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LIST
OF CONTENTS
Introduction
Process Description
Typical
Contactor
Design
Criteria
Photos, Plans & Specs
Treatment
Performance
Operational
Skills
Automation
Potential
Advantages
Limitations
& Concerns
Pilot
Plant Objectives
Costs
References
Contacts & Facilities
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PROCESS DESCRIPTION - CONTINUED
L.I. is the difference between the actual pH and hypothetical
pH at equilibrium. Undersaturated water is represented by a negative
value of L.I. and tends to dissolve CaCO3
whereas oversaturated water is represented by a positive value
of L.I. and tends to precipitate CaCO3.
Other procedures that can be used to determine the state of saturation
of CaCO3 include evaluating the Calcium
Carbonate Dissolution Potential, Ryznar (Saturation) Index, general
saturation index also known as disequilibrium index and Larson's
Ratio (Schock, 1999b). Marble Test and the carbonate saturometer
device can also be used and both operate on the same principle
(Schock, 1999b).
If one assumes that the only aqueous species are H+,
OH-, calcium and carbonate species, then
reactions 1 to 7 
take place when unstabilized water dissolves limestone in a closed
system and reaches equilibrium. In reactions 1 to 7, activities
rather than concentrations are used in expressing the corresponding
equilibrium constants. This is due to increased electrostatic
interactions between ions as concentration of ions in solution
increases (Snoeyink and Jenkins, 1980). As a result, the activity
of ions becomes less than their measured or analytical concentration.
Several mass balances must also be met. Please click .
Calculations for real waters soon become more complicated because
of the presence of other species but the principles are the same.
Realistically, computer softwares such as AQUACHEM, MINEQL,
MINTEQ,
STASOFT or custom programs are used.
Both Letterman and Kothari (1995) and Schott (2003) have developed
programs specifically for solving dissolution of limestone in
contactors as discussed later. |
