Characterization of natural scale deposits formed in southern Algeria groundwater. Effect of its major ions on calcium carbonate precipitation

The structure and morphology of natural scale deposits formed in Ouargla's pipelines, southern Algeria, were characterized by using ICP-AES, X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS). The precipitate is mainly composed of CaCO3 with the prevalence of the aragonite phase. Groundwater of this region was also analyzed. The principal ions identified are Ca2+, Mg2+, Na+, K+, Cl− and SO42−. The influence of these species on scaling was studied by chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) to monitor the CaCO3 precipitation on gold electrodes in calcocarbonically pure water (CCP). The structure and morphology of electrochemically synthesized scale deposits were analyzed by the same techniques used for the natural one. The effect of different cations and the cross effect of Mg2+ and SO42− were highlighted. At 10−1 mol L−1 SO42− inhibits strongly the scale deposition independently of the counter ion nature. At 10−2 mol L−1 SO42− inhibits also totally the scale deposition but only in the presence of Mg2+. At the same concentration but associated to Na+ or K+ counter ions, SO42− does not prevent scaling. These results emphasize the cross inhibition effect of Mg2+ and SO42− and are significant in regard to Algerian groundwater composition.