In the present work two synthetic co-polymers, U-PVPyPEGMA-H and Q-PVPyPEGMA-H, with pyridine and polyethylene glycol grafts on a methacrylate backbone, were studied for their potential to influence silicic acid polycondensation in vitro in silicate-supersaturated (500 ppm, 8.3 mM) aqueous solutions. The aim of this study was to evaluate the impact of several experimental parameters on the silicic acid polycondencation process. Working pH plays a significant role on the silicification reaction either in the absence or presence of polymers. In the presence of polymers, pH affects the protonation state of the pyridine N atom, transforming U-PVPyPEGMA, for example, from a silica formation catalyst (at pH=5.0) to a silicic acid stabilizer (at pH = 7.0). Furthermore, the state of N atom on the pyridine ring (non-protonated, protonated, quaternized) strongly affects the silicic acid autocondensation process. Based on our results, a "free" (non-protonated) pyridine ring induces silica inhibition, whereas protonation or quaternization enhances silica formation. Another parameter that was studied was the concentration of the polymers. As the concentration is increased, enhances the silicic acid stabilization activity or the catalytic activity of the polymers. Polymer MW was found to have no major effect on polymer activity either as stabilizers or catalysts.
Silicon is an important element of our Planet's crust, which is transferred into water streams through dissolution.1 Hence, it is usually found as water-soluble silicate or colloidal silica in natural surface waters (sea, rivers, lakes), or underground waters. When such water is used for industrial purposes (eg. industrial cooling), silicate can enter the operating system and can pose a threat to its proper operation. The main reason is the solubility of amorphous silica, a product of the silicate polycondensation process.2
The solubility of amorphous silica is the main limitation for proper operation of water-dominated production processes. In several areas in the world, the make-up water utilized for industrial applications contains high silica concentrations (50 - 100 parts per million, ppm, commonly expressed as silicon dioxide, SiO2). Water-soluble silica results from quartz (crystalline SiO2) dissolution from rock formations into the groundwater, which then is used as make-up water. The risk for formation and deposition of silica scale puts forth serious challenges that pose severe limitations to proper operation of water systems. Water systems operating personnel in power plants, evaporative cooling systems, semiconductor manufacturing, boiler and geothermal systems have to monitor water silica levels (both soluble and colloidal) very carefully on a daily basis. Silica precipitation/deposition frequently is encountered in evaporative cooling systems, where salt concentrations increase through partial evaporation of the cooling water. Silica solubility in water generally is 150 ppm to 180 ppm, depending on water chemistry and temperature. This imposes severe limits on water users, leading either to operation at very low cycles of concentration and consuming enormous amounts of water, or to use of chemical water treatment techniques that prevent silica-scale formation and deposition. Silica and/or silicate deposits are particularly difficult to remove once they form. Potentially hazardous chemical cleaning (based on hydrofluoric acid) or laborious mechanical cleaning usually is required.3
