Antiscalant-Driven Inhibition and Stabilization of “Magnesium Silicate” under Geothermal Stresses: The Role of Magnesium–Phosphonate Coordination Chemistry

The formation, precipitation, and deposition of so-called “magnesium silicate” in geothermal waters have been subjects of intense interest. Such scaling poses a severe threat to the smooth process of industrial systems. The aim of our approach is the systematic study of the influence of phosphonate-based chemical additives on silica polycondensation chemistry in the presence of magnesium ions. The focus of this work is the prevention of “magnesium silicate” formation using a variety of well-known phosphonate additives. These are 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), hydroxyethylidene-1,1-diphosphonic acid (HEDP), aminotris(methylenephosphonic acid) (AMP), hexamethylenediaminetetrakis(methylenephosphonic acid) (HDTMP), and bishexamethylenetriaminepentakis(methylenephosphonic acid) (BHMTPAMP). Inhibition experiments were carried out in supersaturated solutions of silicate (200 ppm, expressed as SiO2) and magnesium (200 ppm, as Mg) at pH 10.0. The phosphonate additives used were found to act as ...