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PROCESS DESCRIPTION - CONTINUED
(C) FACTORS AFFECTING CaCO3 DISSOLUTION
RATE IN A LIMESTONE CONTACTOR
Dissolution of limestone increases pH, alkalinity and dissolved
inorganic carbon (DIC) of water and depletes the amount of limestone
in a bed (Haddad, 1986). As the amount of limestone lessens over
time, the bed depth and contact time will also be reduced. In
a poorly designed contactor, dissolution takes less time for the
limestone to reach the recharge level and it needs to be refilled
more frequently. This will not only affect the contactor performance
but also the operating cost. Therefore, it is important to know
the factors affecting dissolution rate of limestone before designing
a contactor in order to ensure its long-term performance. Generally,
the dissolution rate of limestone is affected by the physical
and chemical properties of water and limestone as discussed below.
1. Physical and Chemical Properties of Water:
1.1. Extent of CaCO3 undersaturation:
Water can dissolve limestone only if it is undersaturated with
respect to CaCO3. Higher dissolution
rates occur with waters that are more undersaturated (Van Tonder
et. al., 1997; Striebel et. al., 2002).
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