chapter  21
22 Pages

2Chapter 1 Analytical Techniques for Identifying Mineral Scales and Deposits

In many industrial processes, the feed water used contains mixtures of dissolved ions that are unstable with respect to precipitation. Various factors such as pH, temperature, the type and concentration of dissolved ions, ow velocity, equipment metallurgy, and so on 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 de ned 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 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,

21.1 Introduction ......................................................................................................................... 425 21.2 Analytical Techniques for Identifying Mineral Scales and Deposits .................................. 426

21.2.1 Optical Microscopy .............................................................................................. 427 21.2.2 Scanning Electron Microscopy ............................................................................. 428 21.2.3 Energy Dispersive X-Ray Spectrometry Analysis ................................................ 430 21.2.4 Wide Angle X-Ray Diffraction ............................................................................. 432

21.3 Particle Size Analysis .......................................................................................................... 435 21.4 Other Analytical Techniques ............................................................................................... 435 21.5 Infrared Spectroscopy ......................................................................................................... 436

21.5.1 Transmission Spectroscopy .................................................................................. 437 21.5.2 ATR-IR Spectroscopy ........................................................................................... 439

21.6 Applications to Water-Treatment Problems ........................................................................ 441 21.6.1 Metal-Inhibitor Salt Formation ............................................................................. 441 21.6.2 Cationic Polymer-Anionic Polymer Coacervate Formation .................................442 21.6.3 Thermal Treatment of Deposit Control Polymers................................................. 443

21.7 Summary .............................................................................................................................445 References ......................................................................................................................................445