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A B S T R A C TThis work investigated the inhibitive effect of citric acid (CA), sodium citrate (SC), and their mixture (CA-SC) on the CaCO 3 scale. The study was carried out using chronoamperometry, impedancemetry, and fast-controlled precipitation methods. The electrochemical study showed that CA provides a slight inhibition of CaCO 3 deposit at a concentration of 70 ppm on stainless steel surface. The use of SC alone inhibits very little the formation of scale. The use of the mixture (50% of CA and 50% of SC) with small concentration led to significant inhibition of the CaCO 3 formation. The deposits formed were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). The XRD showed that the intensity of the preferential orientation (1 0 4) corresponding to crystallographic plans of calcite decreases and the SEM demonstrated a decrease in calcite crystal size from 10 to about 2 μm.

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The formation of calcium carbonate CaCO3 in water has some important implications in geoscience researches, ocean chemistry studies, CO2 emission issues and biology. In industry, the scaling phenomenon may cause technical problems, such as reduction in heat transfer efficiency in cooling systems and obstruction of pipes. This paper focuses on the study of the glutamic acid (GA) for reducing CaCO3 scale formation on metallic surfaces in the water of Bir Aissa region. The anti-scaling properties of glutamic acid (GA), used as a complexing agent of Ca(2+) ions, have been evaluated by the chronoamperometry and electrochemical impedance spectroscopy methods in conjunction with a microscopic examination. Chemical and electrochemical study of this water shows a high calcium concentration. The characterization using X-ray diffraction reveals that while the CaCO3 scale formed chemically is a mixture of calcite, aragonite and vaterite, the one deposited electrochemically is a pure calcite. The effect of temperature on the efficiency of the inhibitor was investigated. At 30 and 40°C, a complete scaling inhibition was obtained at a GA concentration of 18 mg/L with 90.2% efficiency rate. However, the efficiency of GA decreased at 50 and 60°C.

The formation of CaCO 3 of groundwater has important implications in the industry. Many conventional scale inhibitors are considered environmentally unfriendly. In this study, we investigate the effect of aqueous extract of Paronychia arabica (PA) as new green antiscalant agents on the precipitation of CaCO 3 in an arid desert region. The antiscaling properties of these extracts towards CaCO3 formation were tested using chronoamperometry (CA), electrochemical impedance spectroscopy (EIS) and Fast Controlled Precipitation methods. Electrochemical and chemical analysis of Mkhadma groundwater shows a high calcium concentration and the deposit is a pure calcite. The nucleation and formation time were identified. At 32°C, a complete scaling inhibition was obtained using a concentration of 150 mg/L of green extract. The scale inhibitor effect was analysed by an optical microscopic examination.

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