Technical Marvel

Hologram of Rotary Kiln on your phone

1. Fold the pyramid. If needed, follow these instructions.
2. Attach the hologram pyramid on your smart phone.
3. Play the video in full screen. Enjoy!

Crafted with precision by the renowned Italian factory Saima of Milan under the license of Gordon I. Gould from San Francisco, these kilns marked a turning point in the global mercury extraction industry. The three kilns were inaugurated in 1961, 1964 and 1968.

With the rotary kilns innovation and excellence converged to reclaim Idrija Mercury Mine’s leading position in the worldwide mercury extraction technology.

Photo: Archive of CUDHg Idrija

These weren't just any kilns; they were the world's largest of their kind, each boasting a staggering daily capacity of 250 tons of ore.

Idrija - Topilnica rudnika živega srebra

The rotary furnace was part of the Idrija Mercury Mine smelting plant, which further encompassed the cableway end-station and the ore separation plant. Constructed in the 1960s, the furnace used to be the largest of its kind to smelt cinnabar ore in the world. Three rotary furnaces with the capacity of 250 tonnes of ore per day were in operation until 1995. As part of the mercury heritage of Idrija and Almadén, it is listed on the UNESCO World Heritage List.

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How mercury is produced?

The metallurgy of mercury is at its core very simple. Cinnabar ore that contains mercury needs to be crushed into smaller fractions. The prepared ore is smelted at a temperature of 600-800°C, which results in the evaporation of mercury from the ore. The mercury vapours produced during the smelting process must be captured and cooled by cold water or air, resulting in condensation and liquefaction of mercury.

Photo: Archive of CUDHg Idrija

While three rotary furnaces were in operation between 1961 and 1977, the fourth and the fifth were never installed, due to the global mercury sales crisis and temporary shutdown of mercury production. After production was restored in 1983, only the third furnace was operating. It was shut down for good in 1995, when the last 8 tonnes of mercury were produced. In the 500-year history of the Idrija Mercury Mine, 146,000 tons of mercury were produced.

Photo: Archive of CUDHg Idrija

The ore in the rotary furnace burned inside a 36.6 metre-long iron pipe whose interior was lined with fireclay brick. The inclined pipe revolved during operation, allowing the ore to slide slowly down to the increasingly hotter section. The new rotary furnace had a capacity of smelting up to 250 tons of ore a day. This was the largest rotary furnace for the smelting of mercury ore in the world. The smelted ore was transported from the furnace bunkers to waste piles along Idrijca River, first in wagons by electric locomotive and later in 1973 by dump trucks.

Photo: Arctur