AWWA WQTC60664

Trace concentrations of metal ion impurities, such as Fe²⁺, Fe³⁺ and Mg²⁺, which are commonlyencountered in water, can retard significantly the precipitation of CaCO₃. In view of the paucity of viabletechniques for overcoming scale deposition difficulties, it is important to examine optionsfor CaCO₃ scale control by trace amounts of inhibiting metal ions. The literature cites Zn ²⁺ ions as beingparticularly effective in suppressing CaCO₃ scale deposition.This paper reviews phenomena induced by the presence of ion impurities. Literature data relating to theretardation of CaCO₃ nucleation and crystal growth processes by adsorption of impurities on crystalgrowth sites are analyzed and correlated. The effect of the presence of Zn²⁺ ions on CaCO₃ 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 Zn²⁺ ion, added to the water either by dosing a Zn²⁺ solution or by the release of Zn²⁺ ions throughcontact with a redox Zn-Cu alloy medium such as a granular bed of KDF-55®. Includes references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/15/2004

Number of Pages:

20

File Size:

1 file , 1 MB