gypsum, anhydrite, barite, and celestite, are commonly encountered in oil field operations.
• Calcium-containing minerals are the most abundant due to their relatively low solubility with ions such as oxalate, sulfates, phosphates, and carbonates.
• The precipitation of calcium sulfate onto equipment walls is a serious problem in many industrial processes.

Learn about the conditions under which calcium ions form insoluble salts with acrylic and maleic acid-based polymers used in industrial water systems. Understand the presence of copper and chromium in natural waters and their implications in recirculating water systems.