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Trace concentrations of metal ion impurities, such as Fesup2+/sup, Fesup3+/sup and Mgsup2+/sup, which are commonlyencountered in water, can retard significantly the precipitation of CaCOsub3/sub. In view of the paucity of viabletechniques for overcoming scale deposition difficulties, it is important to examine optionsfor CaCOsub3/sub scale control by trace amounts of inhibiting metal ions. The literature cites Zn sup2+/sup ions as beingparticularly effective in suppressing CaCOsub3/sub scale deposition.This paper reviews phenomena induced by the presence of ion impurities. Literature data relating to theretardation of CaCOsub3/sub nucleation and crystal growth processes by adsorption of impurities on crystalgrowth sites are analyzed and correlated. The effect of the presence of Znsup2+/sup ions on CaCOsub3/sub scaledeposition from hard waters having a Langelier saturation index of 1.0 to 1.5 was measured in twoexperimental heating systems. A marked scale suppression effect was obtained with as little as 1 to 1.5PPM Znsup2+/sup ion, added to the water either by dosing a Znsup2+/sup solution or by the release of Znsup2+/sup ions throughcontact with a redox Zn-Cu alloy medium such as a granular bed of KDF-55. Includes references, tables, figures.

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Edition: Vol. - No. Published: 11/15/2004 Number of Pages: 20File Size: 1 file , 1 MB