In the 1830s the Brunton Calciner was developed for arsenic recovery, which were used many Cornish mines until the 1950s.
With the cassiterite [tin ore] in the lodes are other minerals like copper, iron, and arsenic. These have to be taken out before tin can be made. They used to be removed by roasting in a furnace or ‘burning house’ – a difficult and polluting process. In the 1830’s a Scottish engineer, William Brunton, developed a mechanised furnace called a calciner.
Burning the concentrate converted the arsenic and other unwanted minerals to gases. At some mines these gases were cooled and arsenic ‘soot’ was recovered. This did not happen at Geevor, but at the nearby Botallack mine the cooling chambers can still be seen and explored.
The Brunton Calciner was a circular furnace. The floor rotated at about 5 times an hour. The cassiterite concentrate was fed onto the bed from the room above the furnace. Two coal fuelled fireboxes roasted the concentrate at 600 deg C. Rakes slowly moved the concentrate across the bed. It was collected in a chute.
The burnt concentrate was processed to remove iron oxide and recover clean cassiterite. The arsenic ‘soot’ was scraped from the walls of the flues and refined to produce white arsenic oxide. This was a useful by-product for some mines: following further refinement, the arsenic was ready for sale.
The Geevor western calciner attached to the mill was last used in 1930. The arsenic was probably not recovered, as a photograph dated 1926 shows the calciner at work with what appears to be arsenic oxide smoke discharging into the air via a short chimney. The process was very polluting and damaging to the environment, though was still in use as late as 1950 at South Crofty Mine, Camborne.
At Geevor the calciner was replaced by the new froth flotation process around 1931. This was a chemical engineering process which recovered the sulphides and the arsenic as solids. The roof of the building was restored in 2008 and the building was decontaminated. The internal fittings are complete and it is hoped to open the building up to visitors. The eastern calciner, attached to the Slimes Plant, was also restored but the internal parts were removed many years ago.