2.2. Particle size:
According to Rickard and Sjoberg (1983), Erga and Terjesen found
that the rate of calcite dissolution is proportional to the
surface area per unit volume of media. Smaller media sizes have
a larger surface area exposed to the water, resulting in higher
dissolution rates compared to the larger media sizes (Cox, 1930;
Santoro et al., 1987; Maree et al. 1992; Du Plessis et al.,
1994; Menendez et al., 2000).
2.3. Presence of impurities:
Benjamin et al. (1992) recommended that the type of limestone
to be used in a contactor should be of high calcium limestone
with minimum impurities. Impurities in limestone include iron,
aluminum and silica. According to Letterman (1995), presence
of silica only reduced the effective surface area of limestone
but did not appear to cause a reduction in the dissolution rate
of the calcite surface. However, aluminum and iron content of
the stone reduced the overall dissolution rate. Haddad (1986)
also found that as limestone dissolved from the stone, the rate
of dissolution decreased because a residue layer consists of
insoluble impurities (such as silica, alumino-silicates and
aluminum and iron oxides/hydroxides) is formed and remains on
the surface. As the layer thickness increases, the rate of transport
of calcium ion from CaCO3 surface to
the bulk solution decreases (Letterman, 1995).
