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| Titel |
An integrated study of limestone behavior during calcination and hydration processes |
| VerfasserIn |
George Leontakianakos, Ioannis Baziotis, George Kiousis, Dimitrios Giavis, Stamatios Tsimas |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043302
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| Zusammenfassung |
| One of the most important processes in industrial scale, represents the dissociation of
carbonates to lime and CO2. This process, called calcination, occur at relative high
temperatures (>9000C). Lime rapidly reacts with the water, liberating high amounts of heat
producing Ca(OH)2.
For the purpose of the present study five samples of different limestones from different
quarries from Greece were collected. The aim of the study was to analyze the behavior of
the limestones during calcination and test the hydraulic properties of the quick
lime.
Limestone particles (1.6-2 cm) were reacted in a pre-heated oven at three different
temperatures (900, 1050 and 1200oC) for 30 min in order to produce quick lime.
Petrographic features of studied limestones were done using secondary electron
microscopy (SEM). X-ray diffractometry and Raman micro-spectroscopy were
applied in order to identify the carbonate phases (calcite and dolomite) in the studied
limestones. Chemical composition of limestones and limes were determined by
Atomic absorption spectroscopy (AAS) method. 25 gr of the produced lime were
hydrated by adding 100 ml distilled water having a room temperature (~250C) to
produce Ca(OH)2 through the exothermic reaction CaO(s) + H2O(l)-Ca(OH)2(aq).
We measured the temperature difference in the water until a maximum value is
reached; this value represents the reactivity of the produced slaked lime. Chemical
composition and reactivity estimation were done following European Standards
EN-459-2.
The reactivity of quick lime depends on various factors with the most important being
the internal structure of the limestone, calcination temperature/duration applied to
the limestone, the admixtures such as the MgO content, hard-burned phenomena
etc.
The treatment of the experimental results suggests the following:
i) The (CaO+MgO)Lime value have similar variation for both samples calcined at
temperatures of 1050oC (58-90 wt%) and 1200oC (57-94 wt%); whereas the samples
calcined at 900oC share a small (CaO+MgO)Lime value (5-17wt%).
ii) The limestones calcined at 9000C have the lowest reactivity values in oppose to the
samples calcined at 10500C which show the highest reactivity. The temperature rise of the
limestone samples calcined at 12000C was lower than that of the 10500C.
iii) At constant reactivity rate the water required to complete hydration is lower; for
example, the quick lime calcined at temperature of 10500C needs much less water for
hydration relative to the equivalent samples at 12000C.
A thorough interpretation of our results suggest that the low reactivity values for the
samples calcined at 9000C could be due to the low calcination temperature or the
calcination time of 30 min was too short to produce enough lime. The differences
in hydraulic behavior of the samples calcined at higher temperatures of 12000C
probably indicates that the structure of quick lime becomes more dense and compact
and the grains recrystallized tending to become larger, leading to reduction of the
existing pore space. Consequently, the hydration process cannot entirely proceed
into the interior mass of the quick lime requiring more time to be accomplished. |
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