Amorphous silica, geothermal scaling

Geothermal aquifer waters are close to saturation with some scale-forming minerals (calcite, pyrite) but undersaturated with others (amorphous silica, amorphous metallic sulphides). Only the slightest degassing suffices to produce calcite oversaturated water. By contrast, extensive cooling may be required to produce amorphous-silica oversaturation. As solubility constants are... 

Deposition of amorphous silica (silica scale) onto working surfaces in geothermal power plants (Gunnarson and Arnorsson, 2003) and water desalinization plants (Weng, 1995) reduces rates of heat and mass transfer thereby reducing the efficiency of these enterprises. Silica seating occurs when solutions become supersaturated with respect to amorphotis silica because of cooling, evaporation of water, or a chemical reaction. The reaction between two monomers joins two Si atoms and eliminates a water molecule. 

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