The Calculation of the Universal Index of Water Saturation with Calcium Carbonate

    The article presents a method for calculating the pH value, which corresponds to the saturation of water by calcium carbonate and compares this pH value with the pH value obtained by calculating with Langelier saturation index and Stiff & Davis index.

    Corrosion and scale formation are the main problems in the usage of equipment and pipelines of water supply and water treatment systems. The separation of the solid phase of calcium carbonate from water is a serious problem, but in the absence of conditions for the release of calcium carbonate, conditions for corrosion processes develop. Corrosion in most cases is a more serious problem than scale, because corrosion will eventually require replacement of the equipment and pipelines.

    In the physical sense, the following processes occur in water. If the water tends to release the solid phase of calcium carbonate, it means that the concentration of calcium ions [Са2+] and carbonate [СО32- ] in water is higher than the value of the solubility product for calcium carbonate [KspСаСО3]. Obviously, these conditions imply the absence of free carbon dioxide in the water. If free carbonic acid is present, the water will tend to dissolve the solid calcium carbonate rather than release it. Accordingly, when calcium carbonate is released from the water, the condition for corrosion with a hydrogen depolarizer will be absent, since all the dissolved carbon dioxide provides an equilibrium state of existence of dissolved calcium carbonate. All carbon dioxide is “bound”. In this case, corrosion with oxygen depolarization is possible, but the precipitation of calcium carbonate significantly inhibits the corrosion process on the anode section of the galvanic couple and, accordingly, the entire speed of the corrosion process is significantly reduced.

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Taxonomy

• Scale & Corrosion
• Water Quality
• Water Supply
• Chemistry