Froth Flotation Cells

A row of froth flotation cells at Ashio Copper Mine sits along the main processing floor, each cell a square steel tank with an agitator shaft rising from the centre. The cells are open at the top; the froth that carried the copper-bearing minerals would have skimmed off the surface over weirs along one edge of each tank. The tank walls are streaked with the dried residue of the last cycles run through them, pale blue-green from the copper compounds, white where the lime additions settled out. Steel walkways pass between the rows of cells. The agitator drives are housed in geared casings above each cell, connected by belt to a line shaft running along the back of the room.

Froth flotation is the chemical-physical process that separates copper-bearing minerals from the bulk rock after milling. The finely ground ore is mixed with water, reagents are added, and air is blown through the slurry. The copper minerals attach to the bubbles, rise to the surface as a froth, and are skimmed off; the waste rock sinks. Ashio's flotation circuit ran for decades under the Furukawa modernisation. The Excavation Department closed in 1973 and the cells were drained. The dried residue in the photograph is the last batch of slurry to pass through them, fixed in place since.