Mineral scales and deposits: An overview

Abstract

Pure water (H2O) is colorless, odorless, and tasteless. It is composed of hydrogen and oxygen. Because water becomes contaminated by the substances with which it comes into contact, it is not available for use in its pure state. To some degree, water can dissolve every naturally occurring substance on the earth. Because of this property, water has been termed as the “universal solvent.” Although beneficial to mankind, the solvency power of water can pose a major threat to industrial equipments. In virtually all domestic and industrial processes in which untreated water is heated, the fouling of equipment is the single-most serious problem encountered. The affected application areas include laundry, dairy, dishwashing, cooling, boilers, geothermal, power generation, semiconductor manufacturing, and many other production processes [1]. A significant operating cost factor of a reverse osmosis (RO) system is the membranes themselves, a factor often increased unnecessarily through fouling by deposits of unwanted materials on RO membrane surfaces [2]. A mineral scale is defined as a deposit of certain sparingly soluble salts, such as calcium carbonates, calcium phosphates, and calcium sulfates, from the process fluids after precipitation onto the tubing and other process surfaces. A deposit generally includes various foulants, i.e., corrosion products and microbiological, colloidal, or suspended matter. The fouling of heat exchangers and RO membranes is a complex phenomenon involving the deposition of several different, but related types of foulants. This chapter addresses the quality of feed water available for industrial applications and the impact of water chemistry on system performance. In addition, the causes and types of various mineral scales and deposits commonly encountered in industrial water systems are reviewed.