Rainer Kündig, Christoph Bühler, Heinz Surbeck
Applied Mineralogy and Non-Metallic Resources
IGP/ETHZ HS 2012
651-4097-00
Limestone, Calcium Carbonate
(Modified from Kündig et. al, 1997: p 326.)
Limestone as mineral resource
Essentially, limestone consists of calcite with
minor additions of iron and magnesium
carbonate, silica, alumina, and other substances.
Reef limestone is often very pure as it lacks
clastic material; it can, however, contain high
amounts of dolomite. Well-bedded limestone
often contains clay minerals, a prerequisite for its
transition to marls, or silica, responsible for the
sought-after hard rock (siliceous limestone).
Pure limestone contains 90-95% CaO and is
commonly used as burnt lime or products derived
therefrom by the building industry. It yields wellhydrating white lime. Highly pure limestone
usually finds application in the chemical or iron
industry.
Calcareous marls (75-90% CaCO3) and
marls (40-75% CaCO3) are the key ingredients
of cements, hydraulic binding agents. The
composition of cements is highly variable can be
adapted to suite specific applications.
Dolomites are defined by a CaO:MgO ratio
smaller than 1.7; with increasing CaO content,
they pass into calcareous dolomite or dolomitic
limestone. Highly pure dolomites (CaO:MgO =
1.39-1.45) are used for the production of metallic
magnesium and magnesia cement, but also for
the fabrication of glass and the de-acidification of
water. Sintered, pure dolomite (CaO:MgO =
1.45-1.70) is used for the lining of cement kilns
and smelting furnaces.
The variety of lime, burnt lime, and lime
hydrate products has, in conjunction with a
myriad of applications, lead to considerable
inconsistencies in the nomenclature of raw
(unburned), burnt, and hydrated products. While
Kalk, the German equivalent for lime, is used for
both limestone and burnt lime, the English term
lime is, in a broad sense used for
any of a number of calcium compounds,
especially calcium hydroxide, used as an
additive to soil or water 1
and, in a more restricted sense for
a white caustic alkaline substance consisting of
calcium oxide, which is obtained by heating
limestone and which combines with water with
the production of much heat2.
Usage
Since antiquity, limestone, burnt lime, and
lime hydrate have been indispensable for
numerous uses; there seems to be no limit to the
number of applications of this basic substance.
The following branches of industry are
mentioned with decreasing economic importance:
iron and steel industry, chemical industry,
construction materials industry, building
industry, and agriculture.
The iron and steel industry uses lime in the
metallurgical process to obtain an alkaline slag,
which binds undesirable accompanying elements
such as silicon, aluminium, sulphur, and
phosphorous. Modern metallurgical processes so
1
2
The Oxford Dictionary, Oxford University Press, 2012.
ibid.
strongly rely on calcium oxide that their
operation without them is inconceivable.
The chemical industry offers a very wide
range for the application of lime products. Here,
lime products either are a component of the end
product, e.g., glass, calcium carbide, or calcium
cyanamide, or serve as auxiliary agent in the
production of other substances, e.g., sugar or
soda. Then, the purification of wastewaters from
industry and households, which is of vital
importance for environmental protection and
sustainability, is made possible by the
predominant application of lime as a precipitating
agent.
The construction material industry uses burnt
lime predominantly for the production of
calcareous sandstone and lime-bound aerated
concrete. These products have become the most
important building materials in many countries.
Limestone is also frequently used as aggregate
for artificial stones, terrazzo tiles, etc. Since time
immemorial, limestone has been the most
important raw material in the building industry; it
is needed to produce mortars, plasters, and paints.
Limestone is also used as gravel and filler for
road building, and as additive for cement. Burnt
lime or its hydrate further serves to stabilise
cohesive soils, mainly during construction of
simple paths or stabilisation of highly stressed
roads.
In agriculture, lime prevents the soil from
acidification and leads to a good tilth. Calcium
carbonate added to animal food promotes the
development of the skeleton.
Please note that raw (unburned), burnt, or
hydrated dolomite is just as important as the
calcareous products mentioned above, it simply
has not been mentioned separately as it is not
always possible to clearly delineate the two.
An entry into new markets was achieved by
micronized calcium carbonate in the mid 20th
century. As a consequence of the increasingly
refined production of synthetics, paint, and paper,
the demand for micronized calcium carbonate has
skyrocketed and globally active companies that
deal with these highly specialized products have
sprung up (e.g., Omya). As diverse the product
range is, as diverse are the requirements for
calcium carbonate as filler; the finest grit sizes
and only the purest of substances are used. Today
and especially in Europe, the filler trade
constitutes over 10% to the total lime turnover.
(Tegethoff, 2001: p. 166.)
References
Harben, P.W. 2002. The Industrial Minerals HandyBook: a
Guide to Markets, Specification & Prices. Industrial
Mineral Information, Surrey, United Kingdom, 4th
edition.
Kündig, R., Mumenthaler, T., Eckhardt, P., Keusen, H.R.,
Schindler, C., Hofmann, F., Vogler, R, Guntli, P. 1997.
Die
mineralischen
Rohstoffe
der
Schweiz.
Schweizerische Geotechnische Kommission, ETH
Zurich, Zurich.
(Harben, 2002: p. 83.)
Tegethoff, F.W. (Ed) 2001. Calcium Carbonate: from the
Cretaceous Period into the 21st century. Birkhäuser
Verlag, Basel, Switzerland.