Fouling of equipment surfaces by siliceous materials in industrial water systems is a problem associated with high silica laden waters. The complexity of siliceous deposits formation stems from the limited solubility of amorphous silica and metal silicates. Once formed, these deposits are difficult to remove and often requires the use of chemical and/or mechanical approaches. This paper presents mechanisms of siliceous deposits formation and reviews various approaches attempted to control these deposits in industrial systems. Comparative performance data on a variety of polymeric, nonpolymeric, and formulated products as siliceous deposit control agents are presented. Additionally, information on morphology of various siliceous deposits formed is discussed.
Fouling of equipment surfaces by siliceous salts such as silica, metal silicates, coprecipitated silica with mineral salts such as calcium carbonate, calcium sulfate, etc., is a serious challenge facing the technologists in the efficient operation of industrial systems. Severe fouling at times results in premature expensive equipment replacement, early shutdown, increase in operating pressure of pumps, and enhance the probability of corrosion damage. In many cases, the removal of foulants leads to discontinuous operation of the system, resulting in higher operating costs. In geothermal applications, siliceous scale typically occurs when brine is cooled in the course of brine handling and energy extraction. Factors contributing to siliceous scale formation include variable fluid composition, fluctuating plant operating conditions, and the complex nature of silica formation.1 Siliceous scale is tenuous and once formed it is particularly difficult to remove, and in some cases fouled equipment must be removed.1 Both chemical and mechanical methods are used to remove siliceous scale. However, strong chemical cleaners (e.g., ammonium bifluoride, hydrofluoric acid) pose serious environmental challenges and require care to avoid damaging equipment whereas mechanical cleaning is labor intensive.1 In brackish water reverse osmosis systems (RO) membrane surfaces and spacers are particularly susceptible to fouling by siliceous deposits, easily coagulated by small amounts of cations such as Ca, Mg, Fe, and Al.2 The deposition of siliceous materials in RO systems cause reduced permeate production rates resulting in pressure increase, poor permeate quality, and more frequent membrane cleaning. In evaporative cooling water systems, water technologists must maintain silica at acceptable level (usually <180 mg/L in the absence of antiscalant) to avoid the formation of siliceous scale. The difficulties in using high silica water in cooling systems or in geothermal applications are further aggravated by the presence of iron and phosphate.3
