Effect of tartaric acid (C₄H₆O₆) and temperatures on induction time and variation of crystal phases of CaCO₃ in a piping system

Calcium carbonate scale formation is a serious problem found in pipes of many industrial processes, such as chemical, desalination and oil industries. The presence of scale makes the narrowing of the diameter of pipes and reduction of heat transfer performance. This paper presents result of crystallization behavior of CaCO₃ in pipes. The crystals forming solutions were made by mixing of equimolar solution to CaCl₂ and Na₂CO₃ with Ca²⁺ concentration of 3,000 ppm. The parameters studied were the solution flow rates (25, 35, 50 mL/min), temperatures (27, 35, 50°C) and tartaric acid as additives (0.00, 1.00, 10.00 ppm) for the scaling inhibition. The CaCO₃ scales formation process was monitored by measuring the change in the solution conductivity. The scale obtained was then characterized by SEM/EDS for morphology and elemental analysis, and XRD for phase composition. It was observed that the conductivity of the solution remained constant after a certain period, and subsequently it dropped sharply. This induction time obtained was varied from 28 min to 46 min depending on the parameters studied. The higher flow rates and temperatures in the solution resulted in more CaCO₃ scale mass precipitated, indicating that these two parameters may promote CaCO₃ crystallisation. However, the higher tartaric acid concentrations in the solution lead to less mass of the scale produced and could reduce the mass down to 90%. It can be postulated that the tartaric acid may be an effective additive for CaCO₃ crystallization. SEM and EDS analysis of the scale indicated that the scale was composed of calcium carbonate. In addition, XRD characterization of the scale confirmed that the scale consisted of vaterite, aragonite and calcite minerals. The scale of aragonite mineral was precipitated under the influence of tartaric acid and temperatures. This indicates that the acid could delay the transformation into stable phase of calcite.