Influence of the Scaling Inhibitor on the Phase Composition, Morphology, and Sedimentation Properties of CaCO 3 Deposits
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INFLUENCE OF THE SCALING INHIBITOR ON THE PHASE COMPOSITION, MORPHOLOGY, AND SEDIMENTATION PROPERTIES OF CaCO 3 DEPOSITS V. B. Obraztsov,1 E. D. Rubl’ova,2, 3 and О. S. Baskevych2
UDC 546.41'264: 544.77.023.523
We study the influence of OK-2 scaling inhibitor based on polyhexamethyleneguanidine hydrochloride on the morphology and phase composition of calcium carbonate. It is established that the presence of inhibitor in the solution leads to an increase in the sizes of crystals in the deposit and the predominance of needle structures in it. The aragonite and calcite phases are in excess in the deposits of calcium carbonate and the presence of inhibitor in the solution increases the amount of calcite by 21%. The revealed effects are caused by the adsorption of the inhibitor on carbonate deposits, which can be described by the Langmuir isotherm. The adsorption of the inhibitor leads to the recharging of the CaCO 3 surface and to the increase in the size of particles of the dispersed phase, which promotes its faster precipitation. Keywords: adsorption, calcium carbonate, morphology, sedimentation.
Calcium carbonate CaCO 3 , which can be in different polymorphic states, is the main component of scale formed on the heat exchange surfaces [1–4]. In the absence of inhibitors, at temperatures of 80–100°С, aragonite with small admixtures of calcite precipitates into the solid phase [5]., As compared with calcite, aragonite has is characterized by elevated adhesion to the solid surface and is not washed out with water. Therefore, it is adhered to heat exchange surfaces. The polyelectrolytes containing guanidine, carboxyl, or phosphonic groups prove to be promising inhibitors of scaling because they can form water-soluble complexes with calcium and magnesium ions and can be adsorbed on the surfaces of crystals [6]. A new ОК-2 inhibitor of complex action (modification No. 4 in the TU U 21854083.009-99 of 20.11.2013) based on polyhexamethyleneguanidine hydrochloride was proposed in [7]. It decreases scaling and corrosion rate and possesses high biocide properties. If the mass concentration of OK-2 is 20 mg/liter, then the degree of protection against scaling constitutes 50 ± 5%, which is not worse than for the ZnОЕDF commercial inhibitor. In this case, calcium and magnesium ions partly precipitate in the form of carbonate deposits. However, the influence of the ОК-2 inhibitor on the crystallization of calcium carbonate has not been studied in the literature. Due to the intense adsorption, this inhibitor is incorporated in the deposit and then washed out. Thus, a part of the inhibitor is deposited on the surface of the equipment and another part precipitate together with the deposits and affects the sedimentation properties [8]. Clearly, if the structure of the deposit changes under the influence of inhibitors, then this can lead to a decrease in scaling on the heat exchange surfaces because the deposits formed in this case can be easily washed out by the water flow. The aim of the present work is to study the sedimentation pro
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