Page 149 - Soil Degradation, Conservation and Remediation

138 5 Chemical Soil Degradation

Table 5.6 Calcium carbonate equivalence of common liming materials
Liming material Composition CCE
Calcitic limestone CaCO 3 100
Dolomitic limestone CaMg(CO 3) 2 109
Calcium oxide CaO 179
Calcium hydroxide or Magnesium hydroxide Ca(OH) 2 136
Slag CaSiO 3 80
Source: http://learningstore.uwex.edu/assets/pdfs/a3671.pdf

5.3.3.2 Quality of Lime

The quality of liming materials is determined by (1) the chemical composition or
purity and (2) the particle size or fineness.

Chemical Composition
Acid-neutralizing capacity of a liming material is determined by its calcium car-
bonate equivalence (CCE). It is the acid-neutralizing capacity of the material
compared to pure calcium carbonate. In CCE comparisons, pure calcium carbonate
has been assigned a value of 100. CCE values of some common liming materials are
given in Table 5.6.
Dolomite has a slightly greater CCE than calcium carbonate due to the lower atomic
weight of Mg compared to Ca. Oxide materials have the highest CCE values since
CO 2 is removed in the burning process. Marl and byproduct materials have low CCE
values because of the presence of impurities.

Fineness

The neutralizing capacity of a liming material is determined by its particle size.
100 % of lime particles that pass a 100-mesh sieve will react within the first
year while only 60 % of the liming materials that pass a 20-mesh sieve (but held on
100- mesh sieve) will react within a year of application. Materials that do not pass
the 20-mesh sieve will not react within 1 year after application. So, for practical
purpose, neutralizing power of a liming material needs adjustment for the fineness
of the material. To determine the fineness factor of a liming material of which
70 % passes a 100-mesh sieve and 97 % passes a 20-mesh sieve, the following
calculations need to be done:

(a) To subtract the percentage passing a 100-mesh sieve from the percentage passing
a 20-mesh sieve and multiply this difference with 0.60
(b) To add the percentage passing the 100-mesh sieve and divide the sum by 100

Thus, the fineness of a material of which 70 % passes a 100-mesh sieve and 97 %
passes a 20-mesh sieve is {(97−70) × 0.60 + 70}/100 = 0.86.