chapter  21
Microscopy and X-Ray-Based Analytical Techniques for Identifying Mineral Scales and Deposits
Pages 20

In many industrial processes, the feedwater used contains mixtures of dissolved ions that are unstable with respect to precipitation. Various factors such as pH, temperature, type and concentration of dissolved ions, ow velocity, and equipment metallurgy contribute to the precipitation and deposition of sparingly soluble salts on equipment surfaces. The class of crystalline and amorphous compounds formed in industrial water systems generically known as scale and deposits has a widespread importance across a variety of disciplines, as can be seen from other chapters in this book and from other books [1-3]. Scale is dened as the deposit of certain sparingly soluble salts such as calcium carbonate, calcium phosphate, calcium oxalate, magnesium hydroxide, and calcium sulfate, from the process uids after precipitation onto the tubing and other process surfaces. The commonly encountered deposits

21.1 Introduction .................................................................................................. 387 21.2 Analytical Techniques for Identifying Mineral Scales and Deposits ........... 388

21.2.1 Optical Microscopy .......................................................................... 389 21.2.2 Scanning Electron Microscopy ........................................................ 391 21.2.3 Energy Dispersive X-Ray Spectrometry Analysis ............................ 395 21.2.4 Wide-Angle X-Ray Diffraction ........................................................ 398

21.3 Particle Size Analysis ...................................................................................403 21.4 Other Analytical Techniques ........................................................................404 21.5 Summary ......................................................................................................404 References ..............................................................................................................405

in industrial water systems include carbonates, sulfates, and phosphates of alkaline earth metals, silica, magnesium silicate, corrosion products, microbiological mass, and suspended matter. These deposits, especially on heat transfer surfaces in thermal distillation, cooling, and boiler systems, lead to overheating, loss of system ef- ciency, unscheduled shutdown, and untimely heat exchanger failure. In desalination by reverse osmosis (RO) process, deposition of unwanted precipitates may result in poor water quality and premature membrane failures. Deposition of scale in some cases may be benecial as in the case of drinking water transmission lines wherein the layer of scale deposit protects the piping from corrosion by isolating it from the water. However, in most cases, scale is undesirable as it adversely affects the overall efciency of the process.