Pouring blister copper at the Grandby smelter, Grand Forks, in 1918.
The Grandby Company was originally in Quebec but by the outbreak of the war had become American controlled. It was in this period the largest and most profitable integrated company and its smelter was the biggest in the Boundary area. Yet shortly after this picture was taken, the smelter closed down with the collapse in the copper market as war-time demand came to an end. Copper ore is first treated by blast or reverberatory furnaces to produce copper matte, a mixture of copper and iron sulfides. The molten matte is then placed in the copper converter, shown in the photograph, where it is mixed with silica sand and then air is blown through. The iron forms a ferrous silicate slag which, being lighter than the copper, floats to the surface and is poured off into the bucket shown to the right. The copper sulfide is further oxidized to produce elemental copper and sulphur dioxide, a dangerous gas. During the process the converter is rotated so that the opening lies under the vent hole above the converter, through which the gas is drawn up and dispersed over the countryside by the tall smelter chimneys. The impure end product copper from this process was poured into 'pigs' or ingot bars and is known as blister copper. Further purifying is done by electrolysis at a refinery.
