ABSTRACT
Siliceous scales have deposited in geothermal and petroleum produced waters, desalination plants, and cooling water applications even though designs and operations were predicted not to be scale-forming. The major scaling problems that have arisen are due to the use of predictions based on the solubility of pure silica in pure water rather than in geochemical soup and the design and operation of systems using pure amorphous silica solubility data in pure water, while overlooking precipitation of metal-rich amorphous silica. Typically, one calculates the silica solubility index (SSI), which is the ratio of actual pure amorphous silica concentration in solution to the equilibrium solubility value at a given temperature and pressure, [Si(OH)4]a/ [Si(OH)4]eq, and then operates systems at SSIs ≤ 1 to avoid scaling.
