Lime Kilns

June 08, 2005


Provided and copyright by: Rod Benson, Helena High School
Summary authors & editors: Rod Benson

This photo was taken just outside of Helena, Montana (on April 2, 2005) and shows the ruins of lime kilns that were active from the 1860s until 1910. The lime (calcium oxide; CaO) produced here was used to make mortar, needed to construct buildings of brick and stone in Helena during the late 1800s and early 1900s. Kilns were built at this location because of the availability of the limestone, which can be seen on the slope behind the kilns. Limestone is a sedimentary rock primarily made up of calcite (calcium carbonate; CaCO3). Workers blasted or quarried the limestone and then hauled or rolled the rocks down the slope, dumping them into the tops of the kilns. Pine fires in the furnace beneath the kilns burned constantly changing the calcite into lime.

When heated from 500 to 600 C:

CaCO3 (s) -----> CaO (s) + CO2 (g)

After several days, the powdered lime was shoveled into cooling sheds adjacent to the kilns. Once cooled, it was hauled to building sites around Helena, where it was mixed with sand and water to make mortar. Each kiln could produce about 20 tons of lime every eight hours.

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