Abstract
Low solubility of SiO2 and its occurrence in geothermal waters in the form of ionic, colloidal and suspended state are the main cause of the solid deposit occurrence. Certain chemical types of silica, under the influence of Fe2+, Al3+, F?, OH- ions and other micro-constituents, and due to significantly decreased solubility of SiO2, stimulate nucleation, particle growth and solid deposit formation. The aim of this paper is to inhibit the process of nucleation and solid deposit formation by adding originally designed inhibitor in the form of an emulsion, when the total concentration of the present and added colloidal SiO2 is beyond the solubility limit (120 mg/dm3). By turbidimetric, SEM, EDS and XRD analysis, the processes of solid deposit formation were investigated in Vranjska Banja (Serbia) spa geothermal water source (water hardness of 4?dH), and theoretical and practical conclusions were made.
Highlights
THE EFFECTS OF COLLOIDAL SIO2 AND INHIBITOR ON THE SOLID DEPOSIT FORMATION IN GEOTHERMAL WATER OF LOW HARDNESS
Not enough attention has been paid to the impact of low SiO2 solubility on solid deposit formations, it has been observed [5,6] that this phenomenon in boiler systems occurs due to the presence of dissolved colloidal and suspended solid particles of SiO2 and their interaction with Fe2+ and Al3+
This is attributed to the Si(OH)4 monomer that is rather inert at lower pH values and to the catalytic effects of OH– at higher pH values
Summary
THE EFFECTS OF COLLOIDAL SIO2 AND INHIBITOR ON THE SOLID DEPOSIT FORMATION IN GEOTHERMAL WATER OF LOW HARDNESS. Due to the dominant presence of calcium and magnesium in many hyperthermal geothermal waters, the impact of colloidal silicon(IV) oxide and its other forms on solid deposit formation process was neglected. The composition of colloidal particles is defined by the depends on the pH values [7]: free silicic acid is present at pH < 8, while in the pH range between 8 and 11 free silicic acid and HSiO3– are in equilibrium. This is attributed to the Si(OH) monomer that is rather inert at lower pH values and to the catalytic effects of OH– at higher pH values. When the Si(OH) monomer is in equilibrium with colloidal SiO2 particles at pH 7–8, they have a negative electric charge
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